Effects of high temperature and cooling rate on dynamic tensile mechanical properties of granite

Abstract

Deep high-temperature rock is often subjected to different cooling mediums, and the deterioration of its mechanical properties is easy to induce some rock mass engineering disasters. Based on the three cooling ways, cooled in an oven, cooled in air and cooled in water，firstly, the variations in the P-wave velocity and microscopic cracks of high temperature (200−800 ℃)granite after exposure to heating and cooling treatments were studied. Then, based on the modified SHPB test system, the dynamic tests were conducted by using the disc granite after exposure to heating and cooling treatments, and the stress equilibrium, dynamic tensile strength and deformation and failure of samples were investigated. The results show that the damage degree in the sample increased with the increase of cooling rate, and the water-cooled samples exhibit the largest decrease in P-wave velocity and the largest amounts of newly-generated cracks. The relationship between the dynamic tensile strength and loading rate can be well-fitted using an exponential positive correlation. The cooling rate has less influence on the dynamic tensile strength when the sample reaches 200 ℃. When the sample reaches 400−700 ℃, the temperature and cooling rate have great effects on the dynamic tensile strength, and the dynamic tensile strength decreases with the increase in temperature and cooling rate. The temperature and cooling rate have great influences on the dynamic tensile strain and fracture initiation time of the sample at the initiation position. The dynamic tensile strain increases with the increase in temperature and cooling rate, and the fracture initiation time decreases with the increase in temperature and cooling rate. There are two failure types for samples with different heating/cooling treatments. Type I is the central main crack and the crushed zone at loading ends in the sample. Type II is very complex, there are central main crack, crushed zone at loading ends and cracks in other directions. The present results will be much helpful for providing the theoretical reference for the stability control of deep high-temperature rock engineering.

Keywords

• dynamic tensile strength
• granite
• high temperature
• cooling rate
• cooling way
• rock dynamics