The research on the crack propagation mechanism of bone has important research significance and clinical medical value for the selection of cutting parameters and the development of new surgical tools. In this paper, an extended finite element method (X-FEM) model of ultrasonic bone cutting considering microstructure was developed to further study the ultrasonic bone cutting mechanism and to quantitatively analyze the effects of cutting direction, ultrasonic parameters, and cutting parameters on the mechanism of ultrasonic bone cutting crack propagation. The results show that ultrasonic bone cutting is essentially a controlled crack propagation process, in which brittle crack and fatigue crack are the main crack propagation mechanisms. In order to improve the efficiency of ultrasonic bone cutting, large amplitude and high-frequency ultrasonic vibration are preferred. Compared with the other two cutting directions, the crack propagation deflection angle in the transverse cutting direction is the largest, resulting in the worst cutting surface. Therefore, in the path planning of orthopedic surgical robots, the transverse cutting direction should be avoided as much as possible. Frequency only has a significant effect on the crack propagation rate and has a positive correlation. There is a positive correlation between the deflection angle, propagation length, propagation rate, and amplitude, which provides the possibility to control the direction and length of crack propagation by controlling the amplitude of ultrasonic. The feed speed is much lower than the ultrasonic vibration speed, which makes the influence of ultrasonic vibration speed on the crack propagation characteristics dominant. The X-FEM model of ultrasonic bone cutting provides an effective method for selecting reasonable machining parameters of orthopedic robot and optimize the design of ultrasonic osteotome.

骨裂纹扩展机制的研究对于切割参数的选择和新型手术工具的开发具有重要的研究意义和临床医学价值。本文建立了考虑微观结构的超声骨切割扩展有限元法（X-FEM）模型，以进一步研究超声骨切割机理，并定量分析切割方向、超声参数和切割参数对机理的影响。超声骨切割裂纹扩展的研究 结果表明，超声骨切割本质上是一个受控裂纹扩展过程，其中脆性裂纹和疲劳裂纹是主要的裂纹扩展机制。为了提高超声切骨的效率，优选大振幅、高频的超声振动。与其他两个切割方向相比，横向切割方向的裂纹扩展偏转角最大，导致切割面最差。因此，在骨科手术机器人的路径规划中，应尽可能避免横向切割方向。频率仅对裂纹扩展速率有显着影响，且呈正相关。偏转角度、传播长度、传播速率和振幅之间存在正相关关系，这为通过控制超声波振幅来控制裂纹扩展的方向和长度提供了可能。进给速度远低于超声振动速度，这使得超声振动速度对裂纹扩展特性的影响占主导地位。超声骨切割X-FEM模型为选择合理的骨科机器人加工参数、优化超声骨刀设计提供了有效方法。