Test of Crack Evolution of Coal Samples Under Cyclic Loading and Numerical Simulation

To study the crack development of coal samples under cyclic loading from macroscopic and microscopic perspective, based on acoustic emission monitoring technology, the macroscopic deformation and acoustic emission characteristics of coal samples in cyclic loading and unloading conditions are studied, and the crack evolution law of coal samples during fatigue damage was analyzed by using PFC^2D numerical simulation software. The results showed that: under cyclic loading, the residual deformation of coal samples in the process of single cycle loading and unloading has experienced three stages of decrease, stability and increase, and deformation curve shows the change law of “sparse-dense-sparse”; the acoustic emission parameters are reduced, stable and elevated, the peak ringing count is “U” shape, and the accumulative energy and impact counts are inverted “S” shape. The numerical simulation results showed that: micro-cracks in coal samples are distributed randomly at the beginning of the cycle, the micro-cracks in the middle stage accumulate continuously, and the shear fracture zone is formed initially, and the main shear fracture zone is formed in the late cycle, which leads to the coal sample destruction, the destruction of coal samples is mainly shear failure.