Fracture properties and dynamic failure of three-point bending of yellow sandstone after subjected to high-temperature conditions

Abstract

The effect of high temperature on the fracture mechanical behavior of rocks is a critical topic of research in underground engineering. In this study, a single-side straight-crack three-point bending (SC3PB) yellow sandstone sample was heat treated at 25, 200, 400, 600, and 800 ℃. The fracture toughness of the sample was measured after heat treatment, and the deformation and failure process of yellow sandstone under load was monitored using acoustic emission and digital image correlation technology. The results revealed that the p-wave velocity, peak load and fracture toughness of yellow sandstone decreased considerably when temperature exceeded 400 ℃. By contrast, with the increase in temperature, the crack length and peak propagation rate increased considerably. Furthermore, with the increase in load, a high-strain band was observed in the the von-Mises strain in the loading direction. The fracture toughness was linearly correlated with the p-wave velocity, peak load and thermal damage. When temperature was higher than 400 ℃, the main fracture expanded and the plastic characteristics increased after the peak load. The rapid change in the physical and mechanical properties of 400-600℃ yellow sandstone was attributed to the α/β phase transition of quartz, the dehydroxylation of kaolinite and the escape of intermineral binding water and crystal water. Therefore, the physical and mechanical properties and fracture behavior of SC3PB yellow sandstone changed substantially at the threshold temperature of 400 ℃.