Research on crack cracking mechanism and damage evaluation method of granite under laser action

Abstract Laser rock-breaking will produce cracks on the rock, and the cracking of the cracks affects the efficiency of laser rock-breaking. In this paper, the laser rock-breaking experimental platform was set up, the morphological characteristics of granite damage and the distribution of temperature field under different laser irradiation times (2 ∼ 10 s) were analyzed by SEM and infrared thermal imager. The results show that the temperature of the melting zone under the action of laser is maximum, and the damage manifests itself in the form of step-like pattern fracture. While the damage form of damage zone and thermal affected zone is mainly crack cracking. With the increase of laser irradiation time, the temperature gradient at the same location on the granite surface becomes larger. According to the temperature distribution of granite, innovatively proposed a laser rock breaking simulation model based on the discrete element method, which can reflect the cracking process of rock under the laser. The simulation results show that crack cracking is a dynamic failure process. During the laser irradiation process, the melting zone cracking manifests itself as a tensile failure, while the damage zone and thermal affected zone were dominated by tensile–shear composite damage. The laser rock-breaking efficiency can be improved by controlling the laser damage to the rock in the form of tensile damage. Finally, innovatively established a method for evaluating rock damage under laser action, which can be used to quantitatively evaluate the damage degree of laser rock-breaking and provide a new means for the preferential selection of laser parameters in future drilling processes.