In this study, it was investigated that the validity of small punch (SP) test for the lifetime prediction of polyvinyl chloride (PVC) resin used as an electric insulation material for the electric cable. The degradation behavior of PVC resin under the accelerated high-temperature condition was analyzed using Fourier transform-infrared spectroscopy (FT-IR), tensile testing, and SP testing. The activation energies and estimated lifetime obtained from the Arrhenius method were compared. The peak ratio of the carbonyl group obtained by FT-IR, the elastic modulus obtained by tensile testing, and the apparent elastic modulus obtained by SP testing were used as indicators for lifetime estimation, and the logarithm of these values showed a linear correlation with exposure time. The activation energy obtained from the apparent elastic modulus using SP testing was the smallest and the predicted lifetime was the shortest among all mechanical properties in this research. It indicates that SP testing is sensitive to the degradation. This is because the stress at the surface becomes maximum for SP testing, and the degradation occurs at the surface of the materials by priority degradation. SP testing is an excellent minimally destructive lifetime prediction method for detecting of early-stage degradation.

Natural fiber composites (NFCs) have strong potential to replace glass fiber-reinforced plastics. An instrumental operation in machining composite structures is hole making which facilitates assembly of parts. Understanding the effects of drilling process parameters on feature properties of NFCs has great benefits. In this regard, to make a good quality and accurate hole in composite structures, appropriate selection of drill bit and cutting parameters is important. This paper investigates delamination behavior and hole quality of flax/epoxy composite laminates in response to feed, spindle speed, and three different types of drill bit. As indicated by analysis of variance results, drill bit type and feed have greater influences on the thrust force. It appeared that delamination factor and surface roughness were significantly influenced by drill bit, but not by feed and spindle speed. The choice of drill bit has great impact on the delamination factor (67.27%) and surface roughness (74.44%), respectively.

<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>

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.

<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>

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

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

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

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

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

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

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

Since thermosetting resins have excellent resistance to chemicals, fiber reinforced plastics composed of such resins and reinforcement fibers are widely used as construction materials for equipment in chemical plants. Such equipment is usually used for several decades under severe corrosive conditions so that failure due to degradation may result. One of the degradation behaviors in thermosetting resins under chemical solutions is "corrosion-layer-forming" degradation. In this type of degradation, surface resins in contact with a solution corrode, and some of them remain as a corrosion layer on the pristine part. It is difficult to precisely measure the thickness of the pristine part of such degradation type materials by conventional pulse-echo ultrasonic testing, because the sound velocity depends on the degree of corrosion of the polymeric material. In addition, the ultrasonic reflection interface between the pristine part and the corrosion layer is obscure. Thus, we propose a pitch-catch method using a pair of normal and angle probes to measure four parameters: the thicknesses of the pristine part and the corrosion layer, and their respective sound velocities. The validity of the proposed method was confirmed by measuring a two-layer sample and a sample including corroded parts. The results demonstrate that the pitch-catch method can successfully measure the four parameters and evaluate the residual thickness of the pristine part in the corrosion-layer-forming sample. (C) 2017 Elsevier B.V. All rights reserved.

Fiber reinforced polymer (FRP) composites are commonly used in the chemical industry for storage tanks and pipelines, since most metallic alloys suffer from corrosion and result in costly maintenance and safety hazards. E-glass fiber is commonly used because of its low cost, but it is extremely susceptible to rapid degradation in low-pH environments. C-glass is an acid-resistant substitute, and while not as durable as carbon, it is much cheaper. Nevertheless, durable fibers are not the only key aspect of designing corrosion-resistant composites, as various degradation mechanisms must be considered. In this study, plain-weave laminates of C-glass and amine-cured epoxy are exposed to water and sulfuric acid solutions, and the relationship between diffusion kinetics and strength-loss is discussed. Results show that both solutions attack the fiber surface to some degree, but more importantly sulfuric acid increases the saturation uptake of water in the material, causing high swelling stresses that significantly reduce mechanical properties.

