Numerical investigation on behaviors of composite laminates with initial delamination defects under impact and compression after impact

The initial delamination defects may arise during the preparation of carbon fiber-reinforced polymer (CFRP) composite laminates, so its effects need to be considered in the evolution of mechanical properties. In this article, the behaviors of composite laminates with initial delamination defects under impact and compression after impact (CAI) are investigated by numerical method. The simulation framework composed of the micromechanics of failure (MMF) theory and the mixed mode exponential cohesive zone model (ECZM) is constructed. The numerical analysis compares the effects of the interaction between four different initial delamination defects and impact loading on impact response and CAI strength at two impact velocity levels (1.336 and 2.314 m/s). Furthermore, the failure mechanisms of laminates with initial delamination defect are disclosed under CAI loading. The findings indicate that the difference in impact response is minor. The CAI strength is reduced from 250.5/173.5 to 191.5 MPa/139.1 MPa. The sufficient condition for the further significant reduction of CAI strength is that the initial delamination defects merge with the impact-induced delamination cracks in the width direction of laminates. Moreover, the failure mechanism for CAI condition is mostly matrix damage and interlaminar crack propagation. This work provides a valuable reference for engineering failure analysis of composite laminates.