Abstract: To investigate the performance degradation patterns and thermal damage mechanisms of quartzite, a grain-based model in particle flow code (PFC-GBM) was employed to simulate the uniaxial compression of quartzite under real-time high temperature and after natural cooling. Stress-strain curve, peak stress, elastic modulus, and failure modes under both temperature conditions were analyzed to study the thermal damage mechanisms of quartzite. Further investigation of thermal damage mechanisms was conducted based on thermally induced crack and displacement changes. The following conclusions were drawn: During the natural cooling process, the temperature of quartzite sample generally decreased gradually from the center to the surface. In the 700 ℃ quartzite specimen, crack propagation during cooling caused unstable heat conduction, leading to isotherm displacement. The critical temperature for the brittle-ductile transition of quartzite under real-time high temperature condition ranged from 25 ℃ to 300 ℃, which is lower than the critical temperature from 300 ℃ to 500 ℃ observed in naturally cooled quartzite specimens. Under real-time high temperature, the peak strength and elastic modulus of quartzite samples decreased by approximately 20 MPa and 10 GPa, respectively, compared to those of naturally cooled specimens, with neither parameter showing significant variation with temperature. The elastic modulus was more sensitive to thermal damage within the range of 25 ℃ to 300 ℃ than peak strength. With the increase of temperature, the degree of fragmentation in quartzite under uniaxial compression significantly increases, exhibiting more splitting failure characteristics. The influence of thermally induced microcracks on the failure mode of quartzite becomes progressively stronger. Under both temperature conditions, the macroscopic fracture planes tend to extend along existing thermally induced microcrack paths, with more pronounced macroscopic through-going fractures observed under natural cooling condition.

Key words: quartzite, high temperature, thermal damage, particle flow, uniaxial compression