Analysis of microstructure damage characteristics and energy release law of coal weakened by microwave

Microwave irradiation technology has been proposed as a new method for rock burst prevention and control, which can effectively reduce the physical and mechanical properties of coal. In order to explore the microstructural damage weakening effect of microwave irradiation on coal, through nuclear magnetic resonance, mechanical test and acoustic emission monitoring of coal samples, it is clear that the energy damage amount of coal samples is proportional to the pore damage amount, and it is revealed that the dissipated strain energy and accumulated strain energy of coal samples increase and decrease with the increase of porosity, respectively. It is proposed that microwave irradiation can promote the pore development of coal samples to reduce the risk of impact damage. The results show that: ① microwave irradiation promotes the proportion of large pores to 8.00% after the expansion and development of small and medium pores in coal samples, the porosity of coal samples increases from 1.63% to 3.00%, the amount of energy damage increases from 0.089 to 0.106, and the increment of pore damage of coal samples accounts for 88.24% of the increment of energy damage of coal samples. It is clarified that the damage weakening effect of microwave irradiated coal is affected by the increase of porosity. ② The acoustic emission signal of coal sample moves forward on the stress-strain curve after microwave. The ringing count before the peak increases from 0.48 times/s to 0.58 times/s, and the cumulative acoustic emission ringing count increases by 105.77%. The coal sample was damaged in the fracture compaction stage and the elastic stage in advance. ③ After microwave irradiation, the acoustic emission energy of coal samples increased by 60.29%, 24.53% and 33.79% respectively in the crack compaction stage, elastic stage and unstable fracture development stage, while the acoustic emission energy decreased by 38.17% in the stable fracture development stage of microcracks, and the overall acoustic emission energy in the pre-peak section of stress-strain curve increased significantly. ④ After microwave irradiation, the strain energy accumulated before the peak of the coal sample is reduced by 67.7%, and the pore dissipation strain energy mapped by the acoustic emission energy is increased by 19.68%. Therefore, the residual strain energy released during the loading failure of the coal sample is significantly reduced, which reduces the risk of impact failure.