Fatigue Residual Stiffness Degradation of CFRP Laminates: A Probabilistic Model Considering Stress Level and Constraint Effect

ABSTRACT Carbon fiber–reinforced polymer (CFRP) is extensively used in aerospace, transportation, and wind energy structures, where fatigue durability plays a critical role in structural performance. However, the fatigue stiffness of CFRP laminates exhibits significant dispersion due to complex damage mechanisms and inter‐ply interactions. To address this issue, a probabilistic model is developed in this study to describe the fatigue residual stiffness degradation of CFRP laminates by considering both the stress level and the constraint effect among plies. The proposed model is based on a two‐stage semi‐empirical formulation that incorporates stress‐dependent and constraint parameters to capture nonlinear stiffness degradation behavior. Furthermore, the probabilistic distribution of residual stiffness and its dispersion evolution are established through experimental data obtained from laminates with different layup configurations and stress levels. The model provides a unified framework for describing the stochastic degradation process and evaluating fatigue reliability of CFRP laminates, offering a reference for the design and life prediction of composite structures.