Experimental Study on Dynamic Characteristics of Granite With Different Aspect Ratios Under Three‐Dimensional Cyclic Impact Loading

ABSTRACT To investigate the dynamic response mechanism of deep mine surrounding rock under complex stress and cyclic impact loading, this study takes granite as the research object and systematically conducts dynamic mechanical tests on samples with different aspect ratios (0.5 and 1) under three‐dimensional cyclic impact loading using a Split Hopkinson Pressure Bar system. The study considers different impact air pressures (0.4, 0.5, and 0.6 MPa) and combinations of pre‐applied axial and confining pressures (simulating in situ stress conditions at depths of 400 and 600 m). The dynamic stress–strain behavior, energy dissipation patterns, damage evolution characteristics, and failure modes of the samples are analyzed. The results indicate that aspect ratio and impact air pressure significantly affect the dynamic peak stress, peak strain, and elastic modulus of the samples. The dissipated energy density increases linearly with the number of impacts, with samples of smaller aspect ratios exhibiting higher dissipated energy. The damage variable increases with the number of impacts, and high confining pressure can inhibit damage development. The failure mode transitions from “tensile‐dominated” to “shear‐composite,” with aspect ratio influencing the crack distribution morphology. Based on energy and strain characteristics, a rockburst propensity index D r is proposed, which comprehensively considers peak stress, peak strain, and energy ratio, and its normalized relationship with the number of impacts is established, providing a theoretical basis for rockburst risk assessment in deep mines.