Dynamic Characteristics of Thermal Damage Granite Under Cyclic Impact Loading

In order to study the dynamic mechanical properties of thermally damaged granite under cyclic impact loading, cyclic impact tests were conducted on thermally damaged granite specimens using a Hopkinson compression bar device and a muffle furnace. The effects of the number of cyclic impacts on the mechanical properties and internal structural changes of the thermally damaged granite at different temperature levels were investigated. The results show that: (1) in the dynamic stress–strain curve, both the mechanical strength and the elastic-modulus of rock mass decrease after 400 °C, and the specimen above 400 °C changes from elastic–plastic deformation to brittle deformation. (2) under the action of temperature and axial compression, the peak stress decreases with the increase of cycle times, and the peak stress decreases rapidly with the increase of temperature under the same axial compression, especially after 400 °C, it reaches 30%, the increase of peak stress under axial compression after 400 °C is negligible, which proves that the effect of high temperature on stress is the main part. (3) the internal structure of rock samples at 200 °C and 400 °C is relatively complete, only porosity and cracks appear in the observation of fine structure of rock, while the internal structure of rock samples at 600 °C and 800 °C is obviously damaged, from the initial appearance of micro-cracks and pores to the final appearance of a large number of bulk crystal detachment. For the observation of the macrostructure, the damage of the specimens without axial pressure before 400 °C shows splitting damage, while the specimens with axial pressure show end effect. Specimens above 400°C no longer have the load-bearing capacity but showed broken particles and powder.