Temperature Effect on AE Energy Characteristics and Damage Mechanical Behaviors of Granite

To investigate the acoustic emission (AE) characteristics and damage mechanical behaviors of Huashan granite, two groups of uniaxial compression tests were carried out: the first group of tests was performed on samples after thermal treatment without a cooling-off period (i.e., tested at real-time temperature; RT samples); and a second group of tests was performed on samples after the samples had cooled to room temperature (i.e., tested at post-temperature, PT samples). The experimental results showed that AE energy increased with the increase of treatment temperature, and it became quite large for temperatures over 500°C. The AE accumulative energy counts of the RT sample were higher than the PT sample. It was found in uniaxial compression tests of heat-treated granite that the mutation point in the ∑N/∑E curve could be taken as the indicator of the crack damage threshold (${\sigma }_{cd}$). The peak strain (the strain at the peak of the stress–strain curve) of the RT sample was larger than the PT sample, implying that the ductility of the former was more obvious, while peak stress and elastic modulus were smaller. For treatment temperatures of 500°C and below, the damage of the sample increased exponentially with external load, whereas as the temperature increased to 700°C, the damage-time curve was hyperbolic without an obvious inflection point. The sample under uniaxial compression exhibited axial splitting failure at low temperatures, and the failure mode became more complicated as the temperature rose.