EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Large-scale atomistic simulations with pre-existing defects are rare, but have recently shown promising potential to study defect-defect interactions in a more realistic fashion. Hitertho, atomistic simulations of nanoindentation to determine the hardness of a material, were usually carried out on defect free crystals. While first investigations with a pre-existing dislocation density showed that the calculated hardness is not influenced by these defects, our study shows, for the first time, that at the early stage of indentation, the calculated hardness values are indeed influenced by pre-existing defects in the specimen, they only converge to an unique hardness value at large indentation depths. As a consequence, hardness measured with a typical indenter size as used in molecular-dynamics simulations, is also influenced by the choice of indented position, as the nature of defects under the indenter changes. Atomistic simulation snapshots show, how the pre-existing dislocations evolve leading to pile ups and seamless growth, which in turn influences the hardness calculations. Alongside, we analyze the influence of indenter radius and find, that for large indentation depths the hardness calculation is driven by curvature accommodation at the surface instead of indenter-defect interactions. Our results also conform to in situ experimental studies.