2022/06/27 更新

写真a

カワダ ヒロユキ
川田 宏之
所属
理工学術院 基幹理工学部
職名
教授

兼担

  • 理工学術院   大学院基幹理工学研究科

  • 附属機関・学校   グローバルエデュケーションセンター

学内研究所等

  • 2020年
    -
    2022年

    理工学術院総合研究所   兼任研究員

学歴

  •  
    -
    1980年03月

    早稲田大学   理工学部   機械工学科  

  •  
    -
    1980年

    早稲田大学   理工学研究科  

学位

  • 早稲田大学   博士(工学)

所属学協会

  •  
     
     

    強化プラスチック協会

  •  
     
     

    日本複合材料学会

  •  
     
     

    日本材料学会

  •  
     
     

    日本機械学会

 

研究分野

  • 材料力学、機械材料

  • 複合材料、界面

研究キーワード

  • 複合材料、材料強度学

論文

  • 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年12月

     概要を見る

    © 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年10月

     概要を見る

    © 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

  • 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年

     概要を見る

    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年

     概要を見る

    © 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年

     概要を見る

    © 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年

     概要を見る

    © 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年

     概要を見る

    © 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年12月

     概要を見る

    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年09月

     概要を見る

    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年02月

     概要を見る

    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

  • 熱酸化法により生成したSi基板上のCuOナノワイヤの成長及び界面剥離メカニズム

    柳澤 一星, 松永 光広, 土肥 優希, 木村 文哉, 細井 厚志, 巨 陽, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2019 ( 0 ) 510 - 510  2019年

     概要を見る

    <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>

    DOI CiNii

  • 超音波疲労試験によるクロスプライCFRP積層板の超高サイクル域におけるトランスバースクラック成長挙動の評価

    渥美 建, 宮腰 剛, 小杉 健祐, 細井 厚志, 島村 佳伸, 津田 皓正, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2019 ( 0 ) 121 - 121  2019年

     概要を見る

    <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>

    DOI CiNii

  • 化学的結合を介したグラフェン/CF繊維の作製および機械的特性評価

    村田 惇, 中曽 健輔, 細井 厚志, 川田 宏之

    年次大会   2019 ( 0 ) J04418P  2019年

     概要を見る

    <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>

    DOI CiNii

  • 直接接合されたナノ構造を有するアルミニウム合金とCF/PA6積層板の強度発及び損傷メカニズム

    JESPERSEN Kristine Munk, 阿部 暉, 齊藤 慧, 大田 宙起, 和田 啓汰, 細井 厚志, 川田 宏之

    年次大会   2019 ( 0 ) J04411  2019年

     概要を見る

    <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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  • 疲労負荷を受けた銅合金のすべり帯の変形挙動に及ぼす高密度パルス電流の影響

    前山 太郎, 高橋 秀幸, 細井 厚志, 川田 宏之

    日本機械学会関東支部総会講演会講演論文集   2019 ( 0 ) 19C08  2019年

     概要を見る

    <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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  • 熱混酸処理を用いた黒鉛化無撚カーボンナノチューブ糸の官能基化および高強度化

    奥茂 洸一, 髙橋 祐衣, 金 太成, 二川 秀史, 細井 厚志, 川田 宏之

    日本機械学会論文集   85 ( 874 ) 19 - 00029-19-00029  2019年

     概要を見る

    <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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  • 無撚カーボンナノチューブ/ポリマー複合糸の機械的特性に及ぼすCNT間相互作用力の影響

    金 太成, 林 晏理, 二川 秀史, 細井 厚志, 川田 宏之

    日本機械学会論文集   85 ( 872 ) 18 - 00408-18-00408  2019年

     概要を見る

    <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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  • 海水浸漬における平織CFRP積層板の静的引張強度及び疲労強度劣化特性の評価

    甲嶋 秀平, 梶井 憲弘, 細井 厚志, 川田 宏之

    日本機械学会論文集   85 ( 871 ) 18 - 00435-18-00435  2019年

     概要を見る

    <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年

     概要を見る

    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年

     概要を見る

    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.

    DOI

  • 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年12月

     概要を見る

    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.

    DOI

  • 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年07月

     概要を見る

    © 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.

    DOI

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

    Atsushi Hosoi, Hiroyuki Kawada

    MATERIALS   11 ( 7 )  2018年07月

     概要を見る

    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.

    DOI

  • 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年06月

     概要を見る

    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.

    DOI

  • 無撚カーボンナノチューブ糸の機械的特性に及ぼす黒鉛化の影響と強度発現機構

    金太成, 林晏理, 二川秀史, 白須圭一, 山本剛, 橋田俊之, 細井厚志, 川田宏之

    日本機械学会論文集   84 ( 860 ) 17-00585 - 00585-17-00585  2018年04月  [査読有り]

     概要を見る

    <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>

    DOI CiNii

  • Ti-6Al-4V合金の疲労き裂治癒技術の開発と治癒効果に及ぼす疲労き裂閉口現象の影響

    小林 陸人, 堀内 誠大, 細井 厚志, 貴志 公博, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2018 ( 0 ) 820 - 820  2018年

    DOI CiNii

  • 現場重合型フェノキシ樹脂を母材とする連続繊維強化複合材料の引張強度特性に及ぼす内部欠陥及び母材樹脂の重合度の影響

    宮田 雅文, 鈴木 芽生, 藤本 允人, 細井 厚志, 江藤 和也, 杉山 哲也, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2018 ( 0 ) 227 - 227  2018年

     概要を見る

    <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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  • 高強度無撚CNT糸の創製に向けた薄層CNT合成条件の検討

    奥茂 洸一, 金 太成, 高橋 和彦, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2018 ( 0 ) 217 - 217  2018年

    DOI CiNii

  • アルミニウム合金とCFRTP積層板の直接接着継手における破壊靱性の評価

    阿部 暉, 大田 宙起, 齊藤 慧, 和田 啓汰, Kristine Munk Jespersen, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2018 ( 0 ) 421 - 421  2018年

    DOI CiNii

  • 金属材料の疲労き裂治癒技術の開発と評価

    細井 厚志, 濱田 叡一, 小林 陸人, 川田 宏之

    年次大会   2018 ( 0 ) F041003  2018年

     概要を見る

    <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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  • 一方向および擬似等方層間高靭性化厚肉CFRP積層板の面外方向疲労特性に及ぼす応力比の影響

