Updated on 2022/09/26

写真a

 
KAWADA, Hiroyuki
 
Affiliation
Faculty of Science and Engineering, School of Fundamental Science and Engineering
Job title
Professor

Concurrent Post

  • Faculty of Science and Engineering   Graduate School of Fundamental Science and Engineering

  • Affiliated organization   Global Education Center

Research Institute

  • 2020
    -
    2022

    理工学術院総合研究所   兼任研究員

Education

  •  
    -
    1980.03

    Waseda University   School of Science and Engineering   Department of Mechanical Engineering,  

  •  
    -
    1980

    Waseda University   Graduate School, Division of Science and Engineering  

Degree

  • 早稲田大学   博士(工学)

Professional Memberships

  •  
     
     

    強化プラスチック協会

  •  
     
     

    Japan Society for Composite Materials

  •  
     
     

    日本材料学会

  •  
     
     

    日本機械学会

 

Research Areas

  • Mechanics of materials and materials

  • Composite materials and interfaces

Research Interests

  • Composite materials, Strength of Materials

Papers

  • Experimental evaluation of mode I fracture toughness of dissimilar-material joints with thermal residual stresses

    Kazuki Harada, Kristine Munk Jespersen, Momoka Shima, Atsushi Hosoi, Hiroyuki Kawada

    Composites Science and Technology   224  2022.06

     View Summary

    The mode I interlaminar fracture toughness of dissimilar-material joints with thermal residual stresses is experimentally evaluated. The double cantilever beam (DCB) test is commonly used to assess the interlaminar fracture toughness of composites but is inadequate when dissimilar materials are joined owing to the mixed mode, which arises from differences in the bending stiffness and the thermal residual stresses formed during manufacturing because of differences in the linear expansion coefficient of the adherends. To address these difficulties, a new test, named the constant-load DCB test, was developed to evaluate the mode I interlaminar fracture toughness. In this study, a testing machine, based on the theoretical method previously established to derive the mode I interlaminar fracture toughness of dissimilar-material joints, is manufactured, and the fracture toughness is experimentally determined. As a result, good agreement between the theoretical value and experimental results is obtained, and the mode mixity ratio is significantly decreased compared with that of the general DCB test.

    DOI

  • Influence of covalently-bound graphene oxide on the mechanical properties of carbon fiber composite materials

    Mai Kikuchi, Kensuke Nakaso, Atsushi Murata, Atsushi Hosoi, Hiroyuki Kawada

    Diamond and Related Materials   121  2022.01

     View Summary

    Graphene was used as an additive in fiber-reinforced plastics. The apparent interfacial shear strength (IFSS) was improved by grafting graphene onto the fibers. In this study, the effect of graphene grafted onto carbon fiber via chemical covalent bonding on the mechanical properties of the fibers was evaluated. This method was used to link graphene and carbon fibers via ester linkages, which are stronger than physical adsorption interactions and cause little damage to the fiber strength. Before grafting through an ester linkage, an electrophoretic deposition was conducted to uniformly coat graphene onto the carbon fibers. The purpose of this study was to establish a fabrication method that could control the density and thickness of the graphene layer covalently bound to the fibers. In addition, the optimal production process and composite form of the reinforced fibers were determined by evaluating the fiber strength and IFSS of various graphene-reinforced fibers. Ultimately, it was determined that graphene could be grafted onto carbon fibers relatively uniformly, and that the graphene layer thickness affected their interfacial shear strength. In terms of optimizing the IFSS, a thin and uniform graphene layer was best, and the IFSS was improved by 42.1% compared with untreated fibers containing sizing agents.

    DOI

  • Evaluation of very high cycle fatigue properties for transverse crack initiation in cross-ply carbon fiber-reinforced plastic laminates

    Tsuyoshi Miyakoshi, Takeru Atsumi, Kensuke Kosugi, Atsushi Hosoi, Terumasa Tsuda, Hiroyuki Kawada

    Fatigue and Fracture of Engineering Materials and Structures    2022

     View Summary

    This paper investigates the transverse crack initiation behaviors of carbon fiber-reinforced plastics (CFRPs) in the high-cycle and very high cycle regimes. To accelerate the fatigue test up to the very high cycle fatigue (VHCF) regime, an ultrasonic fatigue testing system that can apply the specimen ultrasonic load at a frequency of 20 kHz was used. The fatigue behavior of cross-ply CFRP laminates formed with T800S/2592 prepreg was investigated. The fatigue behaviors at N = 103–107 cycles and N = 108–109 cycles were obtained by hydraulic and ultrasonic fatigue tests, respectively. The slope of the S–N diagram for transverse crack initiation showed a linear decrease in the region of N = 103–106 cycles and leveled off over N = 106 cycles. Furthermore, no cracks occurred in any specimen tested under the 90°-layer stress σ90°max = 44 MPa up to a maximum of N = 6.56 × 109 cycles.

    DOI

  • Post-synthesis treatment improves the electrical properties of dry-spun carbon nanotube yarns

    Takumi Watanabe, Akira Itoh, Tomohisa Watanabe, Takeshi Kizaki, Masayasu Inaguma, Atushi Hosoi, Hiroyuki Kawada

    Carbon   185   314 - 323  2021.11

     View Summary

    Researchers expect carbon nanotube (CNT) yarns as an alternative to metallic wiring. However, the electrical properties of CNT yarns remain relatively low, necessitating further improvement. In this study, we fabricated CNT yarns by dry-spinning and performed several post-synthesis treatments to enhance the electrical properties. Polymer solution impregnation increased the electrical conductivity 1.82 × and the current capacity 1.58 ×, attributable to densification of the CNT yarn bundles. Graphitization (GT) increased the electrical conductivity 2.58 × and the current capacity 1.83 ×, attributable to purification of the crystalline structure. Iodinemonochloride/dichloromethane (ICl/DCM) doping increased the electrical conductivity 1.79 × and the current capacity 1.31 ×, attributable to the increased electron carrier density. We achieved further enhancement by a two-step treatment—GT and ICl/DCM doping—resulting in a 4.88 × increase in conductivity and reaches a maximum of 5.12 × 105 S/m. We observed greater doping effects after GT, which increased the electrical conductivity 1.89 ×, whereas doping for pristine CNT yarn only increased the electrical conductivity 1.79 ×. The X-ray photoelectron spectra of CNT yarn in each step indicated a positive relationship between the peak area of the π–π∗ transition component and the electrical conductivity. Therefore, we hypothesize that purification of the crystalline structure increases the electron carrier density by doping.

    DOI

  • Fatigue delamination growth characterization of a directly bonded carbon-fiber-reinforced thermoplastic laminates and aluminum alloys with surface nanostructure using DCB test

    Kei Saito, Kristine M. Jespersen, Hiroki Ota, Keita Wada, Atsushi Hosoi, Hiroyuki Kawada

    Journal of Composite Materials   55 ( 22 ) 3131 - 3140  2021.09

     View Summary

    With the recent demand for weight reduction, structural materials for transportation equipment are being replaced by carbon-fiber-reinforced thermoplastics (CFRTPs). Therefore, techniques to join CFRTPs to alloys are needed. In this study, the fatigue delamination growth of bonded CFRTP/aluminum alloy joints was characterized. The specimens were bonded in three ways, using adhesive, direct chemical bonding, and direct chemical bonding with a nanostructured surface. The type of the specimen was double cantilever beam (DCB) specimen, which consisted of aluminum alloy (A5052) and plain woven CFRTP. The lay-up of the CFRTP was [(0,90)]9 and the used matrix was PA6. Fatigue loading was applied in displacement control mode. The ratio between the minimum and maximum displacement was 0.1, and the test frequency was 5 Hz. The crack length during the fatigue tests was obtained by compliance calibration. Fatigue was characterized by constructing a Paris diagram for each specimen type. The fracture surface distinctively changed from smooth brittle-like fracture to hair-like ductile fracture post fabricating a nanostructure and chemical bonding. As a result, the fatigue crack growth resistance of the specimen with the nanostructure significantly improved due to the hair-like ductile fracture.

    DOI

  • Effect of the interfacial nanostructure on the interlaminar fracture toughness and damage mechanisms of directly bonded carbon fiber reinforced thermoplastics and aluminum

    Hiroki Ota, Kristine Munk Jespersen, Kei Saito, Keita Wada, Kazuki Okamoto, Atsushi Hosoi, Hiroyuki Kawada

    Composites Part A: Applied Science and Manufacturing   139  2020.12

     View Summary

    © 2020 Elsevier Ltd Carbon fiber reinforced thermoplastics (CFRTPs) are becoming of interest to mass production industries. In this study, we investigated the characteristics of the direct bonding technique to join an aluminum alloy and a CFRTP laminate by fabricating a nanostructure on the aluminum alloy surface. The effect of the nanostructure on the fracture toughness and the damage mechanisms were investigated. The nanostructure improved the fracture toughness by about 2.6 times compared with that without the nanostructure. From observations of the fracture surface, ductile failure of the matrix owing to the nanostructure occurred, suggesting that plastic deformation improved the fracture toughness. From X-ray computed tomography observations, intralaminar failure caused by the nanostructure occurred, which appeared to be a factor for the improved fracture toughness.

    DOI

  • Experimental measurement of mode-I fracture toughness of dissimilar material joints with thermal residual stresses

    Kristine M. Jespersen, Hiroki Ota, Kazuki Harada, Atsushi Hosoi, Hiroyuki Kawada

    Engineering Fracture Mechanics   238  2020.10

     View Summary

    © 2020 Elsevier Ltd The current study presents a novel test method to experimentally cancel out the thermal stresses in dissimilar material joints. For the commonly used double cantilever beam test the presence of thermal stresses results in a significant mode mixity at the crack tip, which varies with applied load even if the elastic properties of the adherends are similar. This is particularly a challenge for fibre reinforced plastics bonded to metals due to the large difference in thermal expansion coefficients. The presence of mode-II loading is likely to provide a higher fracture energy from experiments than if tested under pure mode-I loading, which can lead to non-conservative results when using standard test methods. To overcome this challenge a novel test method inspired by the mixed mode bending test is developed. It is shown that the thermal stresses can be cancelled by applying initial constant loads during testing, and that the fracture toughness under pure mode-I loading can be obtained under specific conditions. The test method is validated by carrying out virtual compliance calibration experiments using cohesive zone finite element modelling. As the test method relies solely on analytical calculations and can be used with standard test equipment, it is relatively simple to apply in practice.

    DOI

  • Effect of interfacial nanostructure on mode mixity in directly bonded carbon fiber reinforced thermoplastic laminates and aluminum alloy with thermal stresses

    Hiroki Ota, Kristine Munk Jespersen, Kei Saito, Keita Wada, Kazuki Okamoto, Atsushi Hosoi, Hiroyuki Kawada

    JSME 2020 Conference on Leading Edge Manufacturing/Materials and Processing, LEMP 2020    2020

     View Summary

    In recent years, for the aim of weight reduction of transportation equipment, carbon fiber reinforced thermoplastics (CFRTPs), which have high recyclability and formability, are becoming suitable for mass production. Additionally, with the development of multi-material structures, excellent technologies for joining metal and CFRTPs are required. In present industry, joining between dissimilar materials include adhesive bonding and mechanical joining methods, however, these methods still have some problems, and therefore an alternative bonding method without adhesive and mechanical joining is required for joining CFRTPs and metals. Thus, this study focused on direct bonding between CFRTP and an aluminum alloy, by producing a nanostructure on the surface of the aluminum alloy. The nanostructure penetrates the CFRTP matrix causing an anchoring effect, which results in significant bonding strength improvement. The influence of the nanostructure on the fracture toughness for the directly bonded CFRTP and aluminum was evaluated by static double cantilever beam (DCB) testing. Due to the difference of the thermal expansion coefficients between the CFRTP laminates and the aluminum alloy, significant residual stresses are generated. The effect of the thermal residual stresses on the fracture toughness along with the resulting mode mixity (mode ? and ?) was calculated. It is found that the thermal stresses introduce a significant mode mixity of the fracture toughness.

    DOI

  • Enhancing mechanical properties of graphene / epoxy nanocomposites using few-layer graphene produced by liquid phase exfoliation

    K. Oba, Y. Arao, A. Hosoi, H. Kawada

    ECCM 2018 - 18th European Conference on Composite Materials    2020

     View Summary

    In this study, few-layer graphenes (FLGs) were produced by new liquid phase exfoliation (LPE), exfoliation of graphite with weak acid salts. A high concentration dispersion of FLGs in low-boiling point solvents is successfully carried out, achieved by binding molecules with a dispersing function. And then graphene/epoxy nanocomposites were fabricated and tensile properties were evaluated in order to understand the effect of FLGs introduced into the resin. Graphene/epoxy nanocomposite showed improved mechanical properties. Tensile strength and fracture strain were increased by 11.5% and 55.6% compared with as-received one's. Especially, the improvement of fracture strain was outstanding, which indicated that adding FLGs had a positive impact on suppressing effect on crack propagation and improving fracture toughness of matrix resin. These beneficial results were derived from crack trapping by uniformly dispersed FLGs.

  • Very high-cycle fatigue characteristics of cross-ply CFRP laminates in transverse crack initiation

    Atsushi Hosoi, Takuro Suzuki, Kensuke Kosugi, Takeru Atsumi, Yoshinobu Shimamura, Terumasa Tsuda, Hiroyuki Kawada

    Lecture Notes in Mechanical Engineering     838 - 846  2020

     View Summary

    © Springer Nature Switzerland AG 2020. Fan blades are subjected to very high-cycle loadings during the design life, so it is essential to evaluate the giga-cycle fatigue characteristics of carbon fiber reinforced plastic (CFRP) laminates. In this study, the transverse crack initiation of the cross-ply CFRP laminates in very high-cycle fatigue region was evaluated using an ultrasonic fatigue testing machine. The fatigue tests were conducted at the frequency of f = 20 kHz and the stress ratio of R = −1. In order to suppress temperature rise of the specimen, the intermittent operation with the loading time of 200 ms and the dwelling time of 2000 ms was adopted. The fatigue life data to transverse crack initiation in very high-cycle fatigue region was compared with the data of the fatigue test which was conducted at the frequency of f = 5 Hz and the stress ratios of R = 0.1 and −1 using a hydraulic control fatigue test machine. It was evaluated considering the influences of the stress ratio and the thermal residual stress by using the modified Walker model. The fatigue life to the transverse crack initiation of the cross-ply CFRP laminates in the very high-cycle region exceeding 108 cycles was on the extension of the test data in the low cycle region.

    DOI

  • Damage mechanisms and mechanical properties of directly bonded CFRTP and aluminium with nano-structured surface

    Kristine Munk Jespersen, Hikaru Abe, Hiroki Ota, Kei Saito, Keita Wada, Atsushi Hosoi, Hiroyuki Kawada

    Lecture Notes in Mechanical Engineering     104 - 112  2020

     View Summary

    © Springer Nature Switzerland AG 2020. The present work studies the cohesive behaviour of a previously proposed novel direct bonding method for dissimilar bonding between a carbon fibre reinforced thermoplastic (CFRTP) and aluminium. A nanostructure is manufactured on the aluminium surface and is directly bonded to the CFRTP by applying heat and pressure. Double cantilever beam (DCB) testing is carried out to evaluate the bonding properties and the initial results of a method for directly measuring the traction-separation behaviour from experiments is presented. The nanostructure is observed to improve the bonding properties significantly compared to two other considered bonding cases. Furthermore, the measured traction-separation behaviour is seen to be difference for each case. Nevertheless, the applied calculation method shows some challenges related to thermal stresses and plastic deformation that should to be taken into account in future studies.

    DOI

  • Energy absorption mechanism of thermoplastic fiber-reinforced plastics under impact loading using split-hopkinson pressure-bar method

    Ayuta Nambu, Shogo Adachi, Tomoya Yabu, Yuji Ishitsuka, Atushi Hosoi, Hiroyuki Kawada

    Key Engineering Materials   858 KEM   47 - 52  2020

     View Summary

    © 2020 Trans Tech Publications Ltd, Switzerland. The energy absorbing performance in the progressive failure of glass long-fiber-reinforced polyamide was evaluated by using the split Hopkinson pressure-bar method. An impact compression test of glass long-fiber-reinforced polyamide was performed from –30 °C to 90 °C, and the temperature-independent energy absorbing performance was confirmed only for the progressive failure mode. To clarify this phenomenon, compression tests, interlaminar compressive shear tests and mode-I fracture-toughness tests were conducted under static and impact conditions. The compression strength and the shear strength of all specimens decreased with an increase in temperature. The toughness improved with temperature. In addition to the mechanical tests, failure-mode analysis was performed by using a three-dimensional X-ray microscope to clarify the absorbing mechanism. From the above, it was concluded that the temperature-independent energy absorbing performance results from a balance of these mechanical properties against the temperature change.

    DOI

  • X-ray tomography based finite element modelling of non-crIMP fabric based fibre composite

    Kristine M. Jespersen, Leif E. Asp, Atsushi Hosoi, Hiroyuki Kawada, Lars P. Mikkelsen

    ECCM 2018 - 18th European Conference on Composite Materials    2020

     View Summary

    © CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. The current study presents a workflow to import a fibre bundle structure of a non-crimp fabric based fibre composite obtained by X-ray CT to a solvable 3D model in the finite element software ABAQUS. The considered fibre composite is similar to that used for the load carrying parts of wind turbine blades, and each layer of the non-crimp fabric contains fibre bundles oriented in the 0◦, 90◦, and ±45◦ directions. The 3D fibre bundle geometry is first segmented in the software AVIZO and then imported to Geomagic Wrap where the geometry is smoothened and converted into a nurbs surface that can be imported into ABAQUS. The resulting stress distribution is qualitatively compared to previous experimental observations and discussed.

  • Evaluation of strength degradation behavior and fatigue life prediction of plain-woven carbon-fiber-reinforced plastic laminates immersed in seawater

    Shuhei Koshima, Shunsuke Yoneda, Norihiro Kajii, Atsushi Hosoi, Hiroyuki Kawada

    COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING   127  2019.12

     View Summary

    The effect of long-term seawater immersion on the mechanical properties and fatigue life of plain-woven carbon-fiber-reinforced plastic (CFRP) laminates was investigated. Under tension loading, the static strength and low-cycle fatigue strength of the CRFP laminates greatly decreased owing to the rapid growth of interface debonding and delamination. However, under compression loading, the fatigue strength of the CRFP laminates dramatically decreased in the entire fatigue region as fiber budding was likely to occur. These findings indicate that the fatigue strength degradation differed depending on the stress ratio and deterioration of the fiber/matrix interface strength. In addition, the fatigue life after seawater immersion was predicted using Epaarachchi and Clausen's model and constant life diagrams. These models were shown to accurately reflect the decrease in fatigue strength resulting from seawater immersion and can thus be used for fatigue life prediction of CFRPs after long-term immersion in seawater.

    DOI

  • The effect of nanospike structures on direct bonding strength properties between aluminum and carbon fiber reinforced thermoplastics

    Hikaru Abe, Joon Cheol Chung, Takaaki Mori, Atsushi Hosoi, Kristine Munk Jespersen, Hiroyuki Kawada

    COMPOSITES PART B-ENGINEERING   172   26 - 32  2019.09

     View Summary

    With recent design developments in the automotive industry, it has become necessary to join dissimilar materials such as aluminum and carbon fiber reinforced thermoplastics (CFRTPs). In this study, a nanospike structure is fabricated on the surfaces of aluminum plates and directly bonded to CFRTP laminates. The effect of the nanospike structure on the adhesion strength is evaluated by single-lap joint tests. It is found that the nanospike structure improves the adhesion strength. Furthermore, combining the nanospike structure with a silane coupling treatment results in failure in the aluminum part of the single-lap specimens with an overlap length of 12.5 mm, rather than in the joined region. The average adhesion strength of the single lap joint specimens with an overlap length of 5.0 mm is found to be 24.9 MPa. Scanning electron microscopy observations of the fracture surfaces of the joined region only showed cohesive failure. On the fracture surface of the CFRTP laminate, the matrix exhibits a hairy structure due to the presence of the nanospike structure in some regions and in other regions carbon fibers are exposed due to adherend failure. Thus, in addition to an improved joint strength, the results suggest that the nanostructure will also improve the fracture toughness by causing ductile failure of the matrix.

    DOI

  • Direct exfoliation of layered materials in low-boiling point solvents using weak acid salts

    Yoshihiko Arao, Jonathon D. Tanks, Masatoshi Kubouchi, Akira Ito, Atsushi Hosoi, Hiroyuki Kawada

    CARBON   142   261 - 268  2019.02

     View Summary

    The method for mass production of nanosheets is essential for fully realizing their commercial use. Direct exfoliation of layered materials in liquid is the simplest and low-cost technique for exfoliation without introducing defects in basal plane. However, the technique requires toxic and high-boiling point solvents, which makes it difficult for further processing. In addition, solvent exchange involves time-consuming processes such as filtering and redispersion. A breakthrough is necessary to make 2D-crystal-based functional dispersions. Here, we find a new method to directly exfoliate layered materials in low-boiling point solvents. Addition of small amounts of salt prevents reaggregation of exfoliated nanosheets and improves electrical repulsion. In this process, the mechanical force applied by sonication generates active carbon species at the fractured surfaces, leading to a reaction between the active carbon and the salt in liquid. High concentration graphene dispersions (1 g/L) can be obtained in isopropanol with only 5 min of sonication. We also confirm salt-assisted exfoliation is effective for the other 2D crystals such as MoS2 and boron nitride in a wide variety of polar solvents. Direct exfoliation in processable solution opens up a range of large-area applications such as high performance nanocomposites and coatings. (C) 2018 Elsevier Ltd. All rights reserved.

    DOI

  • Growth of CuO nanowires on Si substrate by thermal oxidation method and its interfacial delamination mechanism.

    YANAGISAWA Issei, MATSUNAGA Mitsuhiro, DOI Yuki, KIMURA Fumiya, HOSOI Atsushi, JU Yang, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2019 ( 0 ) 510 - 510  2019

     View Summary

    <p>CuO nanowires are known to have excellent electrochemical properties and can be produced by various methods. Among them a method which directly heat either the Si wafer with Cu layer or pure copper plate so called the thermal oxidation method has lately been drawing attention. However, during its production, interfacial delamination between the Cu layer and the wafer has always been an issue. In this study, the mechanism of interfacial delamination was experimentally elucidated by comparing a Si wafer with Cu layer deposited by electron beam evaporation with a pure copper plate. As a result, it was found that the deposited Cu layer decreased with increasing heating time of the Si wafer production. Moreover, the disappearance of the Cu layer and Cu2O layer on the Si wafer was found in the specimens with a heating time of 6 hours. It was suggested that this disappearance would form an opening between the CuO layer and the Si wafer leading to the delaminating of the interface between the oxide film and the wafer. The disappearance also suggested that the length and density of the CuO nanowires in the specimens with a heating time of 6 hours were minimized. As for the pure copper plate, the disappearance of the Cu layer and Cu2O layer was not seen regardless of the heating time, therefore there was no interfacial delamination and it was able to produce CuO nanowires at a high density.</p>

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  • Evaluation of transverse crack propagation behavior of cross-ply CFRP laminates in VHCF regime using ultrasonic fatigue testing

    ATSUMI Takeru, MIYAKOSHI Tsuyoshi, KOSUGI Kensuke, HOSOI Atsushi, SHIMAMURA Yoshinobu, TSUDA Terumasa, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2019 ( 0 ) 121 - 121  2019

     View Summary

    <p>For further application of carbon fiber reinforced plastics (CFRPs), it is necessary to obtain fatigue properties up to very high-cycle fatigue (VHCF) regime. In this paper, CFRP laminates were subjected to fatigue test up to 109 cycle using an ultrasonic fatigue test machine in order to evaluate the transverse crack initiation life of laminates and the propagation behavior. In this experiment, T800S/2592 prepreg used as the cross-ply [0/906]s laminates. Using an ultrasonic fatigue test machine tension-compression fatigue tests were conducted with stress ratio of R= -1 at a frequency of 20kHz. The specimen dimension was determined by finite element analysis to resonance at the vicinity of the test frequency. It was found that the test was carried out as designed, since the temperature distribution obtained by IR-thermography camera and the displacement measurement by the Laser Doppler vibrometer showed close agreement with the finite element analysis result. It was confirmed that the slope of the S-N diagram would be gradual in the VHCF regime.</p>

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  • Fabrication of graphite / CF fibers using chemical bonding and evaluation of their mechanical properties

    MURATA Atsushi, NAKASO Kensuke, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2019 ( 0 ) J04418P  2019

     View Summary

    <p>In this study, graphene oxide was grafted to carbon fibers using chemical bonding and Electrophoretic Deposition (EPD) to improve the properties of the fiber / resin interface. Graphene oxide grafted on the surface of fibers is expected to improve the mechanical properties of Carbon Fiber Reinforced Plastics (CFRPs) by improving the adhesion and its interlock to resin. At that time, the influence of the grafted graphene oxide on the mechanical properties was investigated. As a result, it was confirmed that the interface properties of the fiber were improved without the fiber strength decreasing by the grafting. In particular, the interface shear strength showed the highest value even under the preparation conditions where a uniform graft morphology was observed, and showed an increase of 41.5% compared to the untreated fiber. Finally, the improvement mechanism of the interface properties was examined. It was suggested that the main factor of the improvement was that graphene oxide was dispersed in resin around the fiber and the physical property of the resin is improved.</p>

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  • Damage and strengthening mechanisms of directly bonded aluminium and CF/PA laminates

    JESPERSEN Kristine Munk, ABE Hikaru, SAITO Kei, OTA Hiroki, Wada Keita, HOSOI Atsushi, Kawada Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2019 ( 0 ) J04411  2019

     View Summary

    <p>The current study investigates the damage and strengthening mechanisms of a novel direct bonding method for joining aluminium and carbon fibre reinforced thermoplastic laminates. The bonding properties are studied using double cantilever beam (DCB) and end notched flexure (ENF) tests. The specimens bonded using the proposed direct bonding method are found to show significantly stronger bonding properties than the considered adhesively bonded specimens. The interface properties are further investigated by extracting the cohesive traction-separation behaviour from DCB and ENF experimental tests and used in the finite element software ABAQUS to simulate the interface behaviour. Good agreement between experiments and simulation is found for the DCB tests, however poor agreement is found for the ENF tests due to significant plastic deformation of the aluminium adherend occurring prior to and during crack propagation. Thus, plasticity will have to be avoided or taken into account in future studies, which is ongoing work.</p>

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  • Influence of high-density pulse current on deformation behavior of slip bands of brass subjected to fatigue loading

    MAEYAMA Taro, TAKAHASHI Hideyuki, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of Conference of Kanto Branch   2019 ( 0 ) 19C08  2019

     View Summary

    <p>It is important to enhance the fatigue life of machines and structures to prevent unexpected fracture. The technique which has influence on plastic deformation in slip bands formed in fatigue loading has been developed. Fatigue test of brass, C2600, was conducted in two stress amplitude level (σA/σB=0.4, σA/σB=0.8), and slip offset transition was measured by atomic force microscope. In this study, to investigate the effect of electric pulse current, electric pulse current of 50A/mm2 was applied to specimens in the interval of fatigue test. As a result, in case of no pulse current, slip offset transition was continued to grow and grow rapidly when reached to specific number of cycle in both of stress amplitude level. On the other hand, when pulse current was applied slip offset in low stress amplitude(σA/σB=0.4) was tended to decrease and slip offset in high stress amplitude(σA/σB=0.8) did not grow rapidly. A slip band was emerged when pulse current was applied. So that, it is suggested that electric pulse current affected plastic deformation of a slip band. This effect could be caused by compression stress of Joule heating around dislocations and shear stress by electron wind force.</p>

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  • Functionalization and strengthening of graphitized untwisted carbon nanotube yarn with hot mixed acid treatment

    OKUMO Kouichi, TAKAHASHI Yui, KIM Taesung, NIKAWA Hidefumi, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   85 ( 874 ) 19 - 00029-19-00029  2019

     View Summary

    <p>Carbon nanotubes (CNT) have remarkable mechanical properties and low density. Since length of the CNT is limited, CNT yarn is regarded as a reinforced fiber of carbon fiber reinforced plastics. However, the CNT yarn does not have remarkable mechanical properties such as the individual CNT. The most popular way for improving the mechanical properties of the CNT yarn is to make composites with polymer such as polyvinyl alcohol or polyimide. If some functional groups such as carboxyl groups are introduced on the surface of CNTs, interaction between the CNTs and the polymer is improved and high mechanical properties will be obtained. In this study, untwisted CNT yarns were prepared by drawing vertical aligned CNTs through a die and functionalized with mixed acid. Mixed acid introduced not only the functional groups but also defects on the surface of CNTs. For reducing the defects, the CNT yarn was graphitized at a temperature of 2800°C before the mixed acid treatment. By the graphitization treatment, crystallinity of the CNT yarn was improved and amorphous carbon was removed. As a result of XPS analysis, a graphitized CNT yarn treated with mixed acid did not contain the functional groups. On the other hand, a graphitized CNT yarn treated with hot mixed acid (90°C) contained the functional groups. Crystallinity of this yarn was 4.5 times higher than the as-received CNT yarn. In addition, as a result of single fiber tensile tests, tensile strength of this yarn was increased by 79 % and Young's modulus was increased by 173 % compared to the as-received CNT yarn.</p>

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  • Effect of interactive force between CNTs on mechanical properties of untwisted carbon nanotube/polymer composite yarn

    KIM Taesung, HAYASHI Anri, NIKAWA Hidefumi, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   85 ( 872 ) 18 - 00408-18-00408  2019

     View Summary

    <p>Carbon nanotube (CNT) yarn is enables CNTs to be used on macro scale. However, the mechanical properties of CNT yarns are smaller than CNT itself, and improvement of the mechanical properties is a challenge for practical application. In this study, untwisted CNT yarns were fabricated by a dry spinning method, and the yarns were graphitized and combined with polymer for the purpose of development of CNT yarns with high strength. As a result of the graphitized treatment to the as-received yarns under inert atmosphere at 2800°C, impure materials and defect structure on CNTs were removed and strength of the yarn was increased by 19%. After combining the as-received yarns with polyacrylic acid (PAA), the strength was increased by 174% and reached 2.3 GPa. Breaking form of the yarns were changed from pulling out of CNT bundles to rapture of CNT bundles by graphitization and combining with PAA, indicating an increase interactive force between the CNT bundles. However, the strengthening effect was limited when graphitized CNT yarns were combined with PAA. As a result of molecular dynamics simulations, it was revealed force transfer capability of PAA was low when the graphitized yarns was combined with PAA. There were functional groups on as-received CNT such as carboxyl groups. On the other hand, the functional groups were removed from CNTs after the graphitization treatment. Consequently, interaction such as hydrogen bond between as-received CNT and PAA was removed by the graphitization, and it lead to the decrease of the force transfer capability of PAA.</p>

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  • Evaluation of static tensile strength and fatigue strength degradation of plain woven CFRP laminates under seawater immersion

    KOSHIMA Shuhei, KAJII Norihiro, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   85 ( 871 ) 18 - 00435-18-00435  2019

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    <p>Carbon fiber reinforced plastics (CFRPs) are widely used as components of marine structures. Thus, it is important to understand the degradation of the mechanical properties and its mechanism under seawater immersion. The object of this study is the influence of seawater immersion on the mechanical properties of plain woven CFRP laminates. Static tensile test and tensile fatigue test were carried out on the CFRP immersed different time under seawater for 300, 2500 and 5400 hours. The mechanical properties immersed for 300 hours was almost the same value compared with those of no immersion. However, the tensile strength immersed for both 2500 and 5400 hours reduced by 22.5% compared with that of no immersion. Then, from the fatigue results, in the low-cycle fatigue region, the fatigue strengths decreased as immersion time was longer, on the other hand, in the high-cycle fatigue region, the fatigue strength did not change significantly regardless of immersion time. As a result, the inclination of S-N curves became gentle as immersion time was longer. From observation of fracture surfaces by scanning electron microscopy (SEM), it was shown that the fiber/matrix interface deteriorated remarkably after seawater immersion. Moreover, the difference of damage growth behaviors due to immersed in seawater under fatigue loading was investigated using soft X-ray photography. On specimen immersed in seawater, the accumulation of damage expanded more widely due to interface degradation compared with that of no immersion. Considering these results, it was suggested that the static tensile strength depended on load transmission efficiency between fiber and matrix, on the other hand, the fatigue strength in high cycle fatigue region depended on the strength of fiber along 0° that had small influences by seawater immersion.</p>

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  • INFLUENCES OF PLASTICITY -INDUCED CRACK CLOSURE ON FATIGUE CRACK HEALING OF CARBON STEEL WITH HEAT TREATMENT

    Eiichi Hamada, Yuto Furuya, Atsushi Hosoi, Yuji Morita, Hiroyuki Kawada

    PROCEEDINGS OF THE ASME INTERNATIONAL MECHANICAL ENGINEERING CONGRESS AND EXPOSITION, 2018, VOL 12    2019

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    Healing technology for metallic materials is an important subject in terms of long-term reliability and durability of structural members, a healing technology to heal fatigue crack by applying heat treatment at annealing temperature level has been discovered. In this study, the influences of plasticity induced crack closure on healing were evaluated by obtaining the crack opening load during the pre-crack introduction and evaluating the fatigue crack propagation characteristics before and after the healing heat treatment, using compact tension specimens made of carbon steel with different test conditions. As a result, the specimen with high crack opening load showed high healing effect and were able to heal up to 95% of the pre crack length. This suggested that the residual compressive stress due to the plasticity-induced crack closure accelerates the solidstate diffusion bonding during the crack healing process and this leads to the improvement of the healing effect.

  • Mechanical properties and microstructural fracture behaviors of dry-spun SiC fibers

    Tatsuya Kimura, Hinako Ozaki, Michimasa Uda, Yoshio Hasegawa, Akiko Koshizaka, Atsushi Hosoi, Hiroyuki Kawada

    MECHANICAL ENGINEERING JOURNAL   6 ( 3 )  2019

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    Research and development of SiC/SiC composite materials as structural members of aerospace engines is progressing. In order to manufacture SiC/SiC composites with excellent high-temperature characteristics, the SiC fibers which have high mechanical properties at high temperature are necessary; thus, further development of SiC fibers is considered a critical issue. In addition, the development of low-cost SiC fibers is necessary for the practical application of SiC/SiC composites. Here, the low-cost SiC fibers can be fabricated by dry spinning method. In the dry-spinning method, the raw material, Polycarbosilane (PCS) is dissolved in an organic solvent and the solution is spun at room temperature. As high-molecular-weight Polycarbosilane is prepared in advance, the infusible process conventionally required in the melt-spinning method is not required. In this study, to evaluate the differences among dry-spun SiC fibers fabricated under various conditions, monofilament tensile tests were conducted. Examination of the fracture surface and elemental analysis of arbitrary cross-sections were then performed to investigate the effects of the fabrication conditions. The tensile strength results indicated that defects were suppressed by excluding low-molecular-weight components and that heat treatment between 1300 degrees C and 1500 degrees C resulted in the maximum strength. Weibull analysis revealed that the dry-spun fibers exhibited lower tensile strength but smaller variation of fiber strength than that of the melt-spun fiber because the dry-spun fibers were more homogeneous. However, evaluation of the crystallinity indicated that the interference pattern derived from the crystal was unclear in the dry-spun fibers but clear in the melt-spun fiber. Therefore, it was suggested that the dry-spun fibers exhibited lower crystallinity than the melt-spun fiber. In addition, the dry-spun and melt-spun fibers exhibited similar C/Si ratios, whereas a large amount of oxygen was detected on the surface of the dry-spun fiber relative to that on the surface of the melt-spun fiber. Further improvement of the mechanical properties is expected upon increasing the molecular weight of the raw material and improving the microstructure.

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  • Ex-situ X-ray computed tomography, tension clamp and in-situ transilluminated white light imaging data of non-crimp fabric based fibre composite under fatigue loading

    Kristine M. Jespersen, Jens A. Glud, Jens Zangenberg, Atsushi Hosoi, Hiroyuki Kawada, Lars P. Mikkelsen

    DATA IN BRIEF   21   228 - 233  2018.12

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    The data published with this paper is obtained during fatigue testing of a unidirectional non-crimp fabric based glass fibre composite by means of ex-situ X-ray CT and in-situ transilluminated white light imaging experiments. The data experimentally shows the damage initiation and progression under fatigue loading both in terms of off-axis cracks in the thin supporting backing fibre bundles and fibre fractures in the load carrying fibre bundles. X-ray CT data comparing the loaded and unloaded state of damage regions by means of a tension clamp solution are also published with this paper. (C) 2018 The Authors. Published by Elsevier Inc.

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  • Damage mechanisms of directly bonded carbon fibre reinforced thermoplastics and aluminium with nanostructured surface

    K. M. Jespersen, J. C. Chung, K. Okamoto, H. Abe, A. Hosoi, H. Kawada

    IOP Conference Series: Materials Science and Engineering   388 ( 1 )  2018.07

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    © Published under licence by IOP Publishing Ltd. The current study presents a direct bonding method making it possible to obtain a high interface strength of aluminium joined to carbon fibre reinforced thermoplastic (CFRTP) plates by hot pressing. This is achieved by subjecting the aluminium to a combination of anodising, etching, and silane-coupling treatments prior to bonding. Different types of aluminium are subjected to different treatments and bonded to different types of CFRTP laminates. The effect of the surface structure on the static bonding strength and fatigue life measured by single-lap testing is compared and discussed. The bonding strength is found to be highly dependent on the anodisation conditions along with the type of thermoplastic resin.

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  • Fatigue Life Prediction for Transverse Crack Initiation of CFRP Cross-Ply and Quasi-Isotropic Laminates

    Atsushi Hosoi, Hiroyuki Kawada

    MATERIALS   11 ( 7 )  2018.07

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    Carbon fiber reinforced plastic (CFRP) laminates are used as main structural members in many applications. Transverse cracks that form in 90 degrees layers of CFRP laminates are mostly initial damage in the case where tensile loading is vertically applied to the 90 degrees layers of CFRP laminates, and they are the origin of more serious damage of delamination and fiber breakage. It is thus important to predict quantitatively the transverse crack initiation of CFRP laminates subjected to cyclic loading to ensure the long-term reliability of the laminates. The initiation and multiplication behaviors of transverse cracks strongly depend on the laminate configuration, thickness, and thermal residual stress. Therefore, a model based on the Walker model was proposed to predict transverse crack initiation in CFRP cross-ply and quasi-isotropic laminates under cyclic loading in the present study. The usefulness of the proposed model was verified with 10 different CFRP laminates formed from four different prepregs with epoxy resin matrices. The analysis results were in good agreement with experimental results. The fatigue life was expressed with three constants, which related to the fatigue strength reduction, the normalized fatigue strength at N = 1 cycle, and the contribution of stress amplitude to the fatigue life, and they are independent of the laminate configuration.

