Multiscale study of dynamic mode-I fracture characteristics of thermally treated granite: Comparison of conventional and microwave heating

High-temperature-assisted rock breaking is a promising technique, with conventional and microwave heating being widely used methods. Understanding the mechanisms of conventional and microwave heating on the dynamic mode-I fracture characteristics of rock is crucial for engineering applications. Dynamic mode-I fracture experiments were conducted on Notched Semi-Circular Bending (NSCB) specimens at 25, 200, 300, 400, and 500 °C under both heating methods. Additionally, a finite element-discrete element coupled numerical method was developed to simulate the dynamic mode-I fracture process in high-temperature granite. The study investigated the effects of both heating methods on the fracture process and morphological features of the rocks, revealing differences in damage mechanisms across various scales. Results indicated that both heating methods similarly influence the fracture toughness of granite, with fracture toughness initially remaining nearly unchanged and then rapidly decreasing, with 200 °C identified as the threshold temperature. Moreover, the fractal dimension increased exponentially with temperature. The fracture mechanisms associated with conventional and microwave heating were also discussed.