Mechanical Behavior and Micromechanical Failure Mechanisms of Pre-Cracked Rocks Under Impact Loading

To elucidate how pre-crack inclination affects the dynamic mechanical response, failure modes, and energy evolution of rocks, uniaxial impact compression tests were conducted on Φ50 mm Baima Iron Mine magnetite specimens with varying pre-crack angles using a split Hopkinson pressure bar (SHPB) system. The experiments were integrated with PFC2D discrete element simulations to investigate crack propagation and stress field characteristics. The results demonstrate that all specimens maintained dynamic stress equilibrium under impact loading. Crack inclination significantly influenced the dynamic stress–strain response: specimens with 0°~30°cracks exhibited gradual post-peak stress decay, indicating ductile behavior, while specimens with larger inclinations (≥45°) displayed pronounced brittle failure. Dynamic compressive strength followed a “U-shaped” trend with crack angle, reaching a minimum at 45°, whereas 0°and 90°specimens exhibited similar strength. Failure modes transitioned from axial splitting to wing-crack dominance, while anti-wing and shear cracks decreased significantly with increasing crack angle. Energy analysis indicated that reflected energy decreased and transmitted energy increased with increasing crack angle. Numerical simulations reproduced the experimental macroscopic failure patterns accurately, revealing the underlying mechanisms of crack-tip coalescence and stress concentration shifts as a function of crack inclination. These findings offer insights into the dynamic failure mechanisms of jointed rocks and provide guidance for engineering safety assessments.