    新井 智貴, 福島 槙一郎, 世木 選, 細井 厚志, 川田 宏之

    日本機械学会論文集   84 ( 863 ) 18 - 00039-18-00039  2018年

     概要を見る

    <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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  • 強化繊維径および界面特性を考慮したGF/PA射出成形材の引張強度予測

    白木 伶治, 岡本 彪, 小澤 憲人, 金 太成, 平山 紀夫, 谷口 憲彦, 西脇 剛史, 細井 厚志, 川田 宏之

    日本機械学会論文集   84 ( 860 ) 17 - 00582-17-00582  2018年

     概要を見る

    <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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  • 電気めっき処理によるカーボンナノチューブ/銅複合配線の創製および許容電流評価

    金 太成, 酒井 貴広, 星 雄大, 二川 秀史, 細井 厚志, 川田 宏之

    日本機械学会論文集   84 ( 857 ) 17 - 00313-17-00313  2018年

     概要を見る

    <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>

    DOI CiNii

  • LFT射出成形材の衝撃エネルギー吸収性能に及ぼす繊維配向性の影響

    白木 伶治, 安達 正悟, 彌武 朋也, 石塚 勇二, 細井 厚志, 川田 宏之

    M&M材料力学カンファレンス   2017 ( 0 ) OS1012  2017年

     概要を見る

    <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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  • 海水環境下におけるFRPの長期寿命予測

    廣津 有記, 細井 厚志, 川田 宏之

    M&M材料力学カンファレンス   2017 ( 0 ) OS1009  2017年

     概要を見る

    <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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  • NI基耐熱超合金INCONEL 718の疲労き裂治癒技術の確立

    小林 陸人, 前山 太郎, 藤田 耕平, 細井 厚志, 貴志 公博, 川田 宏之

    M&M材料力学カンファレンス   2017 ( 0 ) GS1004  2017年

     概要を見る

    <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>

    DOI CiNii

  • 熱処理によるオーステナイト系ステンレス鋼の疲労き裂治癒及び治癒メカニズムの検討

    前山 太郎, 小林 陸人, 藤田 耕平, 細井 厚志, 川田 宏之

    年次大会   2017 ( 0 ) J0450104  2017年

     概要を見る

    <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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  • 長期間海水に浸漬させた平織CFRP積層板の強度劣化特性評価

    甲嶋 秀平, 細井 厚志, 川田 宏之

    年次大会   2017 ( 0 ) J0440201  2017年

     概要を見る

    <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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  • 銀担持グラフェンを用いて作製した透明導電膜の電気特性評価

    大場 圭介, 坂口 大輝, 荒尾 与史彦, 細井 厚志, 川田 宏之

    年次大会   2017 ( 0 ) G0400103  2017年

     概要を見る

    <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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  • 高温環境下におけるクロスプライCFRTP積層板のトランスバースクラック発生及び累積挙動の評価

    細井 厚志, 寺内 幹, 角田 大, 木村 達哉, 古挽 彰, 川田 宏之

    日本機械学会論文集   83 ( 855 ) 17 - 00312-17-00312  2017年

     概要を見る

    <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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  • 層間強化層を有する厚肉CFRP積層板の面外方向及び面内トランスバース方向における疲労寿命の評価

    世木 選, 新井 智貴, 福島 槙一郎, 細井 厚志, 藤田 雄三, 武田 一朗, 川田 宏之

    日本機械学会論文集   83 ( 851 ) 16 - 00571-16-00571  2017年

     概要を見る

    <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年08月

     概要を見る

    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年

     概要を見る

    © 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年

     概要を見る

    © 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.

  • 黒鉛化処理による高強度無撚カーボンナノチューブ糸の機械特性評価

    髙橋 祐衣, 金 太成, 二川 秀史, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2016 ( 0 ) 135 - 135  2016年

    DOI CiNii

  • 大電流容量・高導電率を有する金属複合CNT糸の作製

    酒井 貴広, 金 太成, 二川 秀史, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2016 ( 0 ) 124 - 124  2016年

    DOI CiNii

  • 高温環境下における熱可塑性CFRP積層板のトランスバースクラック発生・進展挙動調査

    寺内 幹, 細井 厚志, 古挽 彰, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2016 ( 0 ) 127 - 127  2016年

     概要を見る

    <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>

    DOI CiNii

  • FRTP射出成形材の逐次破壊におけるエネルギー吸収メカニズムの検討

    角田 大地, 石塚 勇二, 田中 宏幸, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2016 ( 0 ) 126 - 126  2016年

     概要を見る

    <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>

    DOI CiNii

  • 液相剥離法を用いた薄層グラフェンによる透明導電膜の作製および特性評価

    坂口 大輝, 荒尾 与史彦, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2016 ( 0 ) 415 - 415  2016年

     概要を見る

    <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>

    DOI CiNii

  • 熱処理によるオーステナイト系ステンレス鋼の疲労き裂治癒における冷却条件の影響

    藤田 耕平, 古谷 勇人, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2016 ( 0 ) 608 - 608  2016年

    DOI CiNii

  • 高導電性・電流容量を有するカーボンナノチューブ金属複合繊維の創製

    梶原 晃太郎, 金 太成, 酒井 貴広, 二川 秀史, 細井 厚志, 川田 宏之

    年次大会   2016 ( 0 ) G0400104  2016年

     概要を見る

    <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>

    DOI CiNii

  • 熱処理による金属材料疲労き裂の治癒及び疲労き裂進展特性の評価

    古谷 勇人, 岡村 崇史, 武田 翔馬, 細井 厚志, 木村 世弘, 森田 祐司, 川田 宏之

    年次大会   2016 ( 0 ) J0460101  2016年

     概要を見る

    <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>

    DOI CiNii

  • 射出成形ガラス長繊維強化ポリアミドの衝撃引張特性に及ぼす繊維径の影響

    小澤 憲人, 金 太成, 角田 大地, 荒尾 与史彦, 谷口 憲彦, 西脇 剛史, 細井 厚志, 川田 宏之

    日本機械学会論文集   0 ( 0 )  2016年

     概要を見る

    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.

    CiNii

  • CFRP円筒材のねじり疲労特性に及ぼす積層構成の影響

    渡邉 太一, 里村 圭介, 木元 尚紀, 中村 崇人, 金 太成, 細井 厚志, 川田 宏之

    日本機械学会論文集   0 ( 0 )  2016年

     概要を見る

    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 CNTs析出炭素繊維を強化材とした一方向CFRPの力学特性評価

    寺内 幹, 大澤 貞幸, 金 太成, 川田 宏之

    M&M材料力学カンファレンス   2015   "OS1408 - 248-1"-"OS1408-248-3"  2015年11月

     概要を見る

    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.

