Orthogonal cutting of cortical bone: Temperature elevation and fracture toughness

During surgical procedures, the heat development of bone cutting can lead to thermal cell necrosis and secondary implant instability. Therefore, fundamental knowledge on heat development and temperature control is crucial. This paper investigates the basic principles of the machining of cortical bone in an orthogonal cutting process. Cutting forces, temperature elevation and chip formation were measured in real time for two different rake angles and six different cutting depths. A non-linear relationship between cutting depth and cutting forces as well as temperature elevation was found. The cutting behavior changed from a ductile to two distinguishable fracture cutting modes with increasing cutting depth. A linear correlation between cutting forces and temperature elevation of both bone chip and workpiece was determined (R2=0.8697). An increasing rake angle lowered cutting forces and temperature elevations significantly and was explained using a fracture mechanics approach. Additionally, a new method to calculate the fracture toughness of (quasi-)brittle materials from orthogonal cutting tests was introduced.