Research on dynamic tensile energy evolution and fractal characteristics of water bearing coal samples

In order to study the energy dissipation law of dynamic tensile deformation and failure process of coal samples with different water content,the split Hopkinson pressure bar (SHPB) test system was used to carry out the dynamic splitting test of different water bearing coal samples under impact loading,and the dynamic tensile failure process of coal samples was observed with ultra high speed digital image correlation (DIC) test system.Based on the analysis of the test results,the change law of energy dissipation characteristics of coal samples with moisture content in the failure process was obtained,and the influence of moisture content on the fractal dimension of broken coal samples was analyzed.The results show that the stress wave is the main control factor of the damage evolution of a large number of micro damage structures and primary pores and voids in coal samples under impact load.The coal and rock mass fracture is a process of energy absorption and dissipation.With the increase of impact load,the dissipated energy density of coal sample increases linearly,but when the incident energy is small,the value of dissipated energy density of coal sample has little difference.The fractal dimension of coal sample changes with loading.Under the same loading pressure,the fractal dimension of saturated coal sample is the largest,while that of dry coal sample is the smallest.The main failure mode of coal sample is tensile splitting,and the failure crack develops along the loading direction,with the first cracks in the middle of the disc,and then multiple secondary cracks are initiated,which increase with the increase of loading pressure.Based on digital image technology,it is found that there are many main strain concentration regions in the middle of saturated coal sample under impact load,and the range gradually expands,and finally develops and penetrates along the radial direction.