Mechanical behavior and acoustic emission characteristic response of Macaowan coal samples under different loading rates

In coal mining, changes in extraction rate significantly affect the stress field of coal seams. To study the impact of loading rate on the energy and fracture evolution of coal, uniaxial compression tests were conducted on coal samples at different loading rates, with acoustic emission (AE) monitoring. The energy and fracture evolution characteristics were analyzed, along with the spatiotemporal evolution of AE during loading. Results show that the peak stress and strain of the samples gradually increase, but the growth rate decreases. The elastic modulus initially decreases and then increases. Elastic energy continuously increases during loading, while dissipated energy remains stable during the elastic stage and rapidly increases in the plastic stage. The ringdown count significantly increases during the nonlinear crack propagation phase and peaks at sample failure. The b-value, reflecting the distribution of AE event magnitudes, shows a fluctuating downward trend during loading, with values around 2 at the peak point, indicating imminent failure. The upper and lower limits of the b-value are negatively correlated with the loading rate. At low loading rates, shear failure is predominant, while at high loading rates, tensile failure occurs. Microcrack damage is primarily shear-dominated, with the proportion of tensile failure increasing with the loading rate. The locations of concentrated microcrack expansion are related to the distribution of natural fractures in the coal samples. These findings provide a theoretical reference for early warning of coal rock instability and failure.