一方向繊維強化複合材料の破壊強度

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Failure strengths of unidirectional composites are theoretically obtained based on several basic assumptions and strengths of the constituents and the fiber-matrix interface. The following three additional assumptions are introduced. Probabilistic nature of failure phenomena is ignored. Macroscopic failure occurs when one of stress levels in composites reaches a certain semimicroscopic failure criterion. Failure strengths are averaged as for θ, which is a projection angle of the loading direction in the transverse plane. As the first step, thermal residual stress state is calculated using temperature dependent matrix properties. Next, an external loading in an arbitrary direction is resolved into basic loadings in the xyz-coordinate. After solutions for the basic loads and thermal residual stresses are superposed, macroscopic failure strengths are determined. Numerical calculations are carried out for a CFRP with four kinds of criteria in matrix. It is shown that the closest results to TSAI-WU theory for the minimum F12 is obtained based on maximum principal stress criterion in matrix. Thermal residual stresses do not have important effects on strengths if an interface normal strength is large. It is also shown that there are no significant differences between the results on the hexagonal and square models. A possibility of evaluation of strength theories by combinating these results and proper experiments is suggested.