[SY-C5] Multiscale discrete dislocation dynamics modeling of nano-indentation near the grain boundary
Nano-indentaiton is a convenient method to investigate the mechanical properties of material by utilizing the low-loads and small-scale displacements. However, grain boundary (GB) effect on nano-indentation response needs detailed microstructure and mechanism analysis, which has been a long technique challenge. We developed a three-dimensional multiscale modeling framework, which couples the three-dimensional discrete dislocation dynamics with finite element method, and use it to investigate the GB effects on nano-indentation of aluminum bicrystal. The interaction between dislocations and GB is physically considered by introducing a penetrable GB, where dislocation pile-ups can penetrate through GB and dislocation debris at GB can be re-emitted into grain interior. In the simulation, we confirmed two experimentally observed phenomena, i.e., pop-in events and the dependence of indentation hardness on distance to GB. The pop-in events are correlated with the activation and multiplication of dislocations, especially, the GB pop-in event results from the dislocations penetration through GB. By changing the distances from indenter to GB, the simulation shows that the indentation hardness increases with the decrease of GB-indenter distance. The size effect of nano-indentation results from the geometrically necessary dislocation density distributed within the constraint volume between GB and the indenter.