Size dependence of the Poisson's ratio in single-crystal fcc copper nanobeams

Elastic simulations of single-crystal copper nanobeams, of different cross section sizes and with crystallographic orientations [1 0 0] and [1 1 0] along their length directions, have been performed applying tensile mechanical loading. The molecular dynamics code LAMMPS was employed for the simulations. The Poisson's ratio, which is one of the fundamental measures of the elastic deformation behavior of materials, has been determined. In this paper we present numerical evidence that the Poisson's ratio of nanobeams loaded by finite strains varies with both size and crystallographic orientation. In particular, we provide numerical evidence for that, of the two Poisson's ratio that naturally can be defined for nanobeams loaded in the [1 1 0]-direction, one is negative whereas the other one remains almost constant, irrespective of applied strain. We also show that for nanobeams loaded in the [1 0 0]-direction the values of Poisson's ratio initially decrease, reaches a minimum and thereafter increase with applied strain. For the smallest [1 0 0] cross sections the Poisson's ratios are initially negative, but turn positive at larger strains.