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. Fracture tests were conducted using a modified Arcan apparatus, capable of applying pure tension, pure shear, and mixed tension-shear loading conditions.Various crack-tip constraints were obtained by altering the loading angle from mode-I to mode-II and the crack length ratio between 0.3 and 0.7. The experimental results indicate that the material is more susceptible to crack propagation in tension mode than in shear mode. JC in pure shear demonstrates a decrease of 40.8% relative to JC 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. J-Q curves were developed for different constraint levels to reduce the need for extensive experimental testing. These curves facilitate the estimation of critical JC values directly from the crack-tip constraint.The proposed methodology demonstrated deviations between predicted and experimental JC values ranging from 0.15% to 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 minimizing extensive experimental requirements fracture tests.