An interlaminar-shear-stress analysis was developed for deformation and progressive damage in biaxially-loaded bidirectional three-layer composite laminates. The special cases of a crossply laminate under biaxial normal loading and shear loading discussed previously were combined (Tsai and Daniel, 1992a, b, Int. J. Solids Structures (submitted); Tsai et al., 1990, in Microcracking-induced Damage in Composites (Edited by G. J. Dvorak and D. C. Lagoudas), AMD-Vol. 111, MD-Vol. 22. ASME, New York). The model gives closed-form solutions for stress distributions, crack densities and reduced stiffness of the damaged layers and the laminate. The model was partially verified by conducting off-axis uniaxial tensile tests of [ 0 902]s crossply laminates. The stress-strain behavior, matrix cracking and the variation of engineering constants with matrix cracking were predicted and verified experimentally.
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