Thermally Induced Stresses in Laminated Fiber Composites

Abstract

In fiber laminated composites, thermally induced interlayer stresses arise from the thermal expansion mismatch between individual layers and the laminated composite as a whole. In this work, elasticity theory was applied to calculate these stresses based on equilibrium considerations. The effect of various parameters on the magnitude of these stresses was examined. Using a constant strain failure criterion it was shown that an increase in ply transverse modulus improves the thermal shock resistance of the laminate. Experiments were performed to investigate the effect of thermal cycling on graphite-epoxy laminates. The composites were examined microscopically and their thermal expansion behavior determined before and after thermal cycling. Thermal stresses induced by cycling caused transverse cracking and delamination. The extent of such damage is greater for the wider cycling range and is strongly influenced by structural imperfections.