Research on the characteristics of crack propagation at high temperatures based on digital image correlation technology

To understand the mechanism of crack propagation in deep reservoirs during fracturing, it is necessary to research crack propagation characteristics at high temperatures. In this paper, Brazilian splitting tests of sandstone at different high temperatures and a high-speed camera are combined to obtain crack propagation images. The opening displacement modes are then obtained through the displacement data of the sandstone surface obtained by DIC technology. Combining the cohesive zone model and opening displacement modes, a method for identifying the crack plastic zone and no traction crack at high temperatures is established; the initiation and propagation processes of cracks on sandstone surfaces at high temperatures are investigated; and the characteristics of crack propagation at different temperatures are analysed. Based on the method of identifying the crack plastic zone and no traction crack at high temperatures, the research finds that a crack appears from the rock sample centre and extends to both ends of the rock sample. At the beginning of crack initiation, only the crack plastic zone expands along the radial direction, and the no traction crack appears as the crack propagates progressively. Additionally, as the temperature increases, the enhanced plasticity of the sandstone leads to a longer duration of stress concentration just before the crack appears. The opening displacement of the no traction crack and the propagation speed of the crack plastic zone show a decreasing trend with an increase in temperature. The research results can lay a foundation for the study of crack propagation in deep reservoirs.