Surface effects play a central role in the mechanical behaviors of nano-sized solids, causing their properties to be size-dependent. By taking nanofilms and nanowires as examples, a combined continuum-computational approach is adopted to study the properties of solid surfaces. When a nanofilm or nanowire is created by removing from its counterpart bulk material, relaxation occurs inevitably because new surfaces are created. We separate the relaxation process into normal relaxation and parallel relaxation and propose an eigenstress model to calculate the strain energy released during parallel relaxation. After parallel relaxation, a tensile (or compressive) surface eigenstress causes a compressive (or tensile) initial strain in the thin film and the nanowire with respect to its bulk latt...[ Read more ]

Surface effects play a central role in the mechanical behaviors of nano-sized solids, causing their properties to be size-dependent. By taking nanofilms and nanowires as examples, a combined continuum-computational approach is adopted to study the properties of solid surfaces. When a nanofilm or nanowire is created by removing from its counterpart bulk material, relaxation occurs inevitably because new surfaces are created. We separate the relaxation process into normal relaxation and parallel relaxation and propose an eigenstress model to calculate the strain energy released during parallel relaxation. After parallel relaxation, a tensile (or compressive) surface eigenstress causes a compressive (or tensile) initial strain in the thin film and the nanowire with respect to its bulk lattice. The nominal modulus of a thin film or a nanowire is then determined by nonlinear elastic properties of its core and surfaces with initial strain. Moreover, the nominal Young’s modulus of a nanowire determined from bending test exhibit a much more significant size-dependent behavior than in tension/compression. The eigenstress, surface elastic constants, together with bulk nonlinear elastic properties should be used as material constants to predict the elastic behavior of nano-sized solids under various loading conditions.