Abstract
The deformation and fracture evolution of coal and rock under unloading are prone to sudden instability or dynamic damage. To solve the problem, this paper combines interdisciplinary theories such as damage mechanics and electromagnetic field theory. The mathematical model of multiphysics coupling during loading and unloading of composite coal-rock is deduced. In addition, numerical simulations along with experimental verification are carried out to study multi-physical field variation and coupling mechanisms. The composite coal-rock deforms and ruptures under unloading, and the brittle failure of the rock body becomes more sudden when the confining pressure is unloaded. Macroscopically, many microcracks are generated and expanded during the loading and unloading of composite coal-rock. Microscopically, the internal old molecular chains are broken to form new molecular chains by the force. Simulation results show that, during the loading and unloading process, the three physical fields of the composite coal-rock all change regularly. During the unloading of coal and rock, there is a transition period in which the temperature increases sharply and reaches the maximum. Then, the temperature decreases due to the gradual decrease of its bearing capacity. Besides, the electromagnetic field is strongest on the surface of the coal body, and its propagation in the air decays exponentially. There are small fluctuations that appear at the junction of the coal body and the air. The experimental results show that the internal infrared radiation temperature of the composite coal-rock decreases during the initial stage of loading and unloading due to the discharge of internal gas. In the first stage of “loading and unloading,” it increases with the increase in stress, and the temperature suddenly increases in a short time after unloading. The electromagnetic radiation fluctuates in small amplitudes at the initial stage. When the stress is about to reach the peak, the electromagnetic radiation intensity increases and reaches the peak suddenly. Then, the coal-rock ruptures, the stress decreases, and the electromagnetic radiation weakens. The experiment and simulation results are consistent. The multiphysics coupling model is used to study the characteristics of coal and rock unloading under complex conditions, providing a theoretical basis and new method for the prediction and forecast of coal and rock mining dynamic disasters.
Highlights
With the gradual increase of the depth of coal mining in China, the mechanical problems in coal mining have become a research hotspot
Electromagnetic radiation Temperature Stress (b) gradually. e confining pressure influences the triaxial compressive strength but has no effect on the stress change trend in the whole process, and the slope of the curve has not changed. e changing trend of infrared temperature and electromagnetic radiation intensity measured by the experiment is basically consistent with the simulation results; there is no heat exchange between the simulation model and the outside world, so the temperature difference is larger, and the result is more ideal than the experiment, which verifies the correctness of the numerical simulation solution
The crack extends and breaks, the intermolecular chemical bond breaks and recombines, and the variable speed movement of charge causes the change of infrared radiation and electromagnetic radiation
Summary
With the gradual increase of the depth of coal mining in China, the mechanical problems in coal mining have become a research hotspot. In reference [15], the propagation law of ultrasonic signals in coal under different loading conditions was studied, and the ultrasonic testing system for deformation and failure of coal and rock was developed through cyclic loading and unloading. Effective control measures can be taken in time to reduce the casualties and equipment damage caused by rock burst For this reason, the change laws of composite coal-rock under loading and unloading are studied in this paper based on rock mechanics, thermodynamics, and damage mechanics. Evolution laws of stress field, infrared radiation temperature field, and the electromagnetic field of composite coal-rock under the loading and unloading conditions are deeply studied, as well as the relationship among them. Evolution laws of stress field, infrared radiation temperature field, and the electromagnetic field of composite coal-rock under the loading and unloading conditions are deeply studied, as well as the relationship among them. rough multiphysical field simulation and experiment, the prelude change law of composite coal-rock failure and fracture is obtained, which has important theoretical significance and engineering application prospect for coal-rock mining dynamic disaster prediction and prediction
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