Reliability Prediction for Fatigue Damage and Residual Life in Composites

The static and fatigue properties and the failure mechanisms of unnotched and notched CFR composite laminates with different lay-ups to optimize the stacking sequence effect are experimentally investigated, and it is seen that the process of composites fatigue damage under the compression cycles loading appears two different stages. The results of this study provide an insight into fatigue damage development in composites and constitute a fundamental basis for the development of residual strength model. Two new practical fatigue-driven models based on controlling fatigue stress and strain with four parameters are derived to evaluate fatigue residual strength easily and expediently from the small sample test data using the new formulae. A dual fatigue cumulative damage rule to predict fatigue damage formation and propagation of notched composites is presented according to the traditional phenomenological fatigue methodology and a modern continuum damage mechanics theory. Then a three-dimensional damage constitutive equation for anisotropic composites is established. A new damage evolution equation and a damage propagation σ a − σ m − N * surface is derived based on damage strain energy release rate criterion.