Damage Assessment of CFRP [90/±45/0] Composite Laminates over Fatigue Cycles

The present paper develops a stiffness-based model to characterize the progressive fatigue damage in quasi-isotropic carbon fiber reinforced polymer (CFRP) [90/+/- 45/0] composite laminates with various stacking sequences. The damage model is 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 plies of 90A degrees, 0A degrees and angle-ply laminates of +/- 45A degrees as the number of cycles progresses. The proposed model accumulates damages of constituent plies constructing [90/+/- 45/0] laminates by means of weighting factor eta (90), eta (0) and eta (45). These weighting factors were defined based on the damage progress over fatigue cycles within the plies 90A degrees, 0A degrees and +/- 45A degrees of the composite laminates. Damage model has been verified using CFRP [90/+/- 45/0] laminates samples made of graphite/epoxy 3501-6/AS4. Experimental fatigue damage data of [90/+/- 45/0] composite laminates have fell between the predicted damage curves of 0A degrees, 90A degrees plies and +/- 45A degrees, 0/+/- 45A degrees laminates over life cycles at various stress levels. Predicted damage results for CFRP [90/+/- 45/0] laminates showed good agreement with experimental data. Effect of stacking sequence on the model of stiffness reduction has been assessed and it showed that proposed fatigue damage model successfully recognizes the changes in mechanism of fatigue damage development in quasi-isotropic composite laminates.