Characterizing the Influence of Q-Stress on Mixed-Mode I/II Fracture in Elastic-Plastic Materials

A two-parameter fracture framework is used to investigate the fracture behavior of AM60 magnesium alloy under different loading conditions. In order to perform fracture tests, a modified Arcan apparatus capable of applying pure tension, pure shear, and mixed tension-shear loading conditions was used. Various crack-tip constraints were obtained by altering the loading angle from mode-I to mode-II and crack length ratio between 0.3 and 0.7. The experimental results indicate that the material exhibits greater susceptibility to crack propagation under tension mode than shear mode. J _C in pure shear demonstrates a decrease of 40.84% relative to J _C in pure tension at 0.5 crack length ratio. Finite element analysis was employed to determine the crack-tip constraint parameter (Q) under various loading and geometric conditions, revealing a pronounced dependence of crack-tip constraint on them, with the latter's effect increasing at higher loading angles. These dependencies were approximated as linear relationships. To reduce the need for extensive experimental testing, J-Q curves were developed for different constraint levels, facilitating the estimation of critical J _C values directly from the crack-tip constraint. The proposed methodology demonstrated deviations between predicted and experimental J _C values ranging from 0.15–14.43%. Additionally, the J-R resistance curve was refined to incorporate Q-dependency, further minimizing experimental efforts. The findings underscore the robustness and practicality of this approach in accurately predicting fracture parameters while significantly reducing reliance on experimental fracture tests.