Study of the mechanism of nanoscale ductile mode cutting of silicon using molecular dynamics simulation

In cutting of brittle materials, it was observed that there is a brittle-ductile transition when two conditions are satisfied. One is that the undeformed chip thickness is smaller than the tool edge radius; the other is that the tool cutting edge radius should be small enough—on a nanoscale. However, the mechanism has not been clearly understood. In this study, the Molecular Dynamics method is employed to model and simulate the nanoscale ductile mode cutting of monocrystalline silicon wafer. From the simulated results, it is found that when the ductile cutting mode is achieved in the cutting process, the thrust force acting on the cutting tool is larger than the cutting force. As the undeformed chip thickness increases, the compressive stress in the cutting zone decreases, giving way to crack propagation in the chip formation zone. As the tool cutting edge radius increases, the shear stress in the workpiece material around the cutting edge decreases down to a lower level, at which the shear stress is insufficient to sustain dislocation emission in the chip formation zone, and crack propagation becomes dominating. Consequently, the chip formation mode changes from ductile to brittle.