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Karl Sieradzki1

1, Arizona State University, Tempe, Arizona, United States

When metallic alloys are exposed to a corrosive environment, porous nanoscale morphologies spontaneously form that can adversely affect the mechanical integrity of engineered structures. Nanoporous gold (NPG) is the prototypical example of the morphology that evolves as a result of such a dealloying process. I will discuss results of experiments exploring the tensile and dynamic fracture properties of NPG. Tensile properties were examined as a function of ligament size and sample density. The statistical distribution of the ligament diameters in these samples was determined and fit to the Weibull distribution. The Young’s modulus was found to obey a power law, but with an exponent larger than that predicted by Gibson-Ashby scaling. The fracture behavior showed a brittle-ductile transition as a function of increasing ligament size. These results are interpreted within the framework of extreme value statistics. The dynamic fracture properties of NPG were examined using and an experimental realization of the “infinite strip” sample and high-speed photography at frame rates of 1 million frames per second. This sample geometry allows for crack growth to occur under essentially fixed values of the stress intensity factor by controlling the strain energy in the system. The crack speed was found to linearly increase with the imposed strain energy up to ~70% of the Rayleigh velocity, at which point crack bifurcations evolve. Finally, I will describe how these results connect to stress-corrosion cracking processes in important engineering alloys such as stainless steel.

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