Fiber reinforced plastics (FRPs) are often used for chemical equipment because of their high chemical resistance, especially their resistance to acidic conditions. However, serious accidents have been reported when using such tanks with hydrochloric acid (HCl). We gathered FRP tanks used for 35% HCl storage from various chemical companies, and analyzed their changes in appearance, HCl penetration and residual flexural strength. We found that residual strength of FRP decreased to &lt; 50 MPa after 24 years of usage. The strength degradation at the tank roofs was more severe than at other positions in the tanks; in these parts the residual strength was 10-25 MPa after 20 years of usage. The strength degradation of FRP is caused by diffusion of HCl into the FRP. If the diffusion of HCl reaches the reinforced layer of the FRP tank, the FRP strength sharply decreases. Based on our comprehensive analysis of FRP tanks, the lifetime of current FRP tanks for 35% HCl storage is estimated at &lt; 20 years.

Liquid-phase exfoliation (LPE) of graphite is a promising method to produce few-layer graphene (FLG) in large quantities. Selection of the solvent or surfactant is the most important factor in determining the productivity of LPE and the stability of the liquid FLG dispersion. To find efficient solvent systems for improving the production of FLG, various approaches based on previous research, including addition of a surfactant and use of binary solvents, are investigated using a pressure homogenizer. Over the range of solvents and surfactants used in our study, we find that the greatest improvement in the production of FLG results from the addition of an alkaline aqueous solution (pH 11) into organic solvents. Moreover, we find that this approach works for the probe-sonication method of FLG production as well as for various types of natural graphite. Solvent molecular size and electrostatic repulsion of graphene in liquid play important roles in improving the production of FLG because they mitigate the restacking of FLG during exfoliation. (C) 2017 Elsevier Ltd. All rights reserved.

An efficient graphene production technique is essential to realize the commercial use of graphene. Liquid-phase exfoliation (LPE) of graphene is a low-cost method of graphene production. LPE is based on shear mixing or sonication in proper liquid. The applied force to graphite has not been optimized. Thus, the production rate and quality of graphene via LPE can be improved by controlling fluid dynamics in liquid. We demonstrate that the high-speed laminar flow generated by a pressure homogenizer effectively exfoliates large quantities of high-quality graphene. In a lab-scale trial, a production rate of 3.6 g/h of graphene in aqueous solution was achieved. In addition, the average lateral size of graphene obtained by the proposed method was larger than that by traditional sonication method. An industrial-scale machine could exceed a production rate of 1 kg/h, marking a significant step in the commercialization of graphene. We show that the graphene obtained using this method improves the mechanical properties of polymers more than graphene obtained via sonication. (C) 2016 Elsevier Ltd. All rights reserved.

Graphene can be obtained via sonication-assisted liquid-phase exfoliation, but the production rate of few-layer graphene (FLG) is still low. A high-power probe sonicator was used in this study to improve the production rate of FLG, and its performance was optimized by controlling processing parameters such as the initial graphite concentration, surfactant concentration and liquid volume. By optimizing processing parameters, production rate of FLG dispersions in N-methyl-2-pyrrolidone (NMP) were greater than 1 g/h, which is the best value achieved in the sonication-assisted exfoliation process. In the case of liquid exfoliation in water/surfactant solution, production rate of FLG was achieved approximately 0.28 g/h. Our work here demonstrates that graphene concentration in a probe-sonication process does not depend on the shape of vessel, and it is predictable by power law models. (C) 2015 Elsevier Ltd. All rights reserved.

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.

