Real-time mode-I fracture toughness and fracture characteristics of granite from 20 oC to 600 oC

The mode-I fracture toughness of semicircular bend granite specimens at high temperature was tested in real time, and the failure specimens were examined using X-ray computed tomography. The results showed that with increasing temperature, the fracture toughness increased from room temperature (20 C-o) to 200 C-o, then decreased beyond 200 C-o. Quasibrittle failure was observed up to 500 C-o, followed by plastic characteristics at 600 C-o. The cracks tended to propagate along the boundaries of mineral crystals. With increasing temperature, the main cracks became rougher and tended to propagate perpendicular to the tensile stress, and more branch cracks formed. The increase of temperature within a certain range had toughening effect on a variety of rocks and temperature-treatment method affected the mode-I fracture toughness of granite. Compared with the mode-I fracture toughness after cooling to room temperature, the temperature threshold of mode-I fracture toughness of granite at real-time high temperature was higher. The results pro-vide guidance to determine fracture toughness and stability for high-temperature rock engineering.