Evaluation of Fatigue Damage Progress in CFRP Cross-Ply Laminates with an Open Hole Using Cohesive Elements

Abstract

This study experimentally and numerically investigate fatigue damage in CFRP cross-ply laminates with an open hole under some test conditions, and verified the numerical simulation for predicting the fatigue damage progress proposed by the authors. Splits in the 0°plies, transverse cracks in the 90°plies and delaminations at 0°/90°ply interfaces were experimentally observed due to the cyclic loading, even if the maximum stress was much lower than the stress to generate the initial damage under the static loading condition. All the cracks gradually extended with increasing number of cycles under the low stress levels. After a damage analysis with cohesive elements was confirmed to represent the damage under static loading condition, the fatigue damage observed near the hole was analyzed by the damage analysis with a fatigue damage law that was applied to the stiffness degradation process of cohesive elements. The predicted fatigue damage progress agreed well with the observations, and this approach accurately represented the difference of the damage state due to the change in the critical energy release rate or in the maximum stress in cyclic loading. These experiments and simulations demonstrated the validity of the numerical approach for predicting the fatigue damage progress in composite laminates, and the parameters in the fatigue law for cohesive elements were discussed.