Molecular dynamics simulation of time scale effect and lattice transformation of metal nanorod under bending
H.A. WU, G.R.Liu
SMA, National University of Singapore, SG
Keywords: molecular dynamics, nanorod, bending
Mechanical behaviors of materials and structures at nanoscale are essentially different from those at macroscale, resulting from surface effect, size effect and time scale effect. In some experimental research at nanoscale, the bending displacement of nanorod is measured and used to gain the lateral force. But, first, the relation of the force and displacement must be distinctly understood. In our present work, the bending behavior of metal Cu nanorod is simulated by molecular dynamics method. Embedded-atom potential is employed to represent the atomic interactions. The Verlet velocity scheme is implemented as time integration algorithm. A traditional cantilever model is used, but the rod size is 1.6nm×1.6nm×20.2nm. The loading rate varies from 0.2pN/(atom∙0.02ns) to 0.2pN/(atom∙20ns), i.e. from impact loading to quasi-static loading.
The simulation results show that the bending behavior of metal nanorod is significantly loading rate dependent and nonlinear. The deflection-loading curves differ much from each other at different loading rate. The interesting thing is that some deflection curves go down even with the increasing loading, when the bending reaches some extent. The change of behaviors must come from the change of the microstructure of materials. It is found that in the elastic bending process, crystal lattice can transform from FCC structure to HCP structure. After such transformation, the metal nanorod is thickened and shortened. The bending stiffness is remarkablely strengthened. Whether the lattice transformation occurs or not depends on both the loading magnitude and the loading rate. Another deformation mechanism of bending is dislocation, which results in plasticity.
The lattice transformation has not been reported with experimental research results.
NSTI Nanotech 2003 Conference Technical Program Abstract