    CiNii

  • 129 液中プラズマ処理による燃料電池電極用白金ナノ粒子担持CNTの創成

    中村 紘大, 金 太成, 細井 厚志, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2015 ( 23 ) "129 - 1"-"129-5"  2015年11月

     概要を見る

    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%).

    CiNii

  • 120 層間高靭性化厚肉CFRP積層板の面外方向疲労特性に及ぼす圧縮荷重の影響

    柘植 紫苑, 世木 選, 細井 厚志, 藤田 雄三, 武田 一朗, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2015 ( 23 ) "120 - 1"-"120-3"  2015年11月

     概要を見る

    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年05月  [査読有り]

     概要を見る

    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年05月

    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年

     概要を見る

    © 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年

     概要を見る

    © 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年

     概要を見る

    © 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年  [査読有り]

     概要を見る

    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年01月  [査読有り]

     概要を見る

    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.

    DOI

  • 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年11月  [査読有り]

     概要を見る

    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.

    DOI

  • 面外方向繰り返し荷重を受ける層間高靱性化CFRP積層板の疲労強度特性

    重盛 洸, 細井 厚志, 藤田 雄三, 川田 宏之

    日本機械学会論文集   80 ( 812 ) SMM0087 - SMM0087  2014年

     概要を見る

    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.

    CiNii

  • 層間高靱性化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

    川田 宏之, 曽我 理昂, 重盛 洸, 細井 厚志, 藤田 雄三

    日本機械学会論文集   80 ( 812 ) SMM0079 - SMM0079  2014年

     概要を見る

    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.

    CiNii

  • 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年05月

     概要を見る

    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

  • 熱残留応力緩和およびフィジカルエージングによるCFRP擬似等方性積層板の経時寸法変化

    丹羽 智之, 荒尾 与史彦, 川田 宏之

    日本機械学会論文集 A編   79 ( 803 ) 950 - 960  2013年

     概要を見る

    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.

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  • 疲労荷重下におけるCFRPクロスプライ積層板のトランスバースクラック発生に関する層厚さの影響

    栗原 謙, 細井 厚志, 佐藤 成道, 川田 宏之

    日本機械学会論文集 A編   79 ( 799 ) 249 - 265  2013年

     概要を見る

    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.

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  • 816 酸および水環境下における高耐食性GFRP積層板の遅れ破壊寿命評価

    矢島 昌英, 小谷 正浩, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2012 ( 20 ) "816 - 1"-"816-4"  2012年11月

     概要を見る

    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 CF/エポキシ系,CF/シアネート系擬似等方性積層板の経時寸法変化

    丹羽 智之, 荒尾 与史彦, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2012 ( 20 ) "812 - 1"-"812-5"  2012年11月

    CiNii

  • 811 疲労負荷を受けるクロスプライCFRP積層板のトランスバースクラック発生における繊維含有率の影響

    細井 厚志, 重盛 洸, 佐藤 成道, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2012 ( 20 ) "811 - 1"-"811-4"  2012年11月

    CiNii

  • ガラス繊維の衝撃引張り特性に関する実験的検討

    谷口 憲彦, 荒尾 与史彦, 西脇 剛史, 平山 紀夫, 中村 幸一, 川田 宏之

    日本複合材料学会誌 = Journal of the Japan Society for Composite Materials   38 ( 4 ) 137 - 143  2012年07月

    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年06月  [査読有り]

     概要を見る

    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年05月  [査読有り]

     概要を見る

    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年

     概要を見る

    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).

  • 構成材のひずみ速度依存性の影響を考慮した一方向FRPの圧縮強度予測

    井上 直紀, 谷口 憲彦, 西脇 剛史, 平山 紀夫, 中村 幸一, 荒尾 与史彦, 川田 宏之

    日本機械学会論文集 A編   78 ( 793 ) 1284 - 1299  2012年

     概要を見る

    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.

    DOI CiNii

  • 静的引張試験による疲労荷重下における[0m/90n]sクロスプライCFRP積層板に生じるトランスバースクラックの発生予測

    細井 厚志, 高村 啓吾, 佐藤 成道, 川田 宏之

    日本機械学会論文集 A編   78 ( 791 ) 1000 - 1012  2012年

     概要を見る

    A method to predict quantitatively the first of transverse cracks accumulated in the various types of [0m/90n]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.

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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年  [査読有り]

     概要を見る

    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.

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  • J043044 水環境下における平織GFRP積層板±45°方向の遅れ破壊特性([J04304]高分子基複合材料の加工と評価(4))

    服部 聡, 小谷 正浩, 川田 宏之

    年次大会 : Mechanical Engineering Congress, Japan   2011   "J043044 - 1"-"J043044-5"  2011年09月

     概要を見る

    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 繰返し負荷を受けるクロスプライCFRP積層板に生じるトランスパースクラック発生における静的引張試験による疲労寿命予測([J04302]高分子基複合材料の加工と評価(2))

    細井 厚志, 曽我 理昂, 佐藤 成道, 川田 宏之

    年次大会 : Mechanical Engineering Congress, Japan   2011   "J043024 - 1"-"J043024-4"  2011年09月

     概要を見る

    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年06月  [査読有り]

     概要を見る

    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.

    DOI

  • 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年03月  [査読有り]

     概要を見る

    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.

    DOI

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

    KOTANI Masahiro, YAMAMOTO Yohei, KAWADA Hiroyuki

    Journal of Solid Mechanics and Materials Engineering   5 ( 12 ) 669 - 677  2011年

     概要を見る

    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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  • 疲労負荷下におけるクロスプライCFRP積層板のトランスバースクラック発生評価

    髙村 啓吾, 細井 厚志, 佐藤 成道, 川田 宏之

    日本機械学会論文集 A編   77 ( 779 ) 1123 - 1134  2011年

     概要を見る

    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.

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  • 高温水環境下における樹脂中ガラス繊維の残存強度の予測法の提案

    小谷 正浩, 川田 宏之

    日本機械学会論文集 A編   77 ( 783 ) 1956 - 1966  2011年

     概要を見る

    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°C and 75°C 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.

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  • CFRP直交積層板の熱残留応力緩和に伴う経時寸法変化の予測

    荒尾 与史彦, 奥土居 由貴江, 武田 真一, 小柳 潤, 宇都宮 真, 川田 宏之

    日本機械学会論文集 A編   77 ( 780 ) 1238 - 1246  2011年

     概要を見る

    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.

