EFFECT OF THROUGH-THICKNESS TENSILE AND COMPRESSIVE STRESSES ON DELAMINATION PROPAGATION FRACTURE ENERGY

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