An experimental program was initiated to investigate the effect of angle-ply orientations on the compressive strength (X1C) of 0 deg plies in fiber-reinforced composite laminates. Graphite fiber-reinforced epoxy test coupons with the generic architecture 0(SUB 2)/+/- THETA (where theta varied between 0 deg and 90 deg) and for the quasi-isotropic architecture were evaluated. The effective compressive strength of the 0 deg plies varied considerably. The results were related to the Poisson's ratios of the laminates, with high Poisson's ratios leading to high transverse tensile strains in the test coupons and lower-than expected strengths. Specimens with the 0(SUB 2)/+/- 30 architecture had both the highest Poisson's ratio and the lowest calculated ply-level compression strength for the 0 deg plies. This work has implications in the selection of composite failure criteria for compression performance, design of test coupons for acceptance testing and the selection of laminate architectures for optimum combinations of compressive and shear behavior. Two commonly used composite failure criteria, the maximum stress and the Tsai-Wu, predict significantly different laminate strengths depending on the Poisson's ratio of the laminate. This implies that the biaxial stress state in the laminate needs to be carefully considered before backing out unidirectional properties.
展开▼
