Analytical study on low compressive strength of composite laminates with impact damage

This paper analytically investigates the mechanism of compressive strength reduction of composite laminated plates due to impact damage in quasi-isotropic laminates. Simplified mechanistic models are proposed. Explicit form solutions including the upper and lower bounds of applied load against end-shortening are derived for the local post-buckling stage by using the numerically derived load vs. end-shortening relationship of a square plate whose circular portion is allowed to deflect like a plate with circular damage. Based on the solution, explicit expressions of the average energy release rate for self-similar delamination growth are also given for the applied load as a function of the dimensions of the plate and the circular damage. Through the solutions we can roughly estimate the failure load due to delamination instability. The meaning of low CAI strength is discussed through the present solution and previous CAI experiments.