Coal Sample Dynamics Experiment under the Combined Influence of Cyclic Dynamic Load and Gas Pressure: Phenomenon and Mechanism

Abstract

The deterioration of coal strength caused by geological conditions of high gas in deep mines and disturbance from mining operations is one of the elements that influence the incidence of dynamic disasters like gas outbursts and rock bursts. To study how gas pressure and cyclic loads interact to determine the mechanisms and phenomena of coal dynamics, the split Hopkinson pressure bar apparatus was used to perform cyclic impact test on coal samples to investigate the mechanical behavior of gas-bearing coal samples under cyclic dynamic load and gas pressures. The findings indicated that there are three stages in the stress–strain evolution of gas-bearing coal: linear elastic stage, plastic stage, and post-peak stress attenuation. As cycle time grows, the peak stress and attenuation stress of the coal samples decrease, while the maximum and peak strains exhibit a general increasing trend. Under the impact of dynamic load, the macroscopic damage form of the coal sample is mainly a macroscopic crack, and the microscopic examination revealed that the coal samples interior crystal was primarily a trans-granular fracture. By considering dynamic load, gas pressure, and number of cycles, the test results can be more accurately verified by the mechanical damage constitutive model. Finally, based on cyclic dynamic load and gas pressure, the proposed fatigue prediction model of gas-bearing coal can better anticipate coal samples dynamic load-bearing capability.