The Influence of High Temperature Duration on the Thermal Mechanical Properties and Damage Mechanism of Granite: Experimental and Numerical Study

ABSTRACT Investigating the cumulative thermal damage of rocks under prolonged high‐temperature exposure is crucial for the stability of deep rock engineering. This study investigates the temporal effects of thermal exposure (1–32 h) on granite's physico‐mechanical properties and damage mechanisms through experiments at 150°C, 550°C, and 950°C, combined with uniaxial compression tests, acoustic emission (AE), and numerical simulation. The results show that: (1) the mass loss rate, volume expansion rate, P‐wave velocity reduction rate, and porosity increase exponentially with the duration of high temperature. The proportion of large pores increases. (2) Uniaxial compressive strength and elastic modulus decay exponentially, while peak strain grows exponentially. AE dominant frequency shifts from 120–140 kHz to 260–320 kHz, reflecting microcrack‐dominated fracture. (3) Numerical simulations show thermal crack density positively correlates with temperature/duration. Over 80% of cracks are intergranular shear fractures, with orientations transitioning from directional to random, accompanied by brittle‐to‐ductile failure mode evolution. (4) Microscopic analyses identify mineral phase transitions, grain‐boundary cracking, and interconnected pores as primary damage mechanisms, where temperature governs physico‐chemical reactions and duration amplifies cumulative damage. This work provides reference and suggestions for evaluating the long‐term thermal stability of rocks in deep, high‐temperature geotechnical engineering applications.