Understanding spherical indentation experiments across the material scales

This presentation concerns the investigation of mechanical responses and mechanical property extractions from spherical indentation tests performed in polycrystalline metals and single crystals with imprints gradually ranging from millimeter to sub-nanometer sizes. Comprehensive continuum plasticity computational simulations are performed to investigate the applicability and improve the accuracy of classic continuum contact mechanics analyses. Specific features under discussion are the concept of the characteristic or representative strain and the transition from elasto-plastic to fully plastic spherical indentations with increasing tip penetration. The opportunities and challenges that this transition represents in the context of mechanical property extractions are further discussed. Continuum crystal plasticity is employed to highlight the main features from the above isotropic analyses that still hold when it comes to the interpretation of spherical indentations performed in anisotropic single crystalline material units. Finally, molecular dynamics simulations are carried-out with the purpose of examining the distinctive mechanisms by which defect nucleation occurs in BCC metals as compared to in FCC metals, as well as the onset of plastic zones and their correlation with the defect mechanisms that produce permanent nanoimprints. This allows us to unravel the origins of the so-called indentation size effects that naturally emerge in nanoindentation testing.