Experimental investigation of mixed mode I-II fracture property of thermally treated granite under dynamic loading

Abstract

In the process of deep underground resource development and utilization, the surrounding rock mass is not only affected by high temperatures, but also dependent on the dynamic stress environment. In this paper, the dynamic impact loading tests were carried out on the cracked straight-through Brazilian disc (CSTBD) granite specimens after heat treatment using the spilt Hopkinson pressure bar (SHPB) system. The effects of temperature and loading mode on the dynamic fracture toughness, fracture growth path, strain distribution, and fracture angle were analyzed. The results showed that, the fracture toughness of CSTBD granite specimen under dynamic loading decreases gradually as the mixed coefficient increases. The pure mode II fracture toughness is linearly related to that of pure mode I. High temperatures shows a negative effect on the fracture property of granite. Dynamic fracture toughness decreases with the increase of temperature, first gently (25–400 °C) and then sharply (400–800 °C). Under dynamic loading, the main crack initiates from the pre-crack tip, accompanied by obvious strain concentration, and then extends gradually to the loading end. The fracture angle of the main crack presents a generally increasing trend with the increase in loading angle, but is not closely related to the temperature of heat treatment.