Macro-meso mechanical behavior of fractured coal-rock composites subjected to cyclic loading

To study the damage and deterioration characteristics of coal-rock combinations with the same fractures under cyclic loading, experiment and numerical simulation were conducted to investigate the effects of coal-rock ratio and cyclic loading amplitude on the damage evolution and macro-micro failure mechanisms of rock-coal-rock combinations. The results show that the coal fracture network dominates the strength and failure of the combination. During the cyclic loading and unloading process, the stress-strain curve shows a hysteresis effect, which is small and dense at the initial stage and large and sparse at the later stage. The displacement changes sinusoidally with time, and the overall displacement increases in the first few cycles before instability. When the force on the particles is greater than the particle bonding strength, cracks first initiate at the tip of the coal fractures, and then the force concentration point shifts to the surrounding particles, causing the cracks to develop in a band-like manner. Multiple sets of crack bands and fracture zones coalesce through crack bands, causing the specimen to lose its load-bearing capacity. As the proportion of coal in the combination increases, the strength of the combination decreases, the displacement increases, the b value of acoustic emission decreases, and the number of cycles before instability decreases. As the cyclic loading amplitude increases, the displacement of the combination increases, the b value of acoustic emission decreases, the degree of deterioration of the combination deepens, and it is more likely to cause instability of the combination specimen.