Analysis to propagation of stress-wave and delaminating damages of layer symmetrical composite laminates subjected to low velocity impact

By adopting a piecewise impact force model and the First Shearing Deformation Theory (FSDT), the dynamic behavior of composite laminates with simply supported boundary was analyzed under low velocity impact in the geometric center by a steel ball，including the evolution rules of the impact force and contact time with relations to impact velocity，and vibration response of laminates，stress-wave propagation，as well as surface dent. The delamination area of the laminates was calculated and analyzed by adopting hypothesis of no thickness interface with a simplified version of Tsai-Wu‘s Damage Criteria, and the relation between size of delamination area and initial velocity of steel ball is also presented. The study shows that the impact force is in proportion to the initial velocity of the steel ball. And the phase velocity of stress-wave propagation is the same in each layer of composite laminates for a given direction. The velocity of tensional stress-wave propagation in the direction of fiber concentration is faster than that in the other directions，while it is on the contrary for shearing stress-wave propagation. The delamination of composite laminates occurs even under low velocity impact. The damage area expands and its shape changes with increasing the impact velocity.