Modeling contrary size effects of tensile- and torsion-loaded oligocrystalline gold microwires

TL;DR

This paper models the size-dependent mechanical behavior of oligocrystalline gold microwires under tension and torsion using gradient plasticity, highlighting the importance of microstructural texture in explaining contrary size effects.

Contribution

It introduces a finite element gradient plasticity model that accounts for microstructural texture to explain contrary size effects in gold microwires.

Findings

Texture significantly influences size effects in microwires.

Model reproduces experimental size effects only when texture is considered.

Microstructural variations impact deformation behavior under different loadings.

Abstract

When Chen et al. (2015, Acta Mater. 87, 78-85) investigated the deformation behavior of oligocrystalline gold microwires with varying diameters in both uniaxial tension and torsion, contrary size effects were observed for the different load cases. In accompanying microstructural studies it was found, that the microwires of different thickness reveal distinctive differences in grain size and texture, respectively. As a consequence, a significant influence of these microstructural variations on the determined size effects was assumed. However, within the frame of their work, a direct confirmation could only be presented for the effect of the grain size. In the present work, the size-dependent mechanical response of the microwires is modeled with a gradient plasticity theory. By finite element simulations of simplified grain aggregates, the influence of the texture on the size effects is investigated under both loading conditions. It is shown that the experimentally observed contrary size effects can only be reproduced when taking into account the individual textures of the microwires of different thickness within the modeling.