为研究不同长径比煤样动态压缩下能量耗散规律和破碎分形特征.采用50 mm分离式霍普金森压杆(Split Hopkinson Pressure Bars.SHPB)试验系统.以相同冲击气压0.35 MPa对直径50 mm.长径比分别为0.3.0.4.0.5.0.6.0.7.0.8.0.9和1.0的煤样进行单轴冲击压缩试验.定义了可判定应力平衡状态的指标--应力平衡系数ξ.发现了能量耗散的长径比效应并讨论了其与应力平衡的关系.分析了长径比和耗能密度对煤样破碎分形特征的影响.研究结果表明:不同长径比煤样应力-应变曲线形态基本一致.均包含弹性阶段.塑性阶段和破坏阶段3个阶段.随长径比增加.曲线塑性阶段增大,根据应力平衡系数ξ确定煤样的临界长径比为0.6.低于临界长径比的试件易达到应力平衡.超过临界长径比试件将难以在破坏前达成应力平衡,煤样动态压缩破碎耗能与耗能占比的长径比效应表现为:随长径比增加分2个阶段.且其分界点接近临界长径比.各阶段内呈线性增加关系.阶段间呈台阶式下降,试件尺寸增加引起原生缺陷摩擦耗能增加和端部摩擦效应增强.超过临界长径比的试件应力达到峰值前其变形量降低形成了破碎耗能和耗能占比的台阶式下降,碎块平均粒径随长径比增大线性增加.但破碎块度分形维数呈线性降低,煤样的分形维数与耗能密度呈乘幂关系.耗能密度越大试样越破碎.但其破碎效率逐渐降低.

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.

1 冲击压缩试验

   1.1 试样制备

   1.2 加载方案

   1.3 试验结果

   1.4 煤样动态应力平衡状态分析

2 能量耗散的长径比效应

   2.1 能量计算

   2.2 破碎耗能与耗能占比

3 破碎分布特征与能量演化

   3.1 破碎形态

   3.2 破碎块度分布特征

   3.3 碎块分维与耗能密度

4 结论