Study on acoustic emission and infrared radiation characteristics of coal combination with different tectonic coal thickness

To investigate the acoustic emission and infrared radiation characteristics as well as precursor failure signals during the loading and failure processes of composite structures with varying tectonic coal thicknesses, uniaxial compression tests were conducted. The results demonstrate that the deformation and failure of composite specimens undergo four distinct stages: initial compaction, linear elasticity, plasticity, and fracture development. Significant differences in acoustic emission and infrared radiation characteristics are observed across these stages: during the initial compaction stage, acoustic emission signals are weak while infrared temperatures stabilize; in the linear elasticity stage, acoustic emission activity increases slightly with infrared temperatures first decreasing then rising; during the plasticity stage, acoustic emission counts surge rapidly while infrared temperatures continue to climb; and in the fracture development stage, both acoustic emission and infrared temperatures reach their peaks. The evolution patterns remain largely consistent across different tectonic coal thicknesses. The temperature decline during the linear elasticity stage slows slightly compared to the initial compaction stage, while the coal samples maintain continuous temperature increases during the plasticity stage, with the lowest temperature occurring during the elastic phase. As tectonic coal thickness increases, both AE counts and AE energy decrease; acoustic emission activity near peak values diminishes, and the maximum energy released at peaks shows a declining trend; infrared radiation temperatures exhibit a characteristic pattern of stabilization followed by gradual increase. Upon failure, temperatures undergo abrupt changes, with the maximum infrared radiation temperature decreasing as tectonic coal thickness increases. The range of acoustic emission peak count and maximum infrared radiation temperature of tectonic coal assemblages is 1.99 × 10 4 –3.24 × 10 4 , 1.1–5.9 °C, respectively. The acoustic emission test results of coal samples with different tectonic thickness show that the fluctuation of critical precursory point is 77.0–99.6%, and the standard deviation of infrared critical precursory point is 0.74–0.92.