    DOI CiNii

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

    髙村 啓吾, 細井 厚志, 佐藤 成道, 川田 宏之

    日本機械学会論文集A編   77 ( 779 ) 1123 - 1134  2011年

     概要を見る

    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

  • CFRP積層板における層の配向誤差による面外変形(積層構成の熱変形に対する影響)

    荒尾 与史彦, 小柳 潤, 武田 真一, 宇都宮 真, 川田 宏之

    日本機械学会論文集 A編   77 ( 776 ) 619 - 628  2011年

     概要を見る

    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.

    CiNii

  • 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年  [査読有り]

     概要を見る

    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

  • 繊維表面の水分除去による樹脂中ガラス繊維の強度改善

    荒尾 与史彦, 小谷 正浩, 佐藤 慎也, 川田 宏之

    実験力学 : journal of JSEM   10 ( 4 ) 420 - 424  2010年12月

    CiNii

  • 高温水環境下におけるGFRPの界面劣化特性 : 一方向GFRPを用いた界面接着性評価

    小谷 正浩, 荒尾 与史彦, 高橋 綾希, 服部 聡, 古挽 彰, 川田 宏之

    実験力学 : journal of JSEM   10 ( 4 ) 413 - 419  2010年12月

    CiNii

  • 531 極低温環境下におけるガラス繊維の強度発現機構(高分子/高分子基複合材料(3),ものづくりにおける基礎研究と先端技術の融合)

    野口 洋平, 小谷 正浩, 荒尾 与史彦, 谷口 憲彦, 西脇 剛史, 平山 紀夫, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2010 ( 18 ) "531 - 1"-"531-4"  2010年11月

    CiNii

  • 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年02月  [査読有り]

     概要を見る

    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

  • 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年

     概要を見る

    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年  [査読有り]

     概要を見る

    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年  [査読有り]

     概要を見る

    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年  [査読有り]

     概要を見る

    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年  [査読有り]

     概要を見る

    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年01月  [査読有り]

     概要を見る

    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

  • 高分子基複合材料における界面強度のひずみ速度依存性(<小特集>M&P2009機械材料・材料加工部門技術講演会)

    大石 泰至, 佐藤 慎也, 川田 宏之

    日本機械学會論文集. A編   76 ( 766 ) 669 - 671  2010年

     概要を見る

    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.

    DOI CiNii

  • 極低温環境下におけるガラス単繊維の引張破壊特性(<小特集>M&P2009機械材料・材料加工部門技術講演会)

    早川 守, 谷口 憲彦, 西脇 剛史, 平山 紀夫, 川田 宏之

    日本機械学會論文集. A編   76 ( 766 ) 652 - 654  2010年

     概要を見る

    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.

    DOI CiNii

  • 高温水環境下におけるSFC中ガラス繊維の強度劣化挙動

    小谷 正浩, 古挽 彰, 安福 悠祐, 川田 宏之

    日本機械学會論文集. A編   76 ( 767 ) 982 - 987  2010年

     概要を見る

    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.

    DOI CiNii

  • 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年09月  [査読有り]

     概要を見る

    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年07月  [査読有り]

     概要を見る

    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年05月  [査読有り]

     概要を見る

    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

  • 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年12月  [査読有り]

     概要を見る

    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

  • 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年  [査読有り]

     概要を見る

    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

  • 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年

     概要を見る

    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年  [査読有り]

     概要を見る

    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年  [査読有り]

     概要を見る

    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年10月  [査読有り]

     概要を見る

    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

  • 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年12月  [査読有り]

     概要を見る

    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

  • 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年

     概要を見る

    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年03月

  • 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年03月

  • 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年03月

  • 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年03月

  • 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年03月

  • 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年03月

  • 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年03月

  • 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年10月

  • 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年10月

  • 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年10月

  • 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年10月

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

    4th International Conference on Mechanics of Time Dependent Materials   第4巻  2003年10月

  • 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年08月

  • 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年08月

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

    14th International Conference on Composite Materials (ICCM-14)    2003年07月

  • A Study of GFRP on Stress Corrosion Cracking

    14th International Conference on Composite Materials (ICCM-14)    2003年07月

  • 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年07月  [査読有り]

     概要を見る

    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年05月

  • 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年05月

  • 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年05月

  • 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年05月

  • 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年05月

  • 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)

    川田 宏之, 細井 厚志, 山崎 慎一郎

    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年05月

    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年05月

  • 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年

  • 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年11月

  • 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年11月

  • 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年11月

  • 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年11月

  • 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年11月

  • 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年11月

  • 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年08月

  • 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年08月

  • 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年08月

  • 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年06月

  • 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年06月

  • 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年03月

  • 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年03月

  • 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年03月

  • 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年03月

  • 複合材料活用辞典

    産業調査会出版    2001年

  • 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年  [査読有り]

     概要を見る

    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年03月

  • 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年03月

  • 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年03月

  • 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年03月

  • 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年11月

  • 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年11月

  • 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年07月

  • Crack Propagation Properties of GFRP Laminates under Acid Stress Environment

    Proceeds of Twelfth International Conference on Composite Materials   pp.147  1999年07月

  • 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年07月

  • 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年07月

  • 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年07月

  • Crushworthiness of Polymeric Matrix Composites for Automabile

    7th Euro-Japanese Symposium/ECOLE DES MINES DE PARIS   Composite Materials and Transportation  1999年07月

  • 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年04月

  • 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年04月

  • 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年04月

  • 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年04月

  • 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年04月

  • 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年04月

  • 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年04月

  • 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年04月  [査読有り]

     概要を見る

    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年03月

  • 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年03月

  • 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年03月

  • 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年03月

  • 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年03月

    担当区分:最終著者

  • 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年03月

  • 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年03月

  • 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年11月

  • 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年11月

  • 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年10月

  • 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年09月

  • 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年09月

  • 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年09月

  • 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年08月

  • 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年05月

  • 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年05月

  • 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年05月

  • Damage Accumulation and Fracture of Notched Carbon-Carbon Composites

    The Seventh International Conference on Composite Interfaces/ICCI-7   ICCI-7,pp.217  1998年05月

  • 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年05月

  • 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年05月

  • 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年04月

  • 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年  [査読有り]

     概要を見る

    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年  [査読有り]

     概要を見る

    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年  [査読有り]

     概要を見る

    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.

