A fracture mechanics analysis of cutting and machining

The process of cutting and machining is analysed using concepts developed in the fracture analysis of beam specimens. Increasing cutting forces and decreasing tool rake angles lead to a sequence of deformation processes from elastic bending to elastic–plastic bending and finally to shear yielding in the chip. The conditions for each mode of deformation are identified. Fracture toughness is included in the analysis as is, in addition, the notion of root rotation at the crack tip. Under some circumstances this gives rise to the condition of the tool tip touching the crack tip during which energy is transferred directly to the fracture process. The tool–chip interface is characterised by Coulomb friction and by the inclusion of an adhesion toughness to model the effects of hot polymeric chips sticking to the rake face of the tool. The combined effects of bending and shearing leading to chip curling and coiling are also analysed.