Experimental Investigation on Compressive Strength, Ultrasonic Characteristic and Cracks Distribution of Granite Rock Irradiated by a Moving Laser Beam

Abstract

Efficient fracturing is the key issue for the exploitation of geothermal energy in a Hot Dry Rock reservoir. By using the laser irradiation cracking method, this study investigates the changes in uniaxial compressive strength, ultrasonic characteristics and crack distributions of granite specimens by applying a laser beam under various irradiation conditions, including different powers, diameters and moving speeds of the laser beam. The results indicate that the uniaxial compressive strength is considerably dependent on the power, diameter and moving speed of the laser beam. The ultrasonic-wave velocity and amplitude of the first wave both increase with a decreased laser power, increased diameter or moving speed of the laser beam. The wave form of irradiated graphite is flattened by laser irradiation comparing with that of the original specimen without laser irradiation. The crack angle and the ratio of the cracked area at both ends are also related to the irradiation parameters. The interior cracks are observed to be well-developed around the bottom of the grooving kerf generated by the laser beam. The results indicate that laser irradiation is a new economical and practical method that can efficiently fracture graphite.

Mechanical Properties of Rocks under Complex Stress Conditions: Investigations Using Experimental and Numerical Methods

“…Zhang et al [5] proposed a cluster microseism-based method to improve the prediction accuracy of mining earthquakes. Kuang et al [6] investigated changes in the strength, ultrasonic characteristics, and crack distributions of granite after applying a laser beam under various irradiation conditions. The results indicated that the laser irradiation technique can efficiently identify fracture graphite.…”

Risk Assessment and Analysis of Rock Burst under High-Temperature Liquid Nitrogen Cooling

“…Particularly, saturated rocks are more significantly affected. The thermal shock effect of liquid nitrogen can cause shrinkage deformation and reduced pore volume in dry rocks [33,34]. When liquid nitrogen infiltrates the pores and fractures of rocks and forms ice crystals, the expansion of water during the freezing process can generate stress within the rocks, leading to damage and fracture at weakly bonded mineral particle interfaces and potentially causing fractures through propagation.…”