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  • Uncovering the fatigue damage initiation and progression in uni-directional non-crimp fabric reinforced polyester composite

    Kristine M. Jespersen, Jens A. Glud, Jens Zangenberg, Atsushi Hosoi, Hiroyuki Kawada, Lars P. Mikkelsen

    COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING   109   481 - 497  2018.06

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    The current work studies the fatigue damage initiation and progression in a quasi-unidirectional non-crimp fabric based fibre composite used for wind turbine blades. This is done by combining in situ transilluminated white light imagining (TWLI) with ex-situ X-ray computed tomography (CT) experiments along with tension clamp X-ray CT experiments. TWLI is used to monitor the off-axis cracks in the thin supporting backing fibre bundles present in quasi-UD composites, and a crack counting algorithm is applied to automatically count the cracks in images obtained in situ during fatigue testing. It is found that off-axis cracks not only initiate at the specimen edges but also at isolated locations inside the specimen, which could be related to the microstructural features. In addition, a clear effect of strain level on the measured off-axis crack density is observed. From the Xray CT experiments, it is found that the UD fibre fractures initiate and progress from regions where the off-axis backing fibre bundles are 'in contact' with a UD fibre bundle. Damage is seen to first initiate at a cross-over region of the backing fibre bundles, and later at a region with only one backing fibre bundle. In addition, applying tension to the specimen during X-ray CT scanning is found to reveal additional UD fibre fractures that are not visible in scans performed the unloaded state. With load applied, a significant number of UD fibre fractures were observed earlier in the fatigue life than expected. Based on the observations of the study a damage progression scheme is presented for quasi-UD fibre composites.

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  • Effect of graphitization on mechanical properties of untwisted carbon nanotube yarn and its strength development mechanism

    Taesung KIM, Anri HAYASHI, Hidefumi NIKAWA, Keiichi SHIRASU, Go YAMAMOTO, Toshiyuki HASHIDA, Atsushi HOSOI, Hiroyuki KAWADA

    Transactions of the JSME   84 ( 860 ) 17-00585 - 00585-17-00585  2018.04  [Refereed]

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    <p>Carbon nanotube yarn, which is an aggregation of Carbon nanotubes (CNTs), enables CNTs to be used on macro scale. However, tensile strength of the CNT yarn is much lower than CNT itself, and improvement of the mechanical properties is a challenge for practical application of the yarns. CNTs composing the yarns include some defect structures and impure materials, and their presence can cause a decrease in tensile strength of the yarn. In this study, untwisted CNT yarns were fabricated by dry spun method and graphitized at a temperature of 2800°C for the purpose of improving mechanical properties. Additionally, strength of a CNT composing the yarn and interactive force between the CNTs were evaluated to clarify strength development mechanism of the graphitized CNT yarn. Crystallinity of the CNT yarn was improved more than ten times, and defect structures and impure materials was removed by the graphitization treatment. As a result of single fiber tensile tests, strength of the yarn was increased by 20~35% after the graphitization. On the other hand, strength of the CNT composing the yarn was decreased. The breaking form of the CNT yarn was changed from pulling out of CNT bundles to rapture of the bundles by the graphitization, indicating an increase of interactive force between the bundles. In addition, as a result of pulling out simulations by molecular dynamics method, it was indicated that the pulling out of the CNT bundles were suppressed by increase in van der Waals force. Consequently, the improvement of mechanical properties of the untwisted CNT yarns was not due to the change in the strength of the CNT in the yarns but the main cause was the increase in the interactive force between the CNTs.</p>

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  • Development of Fatigue Crack Healing Technology for Ti-6Al-4V Alloy and Influence of Fatigue Crack Closure on Its Healing

    KOBAYASHI Rikuto, HORIUCHI Tomohiro, HOSOI Atsushi, KISHI Kimihiro, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2018 ( 0 ) 820 - 820  2018

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  • Effect of voids and degree of polymerization of matrix on tensile strength properties of continuous fiber reinforced composite materials with in-situ polymerizable phenoxy resin

    MIYATA Masafumi, SUZUKI Megumi, FUJIMOTO Masahito, HOSOI Atsushi, ETO Kazuya, SUGIYAMA Tetsuya, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2018 ( 0 ) 227 - 227  2018

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    <p>Tensile strength properties in the transverse direction of carbon fiber reinforced thermoplastic (CFRTP) laminates with in situ polymerizable phenoxy resin were evaluated. The unidirectional [90]14 laminates were formed using the prepreg, NS-TEPreg. By changing the conditions of fabricating CFRTP laminates, the void content in the laminates and the degree of polymerization of the matrix resin were varied. As the results of tensile tests and image analysis, it was revealed that when the void content inside the laminates is 0.5% or less, the influence of the void on tensile strength properties becomes limited. Also, as the results of measuring the average molecular weight of CFRTP laminates, it became clear that the transverse tensile strength σbT and transverse failure strain εbT increase as the average molecular weight of the matrix resin increases.</p>

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  • CVD synthesis of few-walled carbon nanotubes for creating high-strength untwisted carbon nanotube yarn

    OKUMO Kouichi, Tae Sung KIM, TAKAHASHI Kazuhiko, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2018 ( 0 ) 217 - 217  2018

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  • Evaluation of Fracture Toughness for Directly Bonded Joints between Aluminum Alloy and CFRTP Laminates

    ABE Hikaru, OTA Hiroki, SAITO Kei, WADA Keita, JESPERSEN Kristine Munk, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2018 ( 0 ) 421 - 421  2018

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  • Development of Fatigue Crack Healing Technology for Metallic Materials and Its Evaluation

    HOSOI Atsushi, HAMADA Eiich, KOBAYASHI Rikuto, KAWADA Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2018 ( 0 ) F041003  2018

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    <p>Establishment of fatigue crack healing technology for metallic materials is important to improve the safety and life of machinery and structures. Therefore, the authors developed a novel fatigue crack healing technique removing the oxide film on the crack surface by heat treatment and using plasticity induced crack closure generated during fatigue crack growth as a driving force of the healing. It was found that the resistance of the fatigue crack growth after crack healing was larger as the effect of the plasticity induced crack closure was larger.</p>

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  • Effect of stress ratio on through thickness fatigue properties of unidirectional and quasi-isotropic thick CFRP laminates with toughened interlaminar layers

    ARAI Tomoki, FUKUSHIMA Shinichiro, SEKI Sen, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   84 ( 863 ) 18 - 00039-18-00039  2018

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    <p>The effect of stress ratio on through thickness fatigue properties of thick carbon fiber reinforced plastic (CFRP) laminates with toughened interlaminar layers was evaluated. The unidirectional (UD) [088] and quasi-isotropic (QI) [45/0/-45/90]11S laminates were formed using prepregs (T800S/3900-2B) with toughened interlaminar layers. The spool shaped specimens were cut from the laminates. Static tensile and compressive tests were performed. As the results of the static tests on both laminates, the through thickness compressive strength was more than five times higher than tensile strength. The fracture morphology under compressive loading was difference between each laminate. Fatigue tests were performed under the stress ratio of R=0.1,-1,-3 and -6 on both laminates. As the results of the fatigue tests on both laminates, the fatigue life decreased as the stress ratio was lower. On the other hand, the remarkable difference of the fracture surface was not observed under each fatigue test condition by both macroscopic and microscopic observation in this study. The fatigue life of UD and QI specimens was able to be evaluated by the proposed model, the modified H-κ model based on strain energy approach. The predicted fatigue life was good agreement with the experimental results.</p>

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  • Prediction of tensile strength of injection-molded GF/PA considering effects of reinforcement fiber diameter and interfacial properties

    SHIRAKI Ryoji, OKAMOTO Takeshi, OZAWA Kento, KIM Tae Sung, HIRAYAMA Norio, TANIGUCHI Norihiko, NISHIWAKI Tsuyoshi, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   84 ( 860 ) 17 - 00582-17-00582  2018

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    <p>Fiber reinforced thermoplastics (FRTP) attracts attention as a lightweight material for mass-produced automobiles due to advantages such as excellent formability and recyclability in addition to high specific strength and specific rigidity. Many factors influence the improvement of the mechanical properties of FRTP. We have revealed that the tensile strength of injection-molded glass fiber/polyamide66 (GF/PA) improves as the reinforcement fiber diameter decreases in the wide strain rate range in previous researches. In addition, it was suggested that by using a strength prediction model of discontinuous fiber reinforcement, if the strength can be obtained for one diameter, the strength can be predicted for other diameters. In this study, we investigated the mechanism of the strength enhancement of the GF/PA associated with thinning of the reinforcement fibers and increase of the strain rate. To ascertain the interface properties, single-fiber pull-out tests were conducted on the GF/PA and it was confirmed that the interfacial shear strength (IFSS) of the GF/PA had strain rate dependency. The strength prediction of the GF/PA with the strain rate dependency of IFSS taken into account showed values closer to the experimental values than the values obtained from the prediction with an assumption that IFSS is constant regardless of the strain rate. Furthermore, investigating the factor of the increase in strength due to the thinning of the fibers suggested that the increase of the fiber strength is the dominant factor.</p>

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  • Development of carbon nanotube/copper composite yarn by electrodeposition and evaluation of ampacity

    KIM Taesung, SAKAI Takahiro, HOSHI Yuta, NIKAWA Hidefumi, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   84 ( 857 ) 17 - 00313-17-00313  2018

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    <p>Carbon nanotube yarn, which is an aggregate form of carbon nanotubes (CNTs), is expected to be practically used as a lightweight wiring material. In recent years, CNT/metal composite yarn has been fabricated for making the CNT yarn highly conductive. While improving conductivity in the CNT/metal composite yarns, current capacity, which determines durable current value of the wiring material, has not reached practical value. In this study, composite material of untwisted CNT yarn and copper was fabricated by plating treatment for the purpose of creating a lightweight wiring with larger ampacity than metal wiring. In addition, CNT/copper composite yarns having different composite structures were fabricated and the relationships between the composite structure and electric characteristics were evaluated. One of the composite yarns had a two-layer structure in which copper was deposited on the surface of the CNT yarn, and the other had a structure in which copper precipitated to the inside of the CNT yarn. As a result of the plating treatment using a copper sulfate bath, current capacity of the composite yarn reached 6.87×108 A/m2 at the copper volume fraction of 28.9%, and the specific current capacity was 1.29 times larger than copper wire. From evaluation of the fracture mechanism, it was revealed that combustion of the CNTs and melting of the metal part were suppressed by combining the CNT yarn with copper, and it led to the large ampacity. In addition, it was possible to electroplate inside of the yarn by adding a dipping step to the plating process. In the case of the composite yarn plated the inside, an increase in resistance under large current was suppressed and further improvement of the current capacity was achieved.</p>

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  • Influence of fiber orientation on impact energy absorbing performance of injection molded LFT

    SHIRAKI Ryoji, ADACHI Shogo, YABU Tomoya, ISHITSUKA Yuji, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and Mechanics Conference   2017 ( 0 ) OS1012  2017

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    <p>The energy absorbing performance of glass fiber reinforced thermoplastics was evaluated by progressive crushing tests with the Split Hopkinson Pressure Bar (SHPB) apparatus. Two types of specimens, one was injection molded glass long fiber reinforced polyamide 66 (GF/PA66), the other was twill weave glass fiber reinforced polyamide 6 (GF/PA6), were prepared as specimens. As for injection molded plates of the GF/PA66, it was investigated the influence of the fiber orientation on the impact mechanical behavior of the test specimen cut out from the different position of the plate. Also, the impact behavior of injection molded the GF/PA66 plates and that of twill weave GF/PA6 laminates were compared in order to investigate the influence of the variation of reinforcing types. As a result of the progressive crushing tests at -30, 23, 90°C, it is revealed that the energy absorbing performance has no temperature dependency regardless of the fiber orientation and the reinforcing types. The reason that the SEA of the GF/PA66 increases with the mechanical properties was discussed from the comparison of the specific energy absorption (SEA) and the compressive strength. In the comparison of injection molded the GF/PA66 and the GF/PA6 laminates, the specimens were reinforced by the different mechanisms; therefore, it seems that influence of mechanical properties on the SEA is not critical because those fracture modes are different.</p>

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  • Prediction of long-term durability of FRP under seawater environment

    HIROTSU Yuki, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and Mechanics Conference   2017 ( 0 ) OS1009  2017

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    <p>In recent years, applications of fiber-reinforced plastics (FRPs) to large marine structures are expected to improve their performances due to the high specific strength and stiffness and the corrosion resistance. However, the creep lifetime of FRPs in seawater environment has not been made clear so far. Objective of this study is to predict the creep lifetime of FRPs in seawater environment based on the accelerated test results and reveal the fracture mechanism. In this study, creep tests were carried out using the plain-woven GFRP and CFRP laminates under seawater environment and time-temperature superposition principle (TTSP) was used to predict the long-term creep rupture life. It was shown that the rupture time decreased with increase of the seawater temperature and the applied stress, and it was suggested that decrease of the strength was mainly caused by degradation of the interfacial shear strength between the fibers and the matrix. By using Larson-Miller parameter (LMP) as time-temperature parameter, the analytical results showed good agreement with the experimental results. For the GFRP laminates, behavior of the prediction curves varied in the lower applied stress because the glass fibers deteriorated in seawater. On the other hand, deterioration of carbon fibers was not observed in seawater so that the rupture time showed a consistent tendency to decrease for the CFRP laminates.</p>

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  • Establishment of fatigue crack healing technique of Ni-base superalloy Inconel 718

    KOBAYASHI Rikuto, MAEYAMA Taro, FUJITA Kohei, HOSOI Atsushi, KISHI Kimihiro, KAWADA Hiroyuki

    The Proceedings of the Materials and Mechanics Conference   2017 ( 0 ) GS1004  2017

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    <p>Ni-base superalloy Inconel 718 is used in structural members of aircraft engine parts. Its mechanical properties are deteriorated due to fatigue cracks at high temperature environment, but the processability of the material is poor and it is not easy to repair micro cracks. In this study, the fatigue crack healing technique for Inconel 718 was developed by controlling heating and cooling conditions in a furnace. Especially, the effect of the atmosphere on the fatigue crack healing was investigated. After the pre-fatigue crack was introduced using compact tension (CT) specimens, they were heated in vacuum or hydrogen atmosphere for the crack healing. The behavior of fatigue crack growth was evaluated before and after crack healing. As a result, the fatigue crack was successfully healed by heat treatment in hydrogen atmosphere whereas it was not healed in vacuum. The dimples which were characteristic fracture patterns in solid diffusion bonding were observed on the fracture surface of fatigue crack after crack healing treatment in hydrogen atmosphere. Thus, it was thought that the fatigue crack was healed because the hydrogen gas that has strong reduction power removed oxide film on the crack surfaces and solid diffusion bonding caused between the crack surfaces.</p>

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  • Fatigue Crack Healing in Austenitic Stainless Steel by Heat Treatment and Investigation of Its Healing Mechanisms

    MAEYAMA Taro, KOBAYASHI Rikuto, FUJITA Kohei, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2017 ( 0 ) J0450104  2017

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    <p>It is important to enhance the fatigue life of machines and structures to prevent their accidents. The healing technique of fatigue crack in metallic materials by heat treatment has been developed. A pre-fatigue crack was introduced using a compact tension (CT) specimen of austenitic stainless steel, SUS316, and the fatigue crack growth behavior was investigated before and after crack healing heat treatment. In this study, to investigate the effects of cooling atmosphere and rate on the crack healing treatment, air cooling, N2 gas cooling, rapid cooling in vacuum and slow cooling in vacuum were applied to the specimens. As the results, the healing effect was improved in the specimen cooled rapidly in a vacuum furnace. It was thought that the fatigue crack was healed during cooling process because the fatigue crack healing by air cooling was not done enough due to the oxidization on the crack surfaces. The healed crack length under the condition of slowly cooling in vacuum was improved. It was thought that there was longer time for atomic diffusion between the crack surfaces. U-shape boundary was observed on the fracture surface of the fatigue crack after the crack healing. The detailed observation with scanning electron microscopy (SEM) revealed that the U-shape boundary corresponded to the healed area on the fracture surface. This result suggested that the plasticity induced crack closure caused by fatigue crack growth was one of the driving forces for the crack healing.</p>

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  • Evaluation of Strength Degradation of Plain Woven CFRP laminates Immersed in Seawater for Long Term

    KOSHIMA Shuhei, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2017 ( 0 ) J0440201  2017

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    <p>The influence of long-term seawater immersion on the mechanical properties of plain woven CFRP laminates was evaluated by static tensile and tension fatigue tests. These tests were carried out on the CFRP immersed different time under seawater: 2566 hours and 4967 hours. The mechanical properties of the specimen for 2566 hours immersion decreased drastically; the tensile strength, the elastic modules and the fatigue strength at 106 cycles reduced by 21.3%, 12.3% and 30.7% compared with those of no immersion specimen, respectively. On the other hand, after 4967 hours immersion, it was found that the mechanical properties decreased slightly. From observation of the Scanning Electron Microscopy (SEM), it was clear that morphology of the fiber/matrix interface varied with the immersion time. However, there was a small difference on the interface fracture surface between 2566 hours and 4967 hours. These results indicated that degradation of the fiber/matrix interface progressed dramatically by 2566 hours, and after that, interface degradation gradually converged. Damage growth behavior under fatigue loadings was investigated by non-destructive inspections using soft X-ray photography and ultrasonic inspection. At first, matrix cracks occurred along 90° and ±45° fiber directions. After that, delamination occurred originating from the matrix crack. Then, these damages expanded as the number of cycles increased, and finally, the specimen broke as the longitudinal fiber in the 0°/90° layers damaged.</p>

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  • Evaluation of electrical properties of transparent conductive film prepared using graphene - supported Ag

    OBA Keisuke, SAKAGUCHI Daiki, ARAO Yoshihiko, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2017 ( 0 ) G0400103  2017

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    <p>Recently, Indium tin oxide (ITO) has been widely used as transparent conductive films (TCFs) in various electronic devices. However, ITO has many drawbacks such as high cost and brittleness. Nowadays, graphene is the ideal alternative for ITO because of its excellent transparency, electrical conductivity and mechanical flexibility by the effect of sp2 hybridized orbital. However, the electrical properties of graphene TCFs are inferior to those of ITO so additional processing to improve electrical properties is required. Achieving the purpose, there is a number of studies on composite graphene and conductive materials such as Ag. And now, new simple, low-cost methods are required. In this study, we used the liquid plasma method to combine graphene and Ag. This is a low-cost, simple method for the hybridization. Then we made graphene / Ag hybridized TCFs using thin layer graphene-supported Ag and evaluated some characteristics. Finally, we acquired transmittance and sheet resistance of the graphene / Ag hybridized TCFs.</p>

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  • Evaluation of initiation and multiplication of transverse crack in cross-ply CFRTP laminates at elevated temperatures

    HOSOI Atsushi, TERAUCHI Motoki, TSUNODA Dai, KIMURA Tatsuya, KOBIKI Akira, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   83 ( 855 ) 17 - 00312-17-00312  2017

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    <p>The effects of environment temperature on initiation and multiplication of transverse crack in cross-ply carbon fiber reinforced thermoplastic (CFRTP) laminates have been investigated. Static tensile tests for the cross-ply laminates and the 90° unidirectional laminates were carried out at room temperature, 93 °C and 130 °C, respectively. The transverse cracks were observed by soft X-ray photography. The tensile strength and the failure strain in the cross-ply laminates and the 90° unidirectional laminates at high temperature decreased compared to the values at room temperature. It was also found that the behavior of initiation and multiplication of the transverse cracks in the cross-ply laminates was changed due to the environment temperature. The experimental results under different temperature were analyzed by Weibull distribution on the basis of probabilistic model. Next, the energy release rate was calculated due to formation of a new micro crack based on the Weibull distribution. The predicted transverse crack density by Weibull distribution was compared with the experiment result and the reasonability of using Weibull distribution to CFRTP cross-ply laminates under high temperature was verified. It was found that the critical energy release rate of CFRTP laminates has decreased at high temperature and the experimental results showed that the matrix strength was decreased at high temperature. Also, the fiber-matrix interfacial fracture on the fracture surface of the 90° unidirectional laminates was observed in some areas at high temperature whereas the matrix fracture was observed at room temperature. Therefore, it was suggested that the interface strength between polymer and fiber was decreased at high temperature.</p>

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  • Evaluation of fatigue life of thick CFRP laminates with toughened interlaminar layers in out-of-plane and in-plane transverse directions

    SEKI Sen, ARAI Tomoki, FUKUSHIMA Shinichiro, HOSOI Atsushi, FUJITA Yuzo, TAKETA Ichiro, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   83 ( 851 ) 16 - 00571-16-00571  2017

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    <p>Fatigue properties of the thick carbon fiber reinforced plastic (CFRP) laminates with toughened interlaminar layers in the out-of-plane direction (Z direction) and in the in-plane transverse direction (T direction) were evaluated experimentally. Spool specimens were machined from the thick mother plates which were laminated prepregs of T800S/3900-2B unidirectionally. The specimens were attached to metal tabs to apply loads in the thickness direction of the specimen. The tensile strengths in Z and T direction were measured by static tensile tests and S-N curves were obtained by fatigue tests at a stress ratio of R=0.1. As the results, the tensile strength in Z direction was 24% lower than that in T direction. Fatigue strength in Z direction at 106 cycles was also 25% lower than that in T direction. It was observed using a digital microscope that the fracture occurred in intralaminar layers in both static tensile tests and fatigue tests in Z direction. The thermal residual stress which was generated during the fabrication process and the stress distribution by mechanical loadings in spool specimens were calculated by finite element analysis. The calculated results showed that compressive residual stress applied in intralaminar layers in T direction by restraining the thermal deformation. It is found that the static tensile and fatigue properties in Z direction were almost the same as those in T direction by evaluating with the stresses applied in the nearest intralaminar layer to the minimum cross-section in the spool specimen.</p>

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  • Effects of stacking sequence on static torsional properties of CFRP pipes

    Taichi Watanabe, Keisuke Satomura, Naoki Kimoto, Takato Nakamura, Tae Sung Kim, Atsushi Hosoi, Hiroyuki Kawada

    Zairyo/Journal of the Society of Materials Science, Japan   65 ( 8 ) 567 - 572  2016.08

     View Summary

    Carbon fiber reinforced plastics (CFRP) pipes are expected to substitute for steel drive shafts to improve motorcar's fuel efficiency and driving performance. The static torsional strength of CFRP pipes formed by a modified simultaneous multi ply winding method is 20% higher than that of CFRP pipes formed by a filament winding method owing to few initial flaws. As the results of static torsional tests regarding [90/-45/+45]6 pipes, it was revealed that the delamination from the prepreg end occurred in the innermost layer and propagated in the interlaminar area of the -45°/+45° plies before the final failure. It is expected to design stacking sequence for preventing the delamination. In this study, effects of stacking sequence on the static torsional properties of the CFRP pipes were investigated. [902/-45/+45]6 and [90/-45/90/+45]6 pipes were formed to investigate effects of lamination angle difference between adjacent plies. Maximum lamination angle difference of the [90/-45/90/+45]6 pipe is smaller than that of the [902/-45/+45]6 pipe. In case of the [90/-45/90/+45]6 pipes with small lamination angle difference, the initiation of the delamination was delayed because the interlaminar stress was reduced. Furthermore, [(90/-45/90/+45)6/90] pipes were formed to investigate effects of an application of a 90° layer on the innermost layer. The delamination from the prepreg end did not occur before the final failure by the application of a 90° layer on the innermost layer since the applied load on the prereg end was reduced. Finally, the static torsional strength of the [(90/-45/90/+45)6/90] pipes was 25% higher than that of the [902/-45/+45]6 pipes due to improvement of delamination resistance.

    DOI

  • Fatigue life prediction of thick CFRP laminates with toughnened interlaminar layers in the out-of-plane direction at different stress ratio

    Atsushi Hosoi, Shiwon Tsuge, Sen Seki, Yuzo Fujita, Ichiro Taketa, Hiroyuki Kawada

    ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials    2016

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    © 2016, European Conference on Composite Materials, ECCM. All rights reserved. The fatigue life of thick carbon fiber reinforced plastic (CFRP) laminates with toughened interlaminar layers in the out-of-plane direction was evaluated at different stress ratios. The spool shaped specimens were cut out the unidirectional thick CFRP laminates which pile up 88 plies of the prepreg with toughened interlaminar layer, T800S/3900-2B. The fatigue tests were conducted under the stress ratios of R = 0.1, -1, -3 and -6 to evaluate the effect of the stress ratio. As the results of the fatigue tests, the fatigue life of the specimens became shorter as the stress ratio became smaller, i.e. as the absolute values of the compressive stress became higher. It was found that the fatigue properties of the CFRP laminates in the out-of-plane direction are affected by the stress amplitude from the experimental results. In addition, the fatigue life under the different stress ratio was evaluated equivalently using the proposed model, modified H-κ model, which considers the strain energy. The analytical results showed good agreement with experimental results. In addition, the fatigue properties of the thick CFRP laminates in the out-of-plane direction were evaluated with the constant fatigue life diagram derived from the proposed model.

  • Development of untwisted carbon nanotube yarn with high strength by heat treatment

    Taesung Kim, Hidefumi Nikawa, Atsushi Hosoi, Hiroyuki Kawada

    ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials    2016

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    © 2016, European Conference on Composite Materials, ECCM. All rights reserved. Carbon nanotube (CNT) is increasingly applied as a reinforcement of polymer matrix composite because of extremely high mechanical properties. Among several forms of CNT reinforcement, CNT yarn can be a next-generation reinforcement which enables the use of CNTs in the macro-scale. In this study, untwisted CNT yarns were fabricated by the dry spinning method using a die and graphitized in order to develop CNT yarns with high strength and stiffness. Impure materials and defective structures on MWCNTs were removed after graphitization treatment. G/D ratio was improved more than 10 times. Stress transfer between constituent MWCNTs of CNT yarns became more effectively by removing impure materials. Consequently, macroscopic mechanical properties of CNT yarns were improved by the graphitization treatment in addition to improvement of MWCNT itself.

  • Evaluation of mechanical properties of untwisted carbon nanotube yarn by graphitization treatment

    TAKAHASHI Yui, KIM Tae Sung, NIKAWA Hidefumi, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2016 ( 0 ) 135 - 135  2016

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  • Development of Carbon nanotube yarn with high electric conductivity and current capacity

    SAKAI Takahiro, KIM Tae sung, NIKAWA Hidefumi, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2016 ( 0 ) 124 - 124  2016

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  • Initiation and Propagation of Transverse Crack in CFRTP Laminates at High Temperature

    TERAUCHI Motoki, HOSOI Atsushi, KOBIKI Akira, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2016 ( 0 ) 127 - 127  2016

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    <p>The effects of environment temperature on initiation and propagation of transverse crack in cross-ply carbon fiber reinforced thermoplastic (CFRTP) laminates have been investigated. Static tensile tests for the cross-ply laminates and the 90° unidirectional laminates were carried out at room temperature and high temperature (366K). The transverse cracks were observed by soft X-ray photography. In consequence, the tensile strength and the failure strain in the cross-ply laminates and the 90° unidirectional laminates at 366K decreased compared to the values at room temperature. It was also found that the behavior of initiation and propagation of the transverse cracks in the cross-ply laminates was changed due to the environment temperature. Fiber-matrix interfacial fracture on the fracture surface of the 90° unidirectional laminates was observed in some areas at high temperature whereas matrix fracture was observed at room temperature. Therefore, it was suggested that the interface strength between polymer and fiber was decreased at high temperature.</p>

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  • Study of energy absorption mechanism on progressive crushing of injection molded FRTP

    TSUNODA Daichi, ISHITSUKA Yuji, TANAKA Hiroyuki, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2016 ( 0 ) 126 - 126  2016

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    <p>The energy absorption mechanism on progressive crushing of injection molded fiber reinforced thermoplastics (FRTP) have been investigated with triggered coupon specimens. These materials consist of glass fiber and polyamide 6,6. Progressive crushing tests were carried out at -30, 23 and 90°C. The energy absorption performances on progressive crushing were constant independently of the temperature nevertheless the impact compressive strength decreased as the temperature rises. In the observation of fracture surface, matrix was stretched in the direction of shear. Furthermore, in the observation of fracture morphology using high speed camera, plural crack were formed during crushing. According to the above results, it was suggested that mode I/II fracture toughness affect the energy absorption performance.</p>

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  • Manufacturing and characterization of graphene transparent conductive films by using liquid phase exfoliation

    SAKAGUCHI Daiki, ARAO Yoshihiko, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2016 ( 0 ) 415 - 415  2016

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    <p>Transparent conductive films (TCFs) are widely used in various electronic devices. In addition, due to the excellent transparency (T=97.7%) and electrical conductivity by the effect of sp2 hybridized orbital, using graphene for the materials of TCFs is ideal. Typical method for manufacturing graphene TCFs is chemical vapor deposition (CVD) method. However, CVD method takes a high cost. On the other hand, liquid phase exfoliation (LPE) is the method for obtaining thin-layer graphene by peeling graphite in the organic solvent. In the LPE, method of making graphite oxide and peeling graphite is often used, but this method has problem that falling down conductivity due to structural defect in graphene. In this study, we used pressure homogenizer to obtain thin-layer graphene without using chemical treatment. Then, we made TCFs by using thin-layer graphene and evaluated some characteristics. Finally, we investigated transmittance and sheet resistance of the TCFs.</p>

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  • The Effect of Cooling Conditions on the Fatigue Crack Healing of Austenitic Stainless Steel by Heat Treatment

    FUJITA Kohei, FURUYA Yuto, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of the Materials and processing conference   2016 ( 0 ) 608 - 608  2016

    DOI CiNii

  • Development of Metal Carbon Nanotube Composite Yarn with High Electric Conductivity and Current Capacity

    KAJIHARA Kotaro, KIM Tae Sung, SAKAI Takahiro, NIKAWA Hidefumi, HOSOI Atsushi, KAWADA Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2016 ( 0 ) G0400104  2016

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    <p>Carbon nanotube (CNT) is attracted a lot of attention for new conductors because of its high current capacity, comparing with copper. In past study, carbon nanotube-copper (CNT-Cu) composite sheet was developed, which exhibiting similar conductivity as copper, but with a 100-times higher current capacity. However, since the length of CNT-Cu conductors was limited to several hundred μm long, the problem that using CNT with high electrical properties macroscopically remains to be solved. Therefore, in this study, untwisted CNT yarn was prepared by drawing multiwall carbon nanotube through die and was electroplated to realize metal CNT composite yarn with high electric conductivity and current capacity. For the influence of copper oxide layer, the electrical property of copper CNT composite yarn (CNT-Cu) showed a poor improvement from the untreated CNT yarn. On the other hand, both conductivity and current capacity of gold CNT composite yarn (CNT-Au) showed a higher value by the heat treating at 800°C, comparing with that of untreated CNT-Au.</p>

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  • Healing of Fatigue Crack in Metallic Materials by Heat Treatment and Evaluation of Fatigue Crack Propagation

    FURUYA Yuto, OKAMURA Takashi, TAKEDA Shoma, HOSOI Atsushi, KIMURA Sehiro, MORITA Yuji, KAWADA Hiroyuki

    The Proceedings of Mechanical Engineering Congress, Japan   2016 ( 0 ) J0460101  2016

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    <p>Infrastructures built in the period of high economic growth have been used over their design life and the accidents due to aging and fatigue fracture become a serious problem. Therefore, the technique of healing fatigue cracks in metallic materials was developed by heat treatment. In this study, the effect of the cooing rate during crack healing treatment on the properties of fatigue crack growth was investigated using austenitic stainless steel, SUS316, and low carbon steel, S25C. The specimens were cooled with nitrogen gas or oil to evaluate the effect of cooling rate. As a result, the crack healing effect of SUS316 was improved by rapid cooling with oil. Although the delay of crack growth of S25C was observed, the cause was due to the change of the metallographic structure by rapid cooling. The dimples were observed on the fracture surface of fatigue crack after crack healing treatment. Thus, it was thought that the crack healing was caused by solid diffusion bonding.</p>

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  • Influence of fiber diameter on impact tensile properties of injection-molded long glass fiber reinforced polyamide

    OZAWA Kento, KIM Tae Sung, TSUNODA Daichi, ARAO Yoshihiko, TANIGUCHI Norihiko, NISHIWAKI Tsuyoshi, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   0 ( 0 )  2016

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    Applications of fiber reinforced plastics have been expanding due to improvement of not only fuel efficiency but also the motion performance of some recent vehicles. Especially, the demand for injection-molded fiber reinforced thermoplastics is expected to increase because of their superior moldability, productivity and recyclability. In this study, the influence the fiber diameter has on the impact tensile properties of long glass-fiber reinforced polyamide (GF/PA) is investigated using the split Hopkinson pressure bar method. Prior to the tensile tests, an investigation of the fiber-orientation distribution was conducted in order to cut out specimens with the same fiber orientation angle from the injection molded plate. Two types of specimens, referred to as specimens with high- and low orientation angle, were manufactured using glass fibers with average diameters of 13, 17, 23 μm. In the tensile test, the GF/PA with smallest fiber diameter showed the highest tensile strength and the most significant strain rate dependency on the strength. These effects were more significant for the specimens with high orientation angle. From SEM observations on the fracture surface and an average fiber length measurement, it was observed that the interfacial fracture and the fiber breakage were dominant failure modes under the considered tensile loading conditions. It was suggested that decreasing the stress acting on the fiber/matrix interface by reducing the fiber diameter affected the improvement of the GF/PA strength. Using the modified linear rule of mixtures, the tensile strength was predicted. The predictions showed good agreement with experimental results. Therefore, it is believed that the decrease of critical fiber length is the reason that the impact tensile properties are higher for the samples with smaller fiber diameter.

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  • Effects of stacking sequence on torsional fatigue properties of CFRP pipes

    WATANABE Taichi, SATOMURA Keisuke, KIMOTO Naoki, NAKAMURA Takato, KIM Tae Sung, HOSOI Atsushi, KAWADA Hiroyuki

    Transactions of the JSME (in Japanese)   0 ( 0 )  2016

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    Application of carbon fiber reinforced plastics (CFRP) pipes to torque transmission shafts makes it possible to improve automotive driving performance as well as fuel efficiency. A modified simultaneous multi ply winding method was developed as a new forming method for CFRP pipes using prepregs. The CFRP pipes formed by the method have fewer initial flaws, such as voids and fiber waviness. It resulted in 20 % increase in the static torsional strength than conventional CFRP pipes formed by a filament winding method. In this study, effects of stacking sequence on the torsional fatigue properties of the CFRP pipes formed by the modified method were investigated. Torsional fatigue tests were conducted under load control. All tests were conducted at the test frequency f=1 Hz, the maximum applied torque Tmax=1.0 kNm and the stress ratio R=0.1. [902/-45/+45]6 and [90/-45/90/+45]6 pipes were formed to investigate effects of lamination angle difference between adjacent plies. Maximum lamination angle difference of the [90/-45/90/+45]6 pipe is smaller than that of the [902/-45/+45]6 pipe. When the CFRP pipes had smaller lamination angle difference, the initiation and growth of the delamination from the prepreg end in the innermost layer were delayed because interlaminar stress was reduced. Moreover, [(90/-45/90/+45)6/90] pipes were formed to investigate effects of an application of a 90° layer on the innermost layer. As the result, the delamination hardly initiated since the shear stress on the prereg end was reduced. Consequently, the fatigue life of the [(90/-45/90/+45)6/90] pipes increased seven-fold than that of the [902/-45/+45]6 pipes due to improvement of delamination resistance under cyclic torsional loading.

    CiNii

  • OS1408-248 Mechanical properties of unidirectional CFRP using CNTs-grafted carbon fiber

    TERAUCHI Motoki, OZAWA Sadayuki, Kim Tae Sung, KAWADA Hiroyuki

      2015   "OS1408 - 248-1"-"OS1408-248-3"  2015.11

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    Combining composites with nanoscale materials such as Carbon Nanotubes (CNTs) has attracted much attention, because various synergic effects can be realized easily. Especially, grafting CNTs onto carbon fibers and reinforcing the interface between resin and the fibers are promising approaches in enhancing the mechanical properties. In this study, the effects of CNTs grafted onto carbon fibers on the mechanical properties of multiscale CFRP were investigated. CNTs were grafted on carbon fibers by chemical vapor deposition (CVD) using a Fe-Cu catalyst system at temperature <600 ℃. As a result, degradation of the properties of the carbon fibers was suppressed. Interfacial shear strength (IFSS) was increased by 45.8%. After that, static tensile test of unidirectional CFRP (0° and 10°) was performed. The elastic modulus was increased by CNTs around the carbon fibers. In case of the 10° specimens, the shear yield stress increased by 41.9%. It was the result from improvement of the yield strength of matrix resin around the carbon fibers by grafting CNTs.

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  • 129 Fabrication of carbon nanotube-supported platinum nanoparticles for fuel cell electrode using liquid phase plasma treatment

    NAKAMURA Kodai, KIM Tae Sung, HOSOI Atsushi, KAWADA Hiroyuki

    Materials and processing conference   2015 ( 23 ) "129 - 1"-"129-5"  2015.11

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    In this study, we synthesized cup-stacked carbon nanotubes (CSCNT) supported platinum nanoparticles (PtNPs) using liquid phase plasma treatment, and morphology, particle size distribution and supported amount of the PtNPs supported onto the CSCNT were investigated. PtNPs were supported onto the CSCNT surfaces using liquid phase plasma treatment after adsorption of Pt precursor onto the CSCNT surfaces. First, observation of the CSCNT surfaces with field-emission transmission electron microscopy (FETEM) were conducted to examine the morphology of the PtNPs supported onto the CSCNT surfaces. PtNPs were well anchored and uniformly dispersed on the CSCNT surfaces without any dispersion stabilizer due to an exposure of the dangling bonds of graphene sheet which has high chemical reaction field. Moreover, the PtNPs size distribution of the CSCNT supported PtNPs were investigated with FETEM images of the CSCNT surfaces. The average size of PtNPs supported onto the CSCNT surfaces was about 2.2 nm, which was smaller than the PtNPs of conventional electrode catalysts for PEFC (3〜5 nm). Thermogravimetric analysis (TGA) of the CSCNT supported PtNPs were performed to investigate the supported amount of Pt of the CSCNT supported PtNPs. The supported amount of Pt was about 14.7 wt%, which was smaller than the PtNPs of conventional electrode catalysts for PEFC (50〜60 wt%).

