Dynamics behaviour of gas-bearing coal subjected to SHPB tests

Abstract

During impact dynamics experiments, the stress waves such as incident wave, reflected wave, and transmission wave were recorded by using a strain data-collecting subsystem. Experimental results showed that the amplitude of reflected wave and transmission wave was lower than that of incident wave, which was closely related to loading conditions such as axial static load, confining pressure, gas pressure, and impact load. After processing of data on aforesaid waves, stress–strain curves of gas-bearing coal in the experiments were obtained, which presented the following stages: linear elastic stage, “step” characteristic stage, and postpeak decrease stage. Furthermore, relationships between dynamic strength, failure strain, and strain rate presented an exponential trend under different axial static loads. However, the dynamic strength and failure strain increased linearly with strain rate under different confining pressures, gas pressures, and impact loads. It can be concluded that the strain rate effects enabled dynamic characteristics to be comparable at different loading conditions. The dynamic constitutive equation of gas-bearing coal under impact load was then built and verified by comparison between theoretical and experimental results. This effectively illustrated the effects of axial static load, confining pressure, gas pressure, and impact load on dynamic mechanical characteristics of coal samples.