Energy dissipation and crushing characteristics of coal-rock-like combined body under impact loading

The impact compression tests on a single coal-like body, a rock-like body and a combined coal-rock-like body are carried out by using the split Hopkinson pressure bar (SHPB). The energy dissipation and fragmentation characteristics of the specimens are analyzed. By screening the coal and rock fragments respectively, the average fragment sizes are obtained. The energy dissipation densities of the two sections are obtained according to the relationship among average fragment size, energy dissipation density and incident energy of single bodies, and the energy absorption characteristics of the two sections are investigated. The results show that the existence of the joint surface makes the propagation of stress pulse between combined specimens and elastic bars more complex, and the dissipated energy is close to that of the single coal body, however smaller than that of the single rock body with large impedance. The degree of energy accumulation of coal section is higher because of the deformation inhibition of the rock section, and the energy dissipation density and crushing degree of coal section are greater than those of the single coal body under the same impact intensity, and the energy transfer of rock section aggravates the crushing degree of the coal section. On the contrary, the energy dissipation density and the crushing degree of rock section are smaller than those of the single rock body. The energy needed for dynamic disaster of composite coal and rock is lower than that of the single coal body because of the higher energy accumulation degree. These conclusions should be considered when understanding the mechanism of rock burst and coal and gas outburst and taking prevention and control measures for these dynamic disasters.