Numerical Study on Multi‐Scale Damage of Granite Under Extreme Temperature Shock

ABSTRACT Understanding the real‐time thermomechanical damage of granite under extreme temperature variations is essential for the safe and efficient exploitation of hot dry rock (HDR) geothermal resources. Existing experimental studies primarily focus on macroscopic mechanical deterioration after high‐ or low‐temperature exposure, while the microscale evolution of force chains and their dynamic coupling with macroscopic behavior remain poorly understood. Moreover, conventional DEM‐based models often oversimplify rocks as homogeneous continua, neglecting mineral‐scale heterogeneity and intergranular interactions. To address these gaps, a two‐dimensional grain‐based model (GBM) was developed to explicitly capture mineral heterogeneity and intergranular properties, enabling simulation of heating–cooling cycles and real‐time damage evolution under extreme temperatures. New metrics were proposed to quantitatively evaluate force chain reorganization, load‐bearing degradation, and their correlation with macroscopic strength. Simulation results reveal that although the maximum strength, average strength, and number of force chains increase with temperature, high temperatures destabilize the overall force chain network. Strong thermal shocks from high to extremely low temperatures can reduce the mechanical properties of granite, accelerate the initiation of microcracks, and promote the formation of more complex crack networks, thereby enhancing the efficiency of thermal extraction. This study provides novel insights into microscale mechanisms underlying cyclic thermomechanical damage in granite and offers theoretical guidance for the design and optimization of LN ₂ fracturing strategies in HDR reservoirs.