Length-diameter ratio effect of energy dissipation and fractals of coal samples under impact loading

The research aims to verify the energy dissipation law and fragmentation fractal characteristics under dynamic compression of different length-diameter ratio coal samples. The experiment was to use φ50 mm split Hopkinson pressure bars (SHPB) to compress uniaxial impact with a diameter of 50 mm and a length-diameter ratio of 0.3.0.4.0.5.0.6.0.7.0.8.0.9 and 1.0 with the same impact pressure. This test defines the stress balance coefficient ξ.which can determine the state of stress balance. It also further explores the effects of the length-diameter ratio and stress balance on energy dissipation. The length-diameter ratio and energy consumption density on the fractal characteristics of coal-like crushing were also analyzed. The results show that the morphology of the stress-strain curve of different length-diameter ratio coal samples is elastic stage.plastic stage and failure stage. The study also found that the curve plasticity stage also increases as the length-diameter ratio increases. This means that according to the stress balance coefficient ξ.the critical length-diameter ratio of the coal sample is determined to be 0.6. The specimen below the critical length-diameter ratio can quickly achieve the stress balance. The test piece exceeding the critical length-diameter ratio will be difficult to achieve the stress balance before destruction. In addition.the effect of the energy consumption and energy consumption ratio of coal sample dynamic compression and crushing is manifested as the length-diameter ratio increases in two stages. There is a linear increase relationship within each stage.and there is a step-by-step decline between stages. The increase of specimen size leads to the increase of friction energy consumption of primary defects and the enhancement of friction effect at the end. The decrease of the deformation of the specimen exceeding the critical length-diameter ratio before reaching the peak value results in a step-by-step decrease in the proportion of crushing energy consumption and energy consumption. The conclusion shows that the average particle size of the fragment increases linearly with the increase of the length-diameter ratio. However.the fractal dimension of the fragmentation degree decreases linearly. The fractal dimension of the coal sample has a power relationship with the energy consumption density. Moreover.the larger the energy consumption density.the more the specimen is broken.but its crushing efficiency is gradually reduced.