Nanoindentation of model diamond nanocomposites: Hierarchical molecular dynamics and finite-element simulations

Complementary molecular dynamics (MD) and finite-element (FE) simulations of model diamond nanocomposites (MDN) subjected to nanoindentation were undertaken to understand how contact behavior pertaining to the surface morphology of MDN surfaces can be spanned from the molecular to the continuum scale. The MD simulations determined that the behavior inside the contact region is influenced by atomic-scale features on the tip and surface, indent location, grain tilt and roughness of the MDN surfaces. In addition, if the atomic-scale surface morphology is treated as a surface roughness within the FE simulations, the same grain orientations, and similar elastic properties are used for both MD and FE simulations, there is reasonable agreement between the contact pressures for relatively low indentation loads and shallow substrates. For larger loads, the contact pressures from the FE simulations deviate somewhat from the MD results near the center of the contact. The contact behavior for length scales that are prohibitive for MD models (e.g., deep substrates) was also examined using FE simulations. This allowed for a detailed investigation of how contact conditions and stick-slip events within the contact evolve as a function of contact pressure and continuum surface stresses.