Dynamic Mechanical Testing of Nanoporous Gold Using a Shock-Tube Bulge Test

We investigate the behavior of two nanopourous gold (NPG) thin films with different ligament diameters under dynamic bulge testing to understand the effect of ligament diameter on strength. NPG films were prepared by electrochemical dealloying of the surface of a white gold membrane followed by annealing to modify ligament diameters. Bulge tests were carried out using a shock tube, which generates a uniform pressure with a 1ms rise time, causing the thin film to deflect outwards. The NPG film with larger ligament diameter delaminates on the pressure-facing side of the membrane, whereas the film with smaller ligaments remains attached to the membrane. Finite element analysis (FEA) shows that, in addition to deforming in biaxial strain, the membrane also exhibits a transient tensile stress in the direction normal to the membrane surface. We propose that this stress is responsible for the observed delamination and infer that NPG with larger ligaments is weaker under dynamic tensile loading than the NPG with smaller ligaments. Our analysis permits us to estimate an upper bound for the strength of the large ligament NPG sample and a lower bound for the small ligament sample. We compare these findings to the ligament size-dependent mechanical behavior of NPG under quasistatic loading.