Fracture Behavior and Criterion of Granite Under Combined Static–Dynamic Mixed‐Mode Loading
Deep rock masses in underground engineering are often subjected to combined loading conditions, where pre‐existing static tectonic stresses coexist with dynamic disturbances induced by excavation activities. Additionally, fractures in rock engineering are frequently subjected to mixed tension‐shear loading scenarios. To elucidate the cracking mechanisms of rocks under such complex conditions, this study employs a modified split Hopkinson pressure bar (SHPB) to conduct combined static–dynamic (CSD) fracture experiments on notched semi‐circular bend (NSCB) granite samples, with a particular focus on the mixed‐mode I/II and pure mode II loading. These experiments reveal that the effective fracture toughness (FT) decreases as the loading mixity shifts from mode I toward mode II. In contrast, the crack propagation velocity increases as the mode II loading component decreases. Fracture morphology is found to be governed primarily by the loading mixity rather than the loading rate. Furthermore, this study systematically evaluates various fracture criteria and demonstrates that the GMTS fracture criterion, which incorporates the effects of dynamic loading rate on the critical distance, offers preferable predictions of mixed‐mode I/II crack initiation in granite under CSD loading. Notably, an exponential relationship is identified between the critical distance and loading rate. These findings enhance the understanding and predictive capability of mixed‐mode I/II crack initiation in granite under both pure dynamic and CSD loading conditions.