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  • 120 The effect of compressive load on out-of-plane fatigue properties of thick CFRP laminates with interlaminar toughened layers

    TSUGE Shiwon, SEKI Sen, HOSOI Atsushi, FUJITA Yuzo, TAKETA Ichiro, KAWADA Hiroyuki

    Materials and processing conference   2015 ( 23 ) "120 - 1"-"120-3"  2015.11

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    An effect of compressive loads on the out-of-plane fatigue properties of thick CFRP laminates with the toughened interlaminar layers was investigated. The unidirectional [O_<88>] and quasi-isotropic [45/0/-45/90]_<11s> laminates were fabricated using T800S/3900-2B prepreg. This prepreg is constituted of a fiber layer and an interlaminar toughened layer in which polyamide particles are dispersed uniformly. The spool shaped specimens which were machined from the thick laminates were loaded in the out-of-plane direction of the specimen. The fatigue tests were performed at three types of stress ratios of R= 0.1, -1 and -3. As the results of the fatigue tests, it was conformed that the fatigue life was reduced with the compressive load under same maximum stress. In addition, the effect of the stress ratio on the fatigue life was dependent on the laminate configuration. When the cyclic loading at R= -3 were applied in the unidirectional specimen, the shear fracture mode was observed in the high-cycle region.

    CiNii

  • Dimensional stability of epoxy-based and cyanate-based carbon fiber-reinforced plastics

    Yoshihiko Arao, Taro Fukui, Tomoyuki Niwa, Hiroyuki Kawada

    JOURNAL OF COMPOSITE MATERIALS   49 ( 12 ) 1483 - 1492  2015.05  [Refereed]

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    In this article, the dimensional stability of epoxy- and cyanate-based laminates is discussed, focusing on the thermal deformation, moisture-induced deformation, and deformation induced by relaxation of thermal residual stress. Each of the deformations was calculated independently based on the laminate theory. The material properties of the unidirectional laminates were obtained by conducting thermal mechanical analysis, moisture absorption tests, and tensile creep tests. These material properties were adopted to the laminate theory to predict the deformation of quasi-isotropic laminate, and it was calculated that each type of deformation induced micron-level dimensional instability. The moisture-induced deformation was an order of magnitude larger than that caused by the other factors. The validity of the calculations was confirmed by comparing the calculated results with the experimental ones. It is important to control moisture absorption even if cyanate resin, which has high moisture resistance, is used.

    DOI

  • (6)層間高靭性化CFRPクロスプライ積層板の繰り返し荷重下におけるトランスバースクラック発生評価(論文,日本機械学会賞〔2014年度(平成26年度)審査経過報告〕)

    川田 宏之, 曽我 理昂, 重盛 洸, 細井 厚志, 藤田 雄三

    日本機械学會誌   118 ( 1158 ) 257 - 258  2015.05

    CiNii

  • Effect of stress ratio on fatigue characteristics in the out-of-plane direction of thick CFRP laminates with toughened interlaminar layers

    Atsushi Hosoi, Shigeyoshi Sakuma, Sen Seki, Yuzo Fujita, Ichiro Taketa, Hiroyuki Kawada

    ICCM International Conferences on Composite Materials   2015-July  2015

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    © 2015 International Committee on Composite Materials. All rights reserved. The effect of the stress ratio on fatigue characteristics in the out-of-plane direction of thick carbon fiber reinforced plastic (CFRP) laminates with toughened interlaminar layers was evaluated. The spool shaped specimens cut out the unidirectional thick CFRP laminates, which pile up 88 plies of the prepreg with toughened interlaminar layer, T800S/3900-2B, were used. The fatigue tests were conducted under the stress ratios of R = 0.1 and -1 to evaluate the effect of the stress ratio. As the results of the fatigue tests, the fatigue life of the specimens at R = -1 was shorter than that at R = 0.1. It was found that the fatigue properties of the CFRP laminates in the out-of-plane direction are affected by the stress amplitude from the experimental results. In addition, the fatigue life under the different stress ratio can be evaluated equivalently using the Walker model which can consider the mean stress effect.

  • Strain rate dependent tensile properties of injection molded long glass fiber reinforced thermoplastics

    Taesung Kim, Yoshihiko Arao, Norihiko Taniguchi, Tsuyoshi Nishiwaki, Atsushi Hosoi, Hiroyuki Kawada

    ICCM International Conferences on Composite Materials   2015-July  2015

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    © 2015 International Committee on Composite Materials. All rights reserved. Long Fiber reinforced Thermoplastics (LFT) have been used in a lot of industrial fields such as automotive industries because of their excellent moldabilities, productivities, and high mechanical properties compared with injection molded Short Fiber reinforced Thermoplastics (SFT). On the other hand, mechanical properties of LFT are significantly low compared with continuous fiber reinforced plastics. So, improvements of them are still important study subjects. In past studies, there were some reports about the absorbed impact energy of LFT, and LFT showed higher energy absorption property than SFT. However, there have been few studies focused on strength, stiffness and their strain rate dependencies of LFT in impact loading condition. These quantitative evaluations are essential to material design for developments of impact-resistant LFT. In this study, mechanical properties and strain rate dependency of injection molded long glass fiber reinforced thermoplastics under impact loading were investigated. The effectiveness of longer residual fibers to improvement of impact properties of injection molded composites was indicated. LFT showed higher mechanical properties compared with SFT at any strain rate in this study. Increasing rate of tensile strength in LFT was also much higher than that in SFT, and significant improvement of impact properties of injection molded composites were achieved by longer residual fibers. As a result of observation of micro structures and fracture surfaces after impact tensile test, it was confirmed that the fracture occurred mainly in matrix and fiber/matrix interface in the case of SFT. On the other hand, in LFT specimens, impact tensile loading was effectively transferred to reinforcement glass fibers, and they were broken after impact tensile test. Consequently, it was revealed that strain rate dependency of glass fiber strength resulting from the slow crack growth development led to high impact tensile properties of LFT.

  • Evaluation of transverse crack initiation in cross-ply and quasi-isotropic CFRP laminates under fatigue loading

    Atsushi Hosoi, Yuzo Fujita, Hiroyuki Kawada

    34th ICAF Conference and 28th ICAF Symposium, ICAF 2015   2   550 - 555  2015

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    © 28th ICAF Symposium, ICAF 2015. All rights reserved. A method has been proposed to predict the fatigue life to the transverse crack initiation in cross-ply and quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates. The six kinds of the laminates were formed of the two kinds of the prepregs, T800S/3900-2B with toughened interlaminar layers and T800H/3631 without toughened interlaminar layers. The unidirectional and cross-ply laminates of the stacking sequence of [90]12, [0/904]S and [0/906]S were formed of the T800S/3900-2B prepreg, and the cross-ply and quasi-isotropic laminates of the stacking sequence of [0/902]S, [0/906]S and [45/0/-45/90]S were formed of T800H/3631 prepreg. Tensile fatigue tests were performed under load control using a hydraulic fatigue testing machine. The transverse crack initiation in the laminates under fatigue loading was evaluated by modifying the Smith-Watson-Topper (SWT) model, which can evaluate the mean stress effect on the fatigue life. Finally, it was found that the initiation of transverse crack in the laminates with the various laminate configuration can be predicted using the modified SWT model, and that means that it is possible to predict the initiation of transverse crack in the laminates with the various laminate configuration using S-N curve of unidirectional laminates in 90° direction.

  • Mechanical properties of densified untwisted carbon nanotube yarn / epoxy composites

    Risa Yoshizaki, Kim Tae Sung, Atsushi Hosoi, Hiroyuki Kawada

    ASME 2015 International Manufacturing Science and Engineering Conference, MSEC 2015   1  2015  [Refereed]

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    Carbon nanotubes (CNTs) have very high specific strength and stiffness. The excellent properties make it possible to enhance the mechanical properties of polymer matrix composites. However, it is difficult to use CNTs as the reinforcement of long fibers because of the limitation of CNT growth. In recent years, a method to spin yarns from CNT forests has developed. We have succeeded in manufacturing the unidirectional composites reinforced with the densified untwisted CNT yarns. The untwisted CNT yarns have been manufactured by drawing CNTs through a die from vertically aligned CNT arrays. In this study, the densified untwisted CNT yarns with a polymer treatment were fabricated. The tensile strength and the elastic modulus of the yarns were improved significantly by the treatment, and they were 1.9 GPa and 140 GPa, respectively. Moreover, the polymer treatment prevented the CNT yarns from swelling due to impregnation of the matrix resin. Finally, the high strength CNT yarn composites which have higher volume fraction than a conventional method were successfully fabricated.

    DOI

  • Prediction of initiation of transverse cracks in cross-ply CFRP laminates under fatigue loading by fatigue properties of unidirectional CFRP in 90 degrees direction

    Atsushi Hosoi, Shigeyoshi Sakuma, Yuzo Fujita, Hiroyuki Kawada

    COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING   68   398 - 405  2015.01  [Refereed]

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    A fatigue life to the initiation of transverse cracks in cross-ply carbon fiber-reinforced plastic (CFRP) laminates has been predicted using properties of the fatigue strength of unidirectional CFRP in the 90 degrees direction. In the experiments, unidirectional [90](12) laminates were used to obtain a plot of maximum stress versus number of cycles to breaking, and two types of cross-ply laminates of [0/90(4)](s) and [0/90(6)](s) were used to evaluate the initiation and multiplication of transverse cracks under fatigue loading. Transverse cracks were studied by optical microscopy and soft X-ray photography. Analytical and experimental results showed good agreement, and the fatigue life for transverse crack initiation in cross-ply laminates was predicted successfully from the fatigue strength properties of the unidirectional CFRP in the 90 degrees direction. The prediction results showed a conservative fatigue life than the experimental results. (C) 2014 Elsevier Ltd. All rights reserved.

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  • Evaluation of mechanical properties of untwisted carbon nanotube yarn for application to composite materials

    Kaoru Sugano, Masashi Kurata, Hiroyuki Kawada

    CARBON   78   356 - 365  2014.11  [Refereed]

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    Carbon nanotubes (CNTs) with superior mechanical properties have been of interest as reinforcement for polymer composites. However, the length of individual CNTs is limited. As a solution, yarns spun by twisting together multi-walled carbon nanotubes (MWCNTs) have been reported. In this study, untwisted CNT yams were prepared by a non-conventional method drawing CNTs through a die. The MWCNTs in these yarns are held together by strong van der Waals forces that arise due to the interactions on the long and smooth surfaces of the MWCNTs. Here, mechanical properties of untwisted CNT yarn were studied by tensile tests. The strength of the CNT yarn was increased by increasing the apparent density of the yarn. The CNT yarns showed high tensile strength of 1 GPa and elastic modulus of 79 GPa at a yam diameter of 35 gm. The interfacial shear strength between the CNT yarn and epoxy resin was studied by the microdroplet method, and it was very low. The wettability of the CNT yarn was affected by a type of curing agent. A unidirectional composite of epoxy resin and CNT yam was prepared by the pultrusion molding method. Mechanical properties of the unidirectional composite were affected by the type of curing agent. (C) 2014 Elsevier Ltd. All rights reserved.

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  • Fatigue strength properties of interlaminar toughened CFRP laminates under cyclic loading in the out-of-plane direction

    SHIGEMORI Ko, HOSOI Atsushi, FUJITA Yuzo, KAWADA Hiroyuki

    TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A   80 ( 812 ) SMM0087 - SMM0087  2014

     View Summary

    In this study, fatigue strength properties of interlaminar toughened CFRP laminates in the out-of-plane direction, or through thickness, were investigated. Thick laminates whose stacking sequence was unidirectional were formed with 88 plies of T800S/3900-2B prepreg. The T800S/3900-2B prepreg is constituted of fiber layer and interlaminar toughened layer in which polyamide particles are dispersed. The material properties of the thick laminates were measured by compression test and 4-points shear test. Spool specimens machined from the thick laminates were loaded in the out-of-plane direction. Stress distributions of spool specimens were evaluated by FE analysis. Fiber layer and interlaminar toughened layer in the each ply were modeled separately in the analysis. In comparison to the out-of-plane direction, the properties of in-plane transverse direction were investigated with 90° thin laminates. To evaluate the fatigue strength properties quantitatively, an analytical equation was introduced for the results of fatigue test. The fracture surfaces of the specimens after static and fatigue tests were observed by SEM. From the observation of the fracture surfaces after fatigue test, it was found that the interfacial debonding between fiber and matrix was occurred due to cyclic loading in both of specimens. In addition, it was observed that crack generated from debonding grew in the fiber layer until ultimate fracture. Moreover, the experimental and analytical results showed that, in comparison to the in-plane transverse direction, the fatigue life in the out-of-plane direction is shorter.

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  • Evaluation of transverse crack initiation in interlaminar toughened CFRP cross-ply laminates under cyclic loading

    KAWADA Hiroyuki, SOGA Masaki, SHIGEMORI Ko, HOSOI Atsushi, FUJITA Yuzo

    TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A   80 ( 812 ) SMM0079 - SMM0079  2014

     View Summary

    Initiation and growth behaviors of a transverse crack occurred in interlaminar toughened CFRP cross-ply laminates under cyclic loading were evaluated. Specimens whose stacking sequence is [0/904]S and [0/906]S were formed with T800S/3900-2B prepreg. The specimen edges were observed with an optical microscope and a laser microscope to investigate the behavior of transverse crack initiation and growth. To observe the edge surface of the specimen at arbitrary loading cycles, a replica technique was used. In addition, soft X-ray photography was used to observe internal damage. The number of cycles to transverse crack initiation was predicted quantitatively by applying the normalized modified Paris law, which shows the relationship between transverse crack density growth rate and normalized energy release rate range associated with transverse crack formation. Analytical results showed good agreement with experimental results. It was found that transverse crack initiation in interlaminar toughened CFRP laminates can be evaluated by applying the normalized modified Paris law. Moreover, in comparison to the laminates with and without toughened layers, the fatigue life to transverse crack initiation was prolonged due to the toughened layers. From damage observation, it was cleared that a transverse crack path to the thickness direction of the laminate was prevented by polyamide particles in the toughened layers. Therefore, it was found that the toughened layers dispersed polyamide particles to prevent delamination are effective for obstructing initiation of a transverse crack under cyclic loading.

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  • Lifetime prediction of woven GFRP laminates under constant tensile loading in hydrothermal environment

    Masahiro Kotani, Yusuke Yasufuku, Naoki Inoue, Ken Kurihara, Hiroyuki Kawada

    Mechanics of Time-Dependent Materials   17 ( 2 ) 261 - 274  2013.05

     View Summary

    This study aims to investigate the effects of a hydrothermal environment on the creep behavior of woven glass fiber reinforced plastics (GFRPs) and to propose a method for predicting their lifetime. Toward this end, experiments were carried out in air and deionized water at 40, 60, 80 and 95 °C. Static tensile tests of woven GFRP were conducted in air and in deionized water to evaluate its mechanical properties and to determine suitable experimental conditions for subsequent constant tensile load tests. The mechanical properties of the woven GFRP decreased with an increase in temperature and with water immersion. Constant tensile load tests were also conducted in air and in deionized water to investigate the creep behavior and fracture time. The fracture time decreased with an increase in stress and water temperature and demonstrated the possibility of a threshold stress for fracturing. In addition, the fracture time during each constant tensile load test was predicted using a modified Reiner-Weissenberg (R-W) criterion, which is a failure criterion for linear viscoelastic materials based on the accumulation of dissolved energy within the GFRP. In this study, the R-W criterion was modified to consider the effects of degradation and its acceleration, which are due to the applied stress and immersion in a solution. The predicted results were in good agreement with the experimental data when considering the effects of hydrothermal aging. © 2012 Springer Science+Business Media, B. V.

    DOI

  • Time-dependent deformation of CFRP quasi-isotropic laminates caused by relaxation of thermal residual stress and physical aging

    Tomoyuki Niwa, Yoshihiko Arao, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   79 ( 803 ) 950 - 960  2013

     View Summary

    In this paper, time-dependent dimensional change in quasi-isotropic laminates induced by relaxation of thermal residual stress and physical aging was predicted by the classical lamination theory. CFRP with pitch-based carbon fiber and cyanate ester resin was chosen for the study. Viscoelastic properties were investigated by performing tensile creep test for unidirectional laminates in the transverse direction. In addition, shrinkage strain induced by physical aging was studied by measuring the strain change of unidirectional laminates as well. Shrinkage strain in off-axis layers was calculated by using the coordinate-transform method. Shrinkage strain in 60° and 45° laminates were measured and the results were compared with the calculation. From the comparison, it was found that shrinkage strain of off-axis layers can be calculated by using the coordinate-transform method. Experimental results were applied to the classical theory in order to predict the time-dependent dimensional change of quasi-isotropic laminates. The strain change in quasi-isotropic laminates was obtained experimentally, and the result was compared with the prediction. It was verified that the time-dependent deformation of quasi-isotropic laminates can be predicted with a με-order by using proposed prediction method. © 2013 The Japan Society of Mechanical Engineers.

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  • Effect of ply thickness on transverse crack initiation in CFRP cross-ply laminates under fatigue loading

    Ken Kurihara, Atsushi Hosoi, Narumichi Sato, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   79 ( 799 ) 249 - 265  2013

     View Summary

    The effect of ply thickness on the formation of first transverse crack caused in cross-ply carbon fiber reinforced plastic (CFRP) laminates was evaluated under fatigue loading. In addition, the initiation process of the transverse crack was observed with an atomic force microscopy (AFM) in detail. The formation of the first transverse crack was evaluated quantitatively with the power law between the transverse crack density growth rate and the normalized energy release rate range associated with transverse crack formation. The analytical results showed good agreement with the experimental results. Moreover, from the analytical results with the cross-ply [0/906]s and [02/9012]s laminates, it was shown that the fatigue life to the formation of the first transverse crack in [0/906]s is approximately 100 times longer than that in [02/9012]s. Furthermore, as the results observed the process of the transverse crack initiation with AFM, it was cleared that matrix resins around fibers were uplifted on the laminate edge surface due to cyclic loading. The observation results indicate that the micro cracks are initiated at the interface between fiber and matrix resin by the stress concentration due to the uplift of matrix resins, that the micro cracks grow to the thickness direction in 90° plies with concatenating the interfacial cracks and that the transverse crack is formed finally. © 2013 The Japan Society of Mechanical Engineers.

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  • 816 Lifetime Assessment of Delayed Fracture in High Corrosion Resistance GFRP Laminate under Hydrochloric Acid and Deionized Water

    YAJIMA Masahide, KOTANI Masahiro, KAWADA Hiroyuki

    Materials and processing conference   2012 ( 20 ) "816 - 1"-"816-4"  2012.11

     View Summary

    In this paper, we investigated the lifetime of delayed fracture in woven glass fiber reinforced plastics (GFRP) laminate under corrosive environment, which possess high corrosion resistance. Corrosive environments discussed in this paper were deionized water and hydrochloric acid (1.0mol/l) at 80℃, and in air for comparison. First, static tensile test of GFRP was conducted in order to evaluate its mechanical properties after immersion for 0-2000h into corrosive environment. The mechanical properties of GFRP in deionized water didn't decrease, but, that in hydrochloric acid decreased slightly. Also, the mechanical properties of GFRP after immersion decreased toward certain values with increasing immersion time regardless of the solution. Finally, constant tensile load test of GFRP was conducted in all environments to investigate its lifetime of delayed fracture. The fracture time shortened with the increase of the applied stress. In addition, the fracture time in hydrochloric acid was shorter than that in deionized water. Furthermore, we predicted the lifetime using Reiner-Weissenberg (R-W) criterion. The predicted results showed good agreement with the experimental data while considering the degradation of GFRP in corrosive environments.

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  • 812 Time-dependent dimensional change of Quasi-isotropic laminates for CF/Epoxy and CF/Cyanate

    NIWA Tomoyuki, ARAO Yoshihiko, KAWADA Hiroyuki

    Materials and processing conference   2012 ( 20 ) "812 - 1"-"812-5"  2012.11

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  • 811 Effect of Fiber Content on Transverse Crack Initiation in Cross-Ply CFRP Laminates Subjected to Fatigue Loading

    HOSOI Atsushi, SHIGEMORI Ko, SATO Narumichi, KAWADA Hiroyuki

    Materials and processing conference   2012 ( 20 ) "811 - 1"-"811-4"  2012.11

    CiNii

  • Experimental Study on Impact Tensile Property of Glass Fiber

    TANIGUCHI Norihiko, ARAO Yoshihiko, NISHIWAKI Tsuyoshi, HIRAYAMA Norio, NAKAMURA Koichi, KAWADA Hiroyuki

      38 ( 4 ) 137 - 143  2012.07

    CiNii

  • Strain-rate dependence of the tensile strength of glass fibers

    Yoshihiko Arao, Norihiko Taniguchi, Tsuyoshi Nishiwaki, Norio Hirayama, Hiroyuki Kawada

    JOURNAL OF MATERIALS SCIENCE   47 ( 12 ) 4895 - 4903  2012.06  [Refereed]

     View Summary

    It is well known that the strength of glass fibers increases with increasing strain rate. Consequently, impact strength of glass fiber is competitive with that of carbon fiber. This strengthening phenomenon is well recognized for bulk glass. Strain-rate dependence of the strength for bulk glass was described by considering slow crack growth in glass. The analytical model that considered the slow crack growth of glass is proposed to predict the strength of glass fibers. The proposed model considered the stress corrosion limit and a constant crack velocity region. Calculations showed almost same results with the previous model, however, some differences were confirmed. To discuss the validity of the analysis, tensile tests of E-glass fiber bundles were conducted at various strain rates. It was observed that the fracture behaviors differ with the strain rates. Experimental results showed that the strength of E-glass fibers increased with increasing strain rate. Furthermore, we confirmed that the analytical results were in good agreement with the experimental results. The strain-rate dependence of the strength of glass fibers was successfully predicted by considering the slow crack growth in glass.

    DOI

  • Simple method for obtaining viscoelastic parameters of polymeric materials by incorporating physical-aging effects

    Yoshihiko Arao, Okudoi Yukie, Jun Koyanagi, Shin-ichi Takeda, Hiroyuki Kawada

    MECHANICS OF TIME-DEPENDENT MATERIALS   16 ( 2 ) 169 - 180  2012.05  [Refereed]

     View Summary

    A simple method for obtaining viscoelastic parameters from the results of static tensile tests is presented herein. Viscoelastic parameters were obtained by fitting experimental results and calculated results based on the power law model and linear viscoelasticity. The static tensile tests were carried out at various pre-aging times and the effect of physical aging was determined. The data confirmed that the physical aging process has a significant effect on the viscoelastic behavior. A creep test was conducted in order to discuss the validity of the prediction using the results of the static tensile test. It was confirmed that the predictions based on the viscoelastic parameters obtained from static tensile tests cannot adequately model actual viscoelastic behavior. The effective time theory was incorporated into the prediction in order to account for the progress of physical aging. It was verified that incorporating effective time theory into the prediction allows for the precise prediction of the long-term viscoelastic behavior.

    DOI

  • Prediction of first transverse crack formation in cross-ply CFRP laminates under fatigue loading

    A. Hosoi, K. Kurihara, N. Sato, H. Kawada

    8th Asian-Australasian Conference on Composite Materials 2012, ACCM 2012 - Composites: Enabling Tomorrow's Industry Today   1   173 - 178  2012

     View Summary

    The formation of a first transverse crack in cross-ply CFRP laminates was predicted under fatigue loading and the fatigue limit of transverse crack initiation was evaluated quantitatively. Transverse cracks induce more serious damage, such as delamination or fiber breakage. It is essential to understand the mechanism of the transverse crack initiation for improving long-term durability of CFRP laminates. Therefore, a method was proposed to predict the number of cycles to transverse crack initiation in cross-ply CFRP laminates under fatigue loading. Two types of cross-ply CFRP laminates, [0/90 6]s and [02/9012]s, of different thickness were used for fatigue tests. As the results, we were successful in predicting the number of cycles to transverse crack initiation under fatigue loading and evaluating the fatigue limit of the transverse crack initiation by the proposed analysis. Moreover, it was found that the fatigue life to transverse crack initiation in [0/906]s laminate was approximately 100 times longer than that in [02/90 12]s laminates. © 2012 by Asian-Australian Association for Composite Materials (AACM).

  • Prediction of compressive strength for unidirectional fiber reinforced plastics in considering effect of strain-rate dependency on mechanical properties of constituent materials

    Naoki Inoue, Norihiko Taniguchi, Tsuyoshi Nishiwaki, Norio Hirayama, Koichi Nakamura, Yoshihiko Arao, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   78 ( 793 ) 1284 - 1299  2012

     View Summary

    This study presents an analytical model to predict compressive strength of unidirectional FRP. Proposed model considers the effect of strain-rate dependency on mechanical properties of constituent materials. The model is based on the elastic foundation model and the microbuckling model of fiber which has initial misalignment in matrix. Compressive deformation of unidirectional FRP is considered by dividing into fiber microbuckling region and plastic kinking region. Additionally, to take into consideration the change in compressive deformation mode accompanying fiber volume fraction or fiber microbuckling, A mode function is introduced. The predictions from the proposed model are compared with experimental results of unidirectional E-glass/Epoxy and T700SC/Epoxy evaluated by using the conventional split Hopkinson pressure bar method. Incorporating strain-rate dependency on compressive modulus of reinforcement calculated from composite mixture law, the predictions are found to be in good agreement with experimental results of strain-rate dependency on compressive strength. Accuracy of the prediction is improved by changing the mode function. © 2012 The Japan Society of Mechanical Engineers.

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  • Prediction of transverse crack initiation in [0 m/90 n] s cross-ply CFRP laminates subjected to fatigue loading by static tensile test

    Atsushi Hosoi, Keigo Takamura, Narumichi Sato, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   78 ( 791 ) 1000 - 1012  2012

     View Summary

    A method to predict quantitatively the first of transverse cracks accumulated in the various types of [0 m/90 n] s cross-ply carbon fiber reinforced plastic (CFRP) laminates subjected to fatigue loading was proposed. On the basis of the assumption that the mechanism of transverse crack initiation is equivalent to that of transverse crack increase in the earlier stage of fatigue within low transverse crack density, the cycles at which a transverse crack initiates are calculated by applying the normalized modified Paris law, which shows the relationship between the transverse crack density growth rate and the normalized energy release rate range associated with the transverse crack formation. When the constants of the normalized modified Paris law are given with an arbitrary cross-ply laminate, the proposed method makes possible to predict the initiation of a transverse crack in the other various types of cross-ply laminates under fatigue loading by only measuring the stress at which a transverse crack initiates under static tensile loading. © 2012 The Japan Society of Mechanical Engineers.

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  • Experimental study on impact tensile property of glass fiber

    Norihiko Taniguchi, Yoshihiko Arao, Tsuyoshi Nishiwaki, Norio Hirayama, Koichi Nakamura, Hiroyuki Kawada

    ADVANCED COMPOSITE MATERIALS   21 ( 2 ) 165 - 175  2012  [Refereed]

     View Summary

    The tensile properties of E-glass, which is the most popular reinforcement fiber in composite materials, were determined from the experimental results of fiber bundle testing under a high strain rate. The tests were performed by using two types of experimental methods. One is the tension-type split Hopkinson bar system and the other is the universal highspeed tensile-testing machine. In the results, it was demonstrated that the tensile strength and fracture strain of E-glass fiber increased with the strain rate. The absorbed strain energy, therefore, significantly increased. It was also shown that the strain rate dependency of E-glass fiber tensile strength was strongly affected by fiber diameter. The smaller diameter of E-glass fiber has the stronger strain rate dependency. Finally, the impact tensile strengths of high-strength glass and carbon fibers were investigated. It was confirmed that the tensile strength of the high-strength glass fiber also increased with the strain rate, but the tensile properties of carbon fiber were almost independent of the strain rate.

    DOI

  • J043044 Off-Axis Delayed Fracture Characteristic of Woven GFRP in Hydrothermal Environment

    HATTORI Satoshi, KOTANI Masahiro, KAWADA Hiroyuki

    Mechanical Engineering Congress, Japan   2011   "J043044 - 1"-"J043044-5"  2011.09

     View Summary

    This paper aims to clarify the off-axis delayed fracture characteristic of woven GFRP laminate by the constant tensile load test in hydrothermal environment. Experimental condition discussed in this paper are air and deionized water at 40 -C. Static tensile tests of woven GFRP laminate were conducted to examine the off-axis directionnal mechanical properties and to determine the stress level for the constant tensile load test. It turned out that the maximum stress, elastic modulus and Poisson's ratio slightly decreased and the fracture strain decreased greatly in deionized water. Constant tensile load tests of woven GFRP laminate were conducted to investigate the delayed fracture characteristics: the strain response and fracture time. The stress level of constant tensile load test was determined to be 15, 30 and 45% of the maximum stress obtained from static tensile tests. As a result of constant tensile load test, it was ascertained that the strain increase with the increase of the applied load and the immersion in deionized water.

    CiNii

  • J043024 Fatigue Life Prediction for Initiation of Transverse Crack Caused in Cross-Ply CFRP Laminates under Cyclic Loading by Static Tensile Test

    HOSOI Atsushi, SOGA Masaki, SATO Narumichi, KAWADA Hiroyuki

    Mechanical Engineering Congress, Japan   2011   "J043024 - 1"-"J043024-4"  2011.09

     View Summary

    A method to predict quantitatively the initiation of a transverse crack caused in the various types of [0・90,1 cross-ply carbon fiber reinforced plastic (CFRP) laminates subjected to fatigue loading was proposed. On the basis of the assumption that the mechanism of transverse crack initiation is equivalent to that of transverse crack increase in the earlier stage of fatigue within low transverse crack density, the cycles that a transverse crack initiates are calculated by applying the normalized modified Paris law, which shows the relationship between the transverse crack density growth rate and the normalized energy release rate range associated with the transverse crack formation. Once the constants of the normalized modified Paris law are given with an arbitrary cross-ply laminate, the proposed method makes possible to predict the initiation of a transverse crack in the other various types of cross-ply laminates under fatigue loading by only measuring the stress at which a transverse crack initiates under static tensile loading.

    CiNii

  • Quantitative evaluation of fatigue damage growth in CFRP laminates that changes due to applied stress level

    Atsushi Hosoi, Keigo Takamura, Narumichi Sato, Hiroyuki Kawada

    INTERNATIONAL JOURNAL OF FATIGUE   33 ( 6 ) 781 - 787  2011.06  [Refereed]

     View Summary

    The change of fatigue damage behavior depending on an applied stress level in carbon fiber reinforced plastic (CFRP) laminates was evaluated quantitatively in this study. To evaluate damage growth, the energies released due to transverse crack propagation and delamination growth per unit length with consideration of transverse crack propagation were derived. Moreover, the transverse crack propagation and the delamination growth were evaluated using a modified Paris law that gives the relationship between the damage growth rate and the energy released due to damage growth. As a result, it was found that the growth of the transverse crack and the delamination could be evaluated with the unique Paris law constants, respectively. Finally, it was concluded that the change of the fatigue damage growth behavior was caused due to the difference of the growth rate of the transverse cracks and delamination at an applied stress level. (C) 2011 Elsevier Ltd. All rights reserved.

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  • Effect of ply angle misalignment on out-of-plane deformation of symmetrical cross-ply CFRP laminates: Accuracy of the ply angle alignment

    Yoshihiko Arao, Jun Koyanagi, Shin Utsunomiya, Hiroyuki Kawada

    COMPOSITE STRUCTURES   93 ( 4 ) 1225 - 1230  2011.03  [Refereed]

     View Summary

    This paper discusses the accuracy of ply angle alignment and how it relates to out-of-plane deformation in carbon fiber reinforced plastics (CFRP) laminates. We investigated the deformation of symmetrical cross-ply laminates under hot and humid conditions. In spite of the symmetrically stacked laminates, unpredictable out-of-plane deformation occurred over time due to ply angle misalignment. The deformation was unstable and disproportionate to the absorbed moisture. A Monte Carlo simulation based on laminate theory was performed to quantify the deformation induced by the ply angle misalignment. Symmetrical cross-ply laminates were found to twist as they absorbed water when they underwent ply angle misalignments. By comparing the analytical results with experimental results, we concluded that a standard deviation of approximately 0.4 exists as ply angle misalignment in the laminates used in this study and that this slight ply angle misalignment can be a significant factor in out-of-plane deformation of cross-ply laminates. (C) 2010 Elsevier Ltd. All rights reserved.

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  • Delayed Fracture of GFRP Laminates under Constant Tensile Load in Hydrochloric Acid

    KOTANI Masahiro, YAMAMOTO Yohei, KAWADA Hiroyuki

    JSMME   5 ( 12 ) 669 - 677  2011

     View Summary

    This paper aims to clarify the delayed fracture mechanism for glass fiber reinforced plastics (GFRP) in corrosive environments. The GFRP under study is composed of plain NCR-glass cloth and vinylester resin, which both possess high corrosion resistance. In this study, the experimental conditions were performed in air, deionized water, and hydrochloric acid at 40°C. Static tensile tests of woven GFRP were performed to evaluate the mechanical properties and determine the experimental conditions for the constant tensile load tests in each environment. The mechanical properties of the woven GFRP decreased with its immersion into deionized water and hydrochloric acid. The stress-strain curve decreased intensely after the knee point especially in hydrochloric acid, which is possibly because of the damage accumulation generated by the solution and applied stress. Constant tensile load tests of the woven GFRP were performed to investigate the creep behavior and fracture time in each environment. The strain and strain rate increased in the tests in deionized water and hydrochloric acid, which are the result of decrease in the stiffness owing to immersion in each solution. In addition, delayed fracture occurred in deionized water and hydrochloric acid, and the lifetimes in hydrochloric acid were shorter than those in deionized water. Moreover, it was suggested from fracture surface observations that the delayed fracture of the woven GFRP under a constant tensile load in a corrosive environment is dominated by degradations in the fiber reinforcement and fiber/matrix interface.

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  • Evaluation of transverse crack initiation in cross-ply CFRP laminates under fatigue loading

    Keigo Takamura, Atsushi Hosoi, Narumichi Sato, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   77 ( 779 ) 1123 - 1134  2011

     View Summary

    In this study, transverse crack initiation in cross-ply CFRP laminates under fatigue loading was evaluated focusing on the transverse crack growth and saturation. The number of cycles that a transverse crack initiates was predicted by the analytical model on the basis of the modified Paris law. In addition, the lower threshold of the transverse crack formation was researched by a modified Paris-law, and the fatigue limit of the transverse crack initiation was evaluated by calculating the stress applied in 90° layer where the increase of the transverse cracks was saturated. Moreover, transverse crack was observed by using scanning electron microscope (SEM) in order to investigate the mechanism of transverse crack initiation. As the results, the analytical results for predicting the transverse crack initiation showed good agreement with the experimental results. Moreover, it was shown that the lower threshold of the transverse crack formation existed, and that the stress applied in 90° layer at saturation state was almost equivalent to the fatigue limit of the transverse crack initiation from the experimental results. From the observation with SEM, it was found that the initiation of the transverse crack under fatigue loading depended on the interface property between fiber and matrix. © 2011 The Japan Society of Mechanical Engineers.

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  • Strength Prediction Method for Glass Fiber Embedded in Single Fiber Composite in Hydrothermal Environment

    Masahiro Kotani, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   77 ( 783 ) 1956 - 1966  2011

     View Summary

    Mechanical properties of glass fiber reinforced plastics (GFRP) mainly depend on the mechanical properties of the glass fiber, which decreases with stress and corrosion. Thus, the calculation method to predict the residual fiber strength after exposure to stress and corrosion is required. In this paper, constant strain test of single fiber composite (SFC) was conducted in hydrothermal environment (deionized water) at 40• •and 75• •to apply the stress and the hydrothermal aging. The residual fiber strength after constant strain test was evaluated by fiber fragmentation test. Besides, the residual strength of glass fiber was predicted using subcritical crack growth model. In the subcritical crack growth model, the surface flaw on the fiber surface which arises while manufacturing was assumed as an ideal crack. The crack growth rate was expressed by the combination of Paris law and Arrhenius model, and the strain history of constant strain test was integrated into the calculation. The residual strength of the glass fiber was calculated based on the fracture mechanics discussing the crack length. The predicted results of the fiber strength showed good agreement with the experimental data at various experimental conditions and the validity of the proposed model was ascertained in this paper. © 2011, The Japan Society of Mechanical Engineers. All rights reserved.

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  • Prediction of time-dependent dimensional change induced by thermal residual stress relaxation in CFRP cross-ply laminates

    Yoshihiko Arao, Yukie Okudoi, Shin-Ichi Takeda, Jun Koyanagi, Shin Utsunomiya, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   77 ( 780 ) 1238 - 1246  2011

     View Summary

    In this paper, time-dependent dimensional change in a symmetrical cross-ply laminates was predicted by transverse properties of the CFRP laminates. CFRP with pitch-based carbon fiber and cyanate ester resin was chosen for the study. Viscoelastic property was obtained by performing tensile creep test for unidirectional laminates in the transverse direction. In addition, shrinkage caused by physical aging was obtained by measuring the strain change for unidirectional laminates as well. Experimental results were applied to the classical lamination theory in order to predict the time-dependent dimensional change of a symmetrical cross-ply laminates. The strain change in a symmetrical cross-ply laminates was obtained experimentally using an extensometer, and the result was compared with the prediction. From the comparison, it was concluded that the proposed prediction method is appropriate. It was also found that physical aging shrinkage must be compensated in order to evaluate the relaxation modulus from tensile creep test result. The effect of physical aging shrinkage must also be considered in prediction of time-dependent deformation in cross-ply laminates. © 2011 The Japan Society of Mechanical Engineers.

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  • Evaluation of Transverse Crack Initiation in Cross-Ply CFRP Laminates under Fatigue Loading

    TAKAMURA Keigo, HOSOI Atsushi, SATO Narumichi, KAWADA Hiroyuki

    TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A   77 ( 779 ) 1123 - 1134  2011

     View Summary

    In this study, transverse crack initiation in cross-ply CFRP laminates under fatigue loading was evaluated focusing on the transverse crack growth and saturation. The number of cycles that a transverse crack initiates was predicted by the analytical model on the basis of the modified Paris law. In addition, the lower threshold of the transverse crack formation was researched by a modified Paris-law, and the fatigue limit of the transverse crack initiation was evaluated by calculating the stress applied in 90° layer where the increase of the transverse cracks was saturated. Moreover, transverse crack was observed by using scanning electron microscope (SEM) in order to investigate the mechanism of transverse crack initiation. As the results, the analytical results for predicting the transverse crack initiation showed good agreement with the experimental results. Moreover, it was shown that the lower threshold of the transverse crack formation existed, and that the stress applied in 90° layer at saturation state was almost equivalent to the fatigue limit of the transverse crack initiation from the experimental results. From the observation with SEM, it was found that the initiation of the transverse crack under fatigue loading depended on the interface property between fiber and matrix.

