Mechanical damage characteristics and constitutive model of coal under ultrasonic cavitation erosion

Ultrasonic excitation of coal body represents an effective approach to enhance the extraction rate of low-permeability coal seams. By conducting coal body tests with ultrasonic cavitation erosion of varying durations, the interrelationships between the mechanical damage and failure characteristics of the coal body are quantitatively characterized, and the failure mechanism of ultrasonic cavitation erosion on the coal body is explored. The results indicate that with the prolongation of ultrasonic time, the cavitation bubbles generated by the cavitation effect gradually accumulate and expand within the coal body, and the weakening effect on coal body is gradually enhanced. The number of signals in the shear crack region within the coal body decreases, and the damage form of the coal samples gradually transforms from brittle damage to brittle-ductile damage. Through establishing mechanical damage model of the coal body under ultrasonic excitation for different durations, the peak stress error fluctuates within a narrow range, indicating that the established model is capable of reflecting the impact of ultrasonic excitation on the evolution of coal body damage. In summary, under the action of ultrasonic excitation for different durations, the cavitation effect leads to an increase in the number of alteration points and the size of alteration pits within the coal rock. It weakens the cementation between the mineral particles, reduces the coal macroscopic properties, forms a seepage network, and thereby effectively improves the extraction rate of coalbed methane.