Evaluation of internal microcrack evolution in red sandstone based on time–frequency domain characteristics of acoustic emission signals

Abstract Rocks are commonly used as building stone and construction materials in many engineering applications. To study the internal microcrack evolution characteristics of red sandstone specimens during deformation and failure, a uniaxial compression experiment was conducted based on RMT-150C rock mechanics, PCI-II acoustic emission (AE), and the strain acquisition testing systems. For eight red sandstone specimens, the relationships among axial stress, axial strain, acoustic emission events rate, and average frequency centroid were established. The variability of the AE events rate and average frequency centroid of the specimens was analyzed for five cracking levels. Additionally, the relationship between the loading stress corresponding to the minimum average frequency centroid of the AE signals and the peak stress during deformation and failure of the red sandstone specimens was discussed, and critical failure precursor characteristics revealed. Moreover, statistical analysis of the AE signal distribution characteristics of different frequency bands and amplitudes during rock deformation and failure was performed. Based on the difference between the AE signal duration ratio and the specimen rise time, a method for extracting AE characteristic signals during deformation and failure was proposed. Time-frequency analysis was performed on the extracted AE characteristic signals and results showed that the signals were closely related to the axial stress–strain change in the specimens, and were affected by the degree and development of internal microcracks. The wave peaks of the crack closure and linear elastic deformation stage AE characteristic signal frequency domain waveforms are relatively scattered. The wave peaks of the frequency-domain waveforms of the AE characteristic signals during stable and unstable crack growth stages are relatively concentrated.