Effective local stress intensity factor criterion for prediction of crack growth trajectory under mixed mode fracture conditions

To predict the crack propagation path under static and fatigue loading, a new criterion is proposed for general mixed mode I/II/III conditions. A review on the main brittle fracture criteria in the literature shows that most criteria predict a specific fracture angle in pure mode II without considering material properties, although the empirical results are considerably various for different materials. Moreover most of criteria predict a certain KIIIc/KIc while the experiments show that the ratios of fracture toughness under pure mode III to that of mode I (KIIIc/KIc) are considerably various for different materials. Since these matters are observed even in condition that the T stress term and differences in Poisson's ratios are negligible, thus in order to solve these issues, a material-dependent effective local stress intensity factor is proposed as a main fracture parameter. The ratios of in-plane and out of plane shear fracture strengths to tensile fracture strength are considered by defining two new material parameters. To verify the developed criterion, after characterization of the newly defined material parameters, the predicted crack extension directions and fracture locus have been compared with the available experiments at different mixed mode conditions. The predicted values are in a good agreement with the empirical ones for different materials although the proposed criterion uses the minimum number of experiments required to characterize the model.