Experimental Study on the Dynamic Tensile Characteristics of Coal Samples

As coal mines continue deep mining, the frequency of coal and rock dynamic disasters has also gradually increased. In this paper, dynamic tensile strength deformation, energy evolution, and crack development under an impact test were studied on Brazilian coal samples, using a split Hopkinson pressure bar (SHPB) test device. A high-speed camera was adopted to capture the failure process of the coal specimens. The research results demonstrate that when the impact velocity is greater than 4.75 m/s, the dynamic tensile strength of the vertical bedding direction is higher than that of the parallel bedding direction of the coal samples. With the increase in the impact velocity, the dynamic strain and ultimate strain rate of two types of coal samples are increased, and the average value of the first and second dynamic deformation moduli of coal samples shows decreasing characteristics. As the incident energy increases, the sum of reflected and transmitted energy increases, and the absorbed energy also increases in the two types of coal samples. The two types of Brazilian disc coal samples mainly showed tensile and shear failure characteristics. The dynamic tensile deformation characteristics of the two types of coal specimens are less affected by the impact angles. However, the crack propagation of coal samples was mainly influenced by the impact angles. The test results can be used for the prediction of coal and rock outburst in deep underground coal excavation.