Numerical Investigation of Size Effects in Tension and Torsion of Micro-scale Copper Wires using a Strain Gradient Modified Johnson-Cook Constitutive Model

While material behaviour on the micro to nanoscale may be investigated using various experimental methods, it is of interest to develop complementary 3-dimensional (3D) numerical approaches to simulate material deformation at such small scales. In particular, these simulations provide a means to shed further light on key mechanisms at play, especially in the region of plastic strain. The size effect in tension and torsion of microscale copper wires is numerically investigated in this study using a strain gradient modified Johnson-Cook method. This 3D algorithm is implemented by self-compiled subroutines using the ABAQUS/Explicit solver. The simulated flow stress and yield stress in torsion of micro-scale copper wires were observed to increase with the decrease of the wire diameter, which correlates well with experimental findings reported in the literature. A similar size effect, although not as significant as that in torsion, was also observed in the simulated tension experiments, again in line with existing experimental reports. This work contributes to the efforts of the research community in the simulation material behaviour at the micro- to nanoscale, especially when considering the combined influence of both size effect and strain rate.