Experimental investigation on failure mode and fracture characteristic of rock samples induced by laser irradiation

For hard rock cracking induced by laser irradiation, the failure modes and fracture characteristics among rocks of different types and sizes are still unclear. Therefore, the experiments on laser-induced fracturing of limestone, sandstone, and various-sized granite specimens were conducted. Real-time acoustic emission monitoring and laser scanning were employed to capture acoustic emission signals inside rocks during laser irradiation and to reconstruct the fracture surfaces after laser irradiation. Results indicate that abundant melts in sandstone and granite dissipated laser energy, leading to lower acoustic emission peak energy compared to limestone. Larger-sized specimen delayed the occurrence of peak energy. Crystal thermal expansion and changes in pore pressure induced tensile-shear composite failure in limestone, whereas thermal expansion of minerals in sandstone and granite promoted tensile failure. Fracture surface morphology was influenced by sampling interval, anisotropy, and size effects. The joint roughness coefficient and fractal dimension of sandstone exceed granite and limestone. Asperity heights and slope angles ranged from 1–14 mm and 0–40°, respectively, with the average aspect angles exceeding 110°. Granite exhibited the highest proportion of macropores after laser irradiation, approximately 4.8%. These findings provide valuable insights for the application of laser-assisted fracturing in hard rock excavation.