Fracture resistance characteristics of mild steel under mixed mode I-II loading

The fracture resistance of elasto-plastic materials varies significantly depending on the mode mixities, i.e., the loading combinations. This paper aims to experimentally investigate the fracture resistance and behaviour of two grades of mild steel under various in-plane loading combinations. A loading fixture with high loading capacity and modified compact tension shear (CTS) specimen are designed to conduct fracture tests on elasto-plastic materials under various mode mixities. A digital image correlation (DIC) technique-based method is developed and verified to detect the fracture initiation. It is found in the paper that the sensitivity of the fracture resistance of steel to mode mixity is attributed to the strain hardening capacity and the impurities in chemical composition of the steel. It is also found that the plastic strain concentration, crack tip blunting and fracture mechanism lead to different fracture resistance of both types of steel under various mixed mode loading combinations. The contribution of the paper is that an additional method to determine the fracture initiation under non-mode I loading is developed. The test results show the necessity of considering the mode mixity effect under the mode II loading dominance in practical engineering applications.