A Study on the Collapse of Self-Similar Hardening Behavior of Nanostructures

The rate-dependent tensile responses of nanofilms and nanowires made of tungsten, copper, and gold, respectively, are investigated with the molecular dynamics method to understand the collapse of self-similar hardening (smaller is stronger) behavior of nanostructures. It is shown that such collapse is strongly dependent on material properties and specimen geometry. It is also demonstrated that the critical length scale characterizing the collapse of self-similar hardening decreases with the increase of strain rate. The plastic deformations of tungsten nanostructures and copper nanowires are in agreement with the dislocation starvation model for the self-similar hardening behavior, while the observed deformations of gold specimens and copper nanofilms imply that the phenomenon of "smaller is softer" is mainly due to the surface effects.