Effect of residual-stress evolution during curing process on fatigue-life of fiber-reinforced polymers

The fabrication process of Fiber-reinforced polymer (FRP) composite leads to the formation of residual stresses. The effect of these stresses may be insignificant on the monotonous properties like tensile strength etc. However, residual stresses can significantly affect the fatigue performance of the FRP composites. There is lack of rigorous analysis on connecting the evolution of residual stress and the fatigue life of FRPs. A multi-physics analysis was performed to model the evolution of residual stresses in the curing process under different process and material conditions for unidirectional Glass Fiber Reinforced Polymers. The viscoelastic model also accounted for percolation in the matrix and thus gave realistic estimates of residualstress compared to the past elastic models. It was found that the residual-stress varied by over 25% by just changing the cure thermal cycle. The stress prediction results were found to be in-line with the experimental results reported in the literature. A numerical model was developed to obtain a change in the fatigue life (fiber-dominated failure mode in High Cycle fatigue (HCF)) from residual stresses under the simulated circumstances. This numerical model was validated with the experimental fatigue data using two different cure cycles. Fatigue life for HCF was found to be improved by upto 4% under such conditions. Thus, this study gives insight on various processes and material property handles for manipulation of the residual stresses. Accurate numerical prediction of such stresses can be cardinal in composites processing.