Damage characterization of laser-fractured granite: experimental validation and numerical modeling

Laser-assisted rock-breaking is a promising solution to reduce tool wear in hard rock tunneling. However, research on damage characterization of laser-fractured granite, particularly microscopic damage processes and the effects of mineral grain structures, remains limited. Therefore, this study investigated thermal fracture, temperature distribution, and strength properties of granite under laser irradiation (Gaussian beam, 100–500 W, 30 s). A coupled grain-based model (GBM), cohesive zone model (CZM), and thermo-mechanical damage (TMD) model was developed to simulate laser-fractured granite. Experimental data confirmed the model's accuracy, which outperformed other models in simulating thermal crater formation and the generation and expansion of thermal cracks. Results showed that thermal fracture increased with laser power and irradiation duration. Laser-induced damage to granite occurs in two stages: Stage I is temperature-dependent, while Stage II shows a linear relationship with laser parameters (R² = 0.9). Over two-thirds of the damage occurs at grain boundaries, with the damage rate following the order: Chlorite > Biotite > Albite > Quartz > Microcline. These findings, particularly the high damage rate at grain boundaries, enhance our understanding of laser-fractured granite properties and the impact of its mineral grains, providing theoretical support for optimizing laser rock-breaking technology and suggesting potential cost savings and efficiency improvements in tunnel excavation.