Atomistic Simulation And Study Of The Mechanical Properties Of Copper Nanowires Under Torsion

The torsional response of hollow copper nanowires is studied using molecular dynamics simulations, with different loading rates, temperatures and wire lengths. It is found that the critical torsional angle increases with the increase of loading rate and wire length, while it decreases as the temperature rises. Moreover, it is detected that the critical angle per unit length has a strong dependence on the loading rate and temperature but is less sensitive to the wire length. This suggests that a nanowire at lower temperature or higher torsional loading rate exhibits a higher resistance to plastic deformation while the effect of the wire length is not evident.The local atomic structure is identified using the Voronoi construction. Evolution of atomic configuration is studied, which shows that partial dislocations nucleated from the surfaces accommodate the plastic deformation of the nanowires under torsion. Necking is observed and the corresponding cross-section transforms from a hollow square to a solid circle. Most of the atoms in the necking region are found to experience a phase transformation from fcc to amorphous, then rearranged to fcc again, which is more obvious at higher loading rates, accompanied by the propagation of dislocations from the necking zone to the rest part of the nanowires.Finally, the torsional buckling modes of the nanowires are found to strongly depend on the wire length and temperature. A longer wire at a lower temperature displays a more obvious geometrical instability and will reach a larger deflection before the material instability occurs. As the torsional angle increases, the torsional plastic deformation of the nanowires occurs and is mainly mediated by partial dislocation activities, which result in the formation of various stacking faults.