Prediction of the residual strength of laminated composites subjected to impact loading

An approximate solution of the total strain energy release rate (G) can be developed by treating impact damage as a single delamination near to the surface with an elliptical boundary. After performing the required differentiation and neglecting items of relatively small value, a concise relationship between the total strain energy release rate and the compressive strain can be obtained. By assuming the delamination implanted at the interface to have the maximum strain energy release rate, correlation with test data was obtained. To discuss the effect of the impact energy and the laminate thickness on the strain energy release rate, a parameter defined as the ratio of the impact energy to the square of the laminate thickness is introduced. Based on this analysis, it is shown the approximate solution provides a method for predicting the post-impact strength of either of thick laminate, or a thin laminate at low levels of impact energy. Various compressive failure modes induced by different impact energies, which are of importance in the prediction of residual strength, are discussed also in this paper.