Characteristics of infrared radiation response during coal damage evolution

In order to reveal the damage and failure mechanism of coal samples and provide theoretical basis and technical support for infrared radiation remote sensing monitoring and early warning of coal-rock dynamic disasters, the uniaxial loading process of coal samples was observed by using infrared thermal imaging technology and strain monitoring technology, and the damage evolution of coal samples was analyzed. The response characteristics of the surface average infrared radiation temperature (AIRT) and infrared thermal images at each stage were analyzed, and the infrared radiation response mechanism during the evolution of coal sample damage was attempted to be revealed. The research results show that the infrared radiation response characteristics of coal samples are related to their failure modes, and the shear failure of coal AIRT generally shows an upward trend, while the tensile failure of coal AIRT generally shows a downward trend. The whole process of damage evolution of coal samples was divided into compaction stage, elastic stage, stable crack propagation stage, unstable crack growth stage and failure stage. It was found that the variation amplitude of AIRT in the unsteady crack growth stage was the smallest (average increase rate of shear failure coal sample was 0.03 ℃. The average decrease rate of tensile failure coal sample is 0.02 ℃), and the variation amplitude is the largest in the failure stage. Before the failure and instability of the sheared coal sample, the thermal effects of the two opposite trends in the infrared thermal image cancel each other, resulting in the “quiet period” of the AIRT curve, which can be used as the infrared radiation precursor of the failure and instability of the coal sample. The response mechanism of infrared radiation is different in different stages of coal damage evolution. In the elastic stage, the infrared radiation information of coal is dominated by thermal elastic effect. In the stable crack propagation stage and the unstable crack propagation stage, the infrared radiation information of shear failure of coal is dominated by the frictional thermal effect and the thermal effect of crack propagation, while the infrared radiation information of tensile failure of coal is dominated by the endothermic effect of tensile deformation.