Dynamic fragmentation is one of the primary fracture types for rock mass in rock engineering. The dynamic fragmentation process and dynamic fragment size characteristics are important for the fragmentation optimization in field. Most researchers studied the fragmentation forming process via dynamic compression test using the traditional split Hopkinson pressure bar (SHPB) system, in which the multiple dynamic loading is generally applied on the rock specimen. However, the effect of the multiple loading on the dynamic rock fragmentation characteristics was rarely attempted. In this study, the momentum-trap system is used in SHPB to achieve the single dynamic compressive loading on the rock specimen. Westerly granite and Fangshan marble were chosen to investigate the effect of multiple dynamic compressive loading pulses on the fragmentation characteristics. During the dynamic loading, the fragmentation process was captured using the high-speed camera. The results show that under the specific loading rate, the multiple loading has no influence on measuring the dynamic compressive strength of rocks, but it was observed in the high-speed images that more fragments were produced in the multiple loading. Moreover, the failure mode of tested specimens under distinct compressive loading rates was examined. The results indicate that the fragmentized degree of rocks with single dynamic loading is less than that with multiple dynamic loading at a given loading rate. This trend is relatively obvious when the loading rate is lower. In addition, the D 50 values of rocks with multiple dynamic loading are smaller than those with single dynamic loading. The fragment size distribution also indicates that the multiple loading pulses dominantly influence the produce and size distribution of the fine-grain fragment. Furthermore, the mean fragment size derived from Weibull distribution decreases as the loading rate increases. The multiple loading pulses could decrease the mean fragment size and generate more fine grains when comparing to the fragment size of rocks derived from the single loading pulse. Therefore, the multiple compressive loading may result in an inaccurate fragmentation size analysis, and the single dynamic compressive loading should be applied when evaluating the dynamic fragmentation efficiency of rocks.

中文翻译：

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动态压缩试验中多重动态载荷对破碎特性的影响

动态破碎是岩石工程中岩体的主要断裂类型之一。动态碎片化过程和动态碎片大小特征对于现场碎片化优化具有重要意义。大多数研究人员使用传统的分裂式霍普金森压力棒（SHPB）系统通过动态压缩试验研究破碎形成过程，其中通常对岩石试样施加多重动态载荷。然而，很少有人尝试过多次加载对动态岩石破碎特性的影响。在这项研究中，动量陷阱系统用于 SHPB 以实现对岩石试样的单一动态压缩加载。选择西风花岗岩和房山大理岩研究多个动态压缩加载脉冲对破碎特征的影响。在动态加载过程中，使用高速相机捕捉碎片过程。结果表明，在特定加载速率下，多次加载对岩石动态抗压强度的测量没有影响，但在高速图像中观察到多次加载产生了更多的碎片。此外，还检查了不同压缩载荷速率下测试样品的破坏模式。结果表明，在给定的加载速率下，单次动态加载的岩石破碎程度小于多次动态加载的岩石破碎程度。这种趋势在加载率较低时比较明显。此外，多动载荷岩石的D 50 值小于单动载荷岩石的D 50 值。碎片尺寸分布也表明多次加载脉冲主要影响细粒碎片的产生和尺寸分布。此外，随着加载速率的增加，源自威布尔分布的平均片段大小会减小。与单次加载脉冲产生的岩石碎片尺寸相比，多次加载脉冲可以降低平均碎片尺寸并产生更细的颗粒。因此，多次压缩加载可能导致破碎尺寸分析不准确，评价岩石动态破碎效率时应采用单一动态压缩加载。