The present paper describes a proposal of the modified global response surface method using the lamination parameters to solve the problem of how to create zoomed response surfaces. A new low-cost rule for optimality is also proposed in this study. The new optimality is effective for the search-all method for thin laminated composite structures. The new method is applied to stacking sequence optimizations of the hat-type stiffened composite laminates for maximizations of buckling load. FEM analyses are conducted to create global response surfaces and the optimal stacking sequence is obtained by using this method. As a result, the new method successfully obtained the real optimal stacking sequences.

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In the processes of liquid molding of fiber composites, such as resin transfer molding, fabrics are often formed in deep drawing, which gives rise to large shear deformation. In this paper, we simulate the fabric shaping process using the commercially available FEM program, LS-DYNA, in order to predict the properties of the resulting fiber composites. Plain woven fabric and power-net are modeled using beam and spring elements, which simulate yarn tensile property and fabric bending and shearing property, respectively. Inter-yarn sliding and yarn waviness are neglected. Coulomb law is applied on contact surfaces. The numerical results on yarn deformation are in good agreement with experiments. The deep drawing processes of plain woven fabrics and power-nets have been examined. The good formability of power-net structure has been confirmed numerically.

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Hygroscopicities of plain woven glass cloth and carbon glass cloth reinforced polyamide-6 composites were examined at 80°C. The moisture contents of the composites increased monotonically up to the peek values and then decreased as time increased. This kind of time dependency presumably be related to the crystallization of the matrix, polyamide-6. The mode II interlaminar fracture toughnesses of those composites were also measured at a static and an impact loading rate. The toughnesses were degraded due to the moisture absorption. Scanning electron microscopy exhibited that for both composites, failure was induced at the fiber/matrix interface. This interfacial deterioration is considered to be the primary cause for the degradation of the mode II Interlaminar fracture toughness.

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The damage progression in orthogonal 3-D fabric reinforced Si-Ti-C-O fiber/Si-Ti-C-O ceramic matrix composites (NUSK-CMC) was studied. In-situ measurement of microcrack was conducted by replica observation during loading-unloading tensile test. Effects of microcracks in longitudinal and transverse bundles upon macroscopic inelastic stress-strain behavior were analyzed in detail. Using a simple mechanical model for three-dimensional composites, stress distribution of longitudinal bundles was evaluated from the stiffness change associated with an established theory for matrix crack effects in the transverse bundles. In longitudinal bundles, the nonlinear behavior were calculated from unidirectional mechanical model considering matrix crack, interface debond and fiber fracture, and the fiber-matrix interface parameters were determined from hysteresis measurements and matrix crack density in the bundles. Inelastic stress-strain behavior for this NUSK-CMC was simulated.

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