Evaluation of the Energy Consumption and Fractal Characteristics of Different Length-Diameter Ratios of Coal under Dynamic Impact
Qiupeng Yuan, Lei Wang, Guangxiang Xie, Shuhao Gu, Naseer Muhammad Khan, Zhenhua Jiao, Huaiqian Liu
Abstract
Coal samples having the same diameter (50 mm) and different length-diameter ratios (l/d), i.e., 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 were tested under dynamic uniaxial impact compression using the Split Hopkinson Pressure Bar (SHPB) experimental system. This study evaluates: (a) The effects of l/d on the energy consumption law and fractal characteristics of coal crushing; (b) The effects of l/d and stress balance on energy dissipation; (c) The effects of l/d and energy consumption density on the fractal characteristics of coal crushing. The findings under different l/d are as follows: (1) The coal samples show similar stress–strain curve shapes in stages including elastic, plastic, and failure stage, which is an “open” shape, the proportion of plastic stage increases, and strain-softening occurs; (2) The dynamic compression dissipation energy and energy consumption ratio of coal shows the same trend, showing two stages with the increase of length-diameter ratio, which increases linearly in the first stage and overall decreases step-by-step; (3) The average particle size increases while fractal dimension of fragmentation decreases linearly, which endorses the decreasing trend of fragmentation degree; (4) It is determined that there is a power relationship between fractal dimension and energy dissipation density; (5) A new index Crushing Density Energy Efficiency (CDEE) is proposed, which can be used to characterize the rock-breaking efficiency of crushing energy consumption under different conditions. This index is inversely proportional to l/d. The research results can provide a basis for the design of top coal caving mining, and the determination of blasting parameters.