Ligament size dependency of strain hardening and ductility in nanoporous gold

Abstract

Nanoporous (NP) metals with ligament sizes up to a few tens of nm show exceptional mechanical properties such as high strength and stiffness per weight. While their elasticity and yield strength have been the subject of numerous studies, less is known about the plastic deformability of these materials under large compressive and tensile strains. In this study, the effect of ligament size is investigated using large-scale atomistic simulations to probe the elastic response, plastic response, and deformation mechanisms of nanoporous gold under uniaxial compression and tension to strains in excess of 60 percent. This paper explores the full range of the material response under uniaxial loading, focusing on the modifications to strain hardening under compression and ductility and delayed failure under tension. It was found that the elastic modulus experiences a compression-tension asymmetry that decreases with ligament size increase. Under compression, strain hardening is found to be ligament size dependent. This size dependency can be explained by the coupling effect of the change in surface area to solid volume ratio evolution and defects accumulation. Under tension, the material shows higher ductility with ligament size increase causing a delay in failure. This is attributed to differences in dislocation density. The results reported in this work will help in evaluating the effect of ligament size on the material response, and eventually enhance the design of novel nanoporous foams with tailored mechanical response.