Dynamic multifractal characteristics of acoustic emission about composite coal-rock samples with different strength rock

Abstract

In order to investigate the instability mechanism of composite coal-rock samples with different strength rock, several uniaxial compression experiments of composite samples were carried out, and dynamic multifractal characteristics of acoustics emission (AE) of composite samples were analyzed, and the influence of rock strength on the failure mechanism and energy evolution of composite samples was revealed. The results show the variation of dynamic multifractal spectrum of AE reflects the changing of crack propagation mode of composite samples during the deformation process. The increasing of rock strength changes the dominant mechanism of crack propagation in the composite sample before yield deformation. The crack propagation mode in the coal of composite sample with low strength rock changes from shear propagation to tensile-shear coexistence, and the crack in the coal of composite sample with high strength rock expands in the form of tensile-shear coexistence. In the elastic stage of composite samples, Δαm of AE energy in coal increases obviously indicating the crack extension mode is becoming complicated, while Δαm of AE energy and count in rock increases slightly and Δαm of AE count in coal and its variation range are small indicating the crack extension mode is simple. The Δαm ascending range of AE energy in coal decreases gradually and the proportion of Δƒm < 0 is more and more with the increasing of rock strength before yield deformation. In the yield deformation and post-peak stage, Δαm of AE energy of composite sample with higher strength rock is less than lower strength rock, which is resulted from the elastic energy releasing of composite sample with higher strength rock is less than lower strength rock. The research results are of great significance for understanding the deformation and failure mechanism of composite samples and the influence of rock on the failure process of composite specimens.