Mechanism of Chip Formation and Crack Propagation in Ultrasonically Assisted Cutting of Bone Tissue

doi:10.3901/JME.2021.11.069

Abstract

Abstract: Bone cutting with higher efficiency, and lower forces and damage has great benefits for orthopaedic surgeries. However, the hardness, brittleness and anisotropy of cortical bones make it easy to produce irregular crack propagation, large fractured chips and surface damage during the bone cutting, which seriously affects the cutting precision and the removal of tissues and the postoperative recovery. Based on the orthogonal cutting process, the differences of chip formation, crack propagation and cutting force between conventional and ultrasonically assisted cutting of cortical bones have been investigated. A cutting model of the cortical bone based on the extended finite element method considering microstructures was established, and the law of crack initiation and propagation in ultrasonically assisted cutting was analyzed. The results show that the law of crack propagation is different in various cutting directions of bone, and large pieces of fractured chips and serious surface damage are produced in conventional cutting. In ultrasonically assisted cutting, the cracks mainly propagate along the main shear direction, and produce small triangular chips which quickly leave the tool rake face. Compared with the conventional cutting, the main cutting force of ultrasonically assisted cutting is significantly reduced by nearly 70%. The reason is that the high strain rate produced by the high-frequency impact cutting causes the direct penetration of fractures across the osteonal matrix without deflections along the cement lines. So, the crack mainly propagates along the main shear plane and removes the chip, resulting in different chip morphology, reduced cutting forces and lower damage compared with the conventional cutting. The results of this study made significant contributions in theoretical and practical values to revealing the mechanism of ultrasonically assisted cutting and supporting the innovation in surgical instruments.

Key words: cortical bone, ultrasonically assisted cutting, chip formation, crack propagation, extended finite element method

CLC Number:

TH161

BAI Wei, PAN Pengfei, SHU Liming, WANG Dong, ZHANG Jianguo, XU Jianfeng. Mechanism of Chip Formation and Crack Propagation in Ultrasonically Assisted Cutting of Bone Tissue[J]. Journal of Mechanical Engineering, 2021, 57(11): 69-77.

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