Coupling Mechanism of Dissipated Energy–Electromagnetic Radiation Energy during Deformation and Fracture of Loaded Composite Coal and Rock

Abstract

The nature of composite coal and rock fracture under load is the process of energy conversion inside it, and to explore the coupling mechanism of dissipated energy (DE) and electromagnetic radiation energy (ERE) during the deformation and fracture process of loaded composite coal and rock, based on theoretical mechanics, electromagnetics, and other subject theories, the stress–charge induction signal coupling relationship is deduced and established. On this basis, a coupled mathematical model of dissipated energy–electromagnetic radiation energy (DE–ERE) is established, and uniaxial loading experiments under different loading rates are carried out. The research results show that the energy of the composite coal and rock increases, and the internal free charge transitions from the high-concentration area to the low-concentration area, accumulating charges on the fractured surface, forming a regional electric field, and generating electromagnetic radiation. The change of the charge-induced signal on the surface of the loaded composite coal and rock is phased and has a corresponding relationship with each mechanical phase. Its peak appears earlier than the stress peak. There is a linear relationship between the charge induction signal and stress, and they have a strong correlation, which is consistent with the established mathematical model. The energy conversion characteristics of the composite coal and rock under load have stage characteristics. The elastoplastic period is mostly converted to dissipative energy release, and the increase of plastic deformation leads to rupture. ERE is one of the components of DE. In the early stage of elastoplasticity, the dissipated energy mainly exists in the form of electromagnetic radiation energy, and the change trends of the two are the same. After the peak value, it drops rapidly, and the DE is mainly composed of other destructive energy that causes deformation. The changes in ERE can be used to determine the DE and stress state, providing a new method for preventing coal and rock dynamic disasters.

Stress-Electromagnetic Radiation (EMR) Numerical Model and EMR Evolution Law of Composite Coal-Rock under Load

“…The coal-rock model is a three-layer structure with a diameter of 50 mm and a height of 100 mm. According to the actual and previous results, ,,,, the materials of the coal-rock model from top to bottom are, respectively, set as “rock-coal-rock” and the volume ratio of each layer is 1:1:1. The outer air is spherical with a radius of 150 mm.…”

“…The study showed that the duration of EMR was at the millisecond level. Li et al 25 studied the transformation law between EMR energy and strain energy in the deformation process of loaded composite coal-rock, and their study showed that EMR energy changes have stages, which can be used to obtain the state of coal-rock. Xu et al 26 studied the influence of gas content on the changes of the EMR signal of coal.…”

Destabilization damage characteristics and infrared radiation response of coal-rock complexes

“…The load-damage of coal rock has been broadly researched on by scholars all over the world 9 . They often define the damage criteria form the perspectives of stress and load work and generally believe that the stress–strain of coal rock is bound up with the accumulation and dissipation of energy 10 – 15 . However, some scholars hold the view that the load-damage of coal rock is an energy-driven instability phenomenon, and regard energy accumulation as the essential feature of rock deformation and damage 16 , 17 .…”