Numerical simulation on difference mechanism and post-peak dynamic failure characteristics of coal under uniaxial compression

The identification of coal rock burst tendency is an important foundation for the prevention and control of rock burst, and the identification results are closely related to the stress drop pattern of dynamic failure after coal peak. A study was conducted on the stress drop characteristics and differential mechanisms of coal with impact propensity post-peak dynamic failure. By comprehensively utilizing MTS testing machines, high-speed cameras, and acoustic emission monitoring systems, an acoustic emission localization test was conducted for uniaxial dynamic impact failure of coal with impact propensity. The uniaxial stress-strain curve of coal was obtained, capturing the dynamic impact failure process before and after the coal peak, and synchronously monitoring the spatiotemporal strongly distributed information of acoustic emission micro fracture. Three typical types of dynamic impact failure after coal peak were summarized, and PFC3D three-dimensional fine numerical simulation of prefabricated weak structural surfaces was carried out. The three typical impact failure and energy evolution processes after coal peak were inverted and reproduced, revealing the differential mechanism of stress drop morphology after peak. The simulation results are consistent with the measured impact failure. The results indicate that: ① the stress drop patterns in the pre peak and post peak stages of coal fractures were significantly different, and could be summarized into three typical impact failure modes: single stress drop failure mode, double stress drop failure mode, and multiple stress drop failure mode; ② The spatiotemporal concentration distribution of high-energy micro fracture events was consistent with the spatiotemporal distribution of instantaneous dynamic failure after the peak. The single strain drop failure coal sample after the peak had undergone a large-scale stress drop during the accelerated crack expansion stage before the peak, and the effective bearing area has significantly decreased. The absolute energy emitted by the sound after the peak is the highest; ③ The development of primary or secondary weak planes throughout the location leads to differences in mechanical parameters of weak planes, resulting in variations in the maximum pre-peak damage level and residual bearing area of coal samples, which in turn control the morphological characteristics of the post-peak dynamic stress drop in coal; ④ The higher the peak strain energy of the pre-peak coal sample, the lower the kinetic energy of the coal sample particle ejection, the lower the pre-peak damage level, and the higher the kinetic energy of the post-peak coal sample impact damage ejection, indicating a more severe impact. The research results can provide a deep understanding of the differential mechanism of dynamic failure stress drop after the peak of impact prone coal, providing a reference for the evaluation of impact prone coal bodies with weak structural planes.