    CiNii

  • Out-of-Plane Deformation due to the Ply Angle Misalignment in CFRP Laminates (The Effect of the Stacking Sequence on Thermal Deformation)

    ARAO Yoshihiko, KOYANAGI Jun, TAKEDA Shin-ichi, UTSUNOMIYA Shin, KAWADA Hiroyuki

    Transactions of the Japan Society of Mechanical Engineers Series B   77 ( 776 ) 619 - 628  2011

     View Summary

    Strict geometrical stability is required for the precise structures like telescopes. Unpredictable out-of-plane deformation is a serious problem when we use CFRP (Carbon Fiber Reinforced Plastic) laminate to the precise structure. This out-of plane deformation of symmetrical CFRP laminate mainly arise from combination effects of ply angle misalignment and temperature change. We discussed here is effective stacking sequence of CFRP laminate that mitigate the deformation caused by the ply angle misalignment. The analysis based on laminate theory was performed to calculate the thermal deformation. In this analysis, the random numbers were added to each layers as ply angle misalignments. The analytical results were obtained statistically by Monte Carlo method. Mohr's curvature circle was also incorporated to evaluate the deformation as P-V (peak to Valley) values. We performed the analysis with various stacking sequence. It was calculated that the symmetric cross-ply laminates deformed 10 times larger than the other quasi-symmetric laminates. In the case of the total ply number is less than 12, the stacking sequence in the laminate has a significant effects on the thermal deformation. However, if the total number ply number is more than 24, effect of stacking sequence on the thermal deformation becomes negligible. We also discussed the geometrical stability of CFRP mirror by considering unavoidable ply angle misalignment. It was presumed that the CFRP mirror can be used for wide range of wave length when the back structure was attached to CFRP laminates.

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  • Strength Prediction Method for Unidirectional GFRP after Hydrothermal Aging

    Masahiro Kotani, Yohei Yamamoto, Youhei Shibata, Hiroyuki Kawada

    ADVANCED COMPOSITE MATERIALS   20 ( 6 ) 519 - 535  2011  [Refereed]

     View Summary

    This paper proposes a strength prediction method for unidirectional glass fiber reinforced plastics (GFRPs) after hydrothermal aging: immersion in deionized water at 80 degrees C. First, the strength degradation of the constituents (i.e., the glass fiber and the fiber/matrix interface) of unidirectional GFRP after hydrothermal aging was evaluated from the fiber strength and the interfacial shear stress by using a single-fiber composite (SFC). Both the fiber strength and the interfacial shear stress had a tendency to decrease in the early stage of hydrothermal aging and to saturate toward certain values with long-term aging. In addition, the tensile strength of the unidirectional GFRP was measured after hydrothermal aging. The residual strength of the unidirectional GFRP also had a tendency to decrease sharply in the early stage of hydrothermal aging and to saturate toward a certain strength with long-term aging. Finally, the residual strength of the unidirectional GFRP after hydrothermal aging was predicted using the global loading sharing (GLS) model, by considering the degradation of both the glass fiber and the fiber/matrix interface. The predicted results indicated good agreement with the experimental data while considering not only the degradation of the fiber reinforcement but also the fiber/matrix interface adhesion. It was concluded that the GLS model applied considering the degradation of the GFRP constituents would be a suitable and a simple model to predict the residual strength of the unidirectional GFRP after hydrothermal aging. (C) Koninklijke Brill NV, Leiden, 2011

    DOI

  • An Improvement of the Glass Fiber Strength Embedded in a Resin by Removing Moisture around the Fiber Surface

    ARAO Yoshihiko, KOTANI Masahiro, SATO Shinya, KAWADA Hiroyuki

    Journal of JSEM   10 ( 4 ) 420 - 424  2010.12

    CiNii

  • Interfacial Property of GFRP in Hydrothermal Environment : Evaluation of Interfacial Adhesive Strength Using Unidirectional GFRP

    KOTANI Masahiro, ARAO Yoshihiko, TAKAHASHI Aki, HATTORI Satoshi, KOBIKI Akira, KAWADA Hiroyuki

    Journal of JSEM   10 ( 4 ) 413 - 419  2010.12

    CiNii

  • 531 Strengthening Mechanism of glass fiber under cryogenic temperature

    NOGUCHI Yohei, KOTANI Masahiro, ARAO Yoshihiko, TANIGUCHI Norihiko, NISHIWAKI Takeshi, HIRAYAMA Norio, KAWADA Hiroyuki

    Materials and processing conference   2010 ( 18 ) "531 - 1"-"531-4"  2010.11

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  • A Numerical Simulation of Time-Dependent Interface Failure Under Shear and Compressive Loads in Single-Fiber Composites

    Jun Koyanagi, Akinori Yoshimura, Hiroyuki Kawada, Yuichiro Aoki

    APPLIED COMPOSITE MATERIALS   17 ( 1 ) 31 - 41  2010.02  [Refereed]

     View Summary

    We performed a numerical simulation of a time-dependent interfacial failure accompanied by a fiber failure, and examined their evolution under shear and compressive loads in single-fiber composites. The compressive load on the interface consists of Poisson&apos;s contraction for matrix resin subjected to longitudinal tensile load. As time progresses, compressive stress at the interface in the fiber radial direction relaxes under the constant longitudinal tensile strain condition for the specimen, directly causing the relaxation of the interface frictional stress. This relaxation facilitates the failure of the interface. In this analysis, a specific criterion for interface failure is applied; apparent interfacial shear strength is enhanced by compressive stress, which is referred as quasi-parabolic criterion in the present study. The results of the stress recovery profile around the fiber failure and the interfacial debonding length as a function of time simulated by the finite element analysis employing the criterion are very similar to experimental results obtained using micro-Raman spectroscopy.

    DOI

  • G0400-2-3 Evaluation of Transverse Crack Initiation in Cross-ply CFRP Laminates under Fatigue Loading

    TAKAMURA Keigo, HOSOI Atsushi, SATO Narumichi, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2010   359 - 360  2010

     View Summary

    The initiation of a transverse crack in CFRP laminates under fatigue loading was investigated. Transverse cracks cause serious damage, such as delamination or fiber breakage. It is essential to understand the mechanism of the transverse crack onset for improving long-term durability and reliability of CFRP laminates. Therefore, a method to evaluate and predict the initiation of a transverse crack in cross-ply CFRP laminates under fatigue loading was researched. Fatigue tests at the various stress levels were performed in order to evaluate the initiation and propagation of the transverse cracks. The analytical method on the basis of Paris law in order to predict the number of cycles of transverse crack initiation was proposed. As the results, we were successful in predicting the initiation of the transverse crack under fatigue loadings by the proposed analysis.

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  • High Accurate Space Telescope Mirror Made by Light and Thermally Stable CFRP

    KOYANAGI Jun, ARAO Yoshihiko, UTSUNOMIYA Shin, TAKEDA Shin-ichi, KAWADA Hiroyuki

    JSMME   4 ( 11 ) 1540 - 1549  2010

     View Summary

    This paper reports a development of space telescope mirror made by light and thermally stable CFRP. We first compare thermal stabilities of a mirror made by CFRP with a conventional that made by glass material. The superior point regarding the thermal stability of the CFRP mirror to the glass mirror is described. One of the most critical issues for CFRP mirror is the mirror-surface roughness deterioration induced by "fiber-print through". We made a prototype mirror consisting of only CFRP with a gel-coating on the mirror surface, addressing the issue. The gel-coated mirror-surface roughness was 20 nmRMS just after fabrication. Durability of the surface roughness under various hostile conditions is examined in the present study.

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  • Residual Stress Relaxation in CFRP Cross-ply Laminate

    ARAO Yoshihiko, KOYANAGI Jun, OKUDOI Yukie, OTSUKA Masanori, KAWADA Hiroyuki

    JSMME   4 ( 11 ) 1595 - 1604  2010

     View Summary

    We measured residual stress relaxation in epoxy-based CFRP laminates and cyanate-based CFRP laminates. We estimated the residual stress in symmetric cross-ply laminates by measuring the curvature of unsymmetric cross-ply laminates and investigated the relaxation of the residual stress by measuring the curvature of unbalanced laminates in a nitrogen environment. Our experimental results demonstrated that the residual stress in both kinds of laminate can decay by approximately 15% after 500 hours at 40°C. The stress relaxation can be modeled by the power law model. Viscoelastic parameters were obtained by a quasi-static tensile test to predict stress relaxation. The validity of the prediction is discussed.

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  • Study of Strength Degradation Mechanism of Woven GFRP in Water Environment

    KOTANI Masahiro, YASUFUKU Yusuke, TAMAISHI Yusuke, KAWADA Hiroyuki

    JSMME   4 ( 11 ) 1574 - 1584  2010

     View Summary

    This paper presents an experimental investigation into the effects of water temperature and immersion times on the tensile strength degradation of plain-woven glass fiber reinforced plastics (GFRP) laminates. GFRP specimens were tested as-received and after hydrothermal aging in deionized water at 40 °C, 80 °C, 95 °C to evaluate their tensile properties. The strength and rupture strain had a tendency to decrease drastically in the early stages and to saturate toward certain strength with long-term aging, regardless of the water temperature. The fracture surfaces were examined by scanning electron microscopy (SEM) to study the fracture mechanisms of woven GFRP after hydrothermal aging. While the strength of the glass fiber decreased, the fracture surfaces of the E-glass fibers flattened, and the mirror zones on the fracture surfaces enlarged. Interfacial degradation was confirmed by fiber pull-out, and the debonded fibers showed no resin matrix adhesion to the fiber surfaces. These experimental results suggest that the degradation in the strength of woven GFRP is dominated by degradation of their fiber reinforcement and the fiber/matrix interface.

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  • Evaluation of transverse crack initiation in cross-ply CFRP laminates under high-cycle fatigue loading

    Keigo Takamura, Atsushi Hosoi, Narumichi Sato, Hiroyuki Kawada

    7th Asian-Australasian Conference on Composite Materials 2010, ACCM 2010   1   273 - 276  2010

     View Summary

    This study focused on the initiation of a transverse crack in cross-ply CFRP laminates under fatigue loading. Transverse cracks induce more serious damages, such as delamination or fiber breakage. It is essential to understand the mechanism of the transverse crack onset under fatigue loading for improving long-term durability and reliability of CFRP laminates. Therefore, a method to evaluate and predict the initiation of a transverse crack in cross-ply CFRP laminates under fatigue loading was proposed. Fatigue tests at various stress levels were performed to evaluate the initiation and multiplication of the transverse cracks. Fatigue tests were interrupted at arbitrary loading cycles to observe damage in cross-ply CFRP laminates. The transverse cracks caused in the laminates were observed by an optical microscope and soft X-ray photography. The fatigue limit of transverse crack initiation in this fatigue conditions was indicated by calculating the stress applied in 90° layer of the laminates at the saturated state of the transverse cracks with a variational approach. Moreover, the analytical method on the basis of Paris law in order to predict the number of cycles to transverse crack initiation under fatigue loading was proposed. As the results, the predicted number of cycles to transverse crack initiation shows good agreement with experimental results.

  • Monitoring of internal residual strain changes in CFRP using FBG sensors

    Shin-ichi Takeda, Jun Koyanagi, Shin Utsunomiya, Yuto Kinoshita, Yoshihiko Arao, Hiroyuki Kawada

    FOURTH INTERNATIONAL CONFERENCE ON EXPERIMENTAL MECHANICS   7522  2010  [Refereed]

     View Summary

    FBG (Fiber Bragg Grating) sensors were embedded into CFRP unidirectional composite laminates in a direction perpendicular to the carbon fiber. Residual strains after curing were evaluated by the reflection spectrum from the FBGs. The CFRP laminates were kept at 100 degrees C for monitoring of the residual strain change measured by the FBGs. Without mechanical loading, occurrence of physical aging was confirmed by the residual strain changes. The relationship between the influence of physical aging on residual strain and the thickness of the CFRP was almost linear.

    DOI

  • Time-dependent deformation of surface geometry on light weight and thermally stable CFRP mirror in humid environment

    Yoshihiko Arao, Jun Koyanagi, Shin Utsunomiya, Shin-ichi Takeda, Hiroyuki Kawada

    MODERN TECHNOLOGIES IN SPACE- AND GROUND-BASED TELESCOPES AND INSTRUMENTATION   7739  2010  [Refereed]

     View Summary

    CFRP (Carbon Fiber Reinforced Plastics) is the ideal material for space based mirror due to its low thermal expansion, and high specific modulus. To expand the use of CFRP, we investigated the long-term stability of CFRP under humid environment. CFRP mirror was made as precise as possible by using special class of material and adopting particular design techniques. Dimensional stability of CFRP mirror was evaluated by nano-scale measurement. The factors which cause out-of-plane deformation of the mirror is discussed.

    DOI

  • Development of Space Telescope Mirror Made by Light and Thermally Stable CFRP

    Jun Koyanagi, Yoshihiko Arao, Hiroshi Terada, Shin Utsunomiya, Shin-ichi Takeda, Hiroyuki Kawada

    FOURTH INTERNATIONAL CONFERENCE ON EXPERIMENTAL MECHANICS   7522  2010  [Refereed]

     View Summary

    This study aims development of space telescope mirror made by light and thermally stable CFRP. For that, we must solve a problem called "print-through"; the fiber pattern of the carbon fiber appears on the surface. We investigated the temperature-induced surface roughness variation experimentally and analytically.

    DOI

  • Analysis of Thermal Deformation on a Honeycomb Sandwich CFRP Mirror

    Yoshihiko Arao, Jun Koyanagi, Shin Utsunomiya, Hiroyuki Kawada

    MECHANICS OF ADVANCED MATERIALS AND STRUCTURES   17 ( 5 ) 328 - 334  2010  [Refereed]

     View Summary

    Thermal deformation analysis was performed on a carbon fiber reinforced plastic (CFRP) mirror with sandwich structure. To obtain unexpected asymmetry of the surface sheet, we investigated the deformation of a quasi-isotropic laminate under hot and humid conditions. Despite the symmetric lay-up, quasi-isotropic laminate deforms into twisted saddle shape with time, and this deformation could be simulated by assuming ply angle misalignment. Then, the elastic moduli of honeycomb cores were calculated theoretically. A honeycomb sandwich mirror model was constructed by adopting a sheet model and using honeycomb elements. The thermal deformation analysis was performed considering the ply angle misalignment. The test results clarified that the deformation of the surface sheet was a critical factor in the dimensional stability of the CFRP mirror.

    DOI

  • High-cycle fatigue characteristics of quasi-isotropic CFRP laminates over 10(8) cycles (Initiation and propagation of delamination considering interaction with transverse cracks)

    Atsushi Hosoi, Narumichi Sato, Yasuyuki Kusumoto, Keita Fujiwara, Hiroyuki Kawada

    INTERNATIONAL JOURNAL OF FATIGUE   32 ( 1 ) 29 - 36  2010.01  [Refereed]

     View Summary

    High-cycle fatigue features of over 108 cycles, particularly the initiation and propagation of edge delamination considering the effects of transverse cracks, were investigated using quasi-isotropic carbon-fiber-reinforced plastic (CFRP) laminates with a stacking sequence of [45/0/-45/90](s) in this study. In the relationship between a transverse crack density and initiation and growth of edge delamination, it was found that fatigue damage growth behavior varied depending on applied stress. It was observed that edge delamination initiated and grew at parts where transverse cracks were dense at ordinary applied stress, whereas it was observed that edge delamination grew before or simultaneously with transverse crack propagation at a low applied stress and high-cycle loading. In addition, the critical transverse crack density where delamination begins growing was calculated to evaluate the interaction between transverse crack and edge delamination growth. (C) 2009 Elsevier Ltd. All rights reserved.

    DOI

  • Strain-rate dependency of interfacial strength in Polymer Matrix composite

    Taiji Ohishi, Shinya Sato, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   76 ( 766 ) 669 - 671  2010

     View Summary

    The interfacial strength is the most important mechanical property among those of constituents in Polymer Matrix Composite : PMC. In this study, we conducted the tensile tests on Single Fiber Composite specimen and observed initiation of interfacial debonding at different loading rates. As a result, we recognized dependency of the interfacial strength on strain rates. According to the elasto-plastic analysis assuming that matrix's yield stress varies depending on strain rates, the stress distribution of the interface becomes close to the elastic analysis and it can be concluded that the dependency of interfacial strength on strain rates is caused by matrix's dependency on strain rates.

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  • Tensile fracture properties of single glass fiber in cryogenic environment

    Mamoru Hayakawa, Norihiko Taniguchi, Tsuyoshi Nishiwaki, Norio Hirayama, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   76 ( 766 ) 652 - 654  2010

     View Summary

    The strengthening mechanism of the glass-fiber at cryogenic temperature has not been fully studied so far. In the present study, tensile tests of a single E-glass fiber with heat treatment in air and liquid nitrogen were conducted to reveal the strengthening mechanism. The strength of glass fiber in liquid nitrogen was twice as high as the strength in air. Based on the area of the mirror zone in the fracture surface, the mirror constant was detemined. Besides, the mirror constant of the glass fiber were equal regardless of the heat treatment condition and the testing temperature. From the observation of surface crack, it was clarified that the mirror zone was the mark of surface flaw propagation and therefore it was suggested that the area of mirror zone doesn't have a direct effect on fiber strength.

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  • Strength degradation behavior of glass fiber embedded in single fiber composite under hot water environment

    Masahiro Kotani, Akira Kobiki, Yusuke Yasafuku, Hiroyuki Kawada

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A   76 ( 767 ) 982 - 987  2010

     View Summary

    Long-term durability of glass fiber reinforced plastics (GFRP) under water environment is strongly influenced by the strength degradation of its fiber reinforcement. Constant strain test in water, in which stress corrosion cracking (SCC) is initiated, was conducted for the single fiber composite (SFC) in order to investigate the strength degradation of E-glass fiber within the SFC. The strain applied to the glass fiber during the constant strain test was formulated by taking account of the fiber strain history, such as water absorption, thermal expansion, and the strain applied to the SFC. After the constant strain test, fragmentation test was conducted in order to estimate the residual strength of the embedded fiber. It was clarified that the degradation of the fiber strength progresses at higher applied strain and longer test time, moreover, the degradation of the fiber strength accelerated drastically at higher temperature.

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  • Deformation Behavior of CFRP Cross-Poly Laminate in Hot and Humid Environment

    ARAO Yoshihiko, KOYANAGI Jun, UTSUNOMIYA Shin, TERADA Hiroshi, KAWADA Hiroyuki

    Journal of the Japan Society for Composite Materials   35 ( 6 ) 241 - 247  2009.11

     View Summary

    In this study, we focused on the geometrical change of cross-ply laminates that are widely used for the composite structures. The behavior of time-dependent out-of-plane deformation under high temperature and humidity was examined. The CFRP plates were exposed at 80°C, 90% RH and their change in geometry was measured at arbitrary elapsed time. The initial shape of the specimens was twisted saddle shape, and the shape gradually became flat with time. Up to 500 μm of out-of-plane deformation arose during moisture absorption for CFRP symmetric plate with the size of 280×280×2.4 mm. The displacement in the thickness direction was the most along ±45° directions in which reinforcing fiber was not aligned. Finite element analysis (FEA) was performed to simulate the out-of-plane deformation of cross-ply laminates. The diffusivities D and coefficient of moisture expansion β, which were obtained other experiments in authors' previous work (Arao et al.: Adv. Compos. Mater., 17 (2008), 359-372), were used. The ply angle misalignment was considered as factors of generating out-of-plane deformation. For the analytical results, it was confirmed that the model the surface layer of which was rotated 1° deformed approximately 700 μm, and the plate geometry became twisted saddle shape by moisture absorption.

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  • Time-dependent out-of-plane deformation of UD-CFRP in humid environment

    Yoshihiko Arao, Jun Koyanagi, Shin Utsunomiya, Hiroyuki Kawada

    COMPOSITES SCIENCE AND TECHNOLOGY   69 ( 11-12 ) 1720 - 1725  2009.09  [Refereed]

     View Summary

    Time-dependent out-of-plane deformation of UD-CFRP (unidirectional CFRP laminate) caused by subjection to a humid environment was examined and analyzed. The UD-CFRP plate showed unpredictable geometrical variation with time in a humid environment, like asymmetric materials. The unpredictability was caused by non-uniform fiber distribution in the thickness direction of the specimen. A three-dimensional diffusion-stress coupling analysis considering the non-uniform fiber distribution was conducted based on finite element analysis. The analytical results showed very good agreement with the experimental results. Furthermore, the relationship between the non-uniform fiber distribution and the out-of-plane deformation with time was obtained quantitatively. (C) 2008 Elsevier Ltd. All rights reserved.

    DOI

  • Transverse crack growth behavior considering free-edge effect in quasi-isotropic CFRP laminates under high-cycle fatigue loading

    Atsushi Hosoi, Yoshihiko Arao, Hiroyuki Kawada

    COMPOSITES SCIENCE AND TECHNOLOGY   69 ( 9 ) 1388 - 1393  2009.07  [Refereed]

     View Summary

    The high-cycle fatigue characteristics focused on the behavior of the transverse crack growth up to 10(8) cycles were investigated using quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates whose stacking sequence was [-45/0/45/90](s). To assess the fatigue behavior in the high-cycle region, fatigue tests were conducted at a frequency of 100 Hz in addition to 5 Hz. In this study, to evaluate quantitative characteristics of the transverse crack growth in the high-cycle region, the energy release rate considering the free-edge effect was calculated. Transverse crack growth behavior was evaluated based on a modified Paris law approach. The results revealed that transverse crack growth was delayed under the test conditions of the applied stress level of sigma(max)/sigma(b) = 0.2. (c) 2008 Elsevier Ltd. All rights reserved.

    DOI

  • Analysis of time-dependent deformation of a CFRP mirror under hot and humid conditions

    Yoshihiko Arao, Jun Koyanagi, Shin Utsunomiya, Shin-ichi Takeda, Hiroyuki Kawada

    MECHANICS OF TIME-DEPENDENT MATERIALS   13 ( 2 ) 183 - 197  2009.05  [Refereed]

     View Summary

    The long-term micro-dimensional stability of a carbon fiber reinforced plastic (CFRP) mirror was investigated in terms of creep deformation, moisture swelling and self-shrinkage. A 4-point bending creep test was carried out using specimens made from pitch-based high-modulus CFRP laminates to obtain a creep constant based on linear viscoelasticity, and we then investigated the weight change and geometrical change during a moisture absorption test using a CFRP specimen. The anisotropic diffusivities and coefficients of moisture expansion (CMEs) in CFRP laminates were obtained by fitting analytical data into the experimental data. Finally, the shrinkage behavior caused by physical aging of the polymeric material was examined using a fiber Bragg grating (FBG) sensor embedded in the neat resin specimen. Applying these results, we analyzed the geometrical changes in a CFRP mirror that resulted from time-dependent deformation by the mirror&apos;s weight, moisture absorption and physical aging, respectively. We discuss which factor is dominant in the deformation of CFRP mirrors under various conditions.

    DOI

  • Evaluating the Impact Tensile Properties of Unidirectional Fibre-Reinforced Composites with Thermoplastic Epoxy Resin(<Special Issue>Solid Mechanics Indispensable for Automobile Engineering)

    TANIGUCHI Norihiko, NISHIWAKI Tsuyoshi, HIRAYAMA Norio, NISHIDA Hirofumi, KAWADA Hiroyuki

    Transactions of the Japan Society of Mechanical Engineers Series A   75 ( 758 ) 1284 - 1289  2009

     View Summary

    Impact tensile properties of unidirectional fiber-reinforced composites are evaluated using a tension-type split Hopkinson bar technique. In this study, thermoplastic epoxy resin and three kinds of reinforced fiber such as carbon, E-glass, and T-glass are employed as a matrix and reinforcement, respectively. The experimental results indicate that strain rate has no effect on tensile properties in case that the carbon fiber is employed as reinforcement. On the other hand, the tensile strength and strain of E-glass and T-glass fiber composites are obviously affected by the strain rate. Although both fibreglasses and thermoplastic epoxy resin are shown to be sensitive to the strain rate, the fibreglasses contributes more significantly to the strain rate effects of the maximum stress and strain.

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  • S0406-1-2 Effect of Thermal Residual Stress Relaxation on the Geometrical Changing Process in Unsymmetrical CFRP Laminate

    OKUDOI Yukie, ARAO Yoshihiko, KAI Takeshi, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2009   325 - 326  2009

     View Summary

    As CFRPs (Carbon Fiber Reinforced Plastics) are being sought for the greater use in aerospace and aircraft structures, it is necessary to understand the mechanical behavior for long-term usage. Furthermore, its low thermal expansion and high specific stiffness has brought attention to the application of CFRPs for the next-generation materials of the ultra-precise structure, such as antenna and mirror. In spite of the advantages of CFRPs, it is well known fact that the long-term dimensional stability of CFRP laminates are affected by several factors, such as moisture absorption, residual stress relaxation, and physical aging. Among these factors, residual stresses are due to the mismatch of thermal expansion rate and cannot be eliminated. This research paper introduces an experimental method of using unsymmetrical cross-ply laminates to determine the behavior of residual stress relaxation. Experimental results are compared to the analytical results derived by classical lamination theory (CLT).

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  • S0406-2-1 Characteristics of Tensile Creep Behavior in Woven GFRP under Hot Water Environment

    KOTANI Masahiro, NAKAMICHI Koutarou, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2009   331 - 332  2009

     View Summary

    Present paper deals with the creep behavior in woven GFRP underwater at elevated temperature. The tensile test of GFRP after water immersion was conducted to evaluate the residual strength after immersion at various water temperatures. The residual strength of GFRP decreased with the increase in the water temperature and the immersion time. In fact, the transition in failure mode with water immersion was ascertained from SEM observation of the fracture surface. Additionally, creep test in air and under hot water at 95℃ was conducted. The creep rupture time decreased drastically with water immersion, in contrast, creep rupture wasn't observed from the creep test in air. It was clarified that the water immersion generated the transition in the failure mode of GFRP and therefore led to the acceleration of the strength degradation.

    DOI CiNii

  • S0406-3-2 Evaluation of In-plane Shear Strength of Fiber Reinforced Composites Considering Stress Singularity

    NOGUCHI Yohei, YAMAMOTO Mayumi, KIMURA Souta, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2009   341 - 342  2009

     View Summary

    Double notched shear (DNS) test were performed with unidirectional CFRP specimen varying the shape of the test specimen. In this study, DNS tests using a unidirectional CFRP specimen having various notch shape and temperature were performed. Results of the DNS test indicated that the in-plane shear strength decreased while test temperature rose. In addition, curvature of notch shape is the smaller, the deterioration of in-plane shear strength is larger. These showed that traditional evaluation using an average shear stress is not quantitative due to stress singularity. Therefore, the in-plane shear strength is evaluated considering stress singularity by means of point stress criterion.

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  • S0406-1-4 Initiation of Transverse Crack under High-cycle Fatigue in CFRP Cross-ply Laminates

    TAKAMURA Keigo, KUSUMOTO Yasuyuki, HOSOI Atsushi, SATO Narumichi, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2009   329 - 330  2009

     View Summary

    In this study, initiation of transverse crack for CFRP cross-ply laminates was investigated at various stress levels during high-cycle fatigue tests. Internal damages were observed with soft X-ray photography at arbitrary loading cycles. A variation of transverse crack density and the local delamination length was evaluated as the fatigue damage progression. The stress in 90° layer considering local delamination length was calculated with a variational approach from the experimental data. It was clear from the results that as the applied maximum stress is set to lower, the saturated transverse crack density and 90° layer stress also lowers. Moreover, the fatigue limit of transverse crack initiation is indicated in this fatigue test conditions.

    DOI CiNii

  • Variations of Fatigue Damage Growth in Cross-Ply and Quasi-Isotropic laminates Under High-Cycle Fatigue Loading

    HOSOI Atsushi, SHI Jiadi, SATO Narumichi, KAWADA Hiroyuki

    JSMME   3 ( 2 ) 138 - 149  2009

     View Summary

    The behavior of transverse crack growth and delamination growth under high-cycle fatigue loadings was investigated with cross-ply CFRP laminates, [0/902]s and [0/906]s, and quasi-isotropic CFRP laminates, [45/0/-45/90]s. As a result, it was observed that the behavior of damage growth was different depending on the applied stress level. The growth of local or edge delamination was exacerbated under the test conditions of a low applied stress level and high-cycle loadings, because the areas of stress concentration were applied with high-cyclic loadings. On the other hand, when the fatigue tests were conducted under the applied stress level of 40% of the transverse crack initiation, the growth of transverse cracks was hardly observed until 108 cycles with [0/902]s, [0/906]s and [45/0/-45/90]s laminates.

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  • Stress analysis of laminates of carbon fiber reinforced plastics, containing transverse cracks, considering free-edge effect and residual thermal stress

    Atsushi Hosoi, Hiroyuki Kawada

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   498 ( 1-2 ) 69 - 75  2008.12  [Refereed]

     View Summary

    A variational approach is presented to evaluate the 3-dimensional stress state in cross-ply laminates of the form [(S)/90(n)](s) that contain transverse cracks in the 90, plies, where (S) is any orthotropic sublaminate. Admissible stress states that satisfy equilibrium and all boundary and interface conditions are constructed, and the principle of minimum complementary energy is employed to find an optimal approximation of the composite strain energy. Using this method of analysis, we can express the stress state by considering the free-edge effect, which causes edge delamination in cracked laminates. The calculated results using the proposed model showed good agreement with the results calculated by the finite element method. (C) 2008 Elsevier B.V. All rights reserved.

    DOI

  • Dimensional Change of CFRP Taking Account of Moisture Concentration

    ARAO Yoshihiko, KOYANAGI Jun, HATTA Hiroshi, KAWADA Hiroyuki

    Journal of the Japan Society for Composite Materials   34 ( 3 ) 95 - 101  2008.05

     View Summary

    Moisture absorption behavior of CFRP and its effect on dimensional stability was examined. Moisture diffusivity in CFRP was determined by measuring specimen weight during the moisture absorption test. Three types of CFRP specimens, unidirectionally reinforced, quasi-isotropically laminated and cloth-laminated composites were prepared. Each CFRP was processed into two geometries; a thin plate for determination of diffusion constants and a rod with square cross-section for the discussion of two-dimensional diffusion behavior. Coefficient of moisture expansion (CME) was also obtained from specimen deformation involving moisture absorption. During moisture absorption, the specimen surfaces strongly deformed especially near the edges because of three-dimensional moisture concentration distribution. This deformation was reasonably predicted by the finite element analysis using diffusion constants and CME, which have been experimentally determined. For unidirectional CFRP, an effect of fiber location distribution on CME is discussed by a micromechanical FEA.

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  • 1450 Comprehensive model determining tensile strengths in various unidirectional composites

    Koyanagi Jun, Kotani Masaki, Hatta Hiroshi, Kawada Hiroyuki

    The proceedings of the JSME annual meeting   2008   307 - 308  2008

     View Summary

    A comprehensive model that determines tensile strengths for various systems of unidirectional composites is presented. The model derives the strength of unidirectional composites as a function of single-fiber strength distribution, interfacial shear strength and matrix strength. The point of this model is to consider that a fiber group considered to be experiencing simultaneous fiber failures triggered by neighboring fiber failure is assumed to fail when the weakest fiber in the fiber group fails. A method to determine the magnitude of the fiber group for various systems of composites is discussed based on whether a crack located near a bi-materials interface penetrates into another material or deflects along the interface. The comprehensive model is established by integrating the magnitude of the simultaneous fiber failure into the conventional Global Load Sharing model.

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  • Analysis of Time-Dependent Deformation of CFRP Considering the Anisotropy of Moisture Diffusion

    Yoshihiko Arao, Jun Koyanagi, Hiroshi Hatta, Hiroyuki Kawada

    ADVANCED COMPOSITE MATERIALS   17 ( 4 ) 359 - 372  2008  [Refereed]

     View Summary

    The moisture absorption behavior of carbon fiber-reinforced plastic (CFRP) and its effect on dimensional stability were examined. Moisture diffusivity in CFRP was determined by measuring a specimen&apos;s weight during the moisture absorption test. Three types of CFRP specimens were prepared: a unidirectionally reinforced laminate, a quasi-isotropic laminate and woven fabric. Each CFRP was processed into two geometries - a thin plate for determination of diffusivity and a rod with a square cross-section for the discussion of two-dimensional diffusion behavior. By solving Fick&apos;s law expanded to 3 dimensions, the diffusivities in the three orthogonal directions were obtained and analyzed in terms of the anisotropy of CFRP moisture diffusion. Coefficients of moisture expansion (CMEs) were also obtained from specimen deformation caused by moisture absorption. During moisture absorption, the specimen surfaces showed larger deformation near the edges due to the distribution of moisture contents. This deformation was reasonably predicted by the finite element analysis using experimentally determined diffusivities and CMEs. For unidirectional CFRP, the effect of the fiber alignment on CME was analyzed by micromechanical finite element analysis (FEA) and discussed. (C) Koninklijke Brill NV, Leiden, 2008

    DOI

  • Quantification of Fiber Strength Degradation in SFC Under Water Environment

    KOBIKI Akira, ITOH Seiya, KAWADA Hiroyuki

    Transactions of the Japan Society of Mechanical Engineers Series B   73 ( 732 ) 82 - 89  2007.08

     View Summary

    Long-term durability of FRP under hostile environment is strongly influenced by fiber strength degradation. In this paper, the fiber strength degradation in the FRP in water under constant loading has been investigated using a single fiber composite (SFC). In order to estimate the fiber degradation due to aging in water, distributions of remaining fiber strength were obtained by fragmentation test. The remaining strength distributions have been quantified on the basis of microscopic stress corrosion cracking of initial defects on the fiber surface. Because the initial defect growth depends on the fiber stress history, increase of SFC strain in water has been also formulated. The remaining strength distribution obtained by the proposed model shows a good agreement with the experimental results. Additionally, it has been exhibited that the proposed model is available to predict increase of fiber failure caused by the fiber degradation in the SFC under constant loading in water.

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  • 2742 Universal Determination Method of Tensile Strength in Unidirectional Composites

    Koyanagi Jun, Kotani Masaki, Kawada Hiroyuki, Hatta Hiroshi

    The proceedings of the JSME annual meeting   2007   645 - 646  2007

     View Summary

    Various composites are reinforced by high strength fiber. The contributing efficiency of the reinforcing fiber to composite strength is different in GFRP, CFRP, MMC, C/C, CMC, respectively. It depends on whether a fiber fracture penetrates in the matrix or deflect into interface in the class of omaterials that the composite strength is lower than bundle strength. On the other hand, in the class with poor interface, the tensile strength increases with an increase of interfacial strength. Furthermore, there exist a class of material in which both of mechanisms coexist. This study provides a parameter that determines the contributing efficiency of reinforcing fiber for the various composites.

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  • 2754 Fiber Strength Degradation of FRP under Constant Loading in Water

    KOTANI Masahiro, KAWANISHI Ken, KOBIKI Akira, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2007   669 - 670  2007

     View Summary

    Long-term durability of fiber reinforced plastics (FRP) under hostile environment is strongly influenced by the degradation in the fiber strength. The degradation of the fiber strength has been quantified on the basis of stress corrosion cracking (SCC) of the initial defects on the fiber surface. In this paper, the strength degradation of the embedded fibers under constant loading in water environment has been investigated using the single fiber composite (SFC). Creep test was conducted under water environment using the SFC specimen, to represent the stress corrosion cracking of GFRP. By taking account of the strain concurrent with the water absorption, creep strain, and the thermal expansion, the strain history of the fiber was formulated. From the strain history, the remaining strength distribution was measured by the fragmentation test. The model containing the Paris Law and the Arrhenius model has been developed to predict the remaining strength of fiber embedded in FRP.

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  • 2751 Effect of moisture absorption on dimensional and geometrical variation in CFRP

    Arao Yoshihiko, Koyanagi Jun, Kawada Hiroyuki

    The proceedings of the JSME annual meeting   2007   663 - 664  2007

     View Summary

    Moisture absorption behavior of CFRP and its effect on dimensional stability was examined. Moisture diffusivity in CFRP was determined by measuring specimen weight during the moisture absorption test. Three types CFRP specimens, unidirectional, quasi-isotropic and cloth-laminated composites were prepared. Each CFRP was processed into two geometries; a thin plate for determination of diffusion constants and a rod with square cross-section for the discussion of two-dimensional diffusion behavior. Coefficient of moisture expansion (CME) was also measured from specimen deformation involving moisture absorption. During moisture absorption, the specimen surfaces deformed especially strongly near the edges because of three-dimensional moisture concentration distribution. This deformation mechanism was reasonably predicted by the finite element analysis using diffusion constants and CME, which have been experimentally determined.

    DOI CiNii

  • Interaction between transverse cracks and edge delamination considering free-edge effects in composite laminates

    Atsushi Hosoi, Shinako Yagi, Keiichi Nagata, Hiroyuki Kawada

    ICCM International Conferences on Composite Materials    2007

     View Summary

    The high-cycle fatigue characteristics, especially the initiation and propagation of edge delamination, were investigated with quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates with a stacking sequence of [45/0/-45/90]S. To investigate the influence that transverse cracks have on the initiation and propagation of edge delamination, two types of specimens are used. One was a specimen where transverse cracks were arbitrarily introduced by static tensile loading before conducting the fatigue tests. The other was an undamaged specimen as new. As a result, it was found that the single transverse crack introduced before the fatigue test did not seriously affect the initiation of edge delamination. Moreover, the difference of the fatigue damage growth behavior depending on the applied stress level was observed. Under the test conditions of low-applied stress level and high-cyclic loadings, it was observed that the edge delamination grew before, or simultaneously with, the transverse crack propagation.

  • Quantitative evaluation of curing shrinkage in polymeric matrix composites

    Masahiro Kotani, Yoshihiko Arao, Jun Koyanagi, Hiroyuki Kawada, Hiroshi Hatta, Yuichi Ishida

    ICCM International Conferences on Composite Materials    2007  [Refereed]

     View Summary

    The aim of this study is to measure the cure shrinkage of epoxy resin system used in the CFRP. First, the cure kinetics of Bisphenol A type epoxy resin system was studied by Differential Scanning Calorimetry measurement. From the dynamic DSC measurement, the total heat of cure of the epoxy was determined as 293 [kJ/g]. Also, curing condition and the extent of cure were determined by the isothermal DSC and TGA measurement. By controlling the curing condition, immature cured epoxy bar-shaped specimen was moulded. The cure shrinkage was measured by using the laser confocal displacement meter without any contact with the bar-shaped specimen. Comparing the specimen size after each cure, cure shrinkage of the bar-shaped specimen was measured.

