Fatigue Behavior of Coal‐Rock Composites With Inclined Prefabricated Fractures Under Cyclic Dynamic Disturbance

ABSTRACT In coal mines, the stability of layered coal‐rock strata is strongly controlled by the interaction between preexisting defects and cyclic dynamic loads. Cylindrical coal‐rock specimens with fracture inclinations of 0°, 15°, 30°, 45°, 60°, 75° and 90° were tested under quasi‐static uniaxial compression and superimposed cyclic dynamic loading, complemented by acoustic emission (AE) monitoring and RFPA2D‐cycle simulations. The results reveal a distinct U‐shaped variation in peak strength and strain with fracture inclination, identifying 30° as the critical instability orientation where the composite exhibits minimal resistance. Compared with static loading, dynamic disturbance significantly degrades the load‐bearing capacity, specifically causing a 14.3% decrease in peak strength and a 25.9% decrease in peak strain at the critical 30° inclination. Furthermore, the failure mode shifts from tensile‐dominated splitting to shear‐dominated interface sliding under dynamic loads, a transition characterized by complex fracture networks and validated by the evolution of AE b ‐values and RA‐AF parameters. Finally, recognizing the 30° inclination as the “weakest link,” active reinforcement strategies are proposed to inhibit interface shear slip. These findings provide theoretical thresholds and practical guidance for disaster prevention in deep underground infrastructure construction.