▼全件表示

書籍等出版物

  • 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年01月 ISBN: 9784888981699

Misc

  • アルミニウム合金とCFRTP積層板の異種接合の強度と破壊形態に及ぼす表面ナノ構造の影響 (接着・接合特集号)

    和田 啓汰, 大田 宙起, 齊藤 慧, ムンク イエスパーセン クリスティーン, 細井 厚志, 川田 宏之

    日本複合材料学会誌   46 ( 4 ) 162 - 169  2020年

    CiNii

  • 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年10月

    CiNii

  • OS1713 接着構造試験片を用いた層間高靱性化CFRP積層板の面外方向疲労試験

    佐久間 茂吉, 重盛 洸, 細井 厚志, 藤田 雄三, 武田 一郎, 川田 宏之

    M&M材料力学カンファレンス   2014   "OS1713 - 1"-"OS1713-2"  2014年07月

     概要を見る

    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 ガラス短繊維強化ポリアミドの衝撃特性に及ぼす繊維径および繊維断面形状の影響

    小澤 憲人, 金 太成, 荒尾 与史彦, 谷口 憲彦, 西脇 剛史, 平山 紀夫, 中村 幸一, 川田 宏之

    M&M材料力学カンファレンス   2014   "OS1716 - 1"-"OS1716-3"  2014年07月

     概要を見る

    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 改良型同時多層巻回法によるCFRP円筒材のねじり強度に及ぼす積層構成の影響

    里村 圭介, 中村 崇人, 木元 尚紀, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2013 ( 21 ) "110 - 1"-"110-4"  2013年11月

     概要を見る

    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 マルチスケール一方向GFRPの作製および機械的性質評価

    名取 純希, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2013 ( 21 ) "116 - 1"-"116-4"  2013年11月

     概要を見る

    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 ガラス長繊維および短繊維強化ポリアミドの曲げ特性に対するひずみ速度の影響

    野村 彩英子, 高橋 宏平, 川田 宏之

    機械材料・材料加工技術講演会講演論文集   2013 ( 21 ) "129 - 1"-"129-4"  2013年11月

     概要を見る

    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 Tガラス繊維表面のCNTSが界面強度に及ぼす影響 : 複数のCNTs析出条件間の比較

    亀谷 真帆, 佐藤 慎也, 川田 宏之

    年次大会 : Mechanical Engineering Congress, Japan   2012   "J043033 - 1"-"J043033-4"  2012年09月

     概要を見る

    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 CVD法を用いたCNTs析出チラノ繊維複合材料の成形と界面強度評価

    佐藤 龍, 川田 宏之

    年次大会 : Mechanical Engineering Congress, Japan   2012   "J043023 - 1"-"J043023-4"  2012年09月

     概要を見る

    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 水環境下において定荷重引張を受ける非主軸平織GFRP積層板の寿命調査

    名取 純希, 服部 聡, 小谷 正浩, 川田 宏之

    年次大会 : Mechanical Engineering Congress, Japan   2012   "J043013 - 1"-"J043013-5"  2012年09月

     概要を見る

    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

  • CFRP直交積層板におけるトランスバースクラック発生の温度依存性

    川田 宏之, 小柳 潤, 細井 厚志

    材料システム   28   47 - 52  2010年

    CiNii

  • 酸応力環境下における GFRP 積層板のき裂進展特性と架橋繊維の影響

    川田 宏之, 飯高 誠之

    複合材料シンポジウム講演要旨集   27   201 - 202  2002年10月

    CiNii

  • 複合材料積層中の層間はく離によるエネルギー損失

    西脇 剛史, 谷口 憲彦, 川田 宏之

    複合材料シンポジウム講演要旨集   27   215 - 216  2002年10月

    CiNii

  • 内部欠陥を有する複合材料積層板中の応力波伝播挙動

    谷口 憲彦, 西脇 剛史, 川田 宏之

    複合材料シンポジウム講演要旨集   27   213 - 214  2002年10月

    CiNii

  • モデル試験片を用いた GFRP の応力腐食割れに関する研究 : エネルギバランスモデルによる界面劣化の評価

    川田 宏之, 井上 大輔

    複合材料シンポジウム講演要旨集   27   203 - 204  2002年10月

    CiNii

  • アルミナFRP円筒の引張り/圧縮疲労特性 (繊維巻き角度と疲労強度の関係)

    平野 隆明, 脇 勇一朗, 川田 宏之

    日本複合材料学会研究発表講演会予稿集   2000   51 - 52  2000年

    CiNii

  • Slice Compression TestによるPMC界面の力学的特性評価 〜界面はく離き裂の発生と進展挙動〜

    蔡 昆男, 有岡 紘佑, 川田 宏之

    日本複合材料学会研究発表講演会予稿集   2000   97 - 98  2000年

    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年

    CiNii

▼全件表示

産業財産権

  • 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

    特許権

  • 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

    特許権

  • 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

    特許権

  • FRP円筒及びその製造方法

    川田 宏之

    特許権

  • 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

    特許権

受賞

  • 日本機械学会賞(論文)

    2014年   日本機械学会   層間高靱性化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  

    受賞者: 川田 宏之

共同研究・競争的資金等の研究課題

  • 溶媒可溶性グラフェンを利用した高強度・高耐久性ナノコンポジットの創出

    研究期間:

