Abstract
This study conducts large-scale molecular dynamics (MD) simulations of micro cutting of single crystal 6H silicon carbide (SiC) with up to 19 million atoms to investigate the mechanism of unstable material removal modes within the transitional range of undeformed chip thickness in which either brittle or ductile mode of cutting might occur. Under this transitional range, cracks are always formed in the cutting zone, but the stress states cannot guarantee their propagation. The cutting mode is brittle when the cracks can propagate and otherwise ductile mode cutting happens. Plunge cutting experiment is conducted to produce a taper groove on a 6H SiC wafer. There is a transitional zone between the brittle-cut and ductile-cut regions, which has a mostly smooth surface with a few brittle craters on it. This study contributes to the understanding of the detailed process of brittle-ductile cutting mode transition (BDCMT) as it shows that a transitional range can occur even for single crystals without internal defects and provides guidance for the determination of tcritical from taper grooves made by various techniques, e.g., to adopt larger tcritical around the end of the transitional range to increase machining efficiency for grinding or turning as long as the cracks do not extend below the machined surface.
Highlights
It is well known that brittle materials undergo a transition of cutting mode from brittle to ductile when the machining scale decreases to be small enough, which is referred to as brittle-ductile cutting mode transition (BDCMT) [1,2,3]
This study investigated the transitional process of cutting mode in micro cutting of single crystal 6H silicon carbide (SiC) by large-scale molecular dynamics (MD) simulations with up to 19 million atoms
The mechanism of unstable material removal modes in micro cutting of 6H SiC was investigated by large scale MD simulations and plunge cutting experiment
Summary
It is well known that brittle materials undergo a transition of cutting mode from brittle to ductile when the machining scale decreases to be small enough, which is referred to as brittle-ductile cutting mode transition (BDCMT) [1,2,3] This phenomenon has been extensively studied, e.g., its mechanisms [4,5,6], how it is affected by machining conditions [7,8,9,10], etc., due to its vital importance for achieving super smooth surfaces in ultra-precision machining of brittle materials [11]. While the concept of critical undeformed chip thickness has been widely acknowledged and applied to guide the ultra-precision machining of brittle materials [18,19], the cutting mode transition process around this critical value is not yet physically clear due to the lack of experimental approaches capable of observing the nanoscale cutting process in real time. The findings contribute to the understanding on the detailed process of BDCMT and can be of help for understanding and optimizing the practical machining processes
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