Effect of temperature on mixed mode I/III fracture behavior of diorite: An experimental investigation

Abstract

Rock fracture after high temperature is always a hot topic in the field of rock engineering. However, the mixed mode I/III fracture characteristics of thermal-treated rocks have rarely been reported previously. In this paper, edge-notched disc bend (ENDB) specimens were used to study the mixed mode I/III fracture properties of diorite under different temperatures (25 ℃, 100 ℃, 200 ℃, 400 ℃, and 600 ℃). The P-wave velocities were measured before and after heating, and acoustic emission (AE) signals during fracture were monitored. Furtherly, the fractal dimension was calculated by the box-counting method to quantitatively describe the roughness of the fracture surface. The results showed that the fracture toughness of diorite is significantly affected by the temperature at each mode mixity. When the temperature rises from 25 ℃ to 200 ℃, the fracture toughness at pure mode I is more sensitive to temperature. For the specimens heated under 600 ℃, the reduction in fracture toughness at pure mode III is greater than that at mode I. The AE active period of diorite increases with the increase of temperature, indicating that the brittleness of diorite is weakened by high temperature. Moreover, for pure mode I fracture, the influence of temperature on the fractal dimension is limited. When mode III load is introduced, the fractal dimension is more obviously affected by the temperature and the fractal dimension increases with the increase of temperature. The findings provide new insights into the mechanism of mixed mode I/III fracture in heat-treated rocks.