  • High-cycle fatigue characteristics of quasi-isotropic CFRP laminates

    Atsushi Hosoi, Yoshihiko Arao, Hirokazu Karasawa, Hiroyuki Kawada

    ADVANCED COMPOSITE MATERIALS   16 ( 2 ) 151 - 166  2007  [Refereed]

     View Summary

    High-cycle fatigue characteristics of quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates [-45/0/45/90](8) up to 10(8) cycles were investigated. To assess the fatigue behavior in the high-cycle region, fatigue tests were conducted at a frequency of 100 Hz, since it is difficult to investigate the fatigue characteristics in high-cycle at 5 Hz. Then, the damage behavior of the specimen was observed with a microscope, soft X-ray photography and a 3D ultrasonic inspection System. In this study, to evaluate quantitative characteristics of both transverse crack propagation and delamination growth in the high-cycle region, the energy release rate associated with damage growth in the width direction was calculated. Transverse crack propagation and delamination growth in the width direction were evaluated based on a modified Paris law approach. The results revealed that transverse crack propagation delayed under the test conditions of less than sigma(max)/sigma(b) = 0.3 of the applied stress level.

    DOI

  • Fatigue characteristics of quasi-isotropic CFRP laminates subjected to variable amplitude cyclic two-stage loading

    Atsushi Hosoi, Hiroyuki Kawada, Hiromichi Yoshino

    INTERNATIONAL JOURNAL OF FATIGUE   28 ( 10 ) 1284 - 1289  2006.10  [Refereed]

     View Summary

    In this study the fatigue characteristics of quasi-isotropic carbon fiber reinforced plastics laminates subjected to variable amplitude cyclic two-stage loading were investigated. The cumulative damage was evaluated by considering residual strength as a parameter since the Linear Cumulative Damage rule, i.e., the Palmgren-Miner rule, did not show good agreement. Further, the internal microscopic damage was observed with an optical microscope. As a result, it was found that cumulative damage subjected to variable amplitude cyclic loading could be expressed by considering residual strength. Additionally, we were able to predict the fatigue life of laminates subjected to variable amplitude cyclic two-stage loading. (c) 2006 Elsevier Ltd. All rights reserved.

    DOI

  • Evaluation of Initiation of the Interfacial Debonding in Single Fiber Composite : Energy Balance Method Considering an Energy Dissipation of the Plastic Deformation

    KIMURA Souta, KOYANAGI Jun, KAWADA Hiroyuki

    JSME International Journal Series B Fluids and Thermal Engineering   49 ( 3 ) 451 - 457  2006.07

     View Summary

    Fiber-matrix interfacial adhesion in composites is traditionally evaluated by means of a stress-based parameter. Recently, an interfacial energy parameter is suggested to be a valid alternative. However, the energy-based approaches overestimated the energy release rate to initiate the interfacial debonding (interfacial energy), since the plastic deformation in the vicinity of the debonding was neglected for simplicity. An effect of the plastic deformation on the interfacial energy of a fiber-reinforced polymer matrix composite is studied to evaluate the initiation of the interfacial debonding. The fragmentation tests with a model of glass fiber-reinforced vinylester matrix composite were performed, and the interfacial energy with the energy balance method taking into account an energy dissipation of the plastic deformation was calculated. The following results are confirmed; the plastic deformation has a significant influence on the interfacial energy, and the energy balance scheme taking into account the plastic energy dissipation leads to the constant interfacial energy without reference to the amount of the released potential energy. The differences between our model and the previous one are discussed.

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  • Time-Dependent Interfacial Debonding Propagation in Single Fiber Composite

    KOYANAGI Jun, YAMAZAKI Masashi, KAWADA Hiroyuki

    Transactions of the Japan Society of Mechanical Engineers Series B   72 ( 716 ) 493 - 500  2006.04

     View Summary

    Interfacial debonding propagation is one of the most important problems for long-term creep in unidirectional composites because the strength of the unidirectional composites decreases with increase of the interfacial debonding length. In this study, time-dependent interfacial failure was investigated by using the Micro Raman Spectroscopy. The specimen was single fiber composite consisting of one carbon fiber embedded in the vinylester resin. It was subjected to a constant strain to assume the long-term creep in the unidirectional composites. To discuss the timedependent interfacial debonding propagation behavior, a time-dependency of a criterion for interfacial debonding propagation in the SFC must be determined. In this paper, the time-dependent boundary condition of the interfacial debonding was obtained from experimental results, and the interfacial debonding propagation was formulated. Here, the compression stress applied to the interface in the fiber radius direction was formulated as a function of time on the consideration of Poisson contraction and thermal residual stress. The interfacial debonding propagation and variation of the fiber axial strain distribution as a function of time were formulated by using the following three parameters : a relaxation of the frictional stress, an interfacial shear viscoelastic behavior and the time-dependent boundary condition at the interfacial debonding tip. These formulations showed a good agreement with the corresponding experimental results.

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  • Delayed Fracture of E Glass Fiber under Water Environment

    KOBIKI Akira, IITAKA Seishi, SHIODA Satoshi, KAWADA Hiroyuki

    Transactions of the Japan Society of Mechanical Engineers Series B   72 ( 713 ) 85 - 92  2006.01

     View Summary

    Tests for evaluating delayed fracture of an E-glass fiber were conducted under water environment. Loaded E-glass fibers were immersed in purified water, and time-to-fracture was measured. Since the delayed fracture was confirmed under the water, the moisture was the only environmental factor for the delayed fracture. The relationship between the chemical reaction and the fiber strength was evaluated for estimating moisture-absorption effect on the delayed fracture. The E-glass fiber surface was observed by XPS and AFM. These observations showed that roughness on the glass surface increased due to the moisture-absorption. Furthemore the fiber-bundle strength decreased with increasing immersion time. The results of these observations indicated that microscopic cracks accelerated the delayed fracture under the water. It is concluded that the delayed fracture of the E-glass fiber occurred by microscopic crack growth caused by moisture-absorption on the glass surface.

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  • 418 Time-temperature dependency of microscopic-scale deformation in CFRP

    TAKAKU Hiroyuki, ARAO Yoshihiko, KOYANAGI Jun, KAWADA Hiroyuki, ISHIDA Yuichi

    The Proceedings of the Materials and processing conference   2006   251 - 252  2006

     View Summary

    Viscoelastic property of CFRP is one of most critical parameters which dominate its dimensional stability. In order to investigate the time-temperature dependency of micro-scale deformation, four point bending creep tests were conducted. It is reported that extremely slow cure causes microscopic-scale deformation. So the influence of aged shrinkage upon secular change of dimension was investigated and creep behaviors with two different curing conditions were compared.

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  • 2925 Prediction of creep rupture in unidirectional composites

    KOYANAGI Jun, OGAWA Fumio, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2006   381 - 382  2006

     View Summary

    Delayed fractures in carbon-fiber-reinforced polymer matrix composites can be observed even at room temperature due to an accumulation of micromechanical damages, such as time-dependent interfacial debondings or fiber breakage. In this study, the creep-rupture time in unidirectional composites consisting of carbon fiber reinforcement and vinylester resin is predicted under consideration of the progress of interfacial debonding which decreases rupture strain of the composites due to increase of the stress recovery length in time. The decrease of the rupture strain in unidirectional composites is formulated based on the global load sharing, which assumes that lost load distribution involved a fiber break is uniformly redistributed to all the intact residual fiber in the range of the stress recovery length. Time-dependency of the stress recovery length including the interfacial debonding length is analytically and experimentally investigated using carbon/vinylester single-fiber composite as a function of time and specimen strain. The creep rupture prediction is completed by means of putting the increase of stress recovery length into it. The validity of this creep rupture prediction is discussed by investigation of the residual strength after quasi-creep test, which must be derived by the formulated creep rupture prediction.

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  • 2920 An Improved Method for Evaluation of Fiber Strength Using Fragmentation Test

    KIMURA Souta, KOYANAGI Jun, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2006   371 - 372  2006

     View Summary

    An exact theory is developed to evaluate propagation of an interfacial debonding in single fibre composite by means of the energy release rate due to crack growth. The debonding propagation during fragmentation test is significantly affected by frictional slip at the interface in the debonding region. Hence, frictional dissipation of the energy release rate occurs along with the debonding propagation. An analysis considering the effect of the interfacial friction is conducted. The fragmentation tests are performed varying the amount of fibre pre-stress, and the debonding growth is observed directly. To validate the present analysis, the debonding propagation predicted by the present theory is compared with the experimental one. The theoretical prediction is proved to be in the excellent agreement with the experimental results, which illustrates the importance of including the frictional effect in the energy release rate. An application of the present theory to fibre fragmentation in single-fibre composite test that can evaluate the fibre strength is described.

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  • Long-term durability of polymer matrix composites under hostile environments

    H. Kawada, A. Kobiki, J. Koyanagi, A. Hosoi

    Materials Science and Engineering A   412 ( 1-2 ) 159 - 164  2005.12  [Refereed]

     View Summary

    Long-term durability of polymer-matrix composites (PMCs) in hostile environments is described. Characteristics of a stress-corrosion crack in glass fiber reinforced plastics (GFRP), creep fracture in unidirectional carbon fiber reinforced plastics (CFRP) and predictions of a variable loading fatigue life in CFRP laminates are the main topics of this paper. To enhance the performance of the PMCs as structural materials, many improvements are achieved so far. Characterization of mechanical properties under the hostile environments is still need for the studies. © 2005 Elsevier B.V. All rights reserved.

    DOI

  • 2135 Prediction of Creep Rupture Lifetime in unidirectional fiber reinforced plastics : The Effect of interfacial debonding propagation on creep rupture lifetime

    OGAWA Fumio, Koyanagi Jun, Kawada Hiroyuki

    The proceedings of the JSME annual meeting   2005   579 - 580  2005

     View Summary

    This study investigates an effect of time-dependent debonding propagation of fiber/matrix interface and that of stress concentrations to adjacent fibers from broken fibers on creep rupture lifetime in unidirectional composites. Above two phenomena are concerned to reduce materials strength and effect on creep rupture lifetime in unidirectional composites. A creep rupture model that takes into account the decrease of rupture strain due to time-dependent inter facial debonding propagation, based on the GLS rule is proposed and the rupture lifetime is predicted. It was found that the rupture lifetime is strongly dominated by the interfacial debonding propagation rate, and rupture lifetime is shortened considerably in case that time-dependent debonding propagation is remarkable. Subsequently, the change in the rupture strain due to the stress concentration without interfacial debonding propagation is estimated using a 3D shear-lag model and the rupture lifetime taking into account stress concentration is predicted using the McLean's creep model. Prediction result is compared with the result of Curtin-McLean model in which the stress concentration is not taken into account and the effect of stress concentration is investigated.

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  • 2140 Effect of Moisture Diffusion on Crack Propagation Behavior of GFRP

    KOBIKI Akira, ITO Seiya, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2005   589 - 590  2005

     View Summary

    The effect of water on crack propagation resistance by fiber bridging of glass fiber reinforced plastic (GFRP) has been investigated. Specimens were immersed and weighed just before conducting the crack propagation test. Decrease of critical energy release rate by the water was measured as a function. The critical energy release rate of the matrix decreased with increase of the water absorption. The crack resistance of a bridged crack varied with the water absorption. To investigate the variation in the bridging mechanism under the water environment, we calculated the moisture concentration distribution on the cracked plane. As a result, the moisture concentration affected the crack propagation resistance. The increase of the moisture concentration caused the decrease of crack propagation resistance.

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  • Nonlinear Viscoelastic Constitutive Equation in Consideration of Permanent Strain in Vinylester Resin

    OGAWA Fumio, KOYANAGI Jun, KAWADA Hiroyuki

    Transactions of the Japan Society of Mechanical Engineers Series B   71 ( 709 ) 1243 - 1249  2005

     View Summary

    This paper presents the characterization of nonlinear viscoelastic behavior in vinylester resin. The description of nonlinear viscoelastic behavior is based on well-known Schapery's constitutive equation. Cardon proposed the method that can estimate nonlinear parameters in Schapery's constitutive equation, separately by creep-recovery tests in consideration of permanent deformation nonexistent in original Schapery's constitutive equation. However, formulation of permanent deformation has almost never been discussed in these articles, In this study, the irreversible strain is formulated and nonlinear viscoelastic constitutive equation taking into account the permanent deformation is proposed. It is found that the behavior of irreversible strain is nonlinear and it has a threshold stress value between the linear behavior and the nonlinear behavior same as nonlinear parameters in Schapery's constitutive equation. Tensile tests in which crosshead speed is changed as time-dependent factor is performed to verify that the proposed constitutive equation can predict time-dependent behavior. Fine agreement between the experimental results and prediction is observed and the validity of the constitutive equation is confirmed.

    DOI CiNii

  • Effect of Water Absorption on Interaction between Matrix Cracking and Fiber Bridging for Stress Corrosion Cracking of PMC

    KOBIKI Akira, KAWADA Hiroyuki

    JSME International Journal Series B Fluids and Thermal Engineering   48 ( 4 ) 183 - 188  2005

     View Summary

    The effect of water on fiber bridging of polymer matrix composites (PMCs) has been studied for stress-corrosion cracking (SCC). The fiber bridging during crack propagation in the PMC was observed directly using a transparent polymer matrix. Specimens were immersed and weighed just before conducting the crack propagation test. The contribution of mechanical degradation caused by the water to the bridging was measured as a function of weight gain due to water absorption. The critical energy release rate of the matrix decreased with increase of the water absorption. The energy release rate of a bridged crack varied with the water absorption. To investigate the variation in the bridging mechanism under the water environment, we calculated the bridging stress the σt and the bridging contribution to crack propagation resistance ΔG based on a single-fiber bridging mechanism with the interfacial debonding length and the interfacial debonding energy. The debonding length was measured directly, and the debonding energy was obtained in a fragmentation test. The calculation showed that the increase in the interfacial debonding length influenced the fiber bridging mechanism.

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  • Damage mechanics characterization of high-cycle fatigue in quasi-isotropic CFRP laminates

    Atsushi Hosoi, Hirokazu Karasawa, Hiroyuki Kawada

    Proceedings of the 2005 SEM Annual Conference and Exposition on Experimental and Applied Mechanics     1729 - 1736  2005

     View Summary

    This paper describes the high-cycle fatigue characteristics of quasi-isotropic CFRP laminates [-45/0/45/90] s up to 10 8 cycles. To investigate the fatigue behavior in the high-life region, the fatigue tests were conducted with the frequency of 100Hz since it's difficult to conduct the tests with 5Hz. Then, the damage behavior of the specimen was observed with a microscope, a soft X-ray photography and a 3D ultrasonic inspection system. In this study, to evaluate quantitative characteristics of each the transverse crack propagation and the delamination growth in the high-cycle region, the energy release rate associated with damage growth to the width direction was calculate. The transverse crack propagation and the delamination growth to the width direction were evaluated based on a modified Paris-law approach. As the results, it was found that transverse crack propagation didn't depend on the frequency within the small temperature change and it was observed that delamination growth delayed with the test condition of less than σ max/σ b=0.3 of the applied stress level.

  • 産官学連携の取り組み

    第34回FRPシンポジウム    2004.03

  • 水環境下におけるガラス繊維の劣化(表面状態変化の強度低下に及ぼす影響)

    日本機械学会 関東支部 第10期総会講演会 講演論文集   №040-1 pp.379-380  2004.03

  • GFRPの応力腐食割れに関する研究(環境溶液の影響による微視的き裂進展特性)

    日本機械学会 関東支部 第10期総会講演会 講演論文集   №040-1 pp.377-378  2004.03

  • 擬似等方性炭素繊維強化プラスチックの疲労特性(2段変動荷重試験における疲労寿命の調査)

    日本機械学会 関東支部 第10期総会講演会 講演論文集   №040-1 pp.373-374  2004.03

  • SFCにおける界面はく離の時間依存特性について

    日本機械学会 関東支部 第10期総会講演会 講演論文集   №040-1 pp.369-370  2004.03

  • 高分子材料の粘弾塑性挙動における材料非線形性に関する研究

    日本機械学会 関東支部 第10期総会講演会 講演論文集   №040-1 pp.363-364  2004.03

  • 一方向強化PMCのクリープ寿命予測(3Dシアラグクリープモデルの提案と検討)

    日本機械学会 関東支部 第10期総会講演会 講演論文集   №040-1 pp.359-360  2004.03

  • 擬似等方性炭素繊維強化プラスチックの疲労特性(損傷進展観察による変動荷重下の疲労寿命の考案)

    日本機械学会第11回機械材料・材料加工技術講演会講演論文集   pp.171-172  2003.10

  • 一方向複合材料のクリープ寿命予測(隣接破断繊維による応力集中と界面はく離進展の影響)

    日本機械学会第11回機械材料・材料加工技術講演会講演論文集   pp.165-166  2003.10

  • SFCにおける界面き裂の時間依存特性に関する研究

    日本複合材料学会第28回複合材料シンポジウム講演要旨集   pp.53-54  2003.10

  • GFRPの応力腐食割れに関する研究(環境溶液の影響による微視的き裂進展特性)

    第28回複合材料シンポジウム 講演要旨集 / 日本複合材料学会   pp.33-34  2003.10

  • Creep rupture model taking into account interfacial debonding in unidirectional composites

    4th International Conference on Mechanics of Time Dependent Materials   第4巻  2003.10

  • PMCの応力腐食割れに関する基礎的研究(界面劣化による強じん化機構の変化)

    日本機械学会2003年度年次大会講演論文集Vol.Ⅰ   Vol.Ⅰ №03-1 pp.369-370  2003.08

  • 一方向FRPのクリープ寿命予測(繊維破断部近傍の界面はく離を考慮したクリープ破断モデル)

    日本機械学会2003年度年次大会講演論文集Vol.Ⅰ   Vol.Ⅰ №03-1 pp.367-368  2003.08

  • Prediction of Creep Rupture Unidirectional Composite (Creep Rupture Model with Interfacial Debonding around Broken Fibers)

    14th International Conference on Composite Materials (ICCM-14)    2003.07

  • A Study of GFRP on Stress Corrosion Cracking

    14th International Conference on Composite Materials (ICCM-14)    2003.07

  • A study on stress-corrosion cracking using single fiber model specimen - (Degradation properties of GFRP caused by water absorption)

    H Kawada, A Kobiki

    JSME INTERNATIONAL JOURNAL SERIES A-SOLID MECHANICS AND MATERIAL ENGINEERING   46 ( 3 ) 303 - 307  2003.07  [Refereed]

     View Summary

    Recently the crack propagation properties of GFRP on the stress corrosion cracking (S.C.C) are investigated, and the threshold stress intensity factor K-ICC is verified in some environmental solution. From the investigation, it was found that GFRP reinforced by C-glass fiber has a superior acid resistance. However the microscopic crack propagation mechanisms caused by the material corrosion are not verified, and the microscopic mechanisms are necessary to assure the durability. Therefore the degradation mechanisms of the inner fiber and the matrix and the fiber/ matrix interface should be quantified. In this study, the degradation of the fiber strength and the fiber/matrix interfacial shear strength are investigated using a single fiber composite previously immersed into environmental solutions, distilled water and acid solution. The effects of solution diffusion into the matrix resin on the fiber strength and the interfacial shear strength have been evaluated as a function of immersion time by fragmentation test in the room air. It is found that the diffusion of distilled water influences the degradation earlier than the acid solution. And the diffusion behavior is confirmed by Fickian diffusion analysis. The calculated concentration distribution showed that the water concentration around the fiber is saturated much earlier than the saturation of the acid ion due to the lower diffusion coefficient. Furthermore the crack propagation mechanisms are discussed based on the degradation estimated by the fragmentation test.

  • FW製GFRP円筒材の軸方向引張り特性(強度推定法の提案)

    日本複合材料学会2003年度研究発表講演会予稿集   日本複合材料学会 pp.109-110  2003.05

  • PMCの応力腐食割れに関する基礎的研究(界面劣化による強じん化機構の変化)

    日本複合材料学会2003年度研究発表講演会予稿集   日本複合材料学会 pp.79-80  2003.05

  • 単繊維フラグメンテーション試験を用いた環境溶液拡散による構成要素の劣化(界面の劣化および再接着の検討)

    日本複合材料学会2003年度研究発表講演会予稿集   日本複合材料学会 pp.77-78  2003.05

  • 一方向FRPのクリープ寿命予測(繊維破断部近傍の界面はく離を考慮したクリープ破断モデル)

    日本複合材料学会2003年度研究発表講演会予稿集   日本複合材料学会 pp.75-76  2003.05

  • フェノール基複合材料の長期信頼性評価(温度時間換算則による長期引張りクリープ挙動の推定)

    日本複合材料学会2003年度研究発表講演会予稿集   日本複合材料学会 pp.69-70  2003.05

  • 擬似等方性アルミナFRP積層板の疲労特性(疲労損傷に及ぼす周波数及び積層構成の影響)

    KAWADA Hiroyuki, HOSOI Atsushi, YAMAZAKI Shinichiro

    日本複合材料学会2003年度研究発表講演会予稿集   日本複合材料学会 pp.9-10   9 - 10  2003.05

    CiNii

  • 横方向衝撃負荷を受けるGFRP円筒の応力波伝播挙動

    日本複合材料学会2003年度研究発表講演会予稿集   日本複合材料学会 pp.105-106  2003.05

  • 一方向繊維強化プラスチックのクリープ特性と寿命予測—繊維破断部近傍の界面はく離を考慮したクリープ破断モデル一方向繊維強化

    日本複合材料学会誌   日本複合材料学会 Vol.29 (4) pp.136 2003  2003

  • Long Term Reliability on Unidirectional GFRP under Acidic Stress Environment : Initiation of Damage and Threshold Properties

    KAWADA Hiroyuki, SHINOHARA Atsushi

    The proceedings of the JSME annual meeting   2002   309 - 310  2002

     View Summary

    Over the past several years stress corrosion cracking of the FRP plant applications have been a serious problem for durability. So, the elucidation of the fracture mechanism is indispensable to adopt GFRP as a structure material. The purpose of this study is to clarify the threshold property of crack propagation of C-glass/vinyl ester composite. Load descending test is performed for the unidirectional GFRP (90゜specimen). As a result, the existence of the threshold properties is observed, and it is confirmed that the cause is the fiber bridging by the FEM analysis by which the fiber bridging and the cohesive stress are considered. Additionally, the prediction of initiation of the damage is considered in view of time to failure of the fiber by stress corrosion cracking.

    DOI CiNii

  • Prediction of Creep Rupture in Unidirectional Phenol Composite : Effects of Relaxation on Interfacial Shear Stress and Interfacial Debonding

    KAWADA Hiroyuki, TAKEUCHI Hiroshi

    The proceedings of the JSME annual meeting   2002   301 - 302  2002

     View Summary

    This paper describes creep rupture model considering interfacial debonding and relaxation on interfacial shear stress in broken fibers in unidirectional phenol matrix composites reinforced with glass fibers. Interfacial debonding is accompanied with fiber breaks under the tensile load. It depends on the strain of the composites and is represented as a function of the strain by considering the energy balance equation of interface. Interfacial debonding length, fiber failure probability and interfacial shear stress are measured experimentally on fragmentation test and then formulated as a function of the strain. Interfacial debonding length is taken in Curtin's model that is considering break of fiber and creep rupture time is predicted. Relaxation on interfacial shear stress is also taken in creep rupture model in a long time.

    DOI CiNii

  • 酸応力環境下におけるGFRP 織物積層板のき裂進展特性と微視的損傷過程

    第9回機械材料・材料加工技術講演会/日本機械学会   pp.7  2001.11

  • 単繊維モデルを用いたGFRP の応力腐食割れに関する研究(界面劣化と繊維損傷機構)

    第9回機械材料・材料加工技術講演会/日本機械学会   pp.11  2001.11

  • ウェーブレット変換を用いたGFRP積層板中の応力破伝播挙動の解明

    第5回複合材システムの耐久性解析に関する国際会議   B-21  2001.11

  • Off-axis stress relaxation behavior of unidirectional T800H/Epoxy at elevated temperature and its macromechanical analysis

    第7回 SAMPE先端材料技術国際会議    2001.11

  • Fundamental Study on Flexural Fatigue Properties in Flexible Printed Circuit Properties of Phenoxy/Epoxy Resin with Mixing Ratio

    第7回 SAMPE先端材料技術国際会議    2001.11

  • Fatigue Properties of Quasi-Isotropic Alumina-Fiber Reinforced Plastic laminates

    第7回 SAMPE先端材料技術国際会議    2001.11

  • 擬似等方性アルミナ繊維強化プラスチックの疲労特性(内部損傷の発達と疲労寿命)

    2001年度年次大会講演論文集/日本機械学会r&0d0a;   5.pp.105-106  2001.08

  • 単繊維モデル試験片を用いた複合材料の応力腐食割れ(構成基材と界面の劣化特性)

    2001年度年次大会講演論文集/日本機械学会   5.pp.107-108  2001.08

  • 酸応力環境下におけるGFRP織物積層板のき裂進展挙動(溶媒の拡散と下限界特性)

    2001年度年次大会講演論文集/日本機械学会   5.pp.109-110  2001.08

  • FPC耐久性向上に関する基礎研究〜フェノキシ・エポキシ樹脂の機械的性質と界面破壊じん性における混合率の影響〜

    2001年度研究発表講演会予稿集/日本複合材料学会   pp.15-16  2001.06

  • 極低温下におけるGFRP円筒の疲労特性(疲労特性に及ぼす負荷形式の影響)

    2001年度研究発表講演会予稿集/日本複合材料学会   pp.111-112  2001.06

  • 高強度鋼の超寿命疲労特性に及ぼす内部介在物の影響(介在物の機械的性質と疲労寿命)

    関西支部第76期定時総会講演会講演論文集/日本機械学会関西支部   pp.5.3-5.4  2001.03

  • FPCの屈曲特性に関する基礎的研究(フェノキシ/エポキシ樹脂の機械的特性と界面破壊じん性における混合率の影響)

    第30回FRPシンポジウム講演論文集/日本材料学会    2001.03

  • 酸応力環境下におけるGFRP織物積層板のき裂進展挙動(環境条件と下限界特性)

    第31回FRPシンポジウム講演論文集/日本材料学会    2001.03

  • 繊維モデル試験片を用いたGFRPの応力腐食割れに関する研究(応力下での拡散現象と繊維破壊メカニズム)

    第31回FRPシンポジウム講演論文集/日本材料学会    2001.03

  • 複合材料活用辞典

    産業調査会出版    2001

  • Evaluation of the mechanical properties of PMC interface using slice compression test - Analysis of transfer mechanism of interfacial shear stress

    N Taniguchi, K Toge, H Kawada

    COMPOSITE INTERFACES   7 ( 5-6 ) 349 - 361  2001  [Refereed]

     View Summary

    Properties of the fiber/matrix interface in SiO2/epoxy and SiC/epoxy composite are investigated using the slice compression test (SCT) for the single fiber, where the specimen is loaded and unloaded between a plate which has different mechanical properties. It is found that the interfacial debonding proceeds from the polished surface at a soft plate side and that the fiber protrusion occurs after unloading. The fiber-protrusion length is directly measured at each applied stress level using a scanning electron microscope. Interfacial shear-sliding stress is obtained based on the constant shear-sliding stress analysis employing the obtained protrusion length.
    It is demonstrated that the value of interfacial shear-sliding stress shows good agreement with that obtained from another technique, the push-out test, on the same system. The relation between the fiber-protrusion length and applied stress is proportional to a certain extent. From this result, it is analytically pointed out that the applied stress has a limiting value in this SCT because of Poisson's effect. Also, two interfacial debonding criteria, which are determined analytically for the PMC, are discussed.

  • 非線形ヒステリシツモデルに基づくアルミナFRP円筒の繰返し負荷応力下における応力—ひずみ特性(エネルギーアプローチによる疲労寿命評価の検討)

    第29回FRPシンポジウム講演論文集/日本材料学会   pp.225-228  2000.03

  • 酸応力環境下におけるGFRPのき裂進展挙動(母材樹脂中の拡散現象と下限界特性)

    第29回FRPシンポジウム講演論文集/日本材料学会   pp.343-346  2000.03

  • 極低温下におけるGFRP円筒の圧縮—圧縮疲労特性(粘弾性—塑性モデルを用いたエネルギー損失による疲労寿命推定)

    日本機械学会論文集(A編)/日本機械学会   66; 643, pp.489-495  2000.03

  • 酸応力環境下におけるGFRP織物積層板の応力腐食割れ(拡散係数と下限界特性)

    研究集会報告/九州大学応用力学研究所   11ME-S1, pp.77-81  2000.03

  • Crack Propagation Behaviors of Woven GFRP Laminates under Acid Stress Environment : Threshold Properties of Corrosion-resistant FRP

    MIZUNO Masaru, TSUBOI Takeyo, KAWADA Hiroyuki

    The proceedings of the JSME annual meeting   2000   593 - 594  2000

     View Summary

    Objective of this study is to clarify the crack-propagation properties of corrosion resistant GFRP laminates under various acid stress environments, an effect of the constituents on fracture and the threshold properties of the crack propagation. This experiment was performed under constant loading in HCl solution and the crack propagation behavior was depicted on a K_1-da/dt diagram. The fracture surfaces of the specimens were observed by scanning electron microscope. As the acid concentration increased the crack propagation was accelerated, however, the effect of the acid concentration was not so dominant. The crack propagation behavior in the water was largely enhanced in comparison with that in the air and it was nearly as promoted as that in the acid solution. Therefore it was noted that the failure of the C/VE systems was occurred by not fiber corrosion but absorption and swelling derived from the diffusion of the water into the matrix and a changing of the stress shearing on the fibers at crack tip.

    DOI CiNii

  • アルミナFRP円筒の疲労損傷と粘弾性モデリング

    第24回複合材料シンポジウム講演要旨集/日本複合材料学会   pp.173-174  1999.11

  • 酸応力環境下におけるGFRPのき裂進展挙動(母材樹脂中の拡散現象とシミュレーション)

    第24回複合材料シンポジウム講演要旨集/日本複合材料学会   pp.157-158  1999.11

  • Evaluating the Mechanical Properties of Glass Fiber/Epoxy Interfaces using the Slice Compression Test

    Proceeds of Twelfth International Conference on Composite Materials   pp.227  1999.07

  • Crack Propagation Properties of GFRP Laminates under Acid Stress Environment

    Proceeds of Twelfth International Conference on Composite Materials   pp.147  1999.07

  • Slice Compression試験によるPMC界面の力学的特性評価(界面はく離進展挙動)

    1999年度年次大会講演論文集/日本機械学会   3, pp.225-226  1999.07

  • 酸応力環境下におけるGFRP織物積層板のき裂進展特性(下限界特性と微視的破壊機構)

    1999年度年次大会講演論文集/日本機械学会   3, pp.221-222  1999.07

  • マルチモード光ファイバを用いたGFRP積層板の損傷検出(マイクロクラックの検出とその場観察)

    1999年度年次大会講演論文集/日本機械学会   1, pp.321-322  1999.07

  • Crushworthiness of Polymeric Matrix Composites for Automabile

    7th Euro-Japanese Symposium/ECOLE DES MINES DE PARIS   Composite Materials and Transportation  1999.07

  • PMC単繊維モデルにおける界面はく離き裂の破壊力学特性評価(界面破壊じん性の理論的検討)

    第7回複合材料界面シンポジウム要旨集/複合材料界面科学研究会   O-23  1999.04

  • Evaluation of Inerfacial Mechanical Properties by Pushout Test;Advantages and Un-resolved Problems

    第7回複合材料界面シンポジウム要旨集/複合材料界面科学研究会   O-22  1999.04

  • Slice Compression試験によるPMC界面の力学的特性評価(界面はく離進展挙動の解析)

    第7回複合材料界面シンポジウム要旨集/複合材料界面科学研究会   O-21  1999.04

  • C/C複合材料の切欠き特性とき裂進展挙動に関する研究

    1999年度研究発表講演会予稿集/日本複合材料学会   pp.103-104  1999.04

  • マルチモード光ファイバを用いたGFRP積層板の損傷検出(検出原理とその有効性の評価)

    1999年度研究発表講演会予稿集/日本複合材料学会   pp.61-62  1999.04

  • アルミナFRP円筒の圧縮疲労特性(疲労損傷の過程と剛性低下)

    1999年度研究発表講演会予稿集/日本複合材料学会   pp.53-54  1999.04

  • 酸応力環境下におけるGFRP織物積層板のき裂進展と下限界特性に及ぼす環境温度の影響

    1999年度研究発表講演会予稿集/日本複合材料学会   pp.41-42  1999.04

  • Applicability of fracture toughness concept to fracture behavior of carbon carbon composites

    H Hatta, Y Kogo, H Asano, H Kawada

    JSME INTERNATIONAL JOURNAL SERIES A-SOLID MECHANICS AND MATERIAL ENGINEERING   42 ( 2 ) 265 - 271  1999.04  [Refereed]

     View Summary

    Carbon/Carbon(C/C) composites have attractive mechanical properties such as superior specific strength and high elastic modulus at high temperature exceeding 2000 degrees C in an inert atmosphere. However, mainly due to lack of knowledge of design criteria, C/C composites have not been used in primary heat resistant structures. For example, almost no unified explanation has been given about the fracture behavior of C/C composites. The objective of this paper is to examine the adequacy of the linear elastic fracture mechanics (LEFM) as the fracture criterion of notched C/C composites. Thus the LEFM was tried to be applied to fracture behavior in tensile tests of double-edge-notched and compact tension specimens and in four-point bending tests of single-edge-notched specimens. It was found that the results of three kinds of fracture tests can be consistently and rationally explained in terms of the LEFM concept with the aid of R-curve behavior if the pre-crack length is long enough to be able to neglect the notch tip radius. From fractographic observation it was found that R curve behavior of C/C composites was mainly attributed to the fiber-bridging effect near the notch tip.

  • C/C複合材料の切欠き強度に及ぼすせん断特性の影響

    第28回FRPシンポジウム講演論文集/日本材料学会   pp.351  1999.03

  • 光ファイバを用いた複合材料の初期損傷モニタリング

    第28回FRPシンポジウム講演論文集/日本材料学会   pp.331  1999.03

  • Slice compression試験によるPMC界面の力学的特性評価(界面せん断応力伝達機構の解明)

    第28回FRPシンポジウム講演論文集/日本材料学会   pp.207  1999.03

  • PMC単繊維モデルにおける界面はく離の破壊力学的検討(界面破壊じん性の速度依存性)

    第28回FRPシンポジウム講演論文集/日本材料学会   pp.195  1999.03

  • アルミナFRP円筒の圧縮疲労損傷過程に及ぼす繊維配向角の影響

    第28回FRPシンポジウム講演論文集/日本材料学会   pp.121  1999.03

    Authorship:Last author

  • 酸応力環境下におけるGFRP織物積層板の応力腐食割れ

    研究集会報告10ME-S2(各種環境下における繊維強化複合材料の力学特性)/九州大学応用力学研究所   10ME-S2,pp.105  1999.03

  • 極低温下におけるアルミナFRP薄肉円筒の疲労損傷過程

    材料/日本材料学会   48;3,pp.282-288  1999.03

  • スマート複合材料における初期損傷と修復のモニタリング

    第23回複合材料シンポジウム講演要旨集/日本複合材料学会   pp.150  1998.11

  • Slice compression testによるPMC界面の力学的特性評価(界面せん断すべり応力の算出)

    第23回複合材料シンポジウム講演要旨集/日本複合材料学会   pp.30  1998.11

  • PMCの繊維-マトリクス界面におけるはく離き裂の破壊力学的評価

    材料システム/金沢工業大学 材料システム研究所   17;pp.21-27  1998.10

  • C/C複合材料の損傷領域形成と強度向上

    第6回機械材料・材料加工技術講演会/日本機械学会   pp.43  1998.09

  • DamorheologyによるGFRP円筒の圧縮疲労特性評価

    第42回日本学術会議材料研究連合講演会/日本学術会議   pp.11  1998.09

  • 腐食環境下におけるGFRP織物積層板の疲労き裂進展挙動

    第42回日本学術会議材料研究連合講演会/日本学術会議   pp.3  1998.09

  • 高分子材料・複合材料

    日本機械学会誌/日本機械学会   101;957,pp.569  1998.08

  • GF/Nylon6円筒のエネルギー吸収特性と初期破損過程

    1998年度研究発表講演会/日本複合材料学会    1998.05

  • 極低温下で繰返し圧縮負荷を受けるGFRP円筒の寿命予測の提案

    1998年度研究発表講演会/日本複合材料学会    1998.05

  • 織物GFRP積層板の応力腐食割れに及ぼす酸濃度の影響

    1998年度研究発表講演会/日本複合材料学会    1998.05

  • Damage Accumulation and Fracture of Notched Carbon-Carbon Composites

    The Seventh International Conference on Composite Interfaces/ICCI-7   ICCI-7,pp.217  1998.05

  • Fracture Mechanics Evaluation of Interfacial Debonding in PMC using Push-out Test

    The Seventh International Conference on Composite Interfaces/ICCI-7   ICCI-7,pp.208  1998.05

  • GF/Nylon円筒のエネルギー吸収特性(トリガー形状と試験速度がエネルギー吸収に及ぼす影響)

    材料/日本材料学会   47;5,pp.458-463  1998.05

  • Applicability of Fracture Toughness Concept to Fracture Behavior of Carbon/Carbon Composites

    HATTA Hiroshi, KOGO Yasuo, ASANO Hideyuki, KAWADA Hiroyuki

    Transactions of the Japan Society of Mechanical Engineers Series B   64 ( 620 ) 897 - 903  1998.04

     View Summary

    Carbon/Carbon (C/C) composites have attractive mechanical properties such as superior specific strength and high elastic modulus at high temperature exceeding 2000°C in an inert atmosphere. However, mainly due to lack of knowledge of design criteria, C/C composites have not been used in primary heat resistant structures. For example, almost no unified explanation has been given about fracture behavior of C/C composites. The objective of this paper is to examine whether the linear elastic fracture mechanics (LEFM) is able to be applied to a C/C composite. The LEFM is tried to apply to fracture behavior in tensile tests of the double-edge-notched and compact tension specimens and in the four-point bending test of the single-edge-notched specimens. It was found that the results of three kinds of fracture tests can be consistently and rationally explained by the LEFM concept with the aid of R-curve behavior if the pre-crack length is long enough to be able to neglect the notch tip radius. From fractographic observation it was found that R-curve behavior of the C/C composite was mainly attributed to the fiber-bridging effect near the notch tip.

