Modelling of nanometric cutting in metals using MD simulations

Abstract: This master thesis project has been done within the Mechanics department of Lunds Tekniska Högskola (LTH). It studies the nanometric cutting process of a single crystal copper workpiece by a cubic diamond tool using Molecular Dynamics (MD) simulations on the software LAMMPS. Several simulations are computed in order to study the influence of different factors. In a first place, several tool models are used: one cylindrical shell stiff tool, one cylindrical stiff tool and one cylindrical tool whose atoms are modelled with a Tersoff potential. For these simulations there is first a relaxation of the workpiece and the tool using an NVT ensemble and then the cutting is computed with an NVE one. Because important oscillations are observed, these simulations are repeated with an additional drag function and then with an NPT ensemble using a beam periodic in two dimensions rather than one like before. Even if the latter ensemble do not solve all the oscillations problem, it is relevant enough to be used as a base to test other parameters. A multi-layer cutting is also simulated with a shell stiff tool after an NVT ensemble without drag function. This simulation repeats the cutting process three times in a row on the same workpiece with the same cutting depth for every layer. It is found that the forces and the temperature increase layer after layer. In a second place, the simulations are only performed with a tool whose atoms are modelled with a Tersoff potential, with an NPT relaxation and a two-dimensional periodic beam. Other factors are now studied such as the cutting depth, the tool radius, the workpiece height or the crystallographic orientation of the atoms in the beam. It is shown that the parameters that tend to create a bigger pileup, like deeper cutting depth d or smaller radius r are increasing the cutting forces and the temperature.