Coal failure behavior under dynamic loading is significant for dealing with the failure issues encountered in underground coal mines. In this study, the crack propagation and internal fracture process of coal under dynamic loading were investigated by a split Hopkinson pressure bar (SHPB) experimental system and numerical approach, respectively. The experimental and numerical results show that the coal crack propagation and internal fracture surface manifest significant multifractal features. Further, multifractal analysis suggests that the multifractal feature becomes more and more significant during the dynamic loading. The formation mechanism of the multifractal features was further discussed, and the result demonstrates that the crack propagation path within coal is essentially a multifractal structure, thus causing the total fracture behavior of coal to show multifractal features under dynamic loading. Moreover, the multifractal spectrum parameter ΔαL was proved to be closely related to the brittle fracture property of coal, which transpires that the multifractal feature is feasible to evaluate the coal brittleness under dynamic loading and also applicable to predict the coal failure risk in underground coal mines.

中文翻译：

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动力荷载作用下煤的裂纹扩展和内部断裂过程的时变多分形分析

动态载荷作用下的煤体破坏行为对于解决煤矿井下的破坏问题具有重要意义。在这项研究中，分别通过分裂霍普金森压力棒（SHPB）实验系统和数值方法研究了动态载荷下煤的裂纹扩展和内部断裂过程。实验和数值结果表明，煤的裂纹扩展和内部断口具有显着的多重分形特征。此外，多重分形分析表明，在动态加载过程中，多重分形特征变得越来越重要。进一步讨论了多重分形特征的形成机制，结果表明煤内部的裂纹扩展路径本质上是一个多重分形结构，从而使煤的总断裂行为在动态载荷下表现出多重分形特征。此外，多重分形谱参数Δα大号被证明与煤的脆性断裂特性密切相关，表明多重分形特征对于评价煤在动载荷作用下的脆性是可行的，也适用于预测煤矿井下煤的破坏风险。