EFFECT OF CURING STRESSES ON THE BEHAVIOR OF FIBER REINFORCED PLASTIC COMPOSITES UNDER BIAXIAL LOADING

Residual stresses are induced in fibre reinforced plastic (FRP) composites during fabrication and environmental exposure. The curing residual stresses induced during fabrication are mainly due to the thermal expansion mismatch of the constituents. The residual stresses can be either microresidual or macroresidual stresses. Macroresidual stresses in 0-degree plies and 90-degrees plies of [90/0]s symmetric cross-ply laminates are calculated starting with ply elastic and thermal properties for different material systems. The calculated curing stresses in Kevlar49/Epoxy unidirectional tape plies in the transverse direction are more than the transverse strength of the corresponding ply. First ply failure (FPF) envelopes are plotted using classical lamination theory and Tsai-Wu quadratic failure theory with and without considering the curing residual stresses. There is a significant effect of residual stresses on the FPF envelopes.