Experimental study on damage characteristics and energy evolution of coal by ultrasonic power

In order to study the mechanical damage characteristics and energy evolution law of coal after ultrasonic fracturing, uniaxial compression experiments were carried out on fractured coal with different power by using electronic universal pressure testing machine, acoustic emission system. The mechanical damage parameters of different power ultrasonic fracturing coal were obtained, and the relationship between acoustic emission signal and damage parameters of coal mass with different power fracturing was explored. The fractal characteristics of coal surface cracks were analyzed by box fractal dimension, and the damage degradation mechanism of ultrasonic fracturing coal caused by different ultrasonic power was clarified. The experimental results show that the characteristic strength and elastic modulus of coal gradually decrease with the increase of ultrasonic fracturing power, and the damage parameters of uniaxial compressive strength and elastic modulus of coal are linearly correlated with the fracturing power. During the uniaxial compression process, the acoustic emission ringing count can be divided into three stages, which are quiet period, rising period and fluctuating period. With the increase of ultrasonic power, the incubation period of crack is shorter and the proportion of relative time is smaller. With the increase of crack growth rate, the weakening effect on the strength of coal is gradually enhanced, the sudden increase of acoustic emission signal is obvious., the final failure of coal sample is more broken, and the failure characteristics change from elastic brittleness to ductility-plasticity with the increase of fracturing power. Coal pore fissure extension, and three is a linear positive correlation between the fractal dimension damage parameters of coal surface cracks and the fracturing power. The greater the fractal dimension damage parameter is, the more complex the coal fracture morphology is. Based on the acoustic parameters, the relationship between the damage parameters and the normalized parameters of acoustic emission is analyzed, and it has a good fitting relationship. The above results show that ultrasonic fracturing causes damage to the coal structure, makes the coal seam damage and deformation, and forms a complex coal seam seepage network, thus improving the permeability of coal seam.