Time-frequency evolution law and generation mechanism of electromagnetic radiation in coal friction process

Abstract Coal rock friction generally exists in various geological movements, and it is of great significance to effectively monitor the friction process. In this paper, the commonly used methods of coal rock friction are systematically summarized, and the double shear friction experimental method suitable for coal friction electromagnetic radiation monitoring is preferentially selected. A coal friction device with controllable lateral pressure was independently developed, coal friction experiments were carried out under different lateral pressure, and the time-frequency evolution law and generation mechanism of electromagnetic radiation in coal friction were studied. The results show that coal friction can generate abundant EMR signals. With increasing coal friction lateral pressure, the EMR signal develops from sparse to abundant, and the signal energy, amplitude, and dominant frequency gradually increase. The EMR signal of the coal friction process shows clear stage characteristics. At the stable sliding stage, the EMR signal is weak and energy is low. At the stick slip stage, the EMR signal is generated intermittently along with the load drop cycle, with more signals and strong intensity. The main mechanisms of coal friction EMR are the frictional slip electrification of the micro-convex body on the coal surface, charge separation, and the variable-speed movement of the charged particles formed by crack propagation of the micro-convex body. These results clarify the mechanical behavior of coal friction sliding instability and the time-frequency evolution law of the EMR of coal friction, which further improves the accuracy of EMR monitoring and early warning of coal rock dynamic disasters.