Extensional flow has been shown to be more efficient solution for improving the dispersion of nano-composites as compared to shear flow. One of the production processes of nano-composites is melt extrusion with corotating twin screw extruder (TSE) which is superior in terms of productivity and mixing performance. Our objective is the optimization of Blister Disk geometry which has many holes for improving the dispersion of nano-composites. The holes were drilled through the Blister Disk seal ring segments to create extensional flow in TSE. However, it was difficult to evaluate the mixing effect of Blister Disk because the flow patterns are complex in TSE, and there is some possibility of no flow through the holes of Blister Disk. To evaluate the dispersion effect of only holes, fundamental evaluation equipment was developed. Firstly, the stress magnitude was investigated for each elongational flow and shear flow by changing the geometries (e.g., hole numbers, hole diameter and hole width) with 3D numerical simulation. Then, the dispersibility variation of polypropylene (PP) and Carbon Nano Tube (CNT) nano-composite was investigated by using various geometries of Blister Disk with fundamental evaluation equipment.

von Karman's effective width theory is constructed on the assumption that thin plate of elastic-perfectly plastic solid is subjected to static buckling. We examined whether von Karman's effective width theory is applicable to design of crush absorption structure. As a result, cross section of the member becomes effective against axial crush with increasing crush speed. It is found that the design based on the conventional theory is provided enough evidence of safety, thus, optimized design criteria can be proposed.

Fiber breakage occurs during the injection molding of fiber-reinforced thermoplastics, resulting in the deterioration of the mechanical properties of the molded parts. In this paper, we propose an effective screw geometry for improving both fiber dispersion and residual fiber length. The proposition is based on the results of our study in which we evaluated five types of screws by investigating the molded specimens. We found that the screw geometry in the compression zone dominantly affected the residual fiber length, and that the choice of an appropriate geometry for the melting and mixing processes was the most important factor for improving both fiber dispersion and residual fiber length. Our experimental observations were compared with the results of flow analysis and consistency was observed. We also discuss the effects of the screw size on the quality of the molded parts.

© 2015 International Committee on Composite Materials. All rights reserved. In order to reduce the environmental burden by the weigh saving of vehicles, fibre reinforced plastics have been used as metal substitutes. The application of CFRTP (carbon fibre reinforced thermoplastics) is expected because of its high mechanical property together with process ability. However, there are unavoidable wastes when CFRTP prepreg sheets are cut into specific geometries to charge moulds with them. Therefore, it is necessary to utilize the CFRTP wastes by a recycling system from both the environmental and economical point of view. Recently, hybrid injection moulding that combines the press moulding and insert injection moulding has attracted attentions. The hybrid injection moulding system is as follow. After heated insert material is pre-formed by pressmoulding, the pre-formed insert material is overmoulded by injection moulding machine. These processes are carried out in the one cycle. In this paper, we propose the recycling method of prepreg wastes and characterize the recycled material. Furthermore, we investigated the potency of the recycled material for the hybrid injection moulding. We carried out numerical analysis to examine the interfacial characteristics. Our recycled material is prepared as pellets by neading, the wastes of prepreg in twin-screw extruder with neat polymer. The fuzzless pellets with good fibre dispersion were obtained in low volume fraction of carbon fibres. In spite of the absence of longer fibres, they showed excellent mechanical performance in comparison with conventional materials designing the preferable process conditions. This mechanical advantage would be due to the fact that the recycled pellets were made from the prepreg sheet which had good interfacial adhesion strength. In contrast, the localization of fibres was observed in high volume fraction of fibres and the mechanical property did not improved. This recycled material has a beneficial effort on the hybrid injection moulding. They also achieved excellent interfacial adhesiveness for the hybrid injection moulding between the injected material and the inserted material. It was found that the cost effective recycle pellets which had excellent mechanical performance could be produced optimizing both the fibre volume fraction and process condition in this recycling system.

© 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.