    DOI CiNii

  • 炭素繊維強化炭素複合材料における破壊靭性評価の有効性

    日本機械学会論文集(A編)/日本機械学会   64;620,pp.897-903  1998.04

  • Spin burst test of Carbon-Carbon composite disk

    Y Kogo, H Hatta, H Kawada, T Shigemura, H Ohnabe, T Mizutani, F Tomioka

    JOURNAL OF COMPOSITE MATERIALS   32 ( 11 ) 1016 - 1035  1998  [Refereed]

     View Summary

    In order to establish design criteria for a turbine disk made of Carbon-Carbon (C/C) composites, spin burst tests were performed on quasi-isotropically laminated C/C composite disks. Un-notched and notched flat disks were prepared to evaluate the effect of stress concentration on fracture behavior.
    Strain measurements during rotation tests revealed that deformation of the C/C composite disks with or without notches was in agreement with analytical or finite element calculations in the elastic region, which suggests that the test fixtures of the spin tester have a negligible effect on the deformation of C/C composite disks.
    In the spin burst tests, the un-notched C/C composite disks burst at an average rotation speed of 25000 r.p.m. with a peripheral velocity of 393 mis. A comparison between the mean hoop stress averaged over the radius and the tensile strength of smooth specimen suggests that the burst of the un-notched C/C composite disks obey the mean stress criterion. On the other hand, the fracture toughness criterion was shown to be applied for the notched specimen. The difference in the fracture criterion between the un-notched and the notched C/C composite disks is believed to correspond to that between the double edge notched specimens and specimens with a hole in the static tensile tests, (which was explained by the difference in the magnitude of the damaged zone where the stress concentrations would be relaxed).

  • Progressive crushing of compression-molded thermoplastic composite tubes

    H Kawada, T Honda, M Takashima, H Satoh

    DESIGN AND MANUFACTURING OF COMPOSITES   pp.87-90   87 - 90  1998  [Refereed]

     View Summary

    Compression tests on GF/Nylon6 tubes were performed to clarify the mechanism of the initial failure process and the energy absorption behavior. It was found that all the specimens were crushed in a progressive crushing mode regardless of the trigger geometry, but that the specimens with an asymmetric trigger demonstrated better absorbing characteristics than the symmetric specimens. The formation mechanism of the debris wedge was examined through a stepwise morphology analysis. It was found that changes in the trigger geometries affected the performance of the initial failure process which was characterized by the formation of a debris wedge formation process. It was also shown that at high testing speeds in the range of practical use, GF/Nylon6 tubes exhibited similar energy absorbtion behavior to that of a CF/PEEK system.

  • Effect of stress concentration on tensile fracture behavior of carbon-carbon composites

    Y Kogo, H Hatta, H Kawada, T Machida

    JOURNAL OF COMPOSITE MATERIALS   32 ( 13 ) 1273 - 1294  1998  [Refereed]

     View Summary

    The effect of stress concentrations on tensile fracture behavior of carbon-carbon (CIC) composites was investigated using circularly holed specimens and double-edge-notched (DEN) specimens.
    As for the circularly holed specimens, the tensile fracture stress was much higher than that estimated from the maximum stress criterion, which suggest that major stress relaxation mechanisms should exist. On the other hand, the linear elastic fracture mechanics can be applied to the DEN specimen, which means the damaged zone should be small enough compared with the notch length. In order to discuss the magnitude of the stress relaxation, damaged regions of the two kinds of testing geometry were estimated using the point stress criterion. The estimation led to remarkable difference in the size of the damaged regions, which will explain the difference in the magnitude of the stress relaxation.
    Through the observations of fractured specimen, it was deduced that not only the shear deformation but delamination along fiber bundles and opening of transverse crack would relax the stress concentrations. The other mechanism was also proposed based on the testing results, that is strength increase in the damaged region.

  • Effect of Testing Speed on Energy Absorption in CF/PEEK Tubes

    KAWADA Hiroyuki, OKABE Toshiaki, MAWATARI Tadamichi, SATOH Hajime

    Journal of the Society of Materials Science, Japan   46 ( 6 ) 645 - 650  1997.06

     View Summary

    Compression tests on CF/PEEK tubes were performed using a MTS servo-hydraulic material testing machine and a crush testing machine to clarify the mechanism of the initial failure process and the characteristic of the energy absorption. It was found that all the specimens were fractured in a progressive crushing mode and the specific energy absorption indicated the dependence of testing speed in the range of our study. Morphological observation was conducted to examine the influence of testing speed on the specific energy absorption. The mechanism in the steady state stage which takes place after the maximum load is characterized by the interlaminar cracks and lamina breakage at the crush zone. In the initial failure process, the formation mechanism of the debris wedge was examined through the step-wise morphology analysis. The angle and the dimension of the debris wedge were the essential factors in the specific energy absorption.

    DOI CiNii

  • Stress Corrosion Cracking of Notched GFRP Laminates(Microscopic Fracture Model and Crack Propagation Rate)

    KAWADA Hiroyuki, OKADA Akiyoshi, UENO Hironori, HAYASHI Ikuhiko

    Transactions of the Japan Society of Mechanical Engineers Series B   61 ( 592 ) 2566 - 2571  1995.12

     View Summary

    This paper presents stress corrosion cracking (SCC) of notched GFRP laminates under an acid environment. Based on a fractographic analysis, it is found that the stress-corrosion cracking a is governed by a breakage of the warp fiber strand. The crack propagation rate is possible to estimate from a microscopic fracture model of the warp fiber strand. To obtain the crack propagation rate, a fracture model is proposed on the basis of some assumptions as follows : ( 1 ) A relation between an applied stress and a mirror zone radius (in the fracture surface of the warp fiber) obeys the Jaras's equation, ( 2 ) Shape of the warp strand's shape is almost an ellipse, ( 3 ) The crack is a self-similar one during the propagation. The crack propagation rate is obtained as a function of the stress intensity factor. It is found that its value agrees the experimental value, and confirmed that the proposed microscopic fracture model is appropriate for evaluating the crack propagation rate in an acid environment.

    DOI CiNii

  • Polymer Matrix Composite

    KAWADA Hiroyuki

    Turbomachinery   23 ( 9 ) 507 - 511  1995.09

    DOI CiNii

  • Effect of Hole Diameter on Compressive Strength of Unidirectional AFRP : Application of Two Failure Criteria

    KAWADA Hiroyuki, YAGISAWA Ikuya, WATANABE Tomohiro, HAYASHI Ikuhiko

    Journal of the Society of Materials Science, Japan   44 ( 499 ) 464 - 469  1995.04

     View Summary

    Static compression tests of unidirectional AFRP with a circular hole are carried out. The experimental result shows that the compressive strength of unidirectional AFRP containing a circular hole depends on the hole diameter. As the hole diameter increases, the compressive strength tends to be lower in spite of a decrease in the stress concentration factor α_r. A good agreement between the experimental and the predicted compressive strength is observed by the application of two failure criteria. For the specimen with small hole diameter, the strength can be predicted by the Soutis' theory based on the stress distribution around the hole and linear fracture mechanics. For the specimen with large hole diameter, the strength can be predicted by the point-stress criterion(d_0=1.5mm). Finally, the failure mechanism of the unidirectional AFRP subjected to compressive loads is discussed.

    DOI CiNii

  • Evaluation of In-Plane Mode II Fracture Toughness Tests in Unidirectional GFRP : Fracture Simulation Using FEM

    KAWADA Hiroyuki, SUGINO Masaaki, FUKUYAMA Yoshiyuki, HAYASHI Ikuhiko

    Journal of the Society of Materials Science, Japan   44 ( 499 ) 470 - 476  1995.04

     View Summary

    In-plane Mode II fracture toughness tests of unidirectional GFRPs are conducted using a four-point shear loading test method. In the previous paper, the effect of the pre-crack length on the fracture toughness was investigated, and the advantage of this test method was also discussed. In this study, the same test method is used to evaluate the fracture toughness of the unidirectional GFRP. The normalized stress intensity factor concerning an orthotropic body of the unidirectional GFRP is calculated by a finite element method. The mode II fracture toughness is found to be constant regardless of pre-crack length. Using the finite element method, the propagation of the damage zone at the initial failure process is obtained. The analytical mode is shown to be quite effective and the initial failure process is well simulated by this modelization.

    DOI CiNii

  • Evaluation of Fracture Toughness in C/C Composite under Four-Point Bending. (Difference in Fabrication Method and Fracture Mechanism).

    Kawada Hiroyuki, Matsumori Makoto, Omata Hideo, Uruno Tomoyuki, Hiramoto Jiro, Hayashi Ikuhiko

    Transactions of the Japan Society of Mechanical Engineers Series B   60 ( 572 ) 978 - 983  1994

     View Summary

    To evalute fracture toughness of C/C composites, four-point bending tests (SEN) are performed. The C/C composites are carbonized from the CFRPs, which are fabricated by means of two different methods (a hot-press method and a vacuum-bagging one). It is found that each fabrication method leads to a different distribution of bending strength. The vacuum-bagging method is preferable to obtain uniform bending strength properties. Crack growth resistance curves are obtained based on the compliance matching method. These curves have an inclination of convergence at a nearly equal constant value regardless of fabrication method. Existence of the stress shielding mechanism in the C/C composites is suggested by the R curves. From a fractographic observation, crack propagates three-dimensionally, and then pullouts of the fiber bundle occur at a large scale in the fiber-bridging mechanism.

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  • Evaluation of In-Plane Mode II Fracture Toughness in Unidirectional GFRP Using Four-Point Shear Loading Test : Revised Test Method and Dependence of the Pre-Crack Length

    KAWADA Hiroyuki, SHIMANUKI Hiroshi, OMATA Hideo, HAYASHI Ikuhiko

    Journal of the Society of Materials Science, Japan   42 ( 478 ) 817 - 822  1993.07

     View Summary

    In-plane Mode II fracture toughness tests on unidirectional GFRP are conducted using a four-point shear loading test method.In the previous paper,the four-point shear loading test method was examined as a simple Model II fracture toughness test.Then the effect of pre-crack length on fracture toughness was investigated.In this study,the same test method is applied to evaluate the Mode II fracture toughness.The dependence of the pre-crack length and the initial failure process are clarified.The results obtained are summaruzed as follows;(1) It is revealed that the crack opening displacement is much less than the crack relative sliding displacement in the four-point shear loading test.(2) From an analysis of the damage propagation length,it is found that the initiation of the main crack is close to the maximum load point.The initial failure behavior of the unidirectional GFRP subjected to shear loading is clarified.(3) The normalized stress intensity factor concerning an orthotropic body of the unidirectional FGRP is calculated by a finite element method.The mode II fracture toughness is constant irrespective of the pre-crack length.

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  • Evaluation of Mode II Fracture Toughness in Unidirectional GFRP Using Four-Point Shear Loading Test and Its Fracture Mechanism

    KAWATA Hiroyuki, OCHI Yutaka, SHIMANUKI Hiroshi, HAYASHI Ikuhiko

    Journal of the Society of Materials Science, Japan   40 ( 454 ) 875 - 881  1991.07

     View Summary

    Mode II fracture toughness tests of unidirectional GFRP were conducted using a four-point shear loading test method This test method was a modified Iosipescu test method which was identified to be the most reliable one for obtaining a shear stress-strain relation in composite materials. In this study, a leverage ratio of the loading and a pre-crack length ratio of the specimen were examined to perform the fracture toughness tests. Fracture behavior of the unidirectional GFRP under shear loading was investigated through a fractographic observation. The results obtained are summarized as follows: (1) The four-point shear loading test method can be assessed at a simplified in-plane mode II fracture toughness test. To prevent premature failures without reinforcement attached to the specimen, it is necessary for the pre-crack length ratio, a/W to be larger than 0.3 under the definite leverage ratio. (2) The mode II fracture toughness evaluated in terms of stress intensity factors at the maximum load points was found to be dependent on the pre-crack length ratio. (3) The Hackle patterns were confirmed at a stable crack propagation region which are typical fracture traces on the matrix under the shear loading. The formation mechanism of the Hackle at different parts was investigated in detail, and then the physical meaning of the fracture toughness obtained in this experiment was discussed.

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  • Evaluation of Mode II Fracture Toughness in Glass Cloth/Epoxy Laminates by Rail-Shear Test Method

    KAWADA Hiroyuki, AOKI Toshio, KONDOH Monta, HAYASHI Ikuhiko

    Journal of the Society of Materials Science, Japan   37 ( 417 ) 683 - 689  1988.06

     View Summary

    Rail-shear tests were carried out on the glass cloth/epoxy laminates, and then the mode II fracture toughness value K_<IIin> was obtained as the pre-crack length, 2a/ W, was altered from 0.2 to 0.45. In addition, the spread of damage was obtained under simulation by the finite element method and then compared with the experimental results. The following results were obtained; (1) In this test method, the recommendable pre-crack length existed in order to obtain the fracture toughness value. (2) The material used in this study was assumed to be a homogeneous an isotropic material of a tetragonal system, and then the finite width correction factor of the specimen geometry was calculated. Consequently, K_<IIin> became almost constant in the range of 2a/ W=0.25〜0.45. (3) The spread of damage was simulated by the finite element method, and it was found that the analytical result agreed with the initial failure process obtained in the experiment. In addition, the J_<II> value was calculated from the path integral, and discussed.

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  • Effect of Notch Root Radius on Fracture of Glass/Epoxy Laminates : under Tensile Loading

    KAWADA Hiroyuki, HOSOI Takehiko, HIRAMOTO Jiro, HAYASHI Ikuhiro

    Journal of the Society of Materials Science, Japan   36 ( 403 ) 390 - 396  1987.04

     View Summary

    Tensile tests were conducted on specimens of plain woven glass cloth/epoxy laminates with a notch. The effect of the notch root radius p on fracture was investigated. In the previous study, the three-point bending tests were carried out to make clear the effect of the notch root radius on fracture. In this study, the experimental results were compared with those of the previous study. The F.E.M. simulation was performed, and compared with the experimental results. The following results were obtained: (1) As the notch root radius increased, the smaller ρ specimen showed the fracture behavior which was caused mainly by the propagation of a stable crack, but the larger ρ specimen showed the fracture behavior which was caused mainly by the spread of the damage. (2) The spread of the damage zone was different from that of the three-point bending test, but the effect of the notch root radius on strength remained unchanged for the tension and the bending test. (3) The F.E.M simulation explained the experimental result of the larger ρ specimen well.

    DOI CiNii

  • Effects of Thickness and Specimen Size on Fracture Toughness of Glass/Epoxy Laminates

    KAWADA Hiroyuki, OTSUKA Toshihiro, KAJITANI Tadashi, HAYASHI Ikuhiko

    Journal of the Society of Materials Science, Japan   34 ( 377 ) 164 - 170  1985.02

     View Summary

    Three point bending tests were conducted on specimens of plain woven glass cloth/epoxy laminates (fiber volume fraction≒0.4) with notch and R curves were obtained. The effects of the thickness and the size of the specimens on the fracture toughness were investigated. The crack propagation was experimentally observed with the ink method. The electric potential method and the acoustic emission method were carried out to detect the initiation of the crack. In this study, the validity of these nondestructive inspection method was examined corresponding to the load-displacement curves. The following results were obtained: (1) the effect of the thickness on the fracture toughness was less than that of the specimen size, (2) the outputs in the electric potential method were correlatable with the initiation of the damage and the propagation of macroscopic crack, and classified into three distinct patterns and (3) AE counts gave so much information for the fracture behavior in such a way that the initiation of the damage and the proportional limit corresponded to the initiation and the rapid increase of the AE event counts, respectively.

    DOI CiNii

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Books and Other Publications

  • JSMEテキストシリーズ 機械材料学

    日本機械学会編

    日本機械学会  2008.01 ISBN: 9784888981699

Misc

  • 厚肉CFRP積層板の面外方向の疲労特性評価 (長寿命・寿命予測特集)

    細井 厚志, 川田 宏之

    強化プラスチックス   63 ( 10 ) 485 - 489  2017.10

    CiNii

  • J0450401 Evaluation of mechanical properties in carbon nanotubes grafted carbon fiber reinforced plastics using thermal CVD method

    NAKAMURA Kodai, NATORI Junki, OZAWA Sadayuki, KIM Tae Sung, HOSOI Atsushi, KAWADA Hiroyuki

    Mechanical Engineering Congress, Japan   2015   "J0450401 - 1"-"J0450401-5"  2015.09

     View Summary

    It is well known that grafting carbon nanotubes (CNTs) on the reinforced fiber surface modifies fiber/matrix interface adhesion. In this study, the mechanical properties of unidirectional FRP using the CNT-grafted pitch-based carbon fiber were investigated. CNTs were grafted on the pitch-based carbon fiber surface using thermal chemical deposition (TCVD) method at 750℃. First, the single fiber tensile tests were conducted to examine the mechanical properties of the CNT-grafted carbon fibers. From the results, the mechanical properties of the CNT-grafted carbon fiber were decreased compared with as-received fiber. This degradation was caused by an exposure of the carbon fiber surface and a dissolution of iron particles into the carbon fiber surfaces under the high temperature condition of TCVD method. Moreover, static tensile tests were performed in unidirectional CFRP to investigate the mechanical properties of the CNT-grafted unidirectional CFRP. For these tests, specimens with fibers oriented at longitudinal (0°) or transverse (90°) angle from the load direction were prepared. From the results, the mechanical properties of the CNT-grafted unidirectional CFRP were decreased in longitudinal direction compared with as-received CFRP due to the degradation of the mechanical properties in CNT-grafted carbon fibers. On the other hand, it was revealed that the mechanical properties of the CNT-grafted unidirectional CFRP were increased in transverse direction compared with as-received CFRP. This enhancement was mainly due to a relaxation of stress concentration at the edge of carbon fiber by the constitution of CNT/epoxy nanocomposites around the carbon fibers.

    CiNii

  • OS1713 Fatigue Test of Interlaminar Toughened CFRP Laminates in the Out-of-Plane Direction Using a Specimen with Adhesive Bonding Structure

    SAKUMA Shigeyoshi, SHIGEMORI Ko, HOSOI Atsushi, FUJITA Yuzo, TAKEDA Ichiro, KAWADA Hiroyuki

      2014   "OS1713 - 1"-"OS1713-2"  2014.07

     View Summary

    A test method for interlaminar toughened thick CFRP laminates in the out-of-plane direction was studied. Unidirectional thick CFRP laminates whose thickness is approximately 17 mm were used in this study. Spool specimens machined from that thick laminates were loaded in the out-of-plane direction. Metal tabs were bonded to upper - and - lower surfaces of a specimen. At the bonding process, an alignment fixture was used to enhance alignment precision. In addition, an axis adjuster using wood's metal was used to connect the specimen with a testing machine with high axial precision during the tests. As a result of static test, it was confirmed that tensile and compressive load were applied without bending deformation. As a result of fatigue test, it was confirmed that the fatigue life at stress ratio of R=-1 is shorter than that at R=0.1.

    CiNii

  • OS1716 Influence of Fiber Diameter and Cross Sectional Shape on the Impact Properties of Short Glass Fiber Reinforced Polyamide

    OZAWA Kento, KIM Tae Sung, ARAO Yoshihiko, TANIGUCHI Norihiko, NISHIWAKI Tsuyoshi, HIRAYAMA Norio, NAKAMURA Koichi, KAWADA Hiroyuki

      2014   "OS1716 - 1"-"OS1716-3"  2014.07

     View Summary

    Fiber reinforced plastics is increasingly used to improve fuel efficiency and motion performance of vehicles by weight reduction. Especially, short fiber reinforced thermoplastics is expected to expand its demand because of its superior moldability, productivity, and recyclability. In this study, influences of glass fiber diameter and cross sectional shape on the impact properties of short glass fiber reinforced polyamide were investigated using split Hopkinson pressure bar. In the tensile test, specimen with smaller fiber diameter showed higher tensile strength. Glass fiber reinforced polyamide with flat glass fiber also showed higher strength than that with normal glass fiber. On the other hand, a significant influence of fiber diameter and cross sectional shape on mechanical properties was not found in the compressive test. As a result of the fracture surface observation using scanning electron microscope and the average fiber length measurement, it was revealed that interfacial fracture was a dominant fracture mechanism under tensile loading whereas matrix fracture was dominant under compressive loading. Consequently, the influence of fiber diameter and cross sectional shape on impact properties was different under compressive and tensile loading.

    CiNii

  • 110 Effect of stacking sequence on torsional strength of CFRP tubes by modified simultaneous multi ply winding method

    SATOMURA Keisuke, NAKAMURA Takato, KIMOTO Naoki, KAWADA Hiroyuki

    Materials and processing conference   2013 ( 21 ) "110 - 1"-"110-4"  2013.11

     View Summary

    Application of CFRP tubes for torque transmission shafts is expected to improve driving performance and natural frequency as well as fuel efficiency. CFRP tubes manufactured by modified simultaneous multi ply winding method have less voids and fiber waviness compared with conventional CFRP tubes manufactured by filament winding method, and the modified CFRP tubes showed 20% improvement of the static torsional strength. We investigated the fracture mechanisms of CFRP tubes by modified simultaneous multi ply winding method. As a result, a delamination from the prepreg end occurred at the innermost layer and it progressed through ±45° interlayer just before the failure of the specimen. In order to apply CFRP tubes to torque transmission shafts, it is expected to design the stacking sequence appropriately for preventing the delamination from the prepreg end in terms of long-time reliability. Thus in this study, we investigated an influence of the stacking sequence of CFRP tubes on their torsional strength. According to static torsional tests, it was revealed that the specimen with less lamination angle differences caused less delamination due to relaxation of interlaminar shear stress. Moreover, torsional strength was improved moderately mainly because the small lamination angle differences delayed the initiation of the delamination.

    CiNii

  • 116 Fabrication of multi-scale unidirectional GFRP and characterization of its mechanical properties

    NATORI Junki, KAWADA Hiroyuki

    Materials and processing conference   2013 ( 21 ) "116 - 1"-"116-4"  2013.11

     View Summary

    Carbon nanotubes (CNTs) grafted on the fiber surface improves fiber/matrix interfacial adhesion, and form the CNT-resin local composite around each fiber. This study reports the fabrication method of CNT-grafted unidirectional glass fiber reinforced plastics (GFRP) and their mechanical properties. In this study, CNTs were grafted on the T-glass fiber surface using thermal chemical vapor deposition (CVD) at 750℃. First, quality of grafted CNTs and the mechanical properties of T-glass fiber were evaluated. From the results of investigations and analyses, CNTs grafted onto the fiber surface had relatively-many defects, but were uniform and dense. Moreover, mechanical properties of CNT-grafted T-glass fiber decreased drastically compared with as-received fiber. This degradation was caused by the relaxation of thermal residual stress at fiber surface. Finally, static tensile test were performed to investigate the tensile properties of GFRP. According to static tensile test, it was revealed that fracture strain of CNT-grafted GFRP was decreased by 80% compared with as-received one, and it showed brittle fracture. This fracture was mainly due to the degradation of fiber strength and the improvement of fiber/matrix adhesion.

    CiNii

  • 129 Strain rate effects on flexural properties of long and short glass fiber reinforced polyamide

    NOMURA Saeko, TAKAHASHI Kohei, KAWADA Hiroyuki

    Materials and processing conference   2013 ( 21 ) "129 - 1"-"129-4"  2013.11

     View Summary

    In the automotive industry, reducing vehicle body weight is one of the most effective ways to increase fuel economies. Fiber Reinforced Thermoplastics (FRTP) have several advantages over FRP or thermoplastics such as high specific strength and stiflBiess, high moldability. Fiber reinforced polyamide is one of FRTP and in engine parts (e.g. cylinder head covers, intake manifolds) . However, its applications for structural materials or energy absorption ones are limited due to the strict design standards. Therefore, it is necessary to evaluate impact properties of the material. The objective of this paper is to investigate strain rate effects on flexural properties of glass fiber reinforced polyamide. Reinforcement morphology of the materials were two types, twill weave (TWGF) and short fiber (SGF) . Drop weight impact test was used to determine impact flexural properties. The results showed that both TWGF and SGF had strain rate dependencies on flexural properties. SGF had higher strain rate dependency on flexural modulus owing to its higher viscoelastic property, while TWGF had higher one on flexural strength and specific absorbed strain energy owing to its superior tensile property. Furthermore, it was revealed that both TWGF and SGF had high impact absorption properties.

    CiNii

  • J043033 Effect of CNTs at T-glass fiber surface on interfacial shear strjpnth : Comparison among various CNT-grafting conditions

    KAMEYA Maho, SATO Shinya, KAWADA Hiroyuki

    Mechanical Engineering Congress, Japan   2012   "J043033 - 1"-"J043033-4"  2012.09

     View Summary

    In recent years, carbon nanotubes (CNTs) have attracted a lot of interest as an additional component in fiber reinforced plastics (FRP) to improve the properties of the fiber/matrix interface. An improvement of the apparent interfacial shear strjpnth (1SS) was achieved by grafting CNTs onto reinforcement fibers instead of dispersing CNTs in the matrix. In one study, composites containing CNT-grafted fibers and epoxy resin demonstrated 26% ISS improvement over the baseline composites0). However, few studies are focused on glass fibers, due to their low heat resistance. In this study, the effects of grafting CNTs onto T-glass fibers were investigated, especially focusing on the mechanical and interfacial properties of CNT-grafted T-glass fiber reinforced plastics. We used the chemical vapor deposition (CVD) method to graft CNTs onto T-glass fibers. As a result, CNTs were grafted relatively uniformly and cylindrically onto the fibers, which indicates that the CNT-grafting process was appropriate. The CNT-grafted fiber/epoxy resin model composites showed a significant (46-67%) increase of interfacial shear strjpnth. The formation of an interfacial region containing CNTs was observed around each fiber.

    CiNii

  • J043023 Fabrication of carbon nanotubes grafted Tyranno fiber using chemical deposition method and evaluation of interfacial shear strjpnth

    SATO Ryu, KAWADA Hiroyuki

    Mechanical Engineering Congress, Japan   2012   "J043023 - 1"-"J043023-4"  2012.09

     View Summary

    2Waseda University Dept. of Applied Mechanics and Aerospace jpnineering, Okubo 3-4-1 Shinjyuku-ku, Tokyo Grafting carbon nanotubes (CNTs) on the surface of fibers has the potential to modify fiber-matrix interfacial adhesion enhance the composite delamination resistance, and possibly improve its toughness and matrix-dominated elastic property as well. In this study, CNTs were grafted upon Tyranno fibers by the chemical vapor deposition (CVD) at temperatures of 750℃. The ljpnth of the CNTs was controlled by the surface treatment of the fibers and the grafting time. Tensile tests of the single fiber were conducted to examine the thermal effect during the CVD process. It is well known fact that the high heat resistance of Tyranno fiber, it was clear from the results that CNTs grafting process didn't decrease the mechanical property of Tyranno fiber. Moreover the interfacial shear strjpnth of CNTs grafted Tyranno fiber in an epoxy resin was evaluated using the single fiber composite (SFC) fragmentation test. Results of the SFC fragmentation tests indicate an improvement in interfacial shear strjpnth with the addition of the CNTs grafting.

    CiNii

  • J043013 Study for Lifetime Prediction of Off-Axis Woven GFRP Laminate under Constant Tensile Load in Hydrothermal Environment

    NATORI Junki, HATTORI Satoshi, KOTANI Masahiro, KAWADA Hiroyuki

    Mechanical Engineering Congress, Japan   2012   "J043013 - 1"-"J043013-5"  2012.09

     View Summary

    This study reports the off-axis delayed fracture characteristic of woven glass fiber reinforced plastics (GFRP) laminate under constant tensile load in hydrothermal environment. In this study, static tensile test and constant tensile load test were performed in air and water at 40℃. Mechanical properties of GFRP were evaluated by static tensile test. Static tensile test was conducted in water for 200, 500 and 1000 hours, to find out the effect of hydrothermal environment on mechanical properties of GFRP. Result of static tensile test, the maximum stress decreased and the strain at maximum stress decreased greatly in water. In addition, the maximum stress decreased in short term immersion and converged after 200 hours. Constant tensile load test of GFRP was conducted to investigate compliance and fracture time of GFRP. The applied stress level of constant tensile load test was determined as 15%〜75% of the maximum stress obtained from static tensile test. As the result of constant tensile load test, the compliance increased obviously and delayed fracture occurred earlier in water than air. In this study, prediction was conducted for off-axis woven GFRP laminate under constant tensile load in 40°C water using the Reiner-Weissenberg(R-W) criterion; which is based on the non-linear viscoelasticity response. The prediction data was compared well with the experimental data by considering the degradation of GFRP in 40°C water.

    CiNii

  • Geometrical stability of CFRP laminate considering ply angle misalignment

    Y. Arao, J. Koyanagi, S. Takeda, S. Utsunomiya, H. Kawada

    ICCM International Conferences on Composite Materials    2011.12

     View Summary

    Accurate geometrical stability is required for the precise structures like telescopes. It was reported that symmetrical CFRP (Carbon Fiber Reinforced Plastics) laminates show unpredictable deformation due to the ply angle misalignment and temperature change. This ply angle misalignment is unavoidable. One of the answer to mitigate the deformation due to the ply angle misalignment is to chose effective stacking sequence. We discussed here the effective stacking sequence to reduce the thermal deformation.

  • Time and temperature dependence of surface accuracy of high-precision CFRP mirrors

    J. Koyanagi, Y. Arao, S. Utsunomiya, S. Takeda, H. Kawada

    ICCM International Conferences on Composite Materials    2011.12

  • An effect of physical aging progression on viscoelastic property in carbon/epoxy composites

    Yukie Okudoi, Yoshihiko Arao, Jun Koyanagi, Shin Ichi Takeda, Hiroyuki Kawada

    7th Asian-Australasian Conference on Composite Materials 2010, ACCM 2010   1   194 - 197  2010.01

     View Summary

    This study aims to quantify the effect of physical aging progression on viscoelastic property in carbon/epoxy composites. Understanding viscoelastic behavior of carbon fiber reinforced plastics (CFRPs) has become an essential issue for further application of CFRPs to aerospace structures, which require high dimensional accuracy. In this research, the viscoelastic property was evaluated by quasi-static tensile tests in transverse direction for unidirectional laminates. The progression time of physical aging versus viscoelastic parameters was obtained. It was found that the viscoelastic behavior becomes less significant as the physical aging progresses. Considering the quantitative result, creep compliance function, which is conventionally difficult to predict due to the unknown physical aging effect, was predicted as functions of creep time and preceding aging time. This prediction was verified by actually performing a long-term creep test in transverse direction for unidirectional composites. Creep test result and the calculated results using viscoelastic parameters obtained from quasi-static tensile tests showed similar results up to the aging time given to the specimen before the test, but they showed different trends along with time progression. By taking into account the progression of physical aging, the calculated lines are likely to show better correspondence with the creep curves.

  • 212 Strain-rate dependency of interfacial strength in Polymer-Matrix Composite

    OHISHI Taiji, KAWADA Hiroyuki

    Materials and processing conference   2009 ( 17 ) "212 - 1"-"212-2"  2009.11

     View Summary

    The interfacial strength is especially the important property amongst the other components', reinforcing fiber and matrix which consist of PMC. For the further use in industrial application, the evaluation of interfacial strength under dynamical loading is requested. In this study, we conducted the tensile test on SFC specimen and observation of nucleation of interfacial debonding at different strain rates, and recognized the dependency of interfacial strength on strain rates. According to elasto-plastic analysis with the assumption that matrix's yield stress be the variant of strain rates, stress distribution of the interface asymptotically approaches the elastic analysis, and it can be concluded that the dependency of interfacial strength on strain rates caused by matrix's dependency on strain rates.

    CiNii

  • 204 Tensile fracture properties of glass fibers in cryogenics environment

    HAYAKAWA Mamoru, TANIGUCHI Norihiko, KAWADA Hiroyuki

    Materials and processing conference   2009 ( 17 ) "204 - 1"-"204-2"  2009.11

     View Summary

    The cause of strength increase in the glass-fiber at cryogenic temperature has not been fully studied so far. In the present study, tensile tests of a single E-glass fiber in air and liquid nitrogen were conducted to reveal the mechanism of strength increasement. From the mirror zone measurement on the fracture surface, the mirror constant's value was determined. It was clarified that the mirror constant's values of the fiber were equal regardless of the heat treatment condition and testing temperature. These experimental results suggest that an increase of the glass-fiber strength in cryogenic environment is attributed to not the molecule network changing but the crack blunting of the fiber.

    CiNii

  • Time-dependent Out-of-plane deformation of symmetric laminate including small fiber misaligned

    Yoshihiko Arao, Jun Koyanagi, Hiroshi Terada, Hiroyuki Kawada

    Progress of Composites 2008 in Asia and Australasia - Proceedings of the 6th Asian-Australasian Conference on Composite Materials, ACCM 2008     297 - 299  2008.12

     View Summary

    In this study, we focused on the geometrical change of symmetric laminates that are widely used for the composite structures. The behavior of time-dependent out-of-plane deformation under high temperature and humidity was examined with high accuracy. The geometries of the CFRP plates were measured after constant time. It was obvious that the main factor which causes geometrical change was moisture absorption at 80°C, 90%RH environment. The geometrical change was calculated based on Finite Element Analysis considering fiber misalignment. Coupling analysis including stress and diffusion analysis was performed to reproduce the time-dependent deformation. In this analysis, we rotated the layer of the symmetric laminate about 5 degrees, so specifically the model was asymmetric, and the coupling effects that arose bending by tension took place due to moisture absorption. Quasi-isotropic laminate model including small fiber misalignment deformed into saddle shape and twisted saddle shape. It was predicted that it must be needed to control fiber alignment strictly when we product CFRP laminate with high dimensional stability.

  • Effect of moisture absorption on dimensional stability in carbon/epoxy composites

    Yoshihiko Arao, Jun Koyanagi, Hiroshi Hatta, Yuichiro Aoki, Hiroyuki Kawada

    ICCM International Conferences on Composite Materials    2007.12

     View Summary

    In order to quantify the dimensional stability in CFRPs at humidity environment, the water diffusion considering an anisotropy and moisture expansion behavior are investigated. Water diffusivity coefficients were determined by measuring the specimen weight during the moisture absorption test. The diffusivity coefficients of three main axial directions are obtained from three shapes specimen&#039;s result and solving simultaneous equations. A 3-dimensional locator using laser-displacement measurement was employed to measure micro deformation of the CFRP specimens caused by moisture absorption. The curvature of surface was observed due to the distribution of moisture contents. The coupling analysis which includes mechanical deformation and thermal diffusion was conducted. The numerical results are in good agreement with the test results.

  • Dimensional stability of CFRP in humidity environment

    Yoshihiko Arao, Jun Koyanagi, Hatta Hiroshi, Hiroyuki Kawada, Yuichiro Aoki

    Proceedings of the SEM Annual Conference and Exposition on Experimental and Applied Mechanics 2007   1   365 - 371  2007.11

     View Summary

    In order to quantify the dimensional stability in CFRPs, the water diffusion considering an anisotropy and moisture expansion behavior are investigated. Water diffusivity coefficients were determined by measuring the specimen weight during the moisture absorption test. The diffusivity coefficients of three main axial directions are obtained from three shape specimen&#039;s result and solving simultaneous equations. A 3-dimensional locator using laser-displacement measurement was employed to measure micro deformation of the CFRP specimens. The curvature of surface was observed due to the distribution of moisture contents. The coupling analysis, which includes mechanical deformation and thermal diffusion, was conducted. The numerical results are in good agreement with the test results.

  • 405 Numerical Simulation of Delamination Growth of GFRP Laminates in Wind Turbine Blade

    KAWADA Hiroyuki, TAKENAKA Tatsuya, HOSOI Atushi

    Materials and processing conference   2007 ( 15 ) 247 - 248  2007.11

     View Summary

    A numerical study was performed on the fracture toughness test to obtain the critical strain energy release rate (G_<IC>) of Glass Fiber Reinforced Plastic (GFRP) laminates in wind turbine blade. Two-dimensional numerical analysis, based on an elastic finite element method (FEM) using the static explicit method and the cohesive damage model, was performed to simulate the fracture toughness test. The cohesive damage model used to predict the delamination occurrence and growth is based on a special developed interface finite element including an exponential damage process. The numerical prediction showed good agreement with the experimental results.

    CiNii

  • 407 High Cycle Fatigue Damage Propagation of Cross-ply CFRP Laminates

    KAWADA Hiroyuki, Ono Go, HOSOI Atsushi, SATO Narumichi

    Materials and processing conference   2007 ( 15 ) 251 - 252  2007.11

     View Summary

    Damage growth behavior of transverse crack and delamination in cyclic loading was studied with cross-ply laminates of carbon fiber reinforced plastics (CFRPs) composite. Damage of the specimens during the fatigue test was observed by soft X-ray photography. It was found that delamination growth behavior depended on the inter-laminer stress and the out-plane stress in thickness direction caused by free-edge effect. Quasi-isotropic, [45/0/-45/90]_s, laminates, are applied large peering stress at free edges of the specimen when the specimen is subjected to tensile stress. Therefore they showed edge delamination. On the other hands, cross-ply, [0/90_6]_s laminates, are applied large inter-laminer shear stress at transverse crack tips, and show local delamination originated by a transverse crack. Under the high-cycle loading, it was observed that depending on the applied stress level delamination growth behavior differed.

    CiNii

  • 414 A method for evaluating degradation in strength of unidirectional composite in water environment: an effect of accumulation of microscopic damages

    KOTANI Masahiro, KAWANISHI Ken, KAWADA Hiroyuki

    Materials and processing conference   2007 ( 15 ) 265 - 266  2007.11

     View Summary

    Long-term durability of fiber-reinforced-plastics (FRP) under hostile environment is strongly influenced by the degradation of fiber strength. The degradation of the fiber strength has been quantified on the basis of microscopic stress corrosion cracking (SCC) of the initial defects on the fiber surface. In this paper, the fiber strength degradation in the single-fiber-composite (SFC) has been investigated under constant strain in water to represent the SCC of GFRP. By taking account of the fiber strain history, such as water absorption, thermal expansion, applied strain, the growth of the initial defect after the constant strain test was formulated. After the constant strain test, fragmentation test was conducted in order to estimate strength degradation of the embedded fiber. The remaining fiber strength distribution obtained from the fragmentation test was predicted using the model containing the Paris Law and the Arrhenius model presented by K. Liao.

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  • 411 Evaluation of Impact Tensile Properties of Woven Fabric Reinforced Plastics by SHB Method

    TANIGUCHI Norihiko, KANDA Mamoru, KAWADA Hiroyuki

    Materials and processing conference   2007 ( 15 ) 259 - 260  2007.11

     View Summary

    This paper describes in-plane shear mechanical properties of woven fabric reinforced plastics by the static and dynamic ±45° tension test method. Using the tension-type SHB apparatus, the dynamic tension tests were performed. 8-types of specimens were used. 2-types of epoxy resin (thermo-set and thermo-plastic) were combined with 4-types of fibers (E-glass, T-glass carbon, and aramid fiber). Comparing their mechanical properties, especially, the shear of glass fiber specimens more dependent on strain rate than other specimens.

