Chip formation and removal mechanisms in cutting of cortical bones with heterogeneous tissue structures

Cortical bone cutting is a common operation in surgery. Studying the potential impact of cortical bone heterogeneity on the processing mechanism will help medical staff to have a deeper understanding of the damage caused by cortical bone cutting (drilling and milling). Therefore, in this paper, the chip formation and removal mechanisms of cortical bone with heterogeneous tissue structures under oblique cutting is studied. The theoretical model of energy release rate under different cutting modes is established and verified by experiments. The results show that when cutting cortical bones with different tissue structures, the energy release rate is different due to the different sizes and distributions of bone units. In the shear cutting and shear crack cutting modes, the energy release rate of the cortical bone structure near the endosteum is higher during the cutting process. It will exceed the fracture toughness of the shear crack cutting and shear fracture cutting modes in advance. The shear crack cutting and shear fracture cutting modes occur at a smaller critical uncut chip thickness. When in shear fracture cutting mode, the energy release rate of the cortical bone tissue near the periosteum will exceed that near the endosteum. The effect of cortical bone structure difference on the critical uncut chip thickness of cutting mode transition is analyzed from the perspective of force and chip morphology. In addition, the machined surface topography is poor when cutting tissue closer to the endosteum cortical bone. This paper provides guidance for analyzing bone tissue damage caused by cutting and optimizing the cutting process.