Analysis of damage and energy evolution characteristics of pre-flawed red sandstone based on infrared thermography

The unstable extension of rock fractures is the fundamental cause of danger to the safety of underground engineering. Clarifying the damage and fracture characteristics of rocks under loading is the basis for ensuring the safety of geological engineering. In this paper, an infrared thermography, and acoustic emission (AE) system were used to monitor the damage evolution of red sandstone containing different pre-flawed under uniaxial loading. The mechanical, infrared radiation and AE characteristics of representative specimens containing pre-flawed were investigated. The results show that the crack extension process and failure modes are affected by the different pre-flawed inclinations of the specimens. With the increasing inclination angles, the failure modes of the red sandstones change from axial splitting to tensile-shear conformal damage mode. In addition, the absolute deviation matrix of infrared radiation temperature was proposed, which not only reflects the damage and crack extension process of the specimens but also has an early warning of specimen failure consistent with the AE characteristics. Moreover, the constitutive model of rocks containing pre-flawed under the uniaxial loading was established by combining with cluster analysis, and compared to the experimental results. It is found that the two results have consistency at the peak stresses, while the model stresses of infrared radiation were higher than the test stresses in the initial compaction stage and microcrack extension stage. Furthermore, the rock energy release rate and energy dissipated rate based on infrared radiation were proposed to illustrate the relative intensity of rock energy accumulation and dissipation, which can characterize the rock damage intensity. The research results can provide theoretical and experimental references for real-time, non-destructive, and green monitoring of geoengineering problems using infrared thermography.