The mechanical properties of green-composites based on polylactic acid (PLA) with jute fibers were investigated. A long fiber pellet was developed to obtain a high aspect ratio of residual fiber after injection molding. Comparative studies were carried out, where shorter fiber pellets were compounded by different screw configurations using a twin-screw extruder. To interpret the results of our mechanical tests, the fiber geometry, dispersion state, and fiber fracture surfaces after tensile testing were analyzed. We found that the composites made of short fiber pellet (which suffer high compound intensity), exhibited optimal mechanical performance. Although, compounding with a twin-screw extruder decreased the overall aspect ratio of residual fibers, we observed that it significantly facilitated both the dispersion of the jute yarn to jute bundle and the decohesion of jute bundle to elementary fibers. This fiber separation caused by high intensity mixing led to efficient load transfer from matrix to fiber, and improvement of interfacial strength. These findings provide us with an insight into the critical parameters required to develop a high performing jute/PLA composite. (C) 2014 Elsevier Ltd. All rights reserved.

We investigated the efficient use of cellulose to resolve the problem of the depletion of fossil resources. In this study, as the biomass material, the green composite based on natural rubber (NR) and the flake-shaped cellulose particles (FSCP) was produced. in order to further improvement of functional characteristics, epoxidized natural rubber (ENR) was also used instead of NR. The FSCP were produced by mechanical milling in a planetary ball mill with a grinding aid as a cellulose aggregation inhibitor. Moreover, talc and mica particles were used to compare with FSCP. NR and ENR was mixed with vulcanizing agents and then each filler was added to NR compound in an internal mixer. The vulcanizing agents are as follows: stearic acid, zinc oxide, sulfur, and vulcanization accelerator. The functionalities of the composites were evaluated by a vibration-damping experiment and a gas permeability experiment. As a result, we found that FSCP filler has effects similar to (or more than) inorganic filler in vibration-damping and O-2 barrier properties. And then, vibration-damping and O-2 barrier properties of the composite including FSCP was increased with use of ENR. in particular, we found that ENR-50 composite containing 50 phi FSCP has three times as high vibration-damping property as ENR-50 without FSCP.

Extensional flow has been taken notice as the more efficient solution for improving the dispersion of nanocomposites than shear flow. One of the production processes of nanocomposites is melt extrusion with co-rotating twin-screw extruder (TSE) which is superior in terms of productivity and mixing performance. Then, we focused on "Blister Disk" which had many small holes for generating the extensional flow. However, the influences on the mixing performance by changing the geometry of Blister Disk have not been investigated as far as we know. Therefore, the objective of this study is the optimization of Blister Disk geometry (e.g. hole numbers, hole diameter and disk length) for improving the dispersion of nanocomposites. Primary, the extensional flow state was investigated at the Blister Disk with FEM analysis. Secondly, to validate the simulation results experimentally, the polypropylene reinforced multi-walled carbon nanotube (PP/CNT nanocomposite) was used as the model of nanocomposite, and the dispersion state of CNT was investigated by morphological observation. As the result of these experiments, the better dispersion state of CNT was obtained as total permeation area and shorter hole length of Blister Disk was smaller because extensional and shear stress were increased.

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.

The addition of wood flour improves the mechanical properties of thermoplastics, but also increases the burning rate of neat plastics profoundly. To modify the flammability of wood-plastic composites (WPCs), various additive-type fire retardants such as ammonium polyphosphate (APP), melamine polyphosphate (MPP), and aluminum hydroxide were added to improve the fire performance of WPCs. Both UL94 flame tests and cone calorimetry were used to evaluate the fire performance of WPCs, and the results proved that the addition of 10 wt% APP lead to enhanced self-extinguishing properties. On the other hand, polypropylene with 30 wt% of APP did not achieve self-extinguish properties. The effective parameters in the cone calorimetry test to give self-extinguishing properties were discussed by comparing the results of the burning tests. It was presumed that the most important parameters for self-extinguishing of WPCs was an average heat release rate at initial stage of burning. The effect of fire retardants on the mechanical properties of WPCs was also investigated. The tensile strength and modulus of the composites decreased with the addition of fire retardants. (C) 2013 Elsevier Ltd. All rights reserved.

