Mechanical properties and energy dissipation laws of coal samples with different length-to-diameter ratios under 3D coupled static and dynamic loads

In order to study the mechanical properties and energy dissipation laws of coal samples with different length-to-diameter ratios under three-dimensional(3D) coupled static and dynamic loads, four groups of cylinder specimens with a diameter of 50 mm and length-to-diameter ratios of 0.5, 0.6, 0.8 and 1.0 were respectively used to carry out 3D coupled static and dynamic loading experiment by using the improved split Hopkinson pressure bar(SHPB). The mechanical properties of coal samples with different length-to-diameter ratios were studied from the aspects of dynamic stress and dynamic strain, and the energy of the coal samples after crushed was analyzed. The results show that the dynamic peak stress and the combined peak stress increase as a power function of the strain rate, and the specimens with large length-to-diameter ratio are more sensitive to the strain rate when the length-to-diameter ratio of the samples is in the range of 0.5-1.0. At the same strain rate, the dynamic peak stress and the combined peak stress increase with increasing the length-to-diameter ratio, and the greater the strain rate, the more significant the length-to-diameter ratio effect. The dynamic peak strain and the dynamic maximum strain increase linearly with increasing the strain rate. There is little difference between the strain rate sensitivities of the dynamic peak strain and the dynamic maximum strain with different length-to-diameter ratios. Under the same strain rate, the dynamic peak strain decreases with increasing the length-to-diameter ratio. The dynamic maximum strain, affected by the double factors of the preload and the maximum allowable deformation of the specimens, decreases first and then increases with increasing the length-to-diameter ratio. The larger the length-to-diameter ratio of the samples, the lower the dissipated energy density and the higher the degree of crushing. The failure mode changes from tensile failure to shear failure with increasing the length-to-diameter ratio. The research results are helpful to explore the failure mechanism under the coupled static and dynamic loads, and provide theoretical support for the prevention and control of rockburst. © 2022, Science Press. All right reserved.