On the transition of failure mechanisms during machining process with varied speeds: A molecular dynamics study

Abstract

Conventional machining theory states that the machining of a ductile material may create continuous, serrated, and/or fragmented chips with increasing machining speeds. In this study, transitions of failure mode under varied machining speeds in single-crystalline silicon were analyzed based on molecular dynamics (MD) simulations of the ultra-high-speed machining of single-crystalline silicon. The MD simulations employ the periodic boundary conditions along the third direction which can mimic the material failure in cutting plane. The uncut depth reaches 39 nm, which is sufficiently large to accommodate complex atomic evolutions. The simulation results indicate that jetted chips occurred in front of the cutter, when the machining speed is increased to approximately 2.7 × 103 m/s, which is attributed to the shock pressure induced by the chip inertia. Essentially, the Rankine-Hugoniot jump conditions were introduced to explain the influence of the shock pressure. Both the calculations based on Rankine-Hugoniot jump conditions and the MD results imply that the shock wave speed is equal to the machining speed at the steady machining state. In addition, the transition from fragmented-chip to jetted-chip morphology exhibits a stage wherein the two primary adiabatic shear bands are simultaneously activated. The present work sheds light on the underlying mechanism of chip formation at an ultra-high-machining speed beyond 1000 m/s.