Progressive damage process and destabilization precursor recognition of granite under high temperature based on acoustic emission

Abstract

To investigate the crack evolution and failure precursory characteristics of granite after thermal damage, uniaxial compression acoustic emission (AE) experiments were conducted on granite specimens after various temperature. AE characteristics at different stress stages were analyzed. Characteristics of the AE multiparameter informativeness of post-high-temperature granites and differences in crack precursor information are discussed. The results showed that as the temperature increases, the uniaxial compressive strength and elastic modulus of granite decrease significantly, with reductions of 46.93 % and 73.20 %, respectively, at 800 °C compared to 25 °C. Conversely, the peak strain increased by over 135 % at 800 °C, indicating a transition from brittle to ductile behavior. The characteristic stress showing a significant reduction in their thresholds with increasing temperature. The distribution of AE events during the progressive damage process was significantly influenced by thermal damage. At 25–400 °C, the low, intermediate, and high frequency bands converted to each other, with low-frequency signals being dominant. At 600–800 °C, high-frequency signals prevailed before the peak stress, while low-frequency signals increased after the peak. The RA-AF distribution revealed that tensile cracks dominated in granite during the loading process, and the higher the degree of thermal damage, the more tensile crack is. The progressive damage process of granite shifted from a mixed fracture mode to a small-scale tensile fracture mode as the treatment temperature increased. Before peak stress, the proportion of small-scale shear cracks increased, while after peak stress, the proportion of large-scale tensile cracks became more prominent. The AE entropy curve can well reflect the progressive damage characteristics of granite at different temperature. Entropy rapid increase is the precursor characteristics of granite instability. The dominant frequency entropy precursor response appears the earliest, and the amplitude entropy precursor response is the latest. The precursor response occurred earlier with increasing temperature, providing a reliable warning signal for rock failure.