Abstract: High temperatures have a significant impact on the mechanical properties of rocks in geothermal reservoirs. To investigate the influence of high temperature on the fracture toughness of Type I granite, three-point bending tests were conducted on semi-circular bending (SCB) samples of granite subjected to cyclic high-temperature quenching at 400 ℃ for different numbers of cycles (1, 3, 5, and 7 cycles). The failure characteristics, load-displacement curves, and fracture toughness of the granite specimens after cyclic high-temperature quenching were also analyzed. Results demonstrate that as the number of thermal cycles increases, the mass and density of granite gradually decrease, the peak load continuously declines, the roughness of the fracture surface progressively intensifies, and the fracture toughness noticeably reduces. These findings provide a theoretical basis for the development of geothermal energy and the safety of underground engineering structures.

Key words: granite, high temperature quenching, thermal cycling, fracture toughness, three-point bending test