MICROMECHANICS ANALYSIS OF SPACE SIMULATED THERMAL-STRESSES IN COMPOSITES .2. MULTIDIRECTIONAL LAMINATES AND FAILURE PREDICTIONS

A finite element micromechanics approach was used to predict thermally induced stresses in fiber reinforced polymer matrix composites at temperatures typical of spacecraft operating environments. The influence of laminate orientation was investigated with a simple global/local formulation. Thermal stress calculations were used to predict probable damage initiation locations, and the results were compared to experimentally observed damage in several epoxy matrix composites. Multidirectional [0(2)/ +/- theta]s laminates had larger predicted matrix stresses than unidirectional [0] laminates. The stresses increased with increasing lamination angle-theta, and resulted in large tensile radial stresses at the fiber/matrix interface, that were not present in unidirectional laminates. Thermally induced matrix failure predictions, using a failure criterion based on the maximum radial interfacial stress and the ultimate radial interfacial strength, were in excellent agreement with experimental data. This criterion was able to accurately account for the influence of both laminate configuration and constituent properties. Predictions based on the bulk matrix tensile strength or on lamina stresses (computed from laminated plate theory) and strengths were in poor agreement with experimental data.