Compressive fatigue limit of impact damaged composite laminates

A new analytical model for predicting the compressive fatigue limit strain of composite laminates which contain barely visible impact damage (BVID) is presented. The model represents the complex damage morphology as a single, circular delamination, and calculates the strain at which thin-film buckling of the circular region of delaminated plies occurs. The fatigue limit strain is defined as the strain at which the strain energy release rate for a thin post-buckled strip of the delaminated plies is equal to the critical Mode I value (G(1C)) for the resin. The model predicts a "critical" depth at which propagation of damage during fatigue is likely to occur. Results obtained using the model are compared with two sets of experimental results, and show agreement of fatigue limit strain to within 4% of the experimental value.