Progressive Fatigue Damage Modeling of Laminated Polymer Composites Under Cyclic Stress at Elevated Temperatures Using a Novel Equivalent Cycle Number Approach

The progressive fatigue damage (PFD) model effectively simulates the fatigue behavior of laminated composites under multiaxial cyclic stress. This model employs the generalized material property degradation (GMD) technique to calculate the residual properties of unidirectional (UD) plies subjected to cyclic stress. The present study enhances the PFD model to simulate the fatigue behavior of polymer matrix composite (PMC) materials under cyclic stress at various temperatures by executing it at a single temperature. The equivalent cycle time (ECT) method evaluates property changes in PMCs across different temperature settings, utilizing data from isothermal loading. In the present study, a novel approach based on the ECT concept, termed equivalent cycle number (ECN), is developed and integrated into the GMD technique. Additionally, a combined fatigue life model is employed to improve the predictive capability of the PFD model. This model is constructed by evaluating the results of three commonly used fatigue life models in predicting the fatigue life of UD plies under uniaxial cyclic stress at both room and elevated temperatures. The proposed PFD model effectively predicts the residual properties and fatigue life of a PMC subjected to multiaxial cyclic stress at two distinct temperatures. The findings demonstrate that the ECN method significantly reduces the model's computing load while maintaining a high level of predictive capability compared to available experimental data. Furthermore, the results indicate that using the combined fatigue life model substantially enhances the predictive capability of the PFD model.