    CiNii

  • Present Studies and Future Prospects of Composite Materials

    KAWADA Hiroyuki, KOBIKI Akira

      61 ( 10 ) 4 - 9  2007.10

    CiNii

  • 411 Quantitative evaluation of curing shrinkage in polymeric matrix of CFRP

    KOTANI Masahiro, ARAO Yoshihiko, KOYANAGI Jun, KAWADA Hiroyuki, HATTA Hiroshi, AOKI Takuya

    Materials and processing conference   2006 ( 14 ) 237 - 238  2006.11

     View Summary

    Applying CFRP to precision machinery components and aerospace materials, CFRPs long-time dimensional accuracy must be secured. Matter for consideration about the dimensional accuracy, moisture absorption, chemical shrinkage, and visco-elastic deformation such as creep are presumable to be the leading factor for the deformation. These deformations are very small, so we need to evaluate quantitative analysis with these factors individually. In this study, we deal with the chemical shrinkage. First, we conducted dynamic DSC measurement to determine the total heat of reaction. Heat of reaction during the cure was measured by isothermal DSC measurement and was quoted to define the extent of cure. A Kinetic model, the Arrhenius model was applied to predict the extent of cure. Our aim is to evaluate the dimensional change concurrent with the cure of epoxy by using laser confocal displacement meter.

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  • 419 Prediction of Creep Rupture Lifetime in Unidirectional Composites

    OGAWA Fumio, Koyanagi Jun, Kawada Hiroyuki

    Materials and processing conference   2006 ( 14 ) 253 - 254  2006.11

     View Summary

    Delayed fracture occurs in unidirectional composites as a result of accumulation of micro-damages, such as fiber breakage or time-dependent interfacial debonding. In this study, the creep rupture lifetime in unidirectional composites is predicted under consideration of the propagation of interfacial debonding and its effect on rupture lifetime and damage accumulation is examined. Predictions were performed for two cases that stress concentration on intact fiber adjacent to broken fiber is not taken into account or taken into account. For former case, the decrease in rupture strain due to time-dependent propagation of interfacial debonding is formulated. For latter case, Monte-Carlo simulation under consideration of interfacial debonding propagating fiber breakage point is performed. As a result, the propagation of stress concentration region is observed and it is thought to be dominant factor for time-dependent damage accumulation in unidirectional composites.

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  • 414 Strain rate effect on mechanical properties of CFRP tube

    TANIGUCHI Norihiko, MORITA Tomoya, KAWADA Hiroyuki

    Materials and processing conference   2006 ( 14 ) 243 - 244  2006.11

     View Summary

    This paper describes strain rate effect on mechanical properties of CFRP tube. The investigated relations of CFRP tubes (fiber orientation 0, 30, 60, 75deg) between bending stress and bending strain under lateral impact loading using SHPB (Sprit Hopkinson's Pressures Bar) method. The experimental result pointed that bending stress and bending modulus depended on strain rate. Furthermore, it demonstrated that the higher fiber-oriented specimens produced, the more significant contribution to the strain rate effect.

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  • 420 Time-dependent Fiber Degradation in Polymer Matrix under Water Environment

    KOBIKI Akira, KAWADA Hiroyuki, ITOH Seiya

    Materials and processing conference   2006 ( 14 ) 255 - 256  2006.11

     View Summary

    This paper describes fiber strength degradation of FRP under constant loading in water was investigated using a single fiber composite (SFC) specimen. In experiments, the fiber strength degradation in the SFC specimen was accelerated by water and applied stress. The fiber strength was evaluated by a fragmentation test. We assumed the degradation was caused by microscopic crack propagation and the propagation was accelerated by water and applied stress. Therefore the degradation mechanisms based on the microscopic crack propagation was established to predict the degradation in the SFC specimen. Finally, the experimental results were predicted using the degradation mechanisms.

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  • A Novel Method for Evaluation of Fiber Strength Using Fragmentation Test

    KIMURA Souta, KOYANAGI Jun, YAMAMOTO Daisuke, KAWADA Hiroyuki

    Journal of JSEM   6 ( 2 ) 122 - 127  2006.06

    CiNii

  • 10405 Internal Damage Behavior of the stitched CFRP Laminates Under Tensile Fatigue Loading

    ARAO Yoshihiko, HOSOI Atushi, KAWADA Hiroyuki

      2006 ( 12 ) 363 - 364  2006.03

     View Summary

    This paper studies the effects of edge stitching on tensile fatigue properties of CFRP laminates. Fatigue damage development was investigated through experimental observation. From experimental observation results, it was shown that introduction of the stitch threads suppressed the initiation and propergation of the delamination. But the stitch thread broke in earlier stage under the high stress level cyclic loading. As a result, fatigue lives of the stitched laminates were shorter than that of the unstitched laminates. On the other hand, it was remarkable that the fatigue lives between the both laminates were almost equal due to the difference of internal damage propergation.

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  • 10404 Prediction of creep rupture in unidirectional composites

    KOYANAGI Jun, OGAWA Fumio, KAWADA Hiroyuki

      2006 ( 12 ) 361 - 362  2006.03

     View Summary

    Delayed fractures in carbon-fiber-reinforced polymer matrix composites could be observed even at room temperature due to an accumulation of micromechanical damages, such as interfacial debondings or fiber breaks. In this study, the creep-rupture time of unidirectional composites consisting of carbon fiber and vinylester resin is predicted under consideration of the progress of interfacial debonding, which corresponds to an increase of stress recovery length, and which is accompanied by a fiber break. The time-dependent rupture strain of unidirectional composites is calculated based on the global load sharing theory, which takes into account an increase of the stress recovery length, which is determined using carbon/vinylester single-fiber composite. The creep rupture time of unidirectional composites is formulated, and the prediction of the time-dependent rupture strain decrease are verified by a comparison between the residual strength of the unidirectional composite after a fixed displacement test and the calculated results at that condition.

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  • Evaluating the mechanical properties of a CFRP tube under a lateral impact load using the split Hopkinson bar

    TANIGUCHI NORIHIKO, NISHIWAKI TSUYOSHI, KAWADA HIROYUKI

      14 ( 3 ) 263 - 276  2005.09

    CiNii

  • 10104 High-cycle fatigue characteristics of quasi-isotropic CFRP laminates

    HOSOI Atsushi, KAWADA Hiroyuki

      2005 ( 11 ) 189 - 190  2005.03

     View Summary

    This paper describes high-cycle fatigue characteristics of quasi-isotropic CFRP laminates [-45/0/45/90]_s to 10^8 cycles. To investigate the fatigue behavior in the high-life region, the fatigue tests were conducted with frequency of 100Hz since it's difficult to conduct its with 5Hz and the damage behavior of the specimen was observed with a microscope, a soft X-ray photography and a 3D ultrasonic inspection system. In this study, to evaluate quantitive characteristics of transverse crack propagation in the high-cycle region, the energy release rate associated with transverse crack growth to the width direction was calculated and the transverse crack growth to the width direction was evaluated based on a modified Paris-law approach.

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  • 20106 Evaluation of Interfacial Debonding-Initiation Energy in Single Fiber Composite

    KIMURA Souta, KOYANAGI Jun, KAWADA Hiroyuki

      2005 ( 11 ) 221 - 222  2005.03

     View Summary

    An effect of the plastic deformation on the interfacial energy of a fiber-reinforced polymer matrix composite is studied to evaluate the initiation of the interfacial debonding. We performed the fragmentation test with a model glass fiber-reinforced vinylester matrix composite, and calculated the interfacial energy with the energy balance method taking into account an energy dissipation of the plastic deformation. The following results are confirmed; the plastic deformation has a significant influence on the interfacial energy, and the energy balance scheme considering the plastic energy dissipation leads to the constant interfacial energy without reference to the amount of the released potential energy. The differences between our model and the previous one are discussed.

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  • 20107 Application of Fragmentation Test to Evaluation of Fiber Strength : Evaluation Method Considering Test Speed

    KAWADA Hiroyuki, YAMAMOTO Daisuke, KOYANAGI Jun

      2005 ( 11 ) 223 - 224  2005.03

     View Summary

    Single fiber fragmentation test is one of the methods to evaluate strength of a fiber embedded in matrix resin. This method has two advantages; the Weibull parameter can be obtained from a few tests and an actual strength of the embedded fiber in practice can be obtained. This test evaluates relationship between the fiber strength and the fiber length. However, the fiber length is defined by the length of the gage length divided by the number of fragment points, and the fiber length is overestimated. Therefore, in the conventional evaluation, the fiber strength is not independent to interfacial strength and test speed. To assume the exact fiber length, an interfacial debonding length and a stress recovery length must be considered. In this study, the new corrected evaluation to generalize the fiber strength is suggested. To discuss the validity of the method, several fragmentation tests are performed under the condition of the various interfacial strength and the various test speed.

    CiNii

  • Time-Dependent Behavior of Interfacial Crack in Single Fiber Composite : Interfacial-debonding propagation taking into account relaxation of interfacial frictional stress

    KAYANAGI Jun, YAMAZAKI Masashi, KAWADA Hiroyuki

    Materials and processing conference   2004 ( 12 ) 117 - 118  2004.11

     View Summary

    Interfacial debonding propagation is very important problem for long-term creep in unidirectional composites because material's properties of the unidirectional composite decrease with increase of the interfacial debonding length. In this study, time-dependent interfacial failure was investigated by using the Raman Micro Spectroscopy. The specimen was single fiber conposite consisting one carbon fiber embedded in the vinylester resin and it was subjected to constant strain condition to assume the long-term creep in the unidirectional composites. The interlace between the carbon fiber and the vinylester resin is relatively weak; therefore interfacial frictional stresiss is one of the most important factors, which dominated the interfacial debonding propagation. In this paper, the compression stress applied to the interface in the direction of fiber rudius direction is calculated as a function of time on the consideration of Poisson compression and thermal residual stress. The interfacial frictional stress is assumed to be dominated by the Coulomb's friction and compared with the Experimental results. The interfacial debonding propagation is discussed by using the relaxation of the frictional stress. Long-term behavior of the interfacial debonding propagation is predicted in the single fiba composites.

    CiNii

  • Evaluating the lateral impact properties of CFRP cylindrical tube using the Split Hopkinson Pressure Bar technique

    TANIGUCHI Norihiko, NISHIWAKI Tsuyoshi, KAWADA Hiroyuki

      2004   11 - 12  2004.05

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  • An Effect of the Environmental solution on the Crack propagation properties of GFRP

    KIMURA Souta, KOBIKI Akira, KAWADA Hiroyuki

      2004   55 - 56  2004.05

    CiNii

  • Influence of surface condition to glass fiber strength in water environment

    KOBIKI Akira, SHIODA Satoshi, KAWADA Hiroyuki

      2004   57 - 58  2004.05

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  • Caracteristic of Crack Propagation and Influence of Fiber Bridging in GFRP Laminates under Acid Stress Environment

    KAWADA Hiroyuki, IITAKA Seishi

      27   201 - 202  2002.10

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  • Energy loss produced by interlaminar delamination in laminated composites

    NISHIWAKI Tsuyoshi, TANIGUCHI Norihiko, KAWADA Hiroyuki

      27   215 - 216  2002.10

    CiNii

  • Wave Propagation Behavior in Composite Materials with Internal Defect

    TANIGUCHI Norihiko, NISHIWAKI Tsuyoshi, KAWADA Hiroyuki

      27   213 - 214  2002.10

    CiNii

  • Study on Stress Corrosion Cracking of GFRP Using Model Specimens : Evaluation of Interfacial Degradation by Energy-balance Model

    KAWADA Hiroyuki, INOUE Daisuke

      27   203 - 204  2002.10

    CiNii

  • Wave propagation behavior of GFRP laminates under transverse impact

    TANIGUCHI Norihiko, NISHIWAKI Tsuyoshi, KAWADA Hiroyuki

      2002   139 - 140  2002.05

    CiNii

  • 220 Characteristic of Fatigue in Quasi-Isotropic Alumina-Fiber Reinforced Plastic : Internal Damage Progression and Fatigue Life

    Kawada Hiroyuki, Yamazaki Shinichiro, Matsuzaki Takashi

    JSME Materials and Processing Conference (M&P)   10 ( 1 ) 479 - 482  2002

     View Summary

    This paper describes the results of an experimental investigation of cumulative damage development in quasi-isotropic [0/+45/-45-90]_s alumina FRP laminates subjected to tension-tension fatigue loading. The onset and growth of matrix cracks and delamination were monitored with an optical microscope. The matrix crack density and the normalized length of delamination were measured as a function of the normalized number of stress cycles by edge observation. It was found that a decrease of the stiffness was observed in an early stage due to the initiation of the matrix crack, and that a different pattern of the damage evolution was observed in each lamina under tension-tension fatigue. Results of the study include a detailed description of the chronology of the damage development prior to failure. Additionally, the mechanism of the fracture of quasi-isotropic alumina FRP laminates under tension-tension fatigue was evaluated from the result such that the static strain of [0]_8 Alumina FRP laminates and fatigue failure strain of quasi-isotropic alumina FRP laminates are equivalent.

    CiNii

  • 230 A Study on Stress Corrosion Cracking using Single Fiber Model Specimen : Degradation Properties of GFRP caused by Water Absorption

    Kawada Hiroyuki, Kobiki Akira

    JSME Materials and Processing Conference (M&P)   10 ( 1 ) 529 - 533  2002

     View Summary

    Fragmentation tests have been conducted to investigate the degradation mechanism using a single fiber composite. The effects of environmental solution diffusion into the resin on the fiber strength and the interfacial shear strength have been investigated as a function of immersion time. As a result, the fiber strength did not chang in respect to an environmental solution containing water and acid. It was suggested that only water would diffuse into the resin and reach the inner fiber, and that acid would not reach the fiber. A Fickian diffusion analysis showed that the water concentration around the fiber already reached a saturation limit at the beginning of the acid diffusion. In this study, the importance of water diffusion on each material degradation was discussed. It is suggested that only water would diffuse into the resin and reach the inner fiber, and acid would not reach the fiber. Therefore, it is concluded that the water diffusion influences the degradation of materials, fiber, matrix and interface immediately before acid corrodes the fiber and interface.

    CiNii

  • Effect of Non-metallic Inclusion on High Cycle Fatigue Behavior in High-Strength Steel : Relationship between fatigue life of inclusions and ODA

    Tokuda Naoki, Kawada Hiroyuki, Ochiai Ikuo, Hayashi Hiroaki

      2002 ( 77 ) "8 - 1"-"8-2"  2002

     View Summary

    The primary aim of present study is to clarify the fatigue fracture mechanism of high strength steel at the high cycle region. Oil-tempered high strength steel wire (SWOSC-B) is prepared for fatigue test by using monopodium fatigue testing machine at frequencies of 1kHz. The S-N diagram has a knee point at about 2×(10)^6 cycle. From scanning electron microscopy (SEM) observation of the fracture surface at the long cycle fatigue range, nonmetallic inclusion is identified at the origin of fracture and optically dark area (ODA) is formed around the inclusion. On the other hand, a constitution of the nonmetallic inclusion is measured by using electron probe micro analyzer (EPMA). As a result, the inclusions are decided as Al_2O_3-CaO and TiN. Fatigue fracture from Al_2O_3-CaO is occurred earlier than that of TiN. Based on these results, finite element analysis (FEA) is conducted for analyzing the stress field in vicinity nonmetallic inclusion. Then, the effect of mechanical property of inclusion on fatigue failure behavior and ODA are discussed.

    CiNii

  • 502 Effect of Non-metallic Inclusion on High Cycle Fatigue Behavior in High-Strength Spring Steel : Relationship between mechanical property of inclusion and fatigue life

    Lee Going-Won, Kawada Hiroyuki, Ochiai Ikuo, Hayashi Hiroaki

      2001 ( 76 ) "5 - 3"-"5-4"  2001.03

     View Summary

    The primary aim of present study is to clarify the fatigue fracture mechanism of high strength steel at the high cycle region. Oil-tempered high strength steel wire (SWOSC-V) is prepared for fatigue test by using Nakamura rotating-bending fatigue testing machine. The S-N diagram had a knee point at about 10^5cycle. From scanning electron microscopy (SEM) observation of the fracture surface at the long cycle fatigue range, nonmetallic inclusion was identified at the origin of fracture and it formed "fish-eye". On the other hand, a constitution of the nonmetallic inclusion is measured by using electron probe micro analyzer (EPMA). As a result, Aluminum, calcium and oxygen were detected mainly at the inclusion. Based on these results, finite element analysis (FEA) was conducted for analyzing the stress field and equivalent plastic strain field in vicinity of the nonmetallic inclusion. Then, the effect of mechanical property of inclusion on fatigue failure behavior was discussed.

    CiNii

  • 212 Evolution of Fatigue Damage in Quasi-Isotropic Alumina Fiber Reinforced FRP

    KOBAYASHI Nobuyiiki, KAWADA Hiroyuki, Nishio Kenichi, Sugano Yoshihiko

    Materials and processing conference   2000 ( 8 ) 71 - 72  2000.11

     View Summary

    This paper describes fatigue properties of a quasi-isotropic [0/+45/-45/90]s Alumina. FRP laminates. Matrix crackgrowth behaviors in the laminates under static and fatigue loadings have been studied. Detailed experimental observations were made on the initiation and the growth of individual cracks in 90, -45 and 45 deg plies. Distinctly different crack growth behavior was obtained in each lamina under fatigue loading. At the first of fatigue process, reduction of the stiffness in the laminates due to the 90 deg transverse matrix cracking was obtained. After that, the reduction of that didn't occur, but the transverse cracks in the 90 deg layer were saturated. And then, some delaminations were initiated after the -45 and +45 deg layer's cracks were observed. A higher density of each ply clacks and delaminations would be a characteristic of the fatigue damage in quasi-isotropic Alumina FRP laminates.

    CiNii

  • 215 Characteristics of GFRP Tube Subjected to Fatigue Loading at Cryogenic Temperature

    MUKAI Yoshitarou, KAWADA Hiroyuki

    Materials and processing conference   2000 ( 8 ) 77 - 78  2000.11

     View Summary

    This paper describes the characteristics of tensile fatigue in GFRP tube(±45deg) under dynamic cyclic loading at room temperature and 77K. Dynamic cyclic loading tests were conducted at three levels of the maximum stress and the cyclic frequency 10Hz. The relationship between the visco-elastic plastic properties and the internal fatigue damage was investigated at each stress level. The fatigue strength at cryogenic temp, was greatly improved in the range of this study. However, change of the apparent stiffness and hysteresis loss of the specimen were similar behavior.therefor ,similar fatigue damage mechanisms were conjected at each temperature.

    CiNii

  • 536 Effect of Non-metallic Inclusion on High Cycle Fatigue Behavior in High-Strength Spring Steel

    Lee Going-Won, Ochiai Ikuo, Hayashi Hiroaki, Kawada Hiroyuki

    Materials and processing conference   2000 ( 8 ) 381 - 382  2000.11

     View Summary

    The primary aim of present study is to clarify the fatigue fracture mechanism of high strength steel at the high cycle region. Oil-tempered high strength steel wire (SWOSC-V) is prepared for fatigue test by using Nakamura rotating-bending fatigue testing machine. The S-N diagram had a knee point at about 10^5cycle. From scanning electron microscopy (SEM) observation of the fracture surface at the long cycle fatigue range, nonmetallic inclusion was identified at the origin of fracture and it formed "fish-eye" failure. On the other hand, a constitution of the nonmetallic inclusion is measured by using electron probe micro analyzer (EPMA). As a result, Aluminum, calcium and oxygen were detected mainly at the inclusion. Based on these results, finite element analysis (FEA) was conducted for analyzing the stress field around the neighborhood of the nonmetallic inclusion. Then, the effect of mechanical property of inclusion on fatigue failure behavior was discussed.

    CiNii

  • 228 Study on Stress Corrosion Cracking of GFRP using Single Fiber Model Specimen : Evaluation of Diffusion Phenomenon into Resin

    TOGE Kunihiro, KAWADA Hiroyuki

    Materials and processing conference   2000 ( 8 ) 231 - 232  2000.11

     View Summary

    Single fiber fragmentation test have been conducted to examine the degradation of inner fiber strength surrounded by the resin using E-glass/Vinylestr model composite. Stressed and unstressed specimens under the environmental attack by water and acid have been prepared. The effect of diffusion phenomenon into the resin on inner fiber strength is investigated as a function of immersion time. As a result, the strength of fiber in stressed resin was lower than that in unstressed resin. This result indicates that stressed polymer have the diffusion phenomenon accelerated. In reference to each environment conditions (water and acid), the fiber degradation behavior was unchanged. It seemed that the water would only diffuse into the resin, and the acid would not. These experimental results were explained analytically based on Fickian diffusion analysis. It is expected that water diffusion affect the mechanism of the fiber degradation in the earlier stage than acid diffusion.

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  • 229 Crack Propagation Behavior on Woven GFRP Laminates under Acidic Stress Environment : Discussion of Fracture Mechanism based on Diffusion Simulation

    KATSUNO Hiroyuki, KAWADA Hiroyuki

    Materials and processing conference   2000 ( 8 ) 233 - 234  2000.11

     View Summary

    Over the past several years or so a Stress Corrosion Cracking of the FRP plant applications has been a serious problem. Under such conditions an establishment of a life prediction has been one of the great interests for a long time. A threshold property of the crack propagation, K_<ISCC>, is regarded as one of the fracture criteria for estimating life span. In this study, fracture mechanism in the threshold properties was investigated. C-glass/Vinylester composites were tested under constant load in the hydrochloric acid, sulphuric acid and water. The crack propagation behavior was depicted on the K_I-da-dt diagram. It was found that diffusion behavior of the acid solution ion into the matrix plays an important role in the process of the threshold failure. Especially, judging from the diffusion coefficient, there is a possibility that molecular of water diffuses precedent to hydrogen ion at the crack tip. As the time passes, the resin absorbs the water and this leads to a swelling of the resin. In addition, molecular of water and belated hydrogen ion corrode the C-glass fiber. Therefore it is suggested that the fracture of the C/VE systems was occurred by absorption and swelling derived from the diffusion of the water into the matrix and a changing of the stress sharing on the corroded fibers at the crack tip.

    CiNii

  • Tensile/Compressive Fatigue Characteristics of Alumina FRP Pipes (Relation between Winding Angle and Fatigue Strength)

    HIRANO Takaaki, WAKI Yuichiro, KAWADA Hiroyuki

      2000   51 - 52  2000

    CiNii

  • The Evaluation of Mechanical Properties at PMC Interface by The Slice Compression Test (The Generation and Growth of Interfacial debond crack)

    TSAI Kun-Nan, ARIOKA Kosuke, KAWADA Hiroyuki

      2000   97 - 98  2000

    CiNii

  • Effect of Fiber Orientation on the Compressive Fatigue Properties of Alumina FRP Tubes

    KAWAMATA Akio, KAWADA Hiroyuki

      23   92 - 93  1998.11

    CiNii

  • Evaluation of Interfacial Shear Mechanical Properties in SiO_2 Fiber-Reinforced Epoxy Matrix Composite by Push-out Method

    KAWADA Hiroyuki, NAGAOKA Masahiro, SATO Fuminori, KATO Eiji

      22   32 - 33  1997.11

    CiNii

  • Evaluation of the effect of interface roughness on interface shear frictional stress in fiber-reinforced composite by Push-out/Push-back test

    KAWADA Hiroyuki, KATO Eiji, SATO Fuminori, NAGAOKA Masahiro

      22   34 - 35  1997.11

    CiNii

  • Characteristics of Crack Propagation on Anti-corroded FRP under Stress Acid Environment : Effect of Environmental Conditions on Crack Propagation

    KAWADA Hiroyuki, ONODERA Kazuhiro, MIZUNO Masaru, MIYATA Takahiro

      22   100 - 101  1997.11

    CiNii

  • Characteristic of Compressive Fatigue in GFRP Pipe at Low temperature : Effect of frequency on Fatigue Properties

    KAWADA Hiroyuki, SAKAI Shinsuke, YOSHII Hironari, WAKI Yuichiro

      22   132 - 133  1997.11

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  • 一方向FRPの面内混合モ-ド破壊じん性評価--き裂の進展を考慮した破壊シミュレ-ション

    川田 宏之, 丸尾 和弘, 沼田 浩明

    材料システム   ( 15 ) 49 - 55  1996

    CiNii

  • Characteristic of Stress-Corrosion Cracking in Woven GFRP Laminates

    KAWADA Hiroyuki, UENO Hironori

      20   59 - 60  1995.10

    CiNii

  • 一方向GFRPの層間破壊じん性に及ぼす海面強度の影響

    川田宏之

    複合材料界面シンポジウム要旨集   4   45 - 45  1995

    CiNii

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Industrial Property Rights

  • 酸化銅ナノワイヤおよびその製造方法

    細井 厚志, 川田 宏之, 柳澤 一星, 松永 光広, 土肥 優希

    Patent

  • 樹脂金属接合体の製造方法及び樹脂金属接合体

    細井 厚志, 川田 宏之, 丁 埈澈, 岡本 和起, 阿部 暉

    Patent

  • 繊維強化熱可塑性樹脂プリプレグ及び成形体

    川田 宏之, 細井 厚志

    Patent

  • FRP円筒及びその製造方法

    川田 宏之

    Patent

  • 積層材料の層間破壊じん性試験装置

    川田 宏之, 中屋 久仁康, 森山 英重

    Patent

Awards

  • JSME Medal for Outstanding Paper

    2014   The Japan Society of Mechanical Engineers   Evaluation of transverse crack initiation in interlaminar toughened CFRP cross-ply laminates under cyclic loading

    Winner: KAWADA, Hiroyuki

Research Projects

  • Producing high strenght and durable nanocomposites using soluble graphene

    Project Year :

    2019.04
    -
    2022.03
     

  • 革新的合成法による無撚CNT繊維強化複合材料の創成と高強度化

    Project Year :

    2018.04
    -
    2021.03
     

     View Summary

    本研究では世界最高強度を有するカーボンナノチューブ(CNT)紡績糸の創製を目標としている.CNT紡績糸は,触媒担持化学気相成長法によってシリコン基板上に規則正しく垂直成長したCNTフォレストよりCNTを連続的に引き出し,それを撚り合わせることで作製されることが一般的である.本研究ではCNT紡績糸を構成するCNTの配向性改善を目的として,微細径のダイスにCNTを通すことで撚り角の無い無撚CNT糸を作製し,従来のCNT紡績糸と比較して高い機械的特性を得ている.このことから,無撚CNT糸に対して作製条件の最適化やポリマー含浸処理による高密度化及び架橋構造の付与,CNTの高純度化を目的とした熱処理条件の検討などを行ってきた.昨年度はCNT単体の物性値が紡績糸の機械的特性に及ぼす影響の評価を行い,CNTの薄層化及び細径化が紡績糸の高強度化に有効であることが確認された.本年度は無撚CNT糸の更なる高強度化を目的として,従来の5-10層,直径が10nmのCNT及び1-5層,直径が5.6nmの薄層かつ細径な2種類のCNTについて,それぞれCNT単体及び高密度化処理を施した無撚CNT糸の機械的特性評価を行った結果,CNTの薄層化・細径化に伴いCNT単体,CNT糸の強度が共に向上し,CNT単体及びCNT糸の尺度係数はそれぞれ11.1GPa,2.43GPaとなった.また無撚CNT糸に対しコーミング処理及び延伸処理を行った結果,CNTの配向性向上に伴う強度の向上が確認された.更に実験的に得られたCNTの物性値や強度及びそのばらつき,分子動力学(MD)法を用いた解析により得られた界面せん断強度をCurtinモデルに適用した結果,2種類の無撚CNT糸の実験値と傾向が一致し,また実験値との相対誤差が6~17%の精度でCNT糸の強度予測が可能であることが確認された.本研究では高強度無撚CNT糸の創製を目的としている.これまでにCNTの合成条件検討やCNT紡績糸作製条件の最適化,ポリマー含浸による無撚CNT糸の高強度化を行い,無撚CNT糸の機械的特性の向上に成功してきた.これまでに得られた知見を複合的に最適化することで機械的特性の改善を重ねており,研究の進捗状況としては概ね順調である.現在は無撚CNT糸の更なる機械的特性向上を目的とし,Curtinモデルに基づく強度予測式及び分子動力学計算を用いた各種物性値の検討や,無撚CNT糸の寸法効果による影響の解析的な評価などを行っている.また昨年度CNT単体の走査電子顕微鏡(SEM)内その場観察引張試験を実施するための設備導入を行ったことにより,CNT単体の各種物性値評価が可能となった.これによりCNT単体及び無撚CNT糸双方に関して多様な評価が可能となり,CNT単体の特性が無撚CNT糸機械的特性に及ぼす影響を複数の観点より考察することが可能となっている.これまでの研究の中で,無撚CNT糸の機械的特性を向上させる手法として,CNT無撚糸を構成するCNT単体の薄層化及び細径化が有効であることが確認された.本年度は無撚CNT糸の更なる高強度化を目的として,CNT単体の長さや密度といった他の物性値が無撚CNT糸の機械的特性に及ぼす影響の評価を行う.無撚CNT糸についても,直径や評点間長さが機械的特性に及ぼす影響について評価を行い,寸法効果について検証を行う.そして引き続き強度予測モデルや分子動力学計算を用いて解析的にCNT間相互作用力に関する知見を深め,CNT紡績糸の強度発現機構の解明を目指す.また本年度は,従来の触媒担持化学気相成長法により合成されたCNTだけではなく,より薄層かつ細径で高い結晶性を有するCNTが得られることで知られる,浮遊触媒化学気相成長法により合成されたCNTから作製されたCNT紡績糸に関しても各種評価を行い,従来の無撚CNT糸との比較・検討を行う.これによりCNT紡績糸の強度を決定する要因を明らかにするとともに,CNT紡績糸の強度向上に向けた方針を示すことを目標とする.浮遊触媒法CNT糸に関してもこれまでの知見を反映しポリマー含浸処理による高密度化を行うが,合成方法の違いにより結晶性等の様々な物性値が大きく異なるため,ポリマー含浸処理の最適条件が異なることが予想される.従って浮遊触媒法CNT糸に関しては別途ポリマー含浸処理条件の検討を行い,更なる高強度化を行う

  • Fabrication of innovative carbon nanotube metal composite wiring material with large current capacity

    Project Year :

    2018.06
    -
    2020.03
     

  • Development of Innovative Ultra-Light Weighted and High Strength Composite using Densified Untwisted CNT

    Project Year :

    2015.04
    -
    2018.03
     

     View Summary

    The aim of this study is to fabricate innovative high strength CNT yarns in which excellent mechanical properties of CNTs are fully demonstrated. Untwisted CNT yarns were fabricated by dry spinning method using a ceramics die. Strengthening constituent CNTs of the CNT yarn and improvement of the load transmission efficiency between the CNTs were revealed to be necessary for development of high strength CNT yarns by strength evaluation of a CNT and molecular dynamics method. Untwisted CNT yarns were purified by graphitization treatment and combined with polymers such as PVA and PAN, and their strength reached 2.4 GPa

  • Fabrication of Hierarchical Composite Reinforced with CNT Deposited Fiber and Interfacial Evaluation, and Impact, Fatigue Properties

    Project Year :

    2012.04
    -
    2015.03
     

     View Summary

    The aim of this study is to fabricate the innovative polymer matrix composite (PMC) which is reinforced by carbon nanotubes (CNTs). As an introducing method of CNTs into PMC, synthesizing CNTs on the inorganic fibers such as glass fiber, tyranno fiber and PAN based carbon fiber was conducted. Then, uniform CNTs grafting process with high productivity was established by a combination of various catalysts and deposition conditions. Furthermore, the multi scale interfacial properties of PMC was improved by introducing CNTs, and it was found to be due to the anchor effects of CNTs. The CNTs grafted unidirectional composite was also fabricated and the tensile properties to 0&#61616;, 10&#61616;, 90&#61616; direction were studied. The anisotropy of CNTs composite and the mechanism of the stiffening effect were revealed

  • 極限環境下における先進複合材料の高度利用技術の開発

    文部科学省 

    Project Year :

    1999
    -
    2003
     

  • Development of a Internationally acceptable fatigue test system for prosthetic heart valve

     View Summary

    The purpose of this study is to establish an internationally-acceptable methodology of fatigue testing for prosthetic heart valves, based on the improvement process of a Chinese-made accelerated fatigue test apparatus. This test system had four parallel water cylinders, in which valves were incorporated. Open and closing motion of each valve was controlled at a repetition speed of 10-20 Hz with a displacement of 1-2mm. The Jerryfish (JF) valve was used in this study. It had the longest implantation record in animal trials. In this case, the polyurethane membrane with the thickness of 50-70 mum was ruptured due to a creep effect observed at the middle portion between two spokes after 300days in goat.First of all, in vitro fatigue test machine has been innovated in order to reproduce the above mentioned in-vivo fatigue test results. Dynamic conditions which enabled the identical forces between accelerated and normal cycles were determined : maximum load during valve closure was 5.2N (increased by 20% to the normal), and impulse was 2.5*10^<-2>N・s. Under this condition, valves were ruptured for 1.0*10^7 cycles, but no distinct creep was noticed. Secondary, a temperature of the test-fluid was changed from 20゚C to 50゚C,expecting a creep effect to the membrane shape. Change in shape of the membrane was observed after 3.2*10^6 cycles, however, its distortion value was only 50% of the animal experimental results. For the next step, a material of the membrane was changed from polyurethane to polystirene to achieve bigger change in shape. As a result, the identical distortion level was successfully reproduced, but a location of the ruptured area was different between in vitro and in vivo results. In order to clarify the above mentioned difference, FEM analysis was performed. The calculated result exhibited that there are three major areas of the maximum elastic strain between two spokes. Moreover, it was confirmed that the ruptured areas observed by both in vitro/in vivo results could be fully superimposed to the areas of the calculated maximum elastic strain.Further investigation should by carried out to determine more reliable methodology for fatigue testing, based on the in vitro and FEM analysis data

  • Characteristics of Stress Corrosion Cracking in GFRP Laminates under Acid Stress Environment

     View Summary

    Studies on crack propagation behaviors and threshold properties of GFRP Laminates under an acid stress environment.GF/epoxy specimens, which are made of E-glass fiber and epoxy resin, are investigated, and effects of the loading conditions arid the environmental conditions on crack propagation behaviors and threshold properties in HCI solution are researched.Constant and cyclic loading tests are performed, so that the stress ratio and the frequency are changed for the cyclic loading tests. As a result, it is found that crack propagation depends on a time and the maximum stress intensity factor, K_<lmax>. There is no acceleration of crack propagation due to cyclic loading in a K_<lmax>-da/dt diagram. Furthermore, it is verified that the threshold stress intensity factors, K_<ISCC>, under both loading condition have a distinguished difference in the range of our study. From fractographic observations, interfacial crackings and pull-outs of fibers are remarkable under the cyclic loading condition.As for the environment condition, changes in the crack propagation behaviors due to the alternations of acid concentration and temperature of the HCI solution are researched. As the acid concentration increases, the K_<ISCC> seems to be a constant under the constant loading conditions and the solution temperature of 303K.And it is noted that the K_<ISCC> takes its minimum value at lmoh/l under the cyclic loading conditions and the solution temperature of 303K.Increase of the solution temperature lead to the quickening of crack propagation. Arrhenius' equation can be adopted in a stable crack propagation region according to Paris' power low. As for the threshold properties, there is little effect of temperature under the constant loading conditions. On the other hand, the K_<ISCC> decreases and its minimum value vanished under the cyclic loading conditions and the solution temperature of 343K

  • Crack Progress Behavior of Woven GFRP Laminates under acid stress environment

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    The objective of this study is to clarify the crack-propagation of the corrosion-resistant GFRP that laminates under various acid stress environments, an effect of the constituents on fracture and the threshold of the crack propagation in the C/VE and E/VE systems. Two kinds of experiments of the stress corrosion cracking (SCC) test and the single fiber fragmentation test were performed.SCC tests were performed under constant loading in an HCl solution, H_2SO_4 solution, water and air, and the crack-propagation behavior was depicted on the da/dt-K_1 diagram. The crack-propagation behavior in water was largely enhanced in comparison with that in the air and it was almost as promoted as that in the acid solution. The failure mechanism of C/VE under the acid stress environment differed from E/VE with which the glass fiber was corroded. As expected, the main causes were the interfacial strength decrease and the water absorption of the matrix.Single fiber fragmentation tests were conducted to examine the degradation mechanism using a single fiber E-glass/Vinylestr model composite. Stressed and unstressed specimens under the environmental attack by water and acid were prepared. The effect of diffusion phenomenon into the resin on the fiber strength and the interfacial shear strength were investigated as a function of immersion time. As a result, the strength of fiber in stressed specimens was lower than that in unstressed specimens. This result indicates that the stressed polymer have the diffusion of the corrosive solution acceralated. The fiber degradation behavior was not changed regardless of each environmental condition, such as water and acid. It seemed that only the water would diffuse into the resin, and the acid would not. A Fickian diffusion analysis has shown that the moisture concentration around the fiber already reached a saturation limit at the beginning the acid diffusion

  • 新鮮な血液を用いた機械加工表面性状の定量評価の試み

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    第3年度は,人工弁・人工心臓などの開発の早期に血液適合性をある程度評価でき,また,設計改良の指針となるデータを得ることが可能な,より信頼性のあるin vitro血液適合性評価試験回路の開発を目指した.第一に,回路内での血液と空気の接触面を完全に排除した4つの同一形状の旋回渦流型血液ポンプで構成される一巡閉鎖回路を開発した.4つの血液ポンプのうち1つのみを駆動し,他の1つはコンプライアンス,残りの2つはリザーバの役割を持たせることで,平均大動脈圧100mmHg,平均ポンプ拍出量2.5L/minといった実際の使用環境に近い試験環境にすることができた.また,washout性能の極めて良好な旋回渦流型血液ポンプを回路の構成要素として用いることで,流れの停滞領域のない試験回路を開発することができた.第二に,チューブやコネクタなど試験回路の構成パーツに対する血小板の活性能を同一にするために,血液ポンプと同一材料で回路内面全体をコーティングした.なお,本研究では新開発の高分子製二葉弁を血液適合性評価試験対象とした.開発した回路内をヘパリン化した新鮮牛血液で満たし,その後プロタミンで中和してACTを300sec〜400secに調節した後に試験を開始した.採取した血液中の血小板の活性能時間を考慮して,試験は4時間で終了した.試験後の弁葉表面をSEMによって観察した結果,(1)弁流出側の弁葉表面では血球成分の付着及びフィブリン網などが全く観察されず血液適合性は良好であったが,流入側の弁葉表面では弁閉鎖時にスポークと接触する部分の吸着タンパク質層に磨耗跡が観察された.また,(2)弁座と弁葉の接着部分に血小板の付着が観察された.以上から,新たに開発したin vitro血液適合性評価試験回路は製品開発の早期に問題点を明確にするのに極めて有効であることが明らかとなった

