Mechanical characteristics and microcosmic mechanisms of granite under temperature loads

The relationships between mechanical characteristics of rock and microcosmic mechanism at high temperatures were investigated by MTS815, as well as the stress-strain behavior of granite under the action of temperatures ranging from room temperature to 1200 °C. Based on a micropore structure analyzer and SEM, the changes in rock porosity and micro structural morphology of sample fractures and brittle-plastic characteristics under high temperatures were analyzed. The results are as follows: 1) Mechanical characteristics do not show obvious variations before 800 °C; strength decreases suddenly after 800 °C and bearing capacity is almost lost at 1200 °C. 2) Rock porosity increases with rising temperatures; the threshold temperature is about 800 °C; at this temperature its effect is basically uniform with strength decreasing rapidly. 3) The failure type of granite is a brittle tensile fracture at temperatures below 800 °C which transforms into plasticity at temperatures higher than 800 °C and crystal formation takes place at this time. Chemical reactions take place at 1200 °C. Failure of granite under high temperature is a common result of thermal stress as indicated by an increase in the thermal expansion coefficient, transformation to crystal formation of minerals and structural chemical reactions.