Calculating energy release rates of MD non-symmetric laminate MMELS and C-ELS specimens

The purpose of this investigation is to evaluate the accuracy of global expressions of the energy release rates for laminate composite beam specimens. The specimens considered here are composed of multidirectional woven plies; they include double cantilever beam (DCB), mixed mode end loaded split (MMELS) and calibrated end loaded split (C-ELS) specimens. As a result of the layup, the upper and lower specimen arms possess different heights and stiffnesses. Global expressions that exist in the literature are used in the calculations.Newexpressions are developed to account for the differing stiffnesses. Results from tests carried out elsewhere are used in the calculations. The obtained results are compared to values found by means of finite element analyses. It was seen that for DCB specimens, the best results were obtained when the specimen arm heights and stiffnesses, together with a correction for the deflection and rotation at the delamination front, were accounted for. These are presented in Appendix A. For the MMELS specimens, the best comparison between the finite element results and the global expressions for the interface energy release rate was found when accounting for different specimen arm heights or both different specimen arm heights and stiffnesses but without the delamination length correction. The best results for the C-ELS specimens were obtained when both the specimen arm heights and stiffness were considered, together with the delamination length correction. Thus, it would appear that the global expressions may be used to estimate the energy release rate for beam type specimens.