Study on the effect of heating rate and temperature on the fracture properties of flawed granite

Abstract

The effects of heating rate and temperature on fracture characteristics and mechanical properties of flawed granite were studied by using the cracked straight-through Brazilian disc specimen. Four temperature groups were established, and the specimens were heated in a furnace with different heating rates. After thermal treatment, the specimens were conducted to static compression tests, the compression process was recorded by a camera and the deformation on the specimen surface was calculated by the digital image correlation (DIC) technology. A microscope which can magnify nine times was employed to observe the surface of specimen and the transgranular or intergranular fracture. The results show that: at the same temperature, the thermal cracks increase as the heating rate increases. Within the same temperature group, the mode-I fracture toughness of granite shows a gradual decay characteristic as the rate of heating increases. Due to the DIC results, at the same temperature, when the heating rate increases, the maximum principal strain and the crack tip opening displacement (CTOD) of crack tip show an increasing trend at fracture. At 200 ℃, the CTOD in the range of 0.0781 mm ∼ 0.237 mm, the effect of heating rate is distinct. At 200–400 ℃, the input energy and release energy by fracture decrease with the heating rate. In the same temperature group, the specimen heating rate of 20 ℃/min has more distinct ductile characteristics.