  • Threshold Properties of Woven GFRP Laminates under Acid Environment

     View Summary

    The stress corrosion cracking mechanism of glass fiber reinforced plastics (GFRP) were investigated in this work. First of all, an effect of the constituents on the fracture and the threshold properties on the crack propagation of woven C-glass/vinyl ester laminates. The propagation behavior was evaluated in HCl solution, in water and in air. As a result, the behavior was plotted on the da/dt-K_I diagrams. The crack-propagation rate da/dt distribution in water was largely enhanced in comparison with that in the air, and it was nearly as promoted as that in the HCl solution. Therefore the crack-propagation properties of unidirectional FRP were investigated to confirm the role fiber direction. The threshold properties the 90° unidirectional FRP were appeared on the da/dt-K_I diagrams and the it is confirmed that the cause is the fiber bridging by the FEM analysis.Single fiber model composites were applied to evaluate the interfacial degradation mechanisms. The degradation was described by interfacial debonding energies in this study. And the interfacial debond length near the fiber failure point was measured to calculate the energies. The matrix plastic zone was also measured, therefore the plasticity was considered in the energy balance model to decide the interfacial debonding energies. Furthermore it was suggested that the interfacial debonding energy kept the constant value.In order to estimate the fracture behaviors of the fiber and interface, the double cleavage drilled compression (DCDC) test was applied. And one fiber bundle was embedded in the specimen in order to estimate the fracture mechanisms. The crack was deflected around the fiber bundle and the fiber/matrix interface was debonded. As a result, it was found that the debond length depended on the interfacial degradation. The debonding length and interfacial debonding energy decided the bridging stress on the crack surface. And the bridging stress determined the traction on crack surface, although the traction decreased due to the fiber failure. Finally the toughening effect that depended on the traction was discussed

  • Long-term Durability of GFRP under Corrosive Environment

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    Fiber reinforced plastics (FRP) are widely used in structural applications because of their good specific stiffness and strength. In addition, corrosive resistance of the FRP is superior to conventional materials. Therefore use of the FRP under corrosive environment has been extended, such as a chemical solution storage tank. Under the environments, stress corrosion cracking is a typical problem for the conventional materials. Also, the stress corrosion cracking is a principle problem for the FRP under the corrosive environment.Strength and stiffness depends on fiber strength, therefore strength degradation of single E-glass fiber under the water environment was investigated. The fiber strength is characterized by Weibull shape and scale parameter. As a result, the scale modulus decreased as a function of immersion time in the water. In addition, time-to-failure under constant loading in the water was measured. Distributions of the time-to-failure were predicted assuming initial defect growth on the fiber surface. The result showed that the strength degradation depended on initial strength and applied stress.Fiber bridging of water-absorbed FRP is principle in crack propagation, therefore studied in order to estimate crack propagation resistance under water environment. The crack propagation resistance depended on the weight gain due to water absorption. Therefore the absorbed water was an essential factor to decrease the crack propagation resistance. Finally, increased resistance by the fiber bridging was predicted using bridging stress distribution that was obtained by measurements of debonding length of the bridging fiber. The propagation resistance obtained by the fiber bridging showed a good agreement with experimental results. It was found that the crack propagation under the water environment depended on the fiber/matrix interfacial properties

  • Time Dependent Characteristics and Long-term Reliability of PMC in Hostile Environment

     View Summary

    Polymer matrix composites(PMC) such as Fiber Reinforced Plastics(FRP) have numerous variations in its components, and therefore it is possible to design its mechanical properties corresponding to its application. Previous researches dealing long-term reliability of FRP in corrosive environment mostly focus on macroscopic damage failure such as crack propagation and mechanical properties degradation, but not on its failure mechanism. The failure of FRP occurs from the accumulation of microscopic damage in its components. Thus present research focus on microscopic damage such as degradation in mechanical properties of resin matrix, strength degradation of fiber reinforcement, and interfacial degradation, and furthermore, evaluated these degradation behavior quantitively.Firstly, neat matrix resin specimen was immersed in Deionized water and was statically〜in air to measure its mechanical properties such as stiffness and rupture strain. The stiffness remained unchanged but the rupture strain increased in vicinity of immersion.Secondly, E-glass fiber was embedded in the epoxy resin to mold Single Fiber Composite(SFC) specimen. Constant strain test of SFC specimen was conducted under water environment(40, 75[℃]. Fragmentation test was conducted after the constant strain test to estimate fiber residual strength. It was clarified that the fiber strength degrades by constant strain test, and the degradation accelerates with higher applied strain, immersion time, and higher water temperature. Furthermore subcritical crack growth model was applied to predict the fiber strength degradation.Finally, the length of interfacial debonding accompanied with embedded fiber failure was measured to estimate the maximum shear strength. Also, from the energy balance in vicinity of fiber failure, Energy Release Rate(ERR) was quantified. Wagner's model and Morais's model were applied to estimate maximum shear strength and ERR. It was clarified that both values degrades and showed a tendency to saturation

  • Damage Evolution and Long-Term Durability of Polymer Matrix Composite in Water Environment

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    The aim of this research is to investigate the long term durability of GFRP in hydrothermal environment and to propose its lifetime prediction model. The GFRP under study is consisted with plain E-glass cloth and vinylester resin. The constant tensile load tests were conducted in hydrothermal environment (i.e. deionized water) and in air. The fracture occurred only in hydrothermal environment and the fracture time decreased with the increase in the applied stress and the temperature. The fracture time was predicted based on Reiner-Weissenberg criterion and the predicted results showed good agreement with the experimental data by considering the degradation induced by the hydrothermal aging and its acceleration by the increasing temperature

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Specific Research

  • 溶融紡績法による高強度・高導電性を有するCNT紡績糸の創成

    2021  

     View Summary

    本研究課題では、1)溶融紡績法によるCNT糸の成形、2)無撚CNTの高強度化に向けた高密度化処理方法について研究を行った。CNT糸の合成に関しては、いくつかの成形方法がある、今回行ったのは「溶融紡績法」であり、「基盤法」や「浮遊合成法」とは明確に異なる成形法である。新に溶融紡績装置を導入し、原材料の前処理を先行する研究グループの手法を参考にして行い、コール酸を分散液として成形を試みた。結果的には、CNT紡績糸を成形することに成功し、初めて溶融紡糸法によるCNT糸を得ることができた。さらに、無撚CNTの高強度化に関しては、基盤法で得た無撚CNTに対して研究を行い、PAA/DMSO処理の最適条件を探求することに成功した。

  • エラストマー分散強化CFRTPの 衝撃破壊シミュレーション

    2021  

     View Summary

    炭素繊維強化熱可塑性樹脂は高エネルギー吸収特性を有しており、衝突などのエネルギー吸収部材への適用拡大が期待されている。母材樹脂中にエラストマー(EL)粒子を分散してエネルギー吸収特性の向上を目標とした新コンセプトCFRTPを作成した。EL添加が及ぼす衝撃吸収性への影響および破壊シミュレーションを行い、衝撃吸収機構を調査した。この結果、EL分散による衝撃吸収性能の向上および破壊形態の変化が確認された。またLS-Dynaを用い、離散積層モデル(DPM)を適用した解析から、EL未添加材料の荷重―変位線図を高精度にて再現することができた。一方、EL添加材に関しては、初期損傷以降のシミュレーション結果は実験より高めの結果を示した。

  • エラストマー分散強化CFRTPの 衝撃エネルギー吸収メカニズムの解明

    2020  

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     近年CO₂排出量規制化を背景として自動車の車体軽量化が求められており,優れた比強度・比剛性を有する炭素繊維強化熱可塑性プラスチック(CFRTP)の衝撃吸収部材への適用が期待されている. 本研究では,エラストマー(EL)分散強化CFRTPのクロスプライ積層板に対して落錘衝撃試験を実施し,EL粒子の体積分率による衝撃特性及び破壊形態への影響の調査を行った.衝撃試験の結果よりEL粒子の体積分率を増やすことにより衝撃吸収エネルギー及び初期損傷荷重の向上が確認された.さらに破断面観察の結果よりEL粒子を加えることで面外方向の塑性変形の拡大及び層間剥離領域の減少が確認された.以上,EL分散強化CFRTPは母材樹脂の高靭性化及び面外方向の塑性変形によるエネルギー吸収が衝撃特性向上に寄与していることが確かめられた.

  • CFRTP射出成形材の衝撃エネルギー吸収特性

    2019  

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    繊維強化熱可塑性プラスチック(Fiber Reinforced Thermoplastics;FRTP)は,成型が容易で生産コストが低く,圧縮荷重負荷時に逐次破壊を伴う場合に高いエネルギー吸収性能(EA)を示す特徴があり,量産車への適用に期待が持たれている.過去の研究では,破壊時のEA性能に複合材料の繊維-樹脂界面強度や母材樹脂の応力-ひずみ挙動等が影響することが報告されている.本研究では,繊維-樹脂界面強度や母材樹脂の変更による靭性の違いがFRTP 射出成型材の衝撃EA 性能に及ぼす影響を調査することを目的として,靭性を変化させたFRTP 射出成型材に対して逐次破壊試験による衝撃EA吸収挙動の調査を行った.また,物性値との相関を調査するために圧縮特性取得,ModeⅠ破壊靭性取得を行った.供試材として,母材樹脂にポリアミド(PA)66を用いたNormal材,PA12を用いた高じん性材,Normal材作成時のサイジング剤に不適合なものを適用した低じん性材の3種類として,それぞれ破壊じん性値の異なる射出成型材を採用した.全ての供試体の強化材にはE-glass 繊維を用いた.逐次破壊時に衝撃EA性能が温度に依存しない現象を観察するため,逐次破壊試験を実施した.試験速度は9~10m/s,試験温度は-30℃,23℃,90℃,130℃とした.試験はスプリットホプキンソン棒(Split Hopkinson Pressure Bar;SHPB)法試験機を用いて実施した.試験により得られた荷重・応力-変位線図より,低じん性材及びNormal材の90℃では逐次破壊中の平均応力が試験温度の影響をあまり受けなかったのに対し,高じん性材(90℃)では平均応力が大きく低下する結果が得られ,Normal材(130℃)でも同様の傾向が確認された.また,高じん性材やNormal材の高温雰囲気下では荷重の変動が比較的滑らかであったが,低じん性材やNormal材の低温雰囲気下では荷重の振動が確認された.高じん性材や高温条件の試験の際に振動が発生した原因は,高じん性材やNormal材の高温条件では延性的な破壊が逐次破壊の大きな要因を占めるのに対し,低じん性材やNormal材,高じん性材の低温条件では脆性的な破壊が逐次破壊の大きな要因となったためだと考えられる.また,これまでの研究においては,温度変化に伴う強度とじん性の変化が相殺することでEA性能が温度に依存しない現象が発現すると示唆されている.しかし,本研究では高温条件の際にSCSの低下が確認された.このことは,温度に依存しないEA現象が発現するのは限られた温度領域内のみであることが示唆された.さらに,90℃での試験結果を比較すると,母材樹脂を変更した供試体の試験結果においてSCSの低下が確認された.この現象が生じる温度領域は母材樹脂の特性により変化する可能性が示唆された.加えて,これまでの研究および本研究の逐次破壊試験後の試験片観察より,試験温度に依存した破壊形態が発現し,温度上昇に伴い逐次破壊時の破片サイズが大きくなることを確認している.しかし,破壊形態が変化する温度には上限があり,ある温度を超えると破壊形態には大きな変化が生じなくなると考えられる.そのため,破壊形態変化の上限を超えた高じん性材の高温雰囲気下では強度と靭性のバランスが崩れ,SCSが低下したと考えられる.

  • ガラス長繊維強化熱可塑性ペレットを用いた射出成形材の衝撃引張特性評価

    2018  

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     本研究では、強化繊維の細線化とひずみ速度の増加に伴うガラス繊維/ポリアミド(GF/PA)の強度向上のメカニズムの調査のため,GF/PAの短繊維引抜き試験,低ひずみ域速度域における引張特性評価,および不連続繊維強化材の強度予想モデルであるKelly-Tysonモデルを拡張し強化繊維の配向性を考慮したモデル式による強度予測を実施した.供試体には平均繊維径の異なる3種類の強化繊維からなるLFTペレットより作成した射出成型材を使用した. その結果,界面せん断強度強化繊維と引張強度のひずみ速度依存性,強化繊維の繊維径とGF/PA引張強度の逆相関性が確認された.また,強度予測により強化繊維の強度が繊維径に依らず一定とした場合にはGF/PAの引張強度は繊維径に依らずほぼ一定となることが明らかとなり,繊維径の違いによるGF/PA引張強度への影響は,強化繊維の特性による寄与が支配的であると示唆された.

  • 大電流容量を有する配線用CNT複合繊維の創製

    2017  

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    大電流容量・高導電率を有する配線用CNT金属複合繊維の創製に向け,母材となる高配向CNT糸に黒鉛化処理ならびに高密度化処理を施し,各処理が繊維の電気特性に及ぼす影響の定量評価を行った.CNT糸の黒鉛化処理では,不活性ガス環境下における高温熱処理によって結晶性が改善し,それに伴う比導電率・比電流容量の顕著な増加が確認された.一方,ポリマー溶液浸漬による高密度化処理では,繊維の収縮によってCNTバンドル間の空隙が減少し,導電率が大幅に向上した.ポリマー処理によって線密度の増加が見られたことから,ポリマーがCNT糸に含浸し,残留していることが示唆された.

  • 層間高じん性化CFRP積層板の面外疲労特性に及ぼす内部欠陥の影響

    2017  

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    本研究では層間高靭性化CFRP積層板(T800S/3900-2B)の面外方向(Z方向)疲労特性に及ぼす内部欠陥の影響を評価するため,応力比R=0.1にてZ方向疲労試験を実施し,ボイド等の内部の初期欠陥が積層板のZ方向疲労寿命に及ぼす影響の調査を行った.成形条件を変えることで積層板の空洞率や最大ボイド長さを変えた2種類の積層板を用いた.なお,空洞率や最大ボイド長さは試験片の端面観察および3次元X線CT装置を用いた内部観察により測定した.Z方向疲労試験を行った結果,本研究の範囲では初期欠陥の条件による疲労寿命の差異は見られないこと,試験片の表面性状を変化させた場合でも疲労寿命に差異は見られないことが明らかとなった.破壊力学的には脆性材料である本試験片の疲労寿命は最大ボイドの長さに大きく影響を受ける.しかしながら,本研究で用いた積層板はいずれも最大ボイド長さが2mm以上と大きい.したがって,内部欠陥や表面性状が疲労寿命に及ぼす差異が確認されなかったと示唆された.

  • 繰り返し荷重を受ける層間高靭性化厚肉CFRP積層板の特性評価

    2016   細井厚志

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     本研究では層間高靭性化CFRP積層板(T800S/3900-2B)の面外方向(Z方向)疲労特性に与える応力比の影響を評価するため,複数の応力比条件(-1, -3,-6)にてZ方向疲労試験を実施し,圧縮荷重が積層板のZ方向疲労寿命に与える影響の調査を行った.その結果,応力比が小さくなるにつれて疲労寿命も低下していることから,負荷される圧縮荷重の大きさが疲労寿命に影響を与えることが明らかとなった.損傷観察により,圧縮荷重の増加に伴い繊維/母材樹脂界面でのはく離は促進されるが,破壊形態に変化は与えないことが示唆された.有限要素解析により算出された面外方向応力と修正H-kモデルを用いることで疲労寿命に与える圧縮荷重の影響を定量的に評価し,等寿命線図による疲労寿命予測を行った.

  • 配線用超軽量高導電性CNT複合金属繊維の創製

    2016  

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    本研究では,大電流容量・高導電率を有する金属複合繊維の作製を目的とし,繊維配向性の高いCNT無撚糸を硫酸銅メッキ浴に浸漬させた後,電気メッキ処理を行うことで,繊維内部に銅が析出した銅複合CNT無撚糸の作製を行った.作製した繊維の繊維長手方向には部分的に銅が連結するような析出形態をしていることが確認された.また,作製した繊維に対して,電気特性評価を行ったところ,銅複合CNT無撚糸の電気特性は繊維外周部に堆積した金属層の影響が支配的であるという結果を得た.そこで,繊維内部に析出した銅の電気特性に対して与える影響の調査を行ったところ,繊維内部に銅が析出することにより,電流密度増加に伴う抵抗率の増加が緩やかになることで,電流容量が増加することが確認された.

  • 面外方向繰り返し荷重を受けるCFRP積層板の両振り疲労特性評価

    2015   細井厚志

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     本研究では層間高靭性化CFRP積層板(T800S/3900-2B)の面外方向(Z方向)疲労特性の評価のため,Z方向引張-圧縮疲労試験(R=-1)を行い,Z方向引張-引張疲労試験と比較,応力比および繰り返し圧縮荷重が層間高靭性化CFRP積層板に与える影響を調査した.また同一スプール形状試験片を使用した面内トランスバース方向(T方向)引張-引張疲労試験(R=0.1)を行い,Z方向との比較を行った.その結果,疲労試験にて得られたS-N線図にて整理を行い,疲労強度に及ぼす圧縮応力の影響,およびZ方向試験片はT方向試験片に比べ疲労寿命が短いことが示唆された.有限要素解析によって試験片内の応力分布を評価した.圧縮熱残留応力の影響により,繊維層に作用する応力が異なることを明らかにした.

  • 面外方向繰り返し荷重を受けるCRRP積層板の破壊メカニズム

    2014  

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    本研究では,層間高靱性化CFRP積層板の面外方向における疲労強度特性の評価を行うことを目的とした.層間に熱可塑性粒子を含んだ層間強化層を持つプリプレグ,T800S/3900-2Bを一方向に88 ply積層し,成形された厚肉CFRP積層板よりスプール形状の試験片を作製した.試験片の両端を精度よくタブと接着し,面外方向の負荷を可能とした.また,層間強化層を考慮した有限要素解析を行い,スプール形状試験片の応力状態を評価した.さらに,得られた試験結果に解析式を適用し,面外方向の疲労強度特性を定量的に評価した.以下に得られた成果,結論を述べる.(1)スプール形状試験片および接着冶具を用いることで,接着時に試験片とタブの接着が精度よく行えるため,面外方向特性の厳密な評価が可能となることが示された.さらに,接着後のタブ付き試験片の接着部に補強を行うことで,過去に報告の少ない面外方向の疲労試験を行うことに成功した.(2)静的試験結果について,面外方向垂直応力の応力集中を考慮し評価した結果,面外方向の静的強度特性は,面内トランスバース方向の静的強度特性と比べて低下することが示唆された.また,層間高靱性化CFRP積層板に面外方向の荷重が作用した際には,繊維層での破壊が支配的であることが示唆された.(3)面外一方向材の疲労試験結果について,面外方向応力の応力集中を考慮して評価した結果,面内トランスバース方向の疲労強度特性と比較して,面外方向の疲労強度特性は低下する傾向が見られた.また,静的試験以上に繊維層での破壊が支配的であることが示唆された.(4)疲労試験結果にH-k則を適用し,解析的に疲労強度特性を比較した.S-N線図へのフィッティングにより得られた各材料パラメータは面外方向がH=1.76,k=9.47,面内トランスバース方向がH=0.991,k=16.6となった.さらに,面内トランスバース方向の材料パラメータを用いて面外方向の疲労寿命を予測したところ,長寿命側に予測した.この結果より,面外方向の疲労強度特性が低くなることが解析的に示された.(5)静的試験後の破面と比較し,疲労試験後の破面では繊維への樹脂の付着量が少ないことから,繰り返し荷重による繊維/樹脂界面はく離の発生が示唆された.したがって,面外方向,面内トランスバース方向ともに,疲労荷重下においては,繊維/樹脂界面はく離を起点として発生したクラックが,臨界き裂長さに達した時点で破断することが推察された.さらに,面内トランスバース方向ではクラックの進展方向に破壊靱性値の高い熱可塑性粒子を含む層間強化層をクラックが進展する必要があることから,面外方向は面内トランスバース方向と比較して,疲労強度特性が低下するものと結論付けた.

  • メッキコーティングによる超長寿命複合材料の創出

    2012  

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    繊維強化プラスチック(FRP)の更なる長寿命化を図るために,「FRPの表面に金属薄膜を被覆して強化する」という新しい発想に基づく研究を行った.金属薄膜の目的は,FRP内部への水分拡散を防ぐものであり,水分バリアーとして有効に機能するか検討を行った. 本年度は2011年度に行っためっき技術および吸水試験の結果の妥当性について調査した.・めっき技術について めっき被膜は2011年度と同様に,耐食性,耐摩耗性に優れるNi-Pとした.基板は平織GFRP積層板(母材樹脂:ビニルエステル樹脂,強化繊維:Eガラスクロス)である.2011年度では,通常のめっき工程ではめっき不良が生じたため,めっき工程に物理的エッチング(#120~#2000)を導入することでめっき不良を改善した.さらに,得られるめっき被膜の膜厚および均一性を考慮し,#1200に決定した.2012年度は,3D形状測定顕微鏡を用いた観察から,めっき膜厚の標準偏差と表面粗さに相間関係があることがわかり,2011年度の結果の妥当性を確認した.・吸水試験について 2011年度において,試験片全面を水中に浸漬させる通常の吸水試験方法ではめっき被膜の防水性を評価することは困難であったため,片面のみを浸漬させるように片面吸水試験機を創作し,評価を可能とした.その結果,めっき膜厚の増加に伴い,吸水飽和時の重量増加率および拡散係数の低下が確認された.2012年度では,吸水試験後の試験片表面の観察を行い,前年度の結果を視覚的に考察した.試験片表面の観察から,①めっき時間の増加(めっき膜厚の増加)に伴うめっき粒子の粒径が拡大すること,②めっき被膜は層状の組織を成しており,吸水試験後においてはめっき被膜にき裂が生じ,徐々に剥がれていくことが判明した.めっき膜厚が薄い場合にはき裂がGFRPにまで達してしまい,早い段階で吸水が起きてしまうと推察された.き裂が生じる原因として基板のGFRPとめっき被膜の熱膨張率の差が挙げられる.以上の結果より,2011年度の結果の妥当性が示された. 以上より,金属皮膜が水分バリアーとして機能し得ることが確認され,より最適なめっき被膜の選定,密着性の向上によって更なる防水効果が期待できる.

  • ハイブリッドナノ複合材料の材料創製と強度発現機構

    2011  

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    本研究課題では,ハイブリッドナノ複合材料の材料創製に先駆け,ガラス繊維へのカーボンナノチューブ(CNT)の析出による表面改質の確立・評価を目的とした.CNT析出による表面改質は化学気相成長法(CVD法)を用いて行った.まず,析出温度,析出時間,触媒量,炭素源量をパラメータとした様々な条件下でTガラス繊維へのCNTの析出を行った.その中で析出量に差が出た2条件についてTガラス繊維の機械的性質の変化および樹脂中に埋蔵した場合の界面接着性の測定および定量的な評価を行った.また,比較のため未処理のガラス繊維および熱処理のみを施した繊維も同様に試験を行った.Tガラス繊維の機械的性質についてはCNT析出により引張強度および破断ひずみに約60%の低下がみられた.この原因はCVD法での繊維の加熱および装置からの取り出し時の環境ガスによるものと考えられる.そこで環境ガスを空気から窒素に変更して同様の条件で作製したTガラス繊維の機械的性質を調査した結果,機械的性質の低下が抑制された.次に,CNTを析出させたTガラス繊維をエポキシ樹脂中に1本埋蔵したモデル試験片を作製し,界面接着性の測定および定量的評価を行った.熱処理のみを施した繊維については界面接着性の低下が確認されたものの,CNTを析出させた2条件については界面接着性の向上が確認された.また,得られた結果から界面せん断強度を算出すると,CNTを析出させた場合,未処理のものと比較して約45%以上の上昇が確認された.これは,CNTの析出したTガラス繊維を樹脂中に埋め込むことでCNTに樹脂が含浸してCNT層を形成するためであると考えられる.この層の弾性率をナノインデンテーション試験により測定した結果,CNT層の弾性率はエポキシ樹脂よりも高いことが明らかとなった.これより,CNT析出繊維の界面接着性の上昇の要因はCNT層形成による繊維周囲の弾性率の変化であることが示唆された.以上の結果をもとに弾性軸対称モデルを用いて数値計算を行った結果,CNT層の弾性率の増加を考慮した場合,界面せん断強度が上昇することが解析的にも確認された.ただし,本研究で用いたモデルは実際の実験的事実を考慮していない簡素的なモデルであるため,今後はそれらの要素を導入したモデルの構築が課題となると考えられる.

  • FRPの表面コーティングによる長寿命材料の開発

    2011  

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    繊維強化プラスチック(FRP)の更なる長寿命化を図るために,「FRPの表面に金属薄膜を被覆して強化する」という新しい発想に基づく研究の提案を行った.金属薄膜の目的は,FRPの弱点である水分拡散を防ぐものであり,水分バリアーとして最も有効に機能するか検討を行った.具体的には,GFRPへのNi-Pめっき技術の確立,吸水試験による水分バリアー機能の評価方法の検討,Ni-Pめっきの膜厚変化による吸水特性のモデル化の三点について研究を行った.GFRPへのNi-Pめっき技術の確立:母材をビニルエステル樹脂,強化繊維をEガラスクロスとした平織GFRP積層板(以降平織GFRPと表記)へNi-Pめっきを施す技術の確立を行った.通常の工程でめっきを行った際,亀裂やフクレなどのめっき不良が生じたため,基板である平織GFRPにあらかじめ物理エッチング(サンディング)を施すことでめっき不良が改善された.物理エッチングは#120~#2000まで行い,#1200が最適であると決定した.ビニルエステル樹脂および平織GFRPともにめっき浴浸漬時間と膜厚の関係を調査し,膜厚制御を可能とした.吸水試験による水分バリアー昨日の評価方法の検討:通常の吸水試験を行った場合,同程度のNi-P膜厚に対しての重量増加率の変化の挙動がビニルエステル樹脂と平織GFRPで大きく異なった.この原因として,平織GFRPの端部(側面)をSEMで観察を行ってみたところ,ガラス繊維がむき出しとなっていたため,端部からの吸水が顕著に表れたからであると示唆された.そこで,片面のみから吸水するような試験機(片面吸水試験機)の創作を行った.片面吸水試験を行った結果,ビニルエステル樹脂と平織GFRPの重量増加率は似た挙動となった.Ni-Pめっきの膜厚変化による吸水特性のモデル化:吸水試験の結果から,Ni-Pめっきの膜厚が厚くなるほど,吸水飽和したときの重量増加率が低下することが判明した.このような傾向は吸湿試験において試験片に対する相対湿度が変化すると,飽和したときの重量増加率が変化するという実験結果と酷似している.そこで,Ni-Pコーティングを施すことで,基板(ビニルエステル樹脂,平織GFRP)周囲の水分環境が変化すると仮定した.湿度環境下にさらされた際の吸水飽和したときの重量増加率の理論式の変形を行い,Ni-P膜厚に対する吸水飽和したときの重量増加率の予測が可能となった.今後の展望として,水分バリアー機能がさらに向上されると考えられる多層めっきを施す必要があると考えられる.

  • 炭素繊維強化複合材料の疲労に対する長期信頼性評価

    2006  

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     本研究では,炭素繊維強化プラスチック(CFRP)積層板の超長疲労特性について調査を行った.一般に,CFRP積層板の疲労損傷挙動は次のような3過程を経て破断に至る.(I)層内樹脂割れと呼ばれる微小クラックが積層板内部に多数発生する.(II)層内樹脂割れを起点として層間剥離が発生し,繰返し数が増すとともに進展する.(III)強化繊維が破断することによって試験片の破断に至る.層間剥離の発生は,積層板の圧縮強度を大幅に低下させる原因となる.そこで本研究では,超長寿命域におけるCFRP積層板の層内樹脂割れを起点とした層間剥離の発生挙動について調査を行うことを目的とした. 初期損傷の影響を考慮した層間剥離の発生,進展挙動を調査するために,疲労試験前に予め層内樹脂割れを任意に生じさせた試験片と未損傷状態の試験片の2種類を用意した.その2種類の試験片を用いて繰返し数108回を超える疲労試験を行った.その結果,負荷応力レベル&#61555;max/&#61555;b=0.4~0.6の範囲内では,初期損傷の有無に関わらず,層間剥離は層内樹脂割れが多数集中する箇所から発生が観察され,層内樹脂割れが疎な箇所からの層間剥離の発生は観察されなかった.この負荷応力レベルの範囲内では初期損傷として与えた層内樹脂割れが少数である場合は,層間剥離の発生には大きな影響を及ぼさないことが分かった.負荷応力レベル&#61555;max/&#61555;b=0.3で行った疲労試験では,層内樹脂割れに先行して層間剥離が発生,進展することが観察された.この原因として,試験片端部のエッジ効果と呼ばれる応力特異場の影響が大きく関与していることが考えられる.この現象は従来の疲労損傷挙動とは異なる結果である.CFRP積層板の疲労に対する設計は層内樹脂割れが発生しないような応力レベルで設計されているが,超長寿命域側では層内樹脂割れが発生しなくとも層間剥離が発生する可能性があり,従来の設計基準では危険となる可能性が示唆された.一方,負荷応力レベル&#61555;max/&#61555;b=0.2で行った疲労試験では繰返し数2×108回を超えても層内樹脂割れ及び層間剥離の発生及び進展は観察されなかった. 以上まとめると,超長寿命域のCFRP積層板の疲労特性を調査した結果,初期損傷として存在する層内樹脂割れが少数であれば,層間剥離の発生には影響を及ぼさないことが分かった.しかしながら,低応力レベルの超長疲労域においては,層内樹脂割に先行し,層間剥離が生じることが明らかとなり,従来のなされている層内樹脂割れの発生を基準とした設計ではなく,層間剥離の発生を基準とした設計を行わねばならないことが示唆された.

  • 酸応力環境下におけるGFRP積層板の長期耐久性評価

    2004  

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     応力腐食環境におけるガラス繊維強化プラスチック(GFRP)の長期信頼性評価を目的として,水環境下において材料の吸水により生じるGFRP構成機材の機械的劣化とその劣化によるき裂進展抵抗の変化の関係について調査を行った.き裂進展抵抗としては,繊維架橋による高じん化機構における界面劣化の影響を実験的に調査するため,エポキシ樹脂にECRガラス繊維束を2つ埋蔵し試験片とし,吸水による重量変化率の増加による見かけの破壊じん性値の変化を求めた. 見かけの破壊じん性値は繊維がき裂面間で架橋することによって増加する.実験において得られる高じん化への寄与分の決定には,試験片の吸水による重量増加率が同一となる母材樹脂単体の破壊じん性値と見かけの破壊じん性値の差をとり,母材吸水率と高じん化分の関係を求めた.この高じん化への寄与分は母材の吸水初期状態では増加するが,極値をとり減少を示した.この高じん化分と吸水状態の関係を,繊維束埋蔵位置における水分量の時間変化を用いて評価した.水分量の変化はフィックの第二拡散則に基づいて有限要素解析により求めた.得られた水分量の時間変化と高じん化分の時間変化を比較すると,繊維束部の水分量の増加が開始する時間において,高じん化への寄与は極値をとることが明らかとなった.その時間以後は水分量の増加に従って高じん化分は減少を続けるが,繊維束部における水分量が飽和に至ることで高じん化分の減少も終了し,一定値を示すと考えられる. 構造材料においては使用される環境への露出時間や環境の状態により,内部における水分量は分布を示すと考えられる.本実験で得られた水分量と高じん化機構の関係は,このような構造におけるき裂進展抵抗を考慮する上で重要である.水分量が飽和することで一定値をとることは,水分の影響を強く受ける環境における長期使用において材料の信頼性を確立することが期待される.

  • 酸応力環境下におけるGFRP織物積層板の下限界特性

    2001  

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    横方向繊維の一方向材(90°材)を供試材として応力腐食割れ試験を行った.その結果,クロス材と同様にda/dt-KI線図は低応力拡大係数域と定常き裂進展域に分類され,下限界値の存在も確認された.また,低応力拡大係数域においてはKI値の変動幅が大きく,き裂成長に伴いKI値が上昇していることがわかった.一般に,一方向材で繊維方向に沿い開口型き裂が進展する場合,繊維の架橋現象により閉口応力が作用するとされている.KI値上昇はこの架橋繊維の本数増加が原因であると考えられる.さらに水環境,大気中で試験を行った試験片破面を観察したところ,水環境では大気中に比べ繊維の露出率が高く架橋繊維が形成されやすい状況であり,特に水環境の低応力拡大係数域においては界面先行型の破壊形態であることがわかった.また,架橋繊維を円柱両端固定はりと仮定し算出した閉口応力を用いFEM解析により,各環境下におけるき裂成長に伴うき裂進展抵抗の上昇を再現した. また,微視的観点から劣化メカニズムを評価するため,純水中に浸漬させた単繊維モデル試験片を用いたフラグメンテーション試験を行った.界面はく離,クリープの影響に着目し,これらが繊維強度・界面強度に及ぼす影響について調査し,これらの強度評価モデルについてより厳密な考察を行った.浸漬に伴う試験片の物性変化の影響を正確に評価するため,吸水膨張ひずみ,クリープひずみによるプリテンション応力を算出し,繊維強度に対して評価の補正を行った結果,強度低下の負荷応力依存性は無いことが明らかとなった.また,フラグメント過程で発生する界面はく離を考慮したモデルにより界面せん断応力の分布を検討した結果,界面はく離は界面強度に大きく影響を及ぼすことが明らかとなり,最大界面せん断応力ではなく系全体のエネルギバランスモデルを用いた界面強度の評価方法の有効性を示した.

  • 酸応力環境下におけるGFRP織物積層板のき裂進展挙動

    1999  

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     塩酸応力環境下におけるGFRP織物積層板のき裂進展挙動及び下限界特性の解明を目的に研究を行った。本年度は新たに母材樹脂中への水溶液溶質の拡散現象を考慮した。拡散モデルを構築し、構成基材に依存しない統一的な破壊機構の提案を試みた。 応力腐食割れ試験において、耐食性に優れたガラス繊維及び樹脂を構成基材としたCガラス/ビニルエステル積層板(C/VE)と従来のEガラス/エポキシ積層板(E/Epoxy)とを用い、き裂進展挙動及び下限界特性の環境依存性を明らかにした。E/Epoxy試験片では、塩酸温度上昇よりも塩酸濃度上昇の影響を大きく受けKⅠSCCが低下する。また、濃度上昇が直接関係する水素イオンの影響を顕著に受けているため、破壊機構は水素イオン拡散及びそれに伴う繊維腐食が支配的であると考えられた。一方、C/VE試験片において、塩酸環境下のき裂進展挙動は空気中よりは大きく促進されているが純水環境下と比較してもあまり大きな変化が見られない。すなわち、耐酸性の高いCガラスを用いた試験片においては、水素イオンの拡散による繊維の劣化よりも、水溶液(主に水)の拡散吸着によるき裂先端近傍の樹脂の吸水膨張等による繊維荷重分担率増加に伴う繊維破断による破壊が支配的である事が示唆された。 拡散現象について、母材中の水素イオン拡散がき裂進展に及ぼす影響を明らかにするため、ひずみエネルギ依存の拡散係数及び化学ポテンシャル勾配による拡散方程式を用いた2次元拡散シミュレーションを行った。その結果、外力の負荷により無負荷の時には見られない、き裂先方での高濃度領域が現れた。応力拡大係数の増大に伴いこの領域が顕著に拡大されることを確認し、この領域の拡大がき裂進展挙動に大きく影響を及ぼしていることがわかった。

  • GFRP積層板の応力腐食割れに関する研究

    1995  

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    GFRP(ガラス繊維強化プラスチック)はその汎用性の高さから広範な分野で利用が広まっているが,強化材であるガラス繊維が腐食環境に接触し,応力腐食割れ(SCC)を起こすことが知られており,その破壊形態の解明は重要である。また,工学設計上重要と思われる,応力腐食割れにおけるき裂進展下限界応力拡大係数(KISCC)についての報告例は少なく,また環境条件がKISCCに及ぼす影響など,解決していない課題は多い。 そこで本研究では広範な酸応力腐食環境中での本材料の破壊機構・き裂進展挙動を調査するため,切欠きを有するGFRP織物積層板の応力腐食割れ荷重漸減試験を行い,KISCCの定量化と破壊機構の解明を行う。また破壊メカニズムを基礎とした数値計算モデルを提案し,き裂進展速度の推定を行う。 応力腐食割れ試験の結果,巨視的き裂進展挙動は遷移点を有し,パリス則に沿う定常き裂進展域と,KISCCへの漸近領域である低KI域へと大別できた。この両領域には微視的破壊機構に差異が見られ,特にKISCC近傍では荷重線方向の縦繊維周囲のマトリックスに特徴的な破面である,ポリゴナルラインが観察され,酸の拡散抵抗となっていることが分かった。これに対し定常き裂進展域においてはマトリックスは脆性的な破面を呈しており,ガラス単繊維のSCCにき裂進展挙動が依存していると考えられる。 これらの破面観察の結果から,定常き裂進展域に対してガラス単繊維の腐食モデルを基盤とした,き裂進展速度の予測モデルを提案し,その妥当性を検証するため,理論的観点から数値計算的手法を用いて巨視的き裂進展速度の予測を行った。ガラス繊維表面の初期欠陥が酸による腐食を受け,特徴的な破面であるミラーゾーンが成長し破断に至るモデルである。応力腐食割れにおける反応速度はArrheniusの式で示され,これを積分することによって繊維の破断時間を算出できる。また,これら単繊維の集合体である繊維束は楕円形状にて近似し,繊維配列を考慮することによって縦繊維束の定量的モデルがたてられる。繊維束側面に初期腐食領域を与え,腐食繊維からSCCが開始する。繊維束全体の破断時間を算出することにより,巨視的き裂進展速度が算出できる。 本モデルにより算出されたき裂進展速度は定常き裂進展域において実験値と良い一致を示し,繊維束内のき裂進展シミュレーションにより得られる縦繊維束内のき裂進展過程に関しても実験でのフラクトグラフィと一致し,本モデルの妥当性が示され,本モデルが,GFRP織物積層板のき裂進展速度予測に関して有効であると思われる。 以上より,実験的側面より詳細な破壊機構を解明し,これを基にして,き裂進展速度予測及びき裂進展シミュレーションが可能でかつ妥当性を有する数値計算モデルが提案され,この分野での新しい材料設計へのアプローチが示された。

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    経済産業省  専門家会議(風車)

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    The Japan Society of Mechanical Engineers  President-Elect