The effect of the transverse crack on the ultimate tensile strength (UTS) for carbon fiber reinforced plastic (CFRP) cross-ply laminates was studied experimentally and analytically. For various stacking sequences of CFRP composites, quasi-static tensile tests were carried out. And the fiber bundle strength of 0-degree ply was almost constant. Therefore, it was concluded that there was little notch sensibility in spite of the existence of transverse cracks. A new numerical model based on the finite element method was proposed to investigate the inner micro damage process. In the model the elastoplastic relation of epoxy matrix was considered effectively and the progress of the inner fiber breakage was obtained. Then, using this model, we conducted the simulation based on the Monte-Carlo method. Based on the analysis results of the proposed model, it was shown that the plastic regions at the tip of transverse crack reduce the concentration of stress, and the bundle strength was not affected by the existence of transverse cracks.

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The present study examines the in-plane and out-of-plane shear moduli of an orthogonal 3-D woven SiC fiber/SiC matrix composite. A prismatic composite bar of rectangular cross section was subjected by a small torsional moment, and the torsional rigidity was measured by an optical method. Conventional Lekhnitskii's equations for orthotropic materials subjected by torsion were applied to estimate the shear moduli from the torsional rigidities obtained from the specimens with different cross sections. The estimated in-plane shear modulus agreed with the modulus measured by ±45°off-axis tensile testing. The effect of 0°tensile loading on the shear stiffness degradation was also investigated by the repeated torsion tests after step-wise tensile loading. As a result, it was revealed that both in-plane and out-of-plane shear moduli were reduced by more than 50% of the initial values due to 0°tensile load. Finite element analyses (FEA) based on the homogenization method were conducted in order to evaluate the shear moduli estimated by the torsion tests. By optimizing the void fraction between fiber bundles, the numerical results by FEA were in good agreement to the experimental results.

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The compositional dependence of thermal expansion coefficient of in-situ Al-Si composites has been measured. The thermal expansion coefficient of the Al-Si composites linearly decreases as the volume percent of precipitated Si decreases, almost equal to the rule of mixture. Based on this measurement, a numerical calculation has been carried out on the thermal stress distribution in a centrifugally cast Al-Si thick wall tube, in which the content of the Si precipitates gradually changes in the radial direction. The calculation was made under the condition that temperature decreases linearly along the tube thickness from the inner to the outer wall, while the thermal expansion coefficient and the elastic constant vary linearly towards the outer wall because of the decrease of the Si precipitates. The results are as follows: 1) In the range from the inner to the middle part of the wall thickness, the tangential and axial stresses are more relaxed than that with an assumption of the thermal expansion coefficient to be constant, whereas in the middle to the outer range, the thermal stress relaxation is indiscernible. 2) The biggest relaxation of the radial thermal stress would be at the middle part. 3) If the above through-thickness distributions of temperature and/or Si concentration are inverted, the thermal stress relaxation prevails throughout the wall thickness.

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