A new method for molecular dynamics simulation of nanometric cutting

Abstract

Molecular dynamics (MD) simulation of nanometric cutting (ultraprecision machining involving cutting depths of the order of a few ångströms) involves considerable computational time (a few days to several weeks) and significant memory usage even for a few thousand workpiece atoms using workstations with fast processors (e.g. Digital Alpha workstation with 333 MHz clock speed). Consequently, it becomes necessary to use one of the following alternatives: extremely high cutting speeds, (about 500 m s⁻¹), simulations using a smaller number of atoms, two-dimensional modelling, or acceptance of long computational times (several weeks) to address such problems. In order to reduce the computational time and at the same time to reduce the memory requirements significantly, a new method called length-restricted molecular dynamics (LRMD) simulation is proposed. In this method, the length of the work material is maintained constant but its position shifts along the direction of cut, that is atoms from the machined part of the work material that do not significantly affect the results of simulation, are discarded (or saved separately, if need be) and instead their positions are exchanged to accommodate new atoms in the work material ahead of the tool, thus maintaining a constant length. By this technique, a reduction in both the computational time and the memory (over two to three times) is possible depending on the number of atoms considered in the work material without affecting the final outcome. The larger the number of atoms considered, the greater is the reduction in both computational time and memory requirements. It should be noted that, while the LRMD method is illustrated here for nanometric cutting, it can equally be applied for other MD simulations involving a large number of atoms.