Evaluation of the effects of mixed-mode I-II loading on elastic-plastic ductile fracture of metallic materials

In order to evaluate the mixed-mode fracture behavior of elastic-plastic metallic materials, experimental tests and numerical calculations were carried out. Since the transition of fracture toughness between opening and in-plane shear modes with ductile materials is a question of controversy, single-edge notched bend (SENB) specimens were subjected to asymmetric four-point bending (ASFPB) to provide various mode portions using four materials: A533B pressure vessel steel, F82H ferritic stainless steel, sensitized AISI 304 austenitic stainless steel, and CuA125 copper alloy. Fracture resistance curves were determined and fractographical studies performed. Numerical studies focused on determining the J-integral and stress intensity factor (SIF) solutions for the experimental program and the Gurson-Tvergaard constitutive model was used to simulate continuum features of the fracture process. The results demonstrate that Mode II fracture toughness of ductile metallic materials can be significantly lower than Mode I fracture toughness. Studies of the micromechanical aspects of fracture demonstrate the factors and variables responsible for the behavior noted in this investigation.