    2019年04月
    -
    2022年03月
     

     概要を見る

    本研究は、新規に見出したメカノケミカル反応制御によって、溶媒に可溶な高アスペクト比グラフェンを創出し、分子レベルで分散している分散液を熱硬化性樹脂、熱可塑性樹脂に混合・複合化することで、高強度、高延性を両立し、かつ長期耐久性を有するナノコンポジットを作製する技術を確立することを目的とする。メカノケミカル反応の分子シミュレーションをすることで、グラフェンの新しい反応とその複合物を提案するとともに、その応用として、新規グラフェンを構造材料のアンチエイジング材料として応用する。天然黒鉛を塩と混合してボールミルすることにより、黒鉛端部に塩が吸着した新しい可溶性グラファイトを創出することに成功した。この黒鉛は、端部に塩のカチオン成分が吸着しており、極性溶媒中に分散させると、カチオンが解離し、それによって黒鉛は負のチャージが強まる。負の静電反発力によって、黒鉛は液中で容易に剥離分散可能となることが明らかとなった。分子シミュレーションにより、メカノケミカル反応により、塩が黒鉛端部に吸着し、吸着後もイオン結合性を有していることを確認した。この負に帯電するグラファイトをアニオングラファイトと呼び、アニオングラファイトの液中での剥離分散挙動を詳しく調査した。アニオングラファイトを超音波により分散すると、主に黒鉛の端部で破断が生じ、その結果分散が良好なエッジ部と、分散性の悪いコア部に分離することが分かった。このエッジ割れによって、アニオングラファイトは短時間で容易に分散する一方で、分散性の悪いコア部が残存し、長時間の超音波でもこのコア部は分散しにくいことが明らかとなった。また、エッジ割れによって、グラフェンの端の部分だけが切り取られ、結晶径の大きいグラフェンを得ることは難しいことが分かった。グラフェンをプラスチックと混ぜ、その高強度を発現させるためには、アスペクト比の大きいグラフェンが必要不可欠である。アスペクト比を高めるための塩をスクリーニングした結果、一部の塩において比較的アスペクト比の大きいグラフェンを得られることが分かった。メカノケミカルプロセスをより最適化することで、1μmを超える大きさのグラフェンを得ることが課題である。メカノケミカルプロセスの実験的な研究は一通り行うことができたものの、そのメカニズムは依然と不明であった。そこで分子シミュレーションを専門とされている先生に、黒鉛と塩の反応とその構造の解明を依頼したところ、快諾頂き、分子シミュレーションによる反応の解析を行ってもらった。これらの協力により、我々の実験結果を理論による裏付けで補強することができ、黒鉛と塩との複合化により何故剥離分散性があがるのか、そして塩によってなぜ違いがでるのかが明らかとなった。その理論をもとに様々な塩を用いて、黒鉛とのメカノケミカル反応の調査を行った。これまではグラフェンの評価はAFMで行っていたため、一つの種類を調べるのに1週間程度要していたが、科研費で導入したナノ粒子解析装置で粒径を測ることで、1日で大まかな粒径を知ることができるようになった。それによって、粒径の大きいグラフェンを得るための実験を多数行えることができ、グラフェンの大きさをさらに向上させるための、いくつか新しいプロセスを提案することができた。以上の理由から、当初の予定よりも研究が進んでおり、グラフェンを利用した複合材料に関して、さらに発展させた研究を進めている。グラフェンを添加することでプラスチックの強度を向上させることを目標として研究を行っているが、グラフェンの大きさは平均で400nm程度であり、補強材としての効率をさらに上げるためには1μmを超えるグラフェンを量産化したい。乾式のメカノケミカル反応を最適化しているが、大きさとして1μmを超えることは難しいことが分かりつつあり、今後は湿式によるメカノケミカル反応にも挑戦する予定である。実際にいくつか試しに行ったところ1μmを超える大きさのグラフェンを得られており、いくつか湿式粉砕装置を検討して装置を導入するとともに、その評価を進めていきたい。一方でグラフェンは表面が平滑であるため、プラスチックとの界面ですべりが生じ、補強効果が得られにくいといった報告がされている。この界面での滑りを抑制するようなアイデアをだして、グラフェンによるプラスチックの補強効果を更に高めたい。本年度中には強度向上として30~50%の向上を達成したい

  • 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

    研究期間:

    2018年04月
    -
    2021年03月
     

     概要を見る

    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

  • 大電流容量を有する革新的カーボンナノチューブ金属複合配線材の創製

    研究期間:

    2018年06月
    -
    2020年03月
     

     概要を見る

    本研究では優れた電気的特性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,従来の紡績糸と比較して優れた電気的特性を有するCNT糸を得たる.CNT紡績糸は従来の配線材料の代替が期待されており,更なる電気的特性の向上が急務とである.このことから,CNT無撚糸に対しキャリア導入を目的としたドーピング処理や熱処理,メッキ処理による金属との複合化などを行い,従来のCNT糸と比較し優れた電気的特性を有するCNT無撚糸を得ている.本年度は無撚CNT糸に対し一塩化ヨウ素(ICl)ドーピング処理,高密度化処理,黒鉛化処理を組み合わせて施すことにより更なる高電導化を有したCNT糸の創製を目指した.その結果,高密度化とIClドーピング処理を施した際に導電率3.87×10^5S/m,黒鉛化処理とIClドーピング処理を施した際に導電率5.12×10^5S/mと,より優れた電気特性を有するCNT無撚糸を得た.さらに,黒鉛化処理を施した繊維に関して,比電流容量が172Am/kgと銅線の比電流容量150Am/kgを超える極めて優れた特性を有することが確認された.また,ドーピング処理後にCNTの電子輸送に起因するπ-π*結合が増加したことから,状態密度が増加したことが確認され,ドーピング処理による導電率向上のメカニズムが解明された.また,より高密度なCNT糸を得ることを目的とし CNT撚糸を作製し電気特性の調査を行ったところ,撚り角の影響は非常に少ないことが確認された.より高密度化されたCNT撚糸はIClドーピング処理を施すことで4.7×10^5S/mと高い導電率を示し,細線かつ高密度なCNT撚糸は高い電気特性を有するCNT糸の創製に有効であることが確認された

  • 高密度化無撚CNT糸を用いた革新的超軽量高強度複合材料の開発

    研究期間:

    2015年04月
    -
    2018年03月
     

     概要を見る

    本研究ではCNT単体の優れた機械的特性が十分に発揮された革新的高強度CNT糸の創製を目的とし,乾式紡績法で作製した無撚CNT糸の高強度化を行った.糸を構成するCNT単体の強度評価および分子動力学解析によるCNT間相互作用力の評価によって,CNT糸の高強度化にはCNT単体の高強度化とCNT間の荷重伝達効率の向上が必要であることを明らかにした.また,それに基づいて黒鉛化処理によるCNTの高純度化,CNT糸と各種ポリマーとの複合化を行い,強度2.4 GPaのCNT糸を創製した

  • CNT析出強化階層型複合材料の創成と界面評価および衝撃・疲労特性

    研究期間:

    2012年04月
    -
    2015年03月
     

     概要を見る

    本研究では高分子基複合材料(PMC)へのカーボンナノチューブ(CNTs)導入方法として,複数種の無機系繊維表面へのCNTs析出方法の確立を行った.特に,触媒金属や析出条件の検討によって,一般にCNTs析出が困難とされる炭素繊維表面への短時間かつ均一なCNTs析出プロセスを確立した.また,マルチスケールの界面特性評価から複合材料の界面せん断特性向上へのCNTs析出の有効性を示した.さらに,CNTs析出炭素繊維を強化材とするCFRP一方向材を創製し,CNTs析出による補強効果の異方性とそのメカニズムを明らかにした

  • 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 

    研究期間:

