Effect of Different Cooling Treatments on the Tensile Properties and Fracture Modes of Granite Heated at Different Temperatures

Brazilian tests and 3D fracture surface measurements were carried out on granite subjected to different temperatures (25, 100, 200, 300, and 400 degrees C) followed by different cooling treatments (water cooling and liquid nitrogen cooling treatments). The tensile strength, peak displacement, failure mode, and fracture surface roughness of granite were compared and analyzed. The energy absorption and fracture modes during failure processes were analyzed based on cumulative acoustic emission energy, rise angle (RA), average frequency (AF), and cluster analysis. The results show that the variations in tensile properties can be divided into two temperature zones (25-100 degrees C and 100-400 degrees C) for granite after water cooling and three temperature zones (25-100 degrees C, 100-200 degrees C, and 200-400 degrees C) for granite after liquid nitrogen cooling. There was a turning point temperature in the temperature range of 100-200 degrees C due to the relative heat transfer capacity between liquid nitrogen and water. Below the turning point temperature, the tensile property deterioration after liquid nitrogen cooling was greater than that after water cooling. Above the turning point temperature, the tensile property deterioration after liquid nitrogen cooling was less than that after water cooling due to the Leidenfrost effect. When the temperature was > 200 degrees C, the liquid nitrogen cooling treatment resulted in more shear crack or mixed crack propagation during the failure process of granite, which promoted an increase in the fracture surface roughness.