The purpose of this study is to develop automotive frictional parts, especially continuously variable transmission (CVT) blocks by using a composite material made of thermoplastics resin and fiber. CVT blocks are used at about 100°C under high pressure and friction condition. So, we have used nylon 9T, PA9T. PA9T has high a melting point that is higher than maximum temperature of the state of slip. To apply composite materials to CVT blocks, the material properties such as high strength, modulus of elasticity and fatigue strength are important. Therefore, a purpose of this study is improvements of mechanical properties by adding fillers to PA9T with various compounding and molding condition. PA9T and CF were mixed by using twin screw extruder. After compounding, dumbbell specimens were made by using injection molding machine. Bending, fatigue and abrasion tests were conducted. Moreover, we evaluated the transmission capacity of CVT belt made of PA9T composites and conducted slip test. According to results of tests, PA9T with CF38.8 vol% achieved desired values of CVT. The CVT belt has 40 Nm of torque under 2.0 kN of axle load. © 2014 WIT Press.

Elongation, toughness, and barrier properties of PLA are not sufficient to use for many applications such as food packing and films. But, elongation, toughness and gas barrier can be improved by addingnanoclay in the PLA. Now, the most used Melt-Compounding Method is the twin-screw extruder because of productivity and continuity. The processing conditions such as screw configurations and screw speed determine the dispersions state of nanoclay in the matrix: hence affect the mechanical and barrier properties of PLA/clay nanocomposites. We prepared nanocomposites using three types of screw configulations with various screw speed. Dispersion state of nanoclays in the PLA was evaluated by TEM observation and rheology tests. It was found the screw configurations with mixing and blister elements showed the best in dispersion of clay. Furthermore, elongation of PLA nanocomposites increased from 5% to 15% with improving the dispersion state of nanocomposites. We confirmed that the processing consitions of twin-screw extruder was important to enhance the properties of PLA/clay nanocomposites.

In recent years, the attempt to control mesostructure in metal is actively conducted to give various properties to metal. The purpose of this study is to investigate the influence of formability caused by the mesostructural difference. We performed hat-bending experiment on two sheets of Dual Phase steel with different mesostructure which are defined as the same grade, and measured springback angle. And we compared the scale of Bauschiger effect that affects springback angle under bending / unbending. Additionally to investigate the mechanism of the difference in Bauschinger effect, numerical analysis which was modelled to estimate the influence of the mesostructural difference was performed. As a result, it was found that insignificant different of dual-phase structure should be easy to cause the difference in the scale of Bauschinger effect. (C) 2014 Published by Elsevier Ltd.

Addition of wood flour improve the mechanical properties of thermoplastics, on the other hand it increases the burning speed of the materials. To modify the flammability of wood-plastic composites(WPC), various fire retardants, such as ammonium polysphosphate (APP), melamine polyphosphate (MPP) and aluminum hydroxide were added to WPCs. Burning tests based on UL94 and cone calorimetry were conducted to evaluate a fire performance of WPCs with fire retardants. The addition of fire retardants could lead to self-extinguishing materials when 10 wt% of APP was used. However, in the case of pure polypropylene, addition of 10 wt% of APP did not improve the flammability. Wood flour accelerates the burning behavior of PP, but it can reduce the use of APP to achieve self-extinguishing materials. Synergy effects between wood flour and APP was confirmed. Wood flour facilitates the forming of foamed char layer by APP during the combustion. This protective char surface can reduce the heat and oxygen diffusion toward the WPCs. The effect of fire retardants of mechanical properties of WPCs was also investigated. Tensile strength and modulus of composites decreased with addition of fire retardants. (C) 2014 Elsevier Ltd.

