Understanding fractures creating process during the dynamic indentation of a spherical carbide insert is a key factor to optimize the operation of a percussive drilling system and improve penetration rates and tool life while drilling in hard, abrasive rock formations. This study presents experimental results of dynamic indentation tests with combined action of an impulsive load and a static load of a bit using a single spherical carbide insert on five types of rocks. A dedicated and innovative experimental setup using a gas-gun drop test was developed to reproduce the loading forces and mechanical characteristics of a Down-the-Hole (DTH) hammer drill. A high-speed camera was used to visually determine when the major fractures, such as radial and side cracks, coalesced to create large fragments and to determine the bit displacement curve during the whole indentation process by tracking the end of the bit. To characterize the damage in the rocks, the mass of the fragments was weighed, and the Specific Energy (SE) was calculated. Experimental results showed a strong correlation between the major changes in the slope of the stress signals recorded in the drill bit and the major fragmentation events recorded with the high-speed camera. In the granites, large fragments typically associated to side cracks were generated during the loading phase. In contrast, in the limestone and the sandstone, the fragments were generated during the unloading phase. Finally, it was found that in granites, the earlier the side cracks occur relative to the maximum indentation time, the lower the efficiency of the indentation.

中文翻译：

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岩石单次冲击破碎试验分析


了解球形硬质合金刀片动态压痕过程中的裂缝形成过程是优化冲击钻系统操作并在坚硬、磨蚀性岩层中钻探时提高钻进速度和工具寿命的关键因素。本研究展示了使用单个球形硬质合金刀片在五种岩石上进行冲击载荷和静载荷联合作用的动态压痕测试的实验结果。开发了一种使用气枪跌落测试的专用创新实验装置，用于重现潜孔 (DTH) 冲击钻的负载力和机械特性。使用高速摄像机直观地确定主要裂缝（例如径向裂缝和侧裂缝）何时合并形成大碎片，并通过跟踪钻头末端来确定整个压痕过程中的钻头位移曲线。为了表征岩石中的损坏，对碎片的质量进行了称重，并计算了比能 (SE)。实验结果表明，钻头记录的应力信号斜率的主要变化与高速摄像机记录的主要破碎事件之间存在很强的相关性。在花岗岩中，在加载阶段会产生通常与侧裂纹相关的大碎片。相反，在石灰岩和砂岩中，碎片是在卸载阶段产生的。最后发现，在花岗岩中，相对于最大压痕时间，侧裂纹出现得越早，压痕效率就越低。