A Stiffness Degradation Based Fatigue Damage Model for FRP Composites of (0/θ) Laminate Systems

The present study develops a stiffness reduction—based model to characterize fatigue damage in unidirectional 0˚ and θ° plies and (0/θ) laminates of fiber-reinforced polymer (FRP) composites. The proposed damage model was constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional composite laminates as the number of cycles progresses. The proposed model enabled damage assessment of FRP (0/θ) composite laminates by integrating the fatigue damage values of 0˚ and θ° plies. A weighting factor η was introduced to partition the efficiency of load carrying plies of 0° and θ° in the (0/θ) composite lamina. The fatigue damage curves of unidirectional FRP composite samples with off-axis angles of 0˚, 30˚, 45˚, and 90˚ and composite laminate systems of (0˚/30˚), (0˚/45˚) and (0˚/90˚) predicted based on the proposed damage model were found in good agreement with experimental data reported at various cyclic stress levels and stress ratios in the literature.