Characterization of the strain rate effect under uniaxial loading for nanoporous gold

Abstract

While several studies assessed the behavior of nanoporous gold (NP-Au) under different loading conditions for various material characteristics and loading scenarios, very limited attention was given to the effect of strain rate on material response. In this study, the effect of strain rate is investigated by performing novel atomistic simulations on NP-Au under uniaxial loading up to large compressive and tensile strains (60% strain) for strain rates in the range of 106/s and 109/s. This paper explores the material response under uniaxial loading and proposes a size, relative density, and strain rate dependent dislocation based constitutive model that describes the plastic flow in NP-Au. In addition, modified Gibson and Ashby (G-A) scaling relations that capture the effect of strain rate are proposed to predict the elastic modulus, yield stress and ultimate stress. The simulation results show that the elastic modulus is strain rate independent similar to that of bulk materials. Additionally, the yield stress and its compression-tension asymmetry are strain rate dependent. Under compression, strain hardening is found to be strain rate dependent, and it is controlled by the amount of dislocation density for strain rates below 108/s; whereas, it is controlled by the coupling effect of dislocation density and dislocation mobility for higher strain rates. Under tension, the material shows higher ductility and softening with increasing strain rate. Also, the material deformation and failing mechanisms change at strain rates exceeding 108/s due to the transition in dislocation activity within the ligaments.