Injection molding of fiber-reinforced thermoplastics (FRTP) leads to fiber breakage and in turn deterioration of mechanical properties of the molded parts. In this paper, we propose an effective screw geometry for improving both fiber dispersion and residual fiber length. By evaluating four types of screws by investigation of the molded specimens, we found that the screw geometry in the compression zone had a dominant effect on the residual fiber length, and that choosing the proper geometry for the melting and mixing process was the most important factor for improving both fiber dispersion and residual fiber length. The screw improves both properties at the same time owing to the appropriateness of its geometry for both the melting and mixing zone. Our experimental observations were compared with the results of flow analysis and consistency was observed.

The mechanism of strain rate dependence on the Bauschinger effect in dualphase type high strength steel sheets is investigated and the influence of mesostructure differences on spring-back is estimated in this study. Compression-tensile tests at a strain rate from 0.007/s to 100/s is conducted. To differentiate between the multiphase structure-induced effect and the matrix properties, the same tests are also conducted for ferrite single phase steel. As a result, the Bauschinger effect on dual phase steel is not associated with the matrix properties independently. Moreover, it is revealed that a multiphase structure-induced effect acts a dominant function for deformation characteristics through experiments and micro observations. © 2014 WIT Press.

We investigated the efficient use of cellulose to resolve the problem of the depletion of fossil resources. In this study, as the biomass material, the green composite based on natural rubber (NR) and the flake-shaped cellulose particles (FSCP) was produced. The FSCP were produced by mechanical milling in a planetary ball mill with a grinding aid as a cellulose aggregation inhibitor. Moreover, talc and mica particles were used to compare with FSCP. NR was mixed with vulcanizing agents in an internal mixer. And then each filler was added to NR compound in an internal mixer. The vulcanizing agents are as follows: stearic acid, zinc oxide, sulfur, and vulcanization accelerator. The functionalities of the composites were evaluated by a vibration-damping experiment and a gas permeability experiment. As a result, we found that FSCP filler has effects similar to (or more than) inorganic filler in vibration-damping and O-2 barrier properties.

Short-carbon-fiber/polypropylene composites (CF/PP composites) have high processability and recyclability but low strength. To improve the strength, various nanofillers were hybridized to form fiber-reinforced composites. Adding nanofillers improves not only the strength but also the elastic modulus, with the exception of clay nanofillers. To understand the strengthening mechanism resulting from the addition of nanofillers, the residual fiber length and interfacial shear strength were measured. For CF/PP composites, the addition of alumina, silica, and CNT improves the interfacial shear strength, and thereby, the mechanical properties. On the basis of this result, proper choice of nanofiller type and content for improving the mechanical properties of PP/CF composites is discussed. (C) 2013 Elsevier Ltd. All rights reserved.

A bottle with a vacuum insulation structure is generally called a thermos bottle. It has a dual structure with inner and outer cylinders and a vacuum layer between them. The bottle with the structure maintains the heat and cold. It has been found useful for many years as a container that carries drinking water. Recently, the lightweight design of a vacuum bottle has been required to meet consumer demand. However, the bottle's wall collapses during the process of drawing a vacuum if the stiffness of the cylinder is not enough. To construct the design guide that can prevent the collapse of a double-structured bottle induced by the pressure difference, a numerical simulation was performed. The critical thickness tc, which is the thickness of the bottle when the bottle starts to deform under 1 atm, was defined. tc depends on the length and diameter of the bottle. The index to determine tc from the length and diameter of the bottle was suggested. To evaluate the validity of the analysis, vacuum bottles were prepared and experiments were conducted. The index we suggested showed good agreement with the experimental results. The shift of index within the increase of Young's modulus can be formulated. © 2013 WIT Press.

