On the consequences of intrinsic and extrinsic size effects on the mechanical response of nanoporous Au

Abstract

In this study, the consequence of intrinsic and extrinsic size effects on mechanical responses of nanoporous gold is investigated via microcompression testing. By varying the micropillar diameter (D) between 1 µm and 20 µm and the ligament size (L), 50 nm and 350 nm, a critical ratio (α = D/L = 20) was found, above which the test structure can be considered a representative volume element, resulting in identical mechanical response and uniform deformation. Below that value, both flow stress and elastic modulus decrease with decreasing pillar diameter, as evidenced for a measurement series with a fixed ligament size of 350 nm where the flow stress decreased by more than 50% (from approximately 5 to 2.5 MPa) and the elastic modulus was reduced from approximately 0.5 GPa to almost zero. Stochastic behavior along with non-uniform deformation and failure is observed for α < 10, suggesting that the size of the load-bearing units in this material is about 10 times the corresponding ligament size.