Dynamic Failure Behavior and Energy Evolution Characteristics of Granite under Uniaxial Dynamic–Static Combined Cyclic Loading

In deep underground engineering and mining, rock masses are often subjected to the combined effects of static axial pressure and dynamic impact loads. Understanding the failure behaviors and energy evolution in rock masses is of significant scientific and engineering importance. This study employed a Split Hopkinson pressure bar to investigate the dynamic failure mechanisms and energy evolution of granite under one-dimensional uniaxial dynamic–static combined cyclic loading. The experimental results demonstrate that uniaxial static–dynamic combined loading notably affects microcrack closure in granite. As axial pressure increases, the specimens transition from brittle to plastic deformation, with the dynamic peak stress decreasing and the strain rate increasing. The energy transfer efficiency and dissipation density change, leading to greater damage and enhanced activation and dissipation of internal microcracks in the rock. Under uniaxial static–dynamic combined cyclic loading, the specimens generally remain intact or show minor local cracking after the initial impacts. As the number of impacts increases, energy dissipation density rises at a nonlinear rate. The final impact induces a sudden shift in the damage evolution, culminating in catastrophic failure. Taking into account the influence of axial pressure, impact load, and other factors, a dynamic damage constitutive model based on the Weibull statistical distribution and Kelvin body mechanics model was established.