Ultrasonic vibration-assisted rock breaking is a potentially effective technique to accelerate hard rock drilling processes. Fatigue damage is a primary factor that governs rock fragmentation subject to ultrasonic vibration, and when such damage accumulates to a critical level via crack initiation and propagation, macro-damage (e.g., macro-cracks) will occur. To date, however, the specific fatigue damage mechanism of hard rock materials under high-frequency and low-amplitude cyclic loading conditions is still unclear. In the present study, we applied a 2D digital image correlation (2D-DIC) method to measure the full-field strain in granite samples with different loading amplitudes. From these deformation data, the threshold value for rock fragmentation under ultrasonic vibration was obtained, and it was also found that the logarithm of the time required to meet this value decreases linearly with an increasing amplitude coefficient. Then, we conducted numerical simulation based on a 2D particle flow code (PFC2D) to reproduce the crack initiation and propagation processes and explore their mechanisms. The results from the simulation show that due to irreversible sliding under ultrasonic vibration, the difference in the displacement between particles on either side of a crack tip will increase, which leads to an increase in the concentrated lateral tensile stress. When the tensile stress exceeds the strength limit, the crack will initiate and propagate, resulting in fragmentation of rocks.

超声波振动辅助破岩是一种加速硬岩钻孔过程的潜在有效技术。疲劳损伤是控制受超声波振动影响的岩石破碎的主要因素，并且当这种损伤通过裂纹萌生和扩展累积到临界水平时，将发生宏观损伤（例如，宏观裂纹）。然而，迄今为止，硬岩材料在高频低振幅循环加载条件下的具体疲劳损伤机制仍不清楚。在本研究中，我们应用二维数字图像相关 (2D-DIC) 方法来测量具有不同加载幅度的花岗岩样品的全场应变。根据这些变形数据，得到超声波振动作用下岩石破碎的阈值，并且还发现满足该值所需时间的对数随着幅度系数的增加而线性减小。然后，我们基于二维粒子流代码 (PFC2D) 进行了数值模拟，以重现裂纹萌生和扩展过程并探索其机制。仿真结果表明，由于超声振动下的不可逆滑动，裂纹尖端两侧粒子之间的位移差异会增加，从而导致集中横向拉应力增加。当拉应力超过强度极限时，裂纹将萌生并扩展，导致岩石破碎。我们基于二维粒子流代码 (PFC2D) 进行了数值模拟，以重现裂纹萌生和扩展过程并探索其机制。仿真结果表明，由于超声振动下的不可逆滑动，裂纹尖端两侧粒子之间的位移差异会增加，从而导致集中横向拉应力增加。当拉应力超过强度极限时，裂纹将萌生并扩展，导致岩石破碎。我们基于二维粒子流代码 (PFC2D) 进行了数值模拟，以重现裂纹萌生和扩展过程并探索其机制。仿真结果表明，由于超声振动下的不可逆滑动，裂纹尖端两侧粒子之间的位移差异会增加，从而导致集中横向拉应力增加。当拉应力超过强度极限时，裂纹将萌生并扩展，导致岩石破碎。这导致集中横向拉应力的增加。当拉应力超过强度极限时，裂纹将萌生并扩展，导致岩石破碎。这导致集中横向拉应力的增加。当拉应力超过强度极限时，裂纹将萌生并扩展，导致岩石破碎。