Quasi-continuum study of grain boundary effects on incipient yield of bicrystal aluminum under nanoindentation

In order to study the initial plasticity during nanoindentation of face-centered cubic bicrystal materials in micro-nanoscale, a grain boundary model of twin crystal aluminum was built by the quasicontinuum (QC) multiscale method. Then the nanoindentation process of the model was simulated. The interaction effect of grain boundary (GB) and dislocation was studied when the transition from elastic to plastic deformation happens and the first dislocation emitted. The distance between the indenter and the center of GB was changed in the simulation and the indenter positions during nanoindentation relative to the model might be divided into three regions: GB region, the vicinity of GB, and that far from the GB region. The load versus displacement response curves of different indenter positions in the three regions were presented. The results show that there is no clear change in terms of the incipient yield loading in GB region. With the indenter far away from the GB, the incipient yield strength may fluctuate regularly. It may increase in the vicinity of GB, then decreases when the indenter is further. The force of the incipient yield was affected by quantity, relative position to GB and the density of the first dislocation emission.