Finite strain analysis of size effects in wedge indentation into a Face-Centered Cubic (FCC) single crystal

The size effect in wedge indentation of an FCC single crystal is investigated. Conventional plasticity fails to describe the mechanical response of crystalline materials at the micron level due to the accumulation of Geometric-Necessary Dislocations (GNDs) which experiments have shown to introduce a size-dependent increase in the apparent yield stress and subsequent hardening. GND-densities scale with the gradient of plastic deformation and their effect on the mechanical response is here modelled by adopting a dissipative strain gradient single-crystal plasticity theory. Numerical solutions to the classical wedge indentation problem are obtained from a purpose-built Finite Element model accounting for finite strains. A special 2D plane strain set-up, with three effective in-plane slip systems, is adopted to comply with state-of-the-art experimental results. The indentation process is modelled for a nearly flat wedge as well as a wedge with an included angle of 90∘. The distribution of slip and the GND-densities are investigated and compared to conventional plasticity predictions.