    1999年
    -
    2003年
     

  • 国際規格対応の心臓代用弁多機能評価シュミレータの開発

     概要を見る

    本研究では,生体内における人工弁の耐久性を加速耐久試験においていかに再現するかを検討し,国際規格対応の信頼性の高い装置を開発することを目的とした.その第一歩としてJelly-Fish弁(以下JF弁)を用いて,装置性能を向上させるという方法を採用した.1994年度の動物実験において,約1年間の駆動後人工心臓のJF弁の膜にクリープ破断が生じた.そこで,その結果の再現に必要な加速耐久試験に要求される条件を求めた.加速耐久試験には試験弁が水中シリンダ内を10-20Hzで往復する中国製試験機(TH-2200)の成果を用いた.試験は室温(20℃)で,弁閉鎖期の最大荷重5.2N(生体内の約120%),力積2.5×10^<-2>(生体内の約2%)の力学条件下で行ったが,クリープ変形をJF弁の膜に見ることはできなかった.そこで力学的環境は不変だが材料の温度上昇に伴うヤング率の現象効果を考慮して同実験を行った.その結果,ヤング率低下傾向の大きなポリスチレン(膜厚900μm)を動物実験で確認したものと同等のクリープ変形を再現することに成功した.一方,破断位置については動物実験と異なった.動物実験ではスポ-クの間の扇形部分において破断を生じていたが,加速試験では弁葉がリム内周およびスポ-クと接触する点において破断が生じていた.しかし,これと並行してJF弁の2本のスポ-クに挟まれた部分を取り上げて有限要素法により応力解析した結果,動物実験の結果も加速試験の結果も歪みが大きく生じる部分で破断している点では一致することを確認した.以上より,生体に用いた際のJF弁の破断特性を加速耐久試験で短期間に実現するための条件をある程度確立する基礎を得られた

  • 酸応力環境下におけるGFRP織物積層板の応力腐食割れ特性

     概要を見る

    酸応力環境下におけるGFRP織物積層板のき裂進展挙動および下限界特性について研究を行った.試験片として応力腐食割れの挙動が顕著に現れる,強化材としてEガラス繊維,母材樹脂としてエポキシ樹脂を用いた試験片を用い,塩酸環境での負荷条件,環境条件がき裂進展挙動および下限界特性に与える影響について詳細な調査を行った.負荷条件については静荷重,繰り返し荷重で試験を行い,応力比および周波数を変化させた結果,き裂進展は時間および最大応力拡大係数に依存していることが明らかとなった.また,繰り返しの効果によるき裂進展の促進は見られず,静荷重下での結果と比較してかえってき裂進展が遅くなり,下限界も上昇する現象が見られた.SEMを用いた破面観察により,繰り返し荷重下では界面のはく離,繊維の引き抜けが起こっていることが明らかとなった.環境条件については塩酸濃度および塩酸温度の変化による挙動の変化を詳細に調査した.塩酸濃度に関してその影響はき裂の進展が収束する下限界近傍で顕著に現れ,303K静荷重環境で下限界値は塩酸濃度が上昇するにつれある値に収束する傾向が見られた.303K繰り返し荷重環境では,下限界値は塩酸濃度1mol/lで極小値を持つことが明らかとなった.温度が上昇するとき裂進展は促進されるが,定常き裂進展領域において促進の度合いをアレニウスの式を用いて説明することが出来た.また,下限界特性は温度が上昇すると静荷重下ではそれほど大きな影響が出ないが,繰り返し荷重下ではその影響が顕著に現れ,値が大きく減少し極小値をとらなくなることが明らかとなった

  • 酸応力環境下におけるGFRP織物積層板のき裂進展挙動

     概要を見る

    本研究室では,酸応力環境下におけるEガラス系FRP織物積層板の破壊機構解明を行ってきた.初年度は,耐食性に優れるCガラス系FRPの破壊機構解明に取り組んだが,Eガラス系は酸拡散によるガラス繊維の腐食により,Cガラス系は水拡散による繊維荷重分担率の増加,もしくは界面強度の低下によりき裂進展が促進されていることが明らかになった.また,平行して,Eガラス系の下限界特性解明のため,二次元拡散解析を行い,拡散現象の負荷応力依存性を確認するとともに,その促進効果の飽和点と下限界値が一致することを示唆した.そこで,次年度は,巨視的視点からの考察を行ってきた従来の積層板に加え,単繊維モデル試験を導入することにより,微視的視点からの破壊機構解明を試みた.積層板を用いた実験からは,繊維/樹脂界面の劣化が重要な因子であることが確認された.酸溶液中にGFRPを浸漬させると,酸・水の影響で,ガラス繊維および繊維/樹脂界面の劣化が進行する.繊維の劣化は,き裂進展抵抗の促進因子であるのに対し,界面の劣化はFRP全体のじん性が向上するため,き裂進展抵抗の抑制因子であると考えられる.この促進因子と抑制因子の2つが均衡することにより,下限界応力拡大係数が決定され,短期浸漬(1週間程度)の実験で得られる下限界値が,長期浸漬(1ヶ月程度)の結果に対しても有効であるとの結論を得た.一方,単繊維モデル試験片による,フラグメンテーション試験を実施した.負荷応力の変化により試験片内部への拡散量が変化したことから,高分子材料中の拡散現象の負荷応力依存性を示すとともに,水・硫酸中で結果に大きな差異が観られなかったことからは,酸に対する水の拡散先行性を確認した.以上より,拡散が各構成基材(繊維・樹脂・界面)に与える影響を調査することにより,低応力拡大係数域における微視的視点からき裂進展挙動を考えること有効性を示した