Carbon nanotubes (CNTs) were grown uniformity on the surface of carbon fibers to create hierarchical fibers by use of floating catalyst chemical vapor deposition. The tensile properties of CNTs grafted fibers were measured. The strength of grafted fibers decreased approximately 12% compared to raw carbon fibers in this process. A fiber pull-out test revealed that the interfacial shear strength (IFSS) in polypropylene composites improved by 35% by grafting CNTs onto carbon fibers. It indicates the use of hierarchical fibers in thermoplastic composites is effective due to the improvement of IFSS by mechanical interlocking between CNTs and the matrix. The CNT/fiber joint strength is the most critical property, and the experimental observations also revealed that the joint fracture was the major failure mode. © 2013 WIT Press.

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

In recent years, polymer nanocomposite that is composed of polymer and nano scale filler is getting much attention. The clay, which is a layer compound, is mainly used as filler. One of the most common mixing methods is melt-compounding. A twin-screw extruder is usually used to compound the melted polymer and clay. However, it is difficult to discuss the effective compounding method for exfoliation and dispersion of clay in the polymer because shear stress and flow direction around screws are extremely complex. Therefore, physical factors of clay exfoliation have been not known. From the above reason, the purposes of this research are to clarify the factors for making clay exfoliated to a single layer and to acquire the guideline for optimizing mixing conditions using high speed flow in narrow tube that can give simple high shear stress to the resin. TEM observation and rheological analysis were conducted to quantify the exfoliation state of clay. It was verified that the specific energy was the most important parameter for the exfoliation of clay platelet. © 2013 The Japan Society of Mechanical Engineers.

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.

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.

The forming of thin-walled aluminium housing by impact backward extrusion process was conducted, and the influence of metal microstructure on its formability was investigated. Aluminium alloys of A3003, AC4CH-F and semi-solid state of AC4CH were used as test materials. Additionally, ultrafine-grained metal were fabricated by Equal-Channel Angular Pressing method using a die having channel, φ=90°, Ψ=15 °, from semi-solid AC4CH alloy. And then, cylindrical housings with 9.4mm in diameter and 0.5mm in thickness were formed from as-cast materials and ECAPed samples by impact backward extrusion at room temperature. As a result, press load required for extrusion was decreased using a material processed with increasing the number of ECAP. Vickers hardness of the products was greater than that of the materials before the forming; in the case of using ECAPed materials, the increment was relatively small. This implies that impact extrusion process is a kind of Severe Plastic Deformation that improves mechanical properties of metal materials. Ultrafine-grained semi-solid AC4CH alloy have more possibility to make the housings with further thin thickness than non-ECAP materials.

Various kinds of nanofillers were added to improve the mechanical performance of carbon fiber/polypropylene composites. Nanofillers were well dispersed by a twin-screw extruder. The pellets including nanofiller were compounded with carbon fiber in the same condition. The addition of nanofiller significantly affects the modulus and strength of composites. It was found that the effects of nanofillers for the performance of composites depend on the filler species and filler content. Optimum filler content was found around 1 wt%.

In this paper the indicators that are necessary for the optimal design of stainless steel vacuum insulation bottles are considerd. For the strength of the bottle, the critical strength of the outer cylinder depends on the shape parameters (the ratios between the height and diameter, and the diameter and thickness of the bottle). It was found that the relationship between the critical strength and the shape parameters is useful for the design of the outer cylinder. We prove this result by conducting experiments with three kinds of bottles. © Civil-Comp Press, 2012.

The continuous ECAP process which can provide three-dimensional strain was developed in this study. A die with tri-axis crossed channels having channel angle φ of 90° and curvature ψ of 0° was created. As a result, continuous ECAP process via route Bc for AC4CH aluminium semi-solid alloy could be performed at 573K at pressing speed of 0.5mm/sec using the developed die. The continuous method cut the processing time in half compared to the non-continuously conventional method. The grains became fine from 100μm to approximately 2μm. Workpiece processed 8 passes exhibited four times higher toughness than as-cast alloy. © 2012 WIT Press.

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.

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

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

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&#039;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. © 2011 The Japan Society of Mechanical Engineers.

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.

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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

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

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.

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.

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

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