Investigation of damage to thick composite laminates under low-velocity impact and frequency-sweep vibration loading conditions

A detailed investigation of damage and failure mechanisms of composite laminates under low-velocity impact (LVI) by experimental tests and numerical modeling is presented. Five impact energy levels were investigated on composite laminates by drop-weight tests. Permanent indentations were measured, and delamination areas of each interface induced by each LVI event were captured using an ultrasonic C-scan. The 3D volume elements with a user-defined, material-based finite element model (FEM) has been applied to predict the LVI event considering damage modes, including intra-ply damage and inter-ply damage. The results of the FEM were found to agree well with experimental observations. Internal damage of the laminate during the impact process was analyzed. For thick laminates, the initiation of damage is observed at the first layer, and then spreads from the impact surface to the back, leading to a pine-type damage pattern as the thickness increases. Frequency-sweep vibration tests of composite laminates subjected to LVI events were studied under a “fixed ends” boundary condition. Our results show that it is reasonable to use frequency-sweep vibration experiments to evaluate the damage of laminates subjected to LVI events.