  • 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

     概要を見る

    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

  • 酸応力環境下におけるGFRP織物積層板の下限界特性

     概要を見る

    本研究ではこれまでに酸応力環境下におけるEガラス系FRP,Cガラス系FRPにより試験を行うことで,FRPの応力腐食割れは強化繊維の耐食性に大きく依存することが示唆された.そこで,一方向FRPによりこれまでと同様の応力腐食割れ試験を行い,き裂進展に対して0°方向の繊維が進展挙動,下限界特性に及ぼす影響を調査した.また,単繊維モデル試験による樹脂内部繊維の強度劣化と拡散現象の関係を,長期期間に渡り調査した.さらに,き裂先端における微視的損傷観察を行うモデル試験を実施し,環境劣化による破壊過程の変化を調査した.一方向材による応力腐食割れ試験では,Cガラス繊維を強化材とし,き裂進展挙動を調査した.K_1-da/dt線図より,下限界応力拡大係数の存在が確認された.き裂先端の観察より,き裂面間における繊維架橋現象が確認され,これが下限界特性を支配すると考えられる.また,フラクトグラフィにより純水中での試験では繊維/樹脂界面における破壊が主き裂となる樹脂部に先行することが予測され,界面の先行破壊が繊維架橋を生じさせると考えられた.そこで有限要素解析により,繊維架橋現象を考慮した破壊モデルによりき裂進展方向に対し0°に埋蔵された繊維束が,下限界特性におよぼす影響を調査した.単繊維モデル試験では,これまでよりもさらに長時間浸漬における劣化挙動の調査を行った.この劣化現象を評価する上で,これまでは応力評価であったが,本年度は界面はく離エネルギによる評価を行った.この結果,吸水飽和以後も界面はく離エネルギは低下するが,一定時間を超えると一定の値に収束することが確認された.き裂進展を抑制する主因子と考えられる進展方向に垂直に埋蔵された繊維については,より詳細な調査を行った.き裂進展とともに生ずる微小損傷である繊維破断と界面はく離を観察するために,DCDC試験を実施し,界面の状態とき裂進展を抑制する繊維架橋の関係を調査した

  • 酸応力環境下におけるGFRPの長期信頼性評価

     概要を見る

    繊維強化プラスチック(FRP)は比強度・比剛性に優れることからさまざまな極限環境で用いられている.また,耐食性に優れることから腐食環境で多く用いられている.そのような環境における長期耐久性を向上させるために,腐食環境下におけるFRPの破壊メカニズムの解明が求められる.本研究ではFRPの構成基材である繊維や界面の劣化に着目し,IFRPの破壊現象への影響を調査した.また,構成基材は母材樹脂に覆われることから,母材を拡散した環境因子によって劣化する.拡散速度という点においては酸イオンよりも水分の方が非常に大きいことから,調査する環境因子は水とした.そこで,繊維強度については,水環境下における繊維単体の強度低下を調査した.Eガラス繊維束を水環境,および湿潤環境においたところ,時間経過にしたがって引張強度が低下することが示されたが,いずれの環境下でも強度は収束していくことが明らかとなった.次に強度低下の応力依存性を明らかとするために,Eガラス単繊維を試験片として水中において一定応力を負荷し破断時間の測定を行った.この結果,応力依存性の遅れ破壊を生じることが示された.このとき得られた破断時間分布は,繊維表面に破壊の起点となる初期欠陥が存在し,これが応力と水分の2つを因子として成長することで強度が低下すると仮定して,予測を行った.これは実験結果とよい一致を示し,本モデルを用いてFRPにおける環境依存型の繊維強度の予測可能であることが示された.次に,腐食環境下における巨視的なき裂進展と微視的な内部損傷の関係を求めるため,き裂進展時の界面はく離に着目した.水環境下においては拡散した水分によって内部における界面強度が低下し,はく離も生じやすくなる.モデル試験片により,吸水状態と巨視的き裂進展時のはく離長さの関係を求めたところ,はく離は顕著となり,き裂進展抵抗が変化していくことが明らかとなった

  • 極限環境下におけるPMCの時間依存特性と長期信頼性評価

     概要を見る

    繊維強化プラスチック(FRP)をはじめ高分子基複合材料は構成基材の選定が可能であり,使用目的にあわせた機械的特性の設計が可能である.しかしながら腐食環境下におけるFRPの長期信頼性に関する研究は,き裂進展および材料特性の低下といった巨視的観点により,破壊発生メカニズムの解明にはいたっていない.FRPの巨視的な最終破壊は,FRPの構成基材に蓄積される微視的損傷により引き起こされる.そこで本研究は,微視的損傷として母材樹脂の機械的特性の低下,強化繊維の強度低下,界面劣化に着目し,それぞれを定量的に評価した.エポキシ樹脂製試験片を純水中へ浸漬させた後に,空気中にて静的引張試験を行い,剛性および破断ひずみを調査した.浸漬前後で剛性は変化しなかったが,破断ひずみが浸漬により増加する傾向を示した.また,Eガラス単繊維をエポキシ樹脂に埋蔵した単繊維埋蔵型試験片(SFC)を作製し,水中にてSFC試験片の定ひずみ試験を行った.水中定ひずみ試験後に空気中にて静的引張試験を行い,繊維破断数および破断点に発生したはく離長さを測定した.繊維破断数および破断ひずみから,ワイブル分布を用いて繊維強度を計算し,水中定ひずみ試験により繊維強度が低下することを確認した.繊維の強度低下は負荷ひずみ,浸漬時間,試験温度を大きくすることにより促進されることがわかった。さらに,微小き裂進展モデルを用いるいことにより,さまざまな試験条件のもとの繊維強度低下挙動の予測が可能となった.また,界面はく離長さからはく離先端に作用する最大せんだん応力を,はく離発生前後のエネルギバランスからはく離発生に要するエネルギ解放率を算出した.最大せん断応力およびエネルギ解放率は,浸漬時間とともに低下し,収束する傾向を示した.以上のことから,母材樹脂の機械的特性,繊維強度の低下挙動,界面劣化を定量的に評価することが可能となった

  • 水環境下におけるPMCの損傷発達と長期耐久性

     概要を見る

    本研究では水環境下におけるGFRPの耐久性の評価ならびに寿命の予測法を提案した.平織Eガラスクロスを強化繊維に,ビニルエステル樹脂を母材に用いてGFRPを作成し,純水中および大気中において定荷重引張試験を行った.GFRP は純水中にてのみ破断し,荷重および試験温度の上昇とともに破断時間は短くなった.また試験中のGFRPに蓄積されるエネルギおよび劣化による破壊基準の低下を考慮して破断時間を予測し,実験結果とよい一致を得た

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特定課題研究

  • 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年  

     概要を見る

    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。

  • 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年  

     概要を見る

    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 衝撃エネルギー吸収メカニズムの解明

    2020年  

     概要を見る

     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年  

     概要を見る

    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年  

     概要を見る

     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.

  • 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年  

     概要を見る

    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.

  • 大電流容量を有する配線用CNT複合繊維の創製

    2017年  

     概要を見る

    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.

  • 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年   細井厚志

     概要を見る

     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年  

     概要を見る

    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年   細井厚志

     概要を見る

     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年  

     概要を見る

    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年  

     概要を見る

    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年  

     概要を見る

    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年  

     概要を見る

    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年  

     概要を見る

     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年  

     概要を見る

     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年  

     概要を見る

    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年  

     概要を見る

     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年  

     概要を見る

    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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