Effect of Through Thickness Tensile and Compressive Stresses on Delamination Propagation Fracture Energy

Abstract

Strain energy release rate criteria are often used for predicting delamination. However, the fracture energy for delamination propagation is not a material constant, but varies depending on the through thickness normal stress. For tensile normal stresses this problem is usually overcome by using a mixed mode fracture criterion. However, the mixed mode approach fails to take into account compressive through thickness normal stresses. These can greatly increase the delamination stress and therefore cannot be simply ignored. A new approach is proposed in which it is assumed that the fracture energy for delamination propagation is a linear function of the average through thickness normal stress. Comparison with experimental results for unidirectional specimens with discontinuous plies shows excellent correlation, and accounts for a number of experimental observations that cannot be explained using the standard fracture mechanics approach.