Recently, the study of new foamed plastics using supercritical fluid/ gas as blowing agent has devaloped rapidly and its achivements have become a center of attraction. Foamed plastics are used in various wide fields having effective characterization as materials reduction, light-weight, hight-adiabator and so on. But conventional foamed plastics have a serious problem that the strength decreases extremely owing to voids as a defect. In order to correct the defect, the development of a new processing technology using supercritical fluid/ gas as a blowing agent for foamed plastics, which is called to microcellular plastics arise in USA. In this paper, the present situation and development of this new formed plastics introduced.

抄録全体を表示

A monotonic tensile test and a loading-unloading test are performed to investigate matrix crack initiation and growth in CFRP angle-ply laminates. A material used is T300/2500 carbon/epoxy system. Laminate configuration is［±45]s. During the tests, the polished edge surface of the specimens are examined by using the replica technique. The matrix densities in ＋45°and －45°plies are measured as a function of the laminate strain. To discuss the experimental resutls, the shear-lag analysis is used to obtain the stress fields in angle-ply laminates with matrix cracks. The Young's modulus reduction and change in Poisson's ratio due to matrix cracking is predicted and compared with the experimental results.

抄録全体を表示

Since change of compliance as increasing crack length under mode Ⅱ loading is much smaller than that under mode Ⅰ loading, mode Ⅱ delamination fatigue crack propagation behavior near the threshold of FRP laminates had not been investigated until several studies was reported in recent years. In this paper, the test method of mode Ⅱ delamination fatigue was established using end notched flexure specimens. Loading apparatus and computer software were developed in order to determine the threshold. New equation for the relation between compliance and crack length was proposed, where parameters are independent of specimen thickness. Compliance value under fatigue loading was smaller than that under static loading because of the viscoelasticity of the matrix resin and the friction between the crack surfaces over the support of the loading apparatus. These results show the necessity to obtain the relation between compliance and crack length during fatigue test. Since crack propagation rate under mode Ⅱ loading was independent of crack growth in maximum energy release rate-constant test, maximum energy release rate-decreasing test also can be carried out to obtain the conservative fatigue crack growth behavior. Test results gave the sufficiently low crack propagation rate to obtain the fatigue threshold.

抄録全体を表示

A simple method for evaluating the effect of fiber bridging on the stress field in the vicinity of a crack tip in Double Cantilever Beam (DCB) specimen of unidirectional fiber reinforced composite was proposed. In this method, each bridging fiber was approximated by a beam, and the force and moment acting on the fiber was calculated using conventional beam theory. Stress intensity factor at the crack tip was evaluated by means of the finite element method taking into account the axial force and bending moment carried by the bridging fibers. The analysis was carried out for several types of bridgings. Results of the analysis showed that shorter fiber and/or the fiber situated more behind the crack tip reduced the stress intensity factor much, because those fibers were thought to be subjected to large displacement and brought about large force in crack closing direction. Moreover, when bundled fibers bridged the crack, i.e., when the bridging fibers were connected and deformed as one composite beam, reduction in stress intensity factor was striking. This shows that bundling of bridging fibers plays an important role in stress shielding.

抄録全体を表示

Recently, applications of integrated large composite structures have been attempted to many structures of vehicles. In order to improve the cost performance and reliability, it is necessary to judge the structural integrity of the composite structures. Fracture simulation techniques using the finite element method have been developed for the purpose. Since iteration of finite element analysis is indispensable in the process of fracture simulation, the simulation techniques consume many memory resources and much of calculation time. A local area network with several personal computers can be utilized as a parallel computing system because of rapid development of personal computer architecture and network system. In this study, we developed a fracture simulation system with lower cost and faster calculation ability using the parallel computing system called a PC cluster. Several simulations with different calculation conditions were conducted to confirm the efficiency of the proposed simulation system. As a result, it is shown that the fracture simulation is suitable for the parallel computing system and can be accelerated inexpensively using the PC cluster.

抄録全体を表示

This paper discussed a nonlinear compressive behavior of CFRP laminated plates with a hole under an uniaxial compression. Experimental results were obtained from the compressive response of CFRP laminates with a hole and three laminated plates including two kinds of hole diameter were choosed as a specimen. In the analysis, the nonlinear behaviors of CFRP laminated plates with a hole were excuted by an increament displacement method in FEM. Both experimental and analytical results for the buckilng load and nonlinear behaviors after buckling were compared with each other and a good agreement was obtained. In addition to these, a failure prediction by using maximum stress criterion was also discussed.

