Size Effects on the Mechanical Behavior

Recent nanomechanical tests on submicron metal columns and wires have revealed a dramatic increase in yield strength with decreasing sample size. Here, we demonstrate that nanoporous metal foams can be envisioned as a three-dimensional network of ultrahigh-strength nanowires, thus bringing together two seemingly conflicting properties: high strength and high porosity. Specifically, we characterized the size-dependent mechanical properties of nanoporous gold using a combination of nanoindentation, column microcompression, and molecular dynamics simulations. We find that nanoporous gold can be as strong as bulk Au, despite being a highly porous material, and that the ligaments in nanoporous gold approach the theoretical yield strength of Au. According to current models, the mechanical properties of foams can be described by scaling equations with the relative density of the material as the dominating parameter.1 The mechanical properties of the foam ligaments (or struts), such as the yield strength, are assumed to be bulklike and size-independent, implying that the strength of foam materials always decreases with increasing porosity. On the other hand, recent nanomechanical measurements on submicron A