Research on dynamic damage path of multi-layered combined coal mass under impact load

Abstract

In this paper, similar materials are used to prepare the multi-layered composited coal mass. Through drop hammer impact multi-layered combined coal mass test, it's found that each layer appears multiple radial cracks, local coal layer appears circumferential cracks to generate petal-shaped fragments. The number of radial and circumferential cracks and petal-like fragments first increases and then decreases with layers increase. Combining the dynamic strain response characteristics, the first layer radial plane produces compression wave in radial direction and tension wave in circumferential direction due to the loading wave. And then, the unloading wave leads to the tension wave in the radial direction and compression wave in the circumferential direction. The impact load propagates as spherical wave within the coal mass, resulting in compressive strains along the axial direction and tensile strains of the coal mass lateral face. Combined with the failure characteristics and dynamic strain response characteristics, it's clear that the radial cracks first appear in each layer, the process of unloading wave meets with plastic loading wave results in tensile stress wave in some layers to form circumferential cracks. The energy attenuation of stress waves affects the number of circumferential cracks and petal-like fragments. In the axial direction, the coal mass forms dense nuclei and undergoes splitting. The radial and circumferential cracks in the radial plane intersect with the boundary to form axial cracks, finally forming the lateral face axial failure mode with less axial cracks in the top and bottom layers, more axial cracks in the middle layers.