抄録全体を表示

Fracture and impact properties for various long fibers such as glass fiber and organic fibers (Aramid and Polyvinyl alchol fiber) reinforced polypropylenes were investigated. Chopped glass fibers in various lengths were also used in order to investigate in the influence of fiber length on the properties. Surface treatment by different kinds of silane coupling agents with different concentrations was performed on glass fiber. Reinforcement fiber and polypropylene fiber mixed mats were prepared by a mixing machine which is called “Fiber separating/flying machine” and then compression molded. Fracture and impact properties were evaluated by Izod impact, high rate impact and fracture toughness, and the results were compared with those of short glass fiber reinforced polypropylenes. It was found that impact properties increase with volume fraction of reinforcement fibers although these improvement rates were different with reinforcement fibers, and that the impact properties of glass fiber reinforced polypropylenes were significantly improved by surface treatment of fibers. Correlation between Izod impact strength and fracture surface was observed clearly. Fracture toughness of glass fiber filled systems showed the peak at a critical volume fraction of fiber, but that of organic fiber filled systems increased linearly with volume fraction of fiber.

抄録全体を表示

Increased use of Carbon/Carbon (C/C）composites has necessitated forming complex structures, which require high temperature secondary bonding. Secondary bonding of C/C interfaces provides design flexibility and also alleviates complicated fabrication problems. In this study, secondary bonding of C/C composites was studied by use of reaction-formed SiC process and resin-carbonization process. In the reaction-formed SiC process, Si powders set between C/C plates were heated to form SiC adhesive layer by liquid silicon-carbon reaction. On the other hand in the resin-carbonization process, C/C plates were at first bonded by resin. The resin bonded C/C composites were then heat-treated to carbonize the resin. Finally bonding strength were measured by a plunger method which was specially designed shear loading method.

抄録全体を表示

This paper concerns the determination of time and temperature dependent tensile strength in the longitudinal direction of unidirectional carbon fiber reinforced plastics (CFRP). Applying the strand-testing method with the newly-devised temperature chamber and grip ends to carbon fibers/epoxy composite strands (CF/Ep strand; T400/828), the tensile strengths under constant strain-rate (CSR）and fatigue loadings were measured at various loading-rates and temperatures. Same strengths were measured also by the conventional split-disk method, in which carbon fibers/epoxy composite rings (CF/Ep ring）were used as the specimens. Similarities and differences between the two results, one by the proposed method and another by the split-disk method, are discussed. Our proposed strand-testing method is excellent for the determination of tensile strength in the longitudinal direction of unidirectional CFRP because of its small size of the apparatus and unidirectional state of stress for the entire specimen except the grip region. Furthermore, the tensile CSR strengths under various loading rates and temperatures for four types of CF/Ep strand (T400/828, T800/828, M40J/828, and XN40/25SX）are determined by this strand testing method. It is confirmed that the time and temperature dependence on tensile strength for all of four types of CF/Ep strand is controlled by the viscoelastic behavior of corresponding matrix resin. However, the time and temperature dependence on these tensile strengths differ with the type of carbon fiber.

抄録全体を表示

It is important to reduce the residual stresses induced in a molded polymeric solid during the curing and cooling processes with heat treatment. The authors investigate the variation of volume shrinkage, gel temperature, gelling time and stresses around interfaces between resin and other inserted material over the whole process involving the phase change of resin from liquid to solid under various cure conditions. Then, the influence of several factors mentioned above on internal residual stress is discussed. Also, the time-and temperature-dependent mechanical properties of resins cured under different conditions are investigated. To evaluate stresses around the interface between resin and insert, the photoviscoelastic technique is employed. Consequently, it is shown that the shorter gelling time becomes the larger amount of volume shrinkage and high internal residual stress are generated. Therefore, as one of the methods to reduce the internal residual stress during curing process, it is pointed out that gelling time should be lengthened.

抄録全体を表示

Illumination using light guide is isolated light source from luminescent part. Therefore the system shows easy maintenance and electrical insulating characteristics. However commercial light guide, glass or plastic optical bundle, have some problems, e.g. rigid, heavy weight, expensive or low heat -resistance. Then, a large diameter single core plastic light guide, is suitable for Illumination, has been developed. The light guide consist silicone rubber core and fluoro elastomer cladding. The core diameter is very large, 4-20mm, and the flexibility of light guide is excellent. And it shows not only good light transmission<0.2dB/m at 660nm but also high heat-resistance 130℃ 1000hrs after excess loss<0.2dB/m and side luminescent characteristics.

抄録全体を表示

The authors discuss the validity of the results obtained experimental and numerical analyses for the viscoelastic boundary value problem under a typical type of non-proportional loading condition. A rectangular viscoelastic strip plate made of epoxy resin is loaded by a cylindrical hard roller moving along the upper straight edge. A convenient computer image processing aided photoviscoelastic method is applied to investigate the time dependent principal stress/strain difference and principal directions of stress/strain around a contact region. On the other hand, a finite element method-FEM -is attempted to analyze the viscoelastic stress and strain under several conditions. The time variations of photoviscoelastic fringe pattern are compared with the contour bands of principal stress/strain differences qualitatively, and the time variations of principal stress/strain differences and directions of principal stress/strain under non-proportional condition, are evaluated at which the material shows remarkable viscoelastic and rubber-like behavior.

抄録全体を表示