Experimental study on the synchronous response of dielectric constant and electromagnetic radiation under uniaxial compression of coal

In order to study the response of relative dielectric constant and electromagnetic radiation of coal at different stages of deformation and failure under uniaxial loading conditions, a synchronous monitoring system for cracks, electrical parameters and the pulse number of electromagnetic radiation of uniaxial compression coal was established. The variation characteristics of relative dielectric constant and electromagnetic radiation with time were tested respectively in the vertical bedding direction of different coal under uniaxial loading, and the variation regularity was discussed. The research results indicate that during the compaction stage of micro-crack, the pulse number of electromagnetic radiation increases and the relative dielectric constant fluctuates to a certain extent with the closure of coal pores and fissures. During the elastic deformation stage, the pulse number of electromagnetic radiation and change of relative dielectric constant decrease and the change curve of relative dielectric constant is close to be linear. During the occurrence and propagation stage of crack, the pulse number of electromagnetic radiation increases compared to the previous stage, the relative dielectric constant fluctuates to a certain extent, and shows the trend of first decreasing and then increasing. During the stage of unstable development of crack until the stage of fracture, the pulse number of electromagnetic radiation shows the peak value, the relative dielectric constant fluctuates obviously and tends to increase at first, then decrease and finally increase again before the stress peak. Through the comparative analysis of relative dielectric constant and the pulse number of electromagnetic radiation, it is found that the increase of electromagnetic radiation generally appears in the area with the large changes of relative dielectric constant.