This review is mainly concerned with the computer aided designing with composite materials. The history of research and development of composite materials is similar to that of computers in the fact that both were born about 45 years ago, have grown up rapidly along with the development of space technology in 1960's and now are being among government projects. It is no exaggeration to say that the high technology of computers has spurred the growth of composites technology. Especially in recent micro-or personal computers are greatly utilized in various fields of research on composite mateials such as in stress analysis, designing, data processing, laboratory automation in materials testing and molding or manufacturing processes. Composite materials can be characterized as what we call tailored materials. This implies the possibility of designing in a well-balance state between considerations of manufacturing and cost, and the requirement for stiffness and strength. In order to realize this, our attention is now being paid to the establishment of the optimum materials designing method using the laminated plate theory as well as the optimum design technique of structural systems. This problem leads to the construction of computer aided design or computer aided engineering system and the ultimate object will be the completion of the micro-computer expert system for the research and development of composite materials.

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Polymeric materials can be essentially characterized from the view points of molecular structure, morphology of molecular chains and surface structure. The methods for carrying out the characterization on molecular structure and surface one are reviewed in this paper. Two factors, molecular weight and its distribution, at least must be taken into account in the case of homopolymers, which have the most simple molecular structure among all polymers. Molecular weights are directly obtained by osmometry with semi-permeable membrane, vapour pressure osmometry and light scattering. These methods are applicable for almost all thermoplastic polymers in these days. Gel permeation chromatography (GPC) is a very useful method for determining molecular weight distribution. The idea of universal calibration presented by Benoit et al. is very significant in the practical use of GPC. The usability of this idea for various polymers is discussed in detail. In the case of copolymers, characterization of molecular structure becomes markedly complicated compared with that of homopolymers because of the introduction of comonomer into molecular chain. Average and distribution factors on comonomer content and sequence length must be taken into account as well as molecular weight. Compositional distribution is especially focused in this paper. The characterization of ethylene/propylene copolymers is mainly discussed as an example. It is already known that mechanical properties, such as tensile strength and impact strength, can be empirically related to molecular structure. Some examples are shown, i. e., relationships between molecular weight and tensile strength, impact strength or glass transition temperature. The methods on surface analyses of polymers have considerably advanced in the last decade. Electron microscopy, especially electron probe for microanalysis (EPMA), is very common among most research laboratories in polymer industries. Electron spectroscopy for chemical analysis (ESCA) is also useful in the study related to adhesion and composites. We can detect and determine directly organic groups present on the surface to around 40A in depth. Infrared and laser laman spectroscopy are also useful for detecting organic groups on surface. Unfortunately, the application of the latter one to polymers is not yet sufficient at this stage. However, this method will play a very important role to make clear the properties of composites in near future.

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As Reinforced Reaction Injection Molding (R-RIM) Polyurethane has an excellent impact resistant properties, this material has been used for components in motorcars, and so the studies on fracture characteristics under impact loadings are needed. The aim of this work was to clarify the effects of void, fiber content and impact velocity on the dynamic fracture toughness. The dynamic fracture toughness values decreased with an increase in void content, and took a minimum value at 5% of fiber weight content and increased again with fiber content for impact velocity from 1.4 to 5.1m/s. It was found that the values increased with an increase of impact veiocity and the stable crack extension appeared during impact. Therefore, it is concluded that the dynamic fracture toughness values corrected by the stable crack extension are almost constant in this impact velocity range, but that the dynamic fracture toughness values at impact speed of 5.1m/s are higher than the static equivalent fracture toughness values at displacement speed of 1mm/min.

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In this paper, investigations were made on the roles of fibers to the fracture behavior of the fiber reinforced plastics (FRP), which are widely known as one of the “Tailored Materials”, with special attentions of crack generation and its growth closely related to the fracture toughness value. As the results, it was found that the fracture behaviors of FRP are affected by not only the fiber volume fraction but also the dispersed state of fibers in the matrix resin, and also that scatters of the fracture strength are fundamentally attributable to the latter.

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The transient thermal stresses and strains in epoxy strips with a circular hole subjected to rapid cooling from both sides were analyzed by the phtoviscoelastic technique. The results indicated the concentrations of thermal stresses and strains clearly as characteristic of a thermoviscoelastic body. Specifically, high birefrigence concentration was observed at the edge of the circular hole immediately after rapid cooling. However, low thermal stresses and high compressive strain concentrations at the edge were found from the measurements of the birefringence and the temperature. When the whole specimen attained the cooling water temperature after an extended period of time, the high tensile stress and high compressive strain concentrations were observed in spite of the disappearance of the birefringence at the edge of the hole in the strip.

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This paper presents the theoretical and experimental method of finding the residual stress in an epoxy plate subjected to rapid cooling on both surfaces. The theoretical residual stress distributions in a plate are calculated by using the fundamental equations based on the linear-viscoelastic theory. The specimens in the experiment are subjected to rapid cooling, and the residual stresses are measured by the layer removal method. The theoretical and experimental results are compared and discussed.

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It is well-known that there is coupling between extension and twisting when tensile forces are applied to two-layered angle-ply laminates. The characteristics are due to anisotropy of the laminates. In the present paper the coupling phenomena are analyzed and the direction of twisting is shown to be either plus or minus depending on the material properties and the fiber directions. The fiber directions which give zero twisting under tensile forces are obtained rigorously.

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The effect of bending and torsional stresses on the fracture characteristics of thin-walled square and rectangular box beams has investigated under static and impact loadings by use of the apparatus capable of applying bending and torsional moments in various proportions. The thin-walled box beams were fabricated from glass-fiber strand, chopped strand mat and unsaturated polyester resin. Comparisons between experimentally determined strength and theoretical predictions using the failure criteria are presented. As a result of this investigation, the existence of the relation between the fracture mode and the strength was recognized and the failure criteria examined could be used successfully to predict the combined impact bending and torsional strength of thin-walled box beams.

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The static tensile and flexural strengths of C/A hybrid Unidirectional reinforced FRP laminates of which the volume ratio of CFRP to AFRP is 50% to 50% were measured. The effects of formation of laminates on these strengths were discussed. As the results, it was found that (1) C/A hybrid FRP has an equivalent tensile strength of the CFRP and an equivalent failure strain of the AFRP in case that the thickness of one layer is thin. (2) The flexural behaviors of C/A hybrid FRP are influenced significantly by the formation of laminates. Concretely, the knee points apear in case that the surface layer is AFRP and the formation of laminates which maximizes the flexural strength exists.

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