Research on Brittleness Characteristic Coefficient of Thermal Damage Rock Based on Postpeak Stage of Stress-Strain Curve

In order to study the brittleness characteristic of the rock failure process, firstly, the brittleness characteristic coefficient of rock is established based on the back-front stage of the stress-strain curve. Second, the brittleness characteristic coefficient of rocks at high temperatures ( T = 100 degrees C, 200 degrees C, 300 degrees C, 400 degrees C, 500 degrees C, 600 degrees C, 700 degrees C, and 800 degrees C) was obtained by impact compression of the Hopkinson pressure bar test system. Thirdly, the brittleness characteristic coefficient was verified by the microscopic characteristics of the fragments under SEM. Finally, the temperature effect of the brittleness characteristic coefficient was analyzed by the principal component analysis method. The results show that the brittleness failure characteristic coefficient based on the postfrontal phase of the stress-strain curve can accurately describe the brittleness change characteristics of high-temperature rock under the Hopkinson shock. The higher the temperature of sandstone, the weaker the brittleness. At the same time, the microstructure of sandstone shows that the failure process is intergranular failure-intergranular failure + transgranular failure-transgranular failure, which effectively confirms the change characteristics of the brittleness characteristic coefficient during the failure process of sandstone. Using principal component analysis, it is found that the main internal factors for the change of the brittleness characteristic coefficient of sandstone are the deformation of brittle feldspar under heat and the energy dissipation of sandstone influenced by the thermal expansion of quartz.