Study on thermal damage evolution of rock based on acoustic emission

To establish a thermal damage evolution model, an acoustic emission(AE) monitoring system of real-time thermal damage for rock based on NI high-performance test system and LabVIEW programming environment were developed. The AE information of rocks (three types of granite, three types of sandstone) during heating (from room temperature to 500 ℃) and cooling processes was captured by a series of thermal damage experiments. The alteration of microstructure of rock thin sections before and after heat treatment was also analyzed under the orthogonal polarized condition. According to the cumulative AE energy and elastic modulus, a thermal damage evolution model was established. The resutls show that the micro cracks in rock after heat treatment increase, and the roughness of thin surface becomes larger. The AE results reveal that the frequency of AE waveforms induced by heating or cooling has two intervals: 0.1-20 kHz and 20-80 kHz. The amplitudes are among 50-70 dB. Different rocks show big alteration in cumulative AE energy. The thermal damage of granites mainly occurs during heating process, while the thermal damage of sandstones mainly appears during cooling process, which reveals a lithology dependency of thermal damage evolution of rocks. The thermal damage evolution model well characterizes the damage variable of rock during heating and cooling processes. The damage mechanisms of granites and sandstones are different. The face-face contact of mineral particles in granite is the reason of dual damages caused by heterogeneous deformation and defective minerals, while the point-point contact of particles in sandstone results in the main damage mechanism due to the defective minerals during cooling process. © 2021, Central South University Press. All right reserved.