Atomistic finite element modeling of superlubricity in long double walled carbon nanotubes

Abstract

The question of how much the nanotubes are really superlubricious when they are at macro lengths, is still intriguing. In this research, multiscale modeling of wall separation for various double walled carbon nanotube pairs has been done. VDW forces are modeled by a 3D truss element based on Lennard-Jones potentials, while C–C bonds are modeled by a deformable and equivalent beam elements. In the steady pullout process, we divided DWCNT into 3 main effective segments and characterized their effects separately; (a) free and pulled out length, (b) end atom VDWs, and (c) overlapping region. The effects of each aforementioned segments are separated by doing a proper finite element coding. For the zigzag/zigzag pairs, the end atoms are responsible for the average load while the overlapping region answers the load fluctuation during pullout. Otherwise, for the incommensurate case of zigzag/armchair pair, both end atoms and overlapping loads are constant. Finally for the armchair/armchair DWCNT, the end atom and the overlapping loads both are fluctuating, however at different phases that makes its overall pullout force constant. The methodology and coding introduced in this numerical effort makes it possible to precisely determine the average pullout load for long nanotubes with lengths in the order of hundreds of nanometers in short computational time.