Multiscale modeling of ductile crystals at the nanoscale subjected to cyclic indentation

A multiscale method is applied to study the response of an aluminum single-crystal substrate to cyclic indentation at finite temperature. The evolution of contact-induced deformation on the nanoscale is controlled based on defect nucleation beneath the indenter. The method allows for visualization of atomistic deformation during loading and unloading. Although there are inherent limitations to our two-dimensional model, we have found qualitative similarities to the mechanisms of homogeneous defect nucleation and deformation in three-dimensional face-centered cubic crystals. It is shown that the atomistic surface roughening process mostly arises from homogeneous dislocation nucleation during successive loading/unloading processes. These sub-surface defects cause major permanent deformation of the substrate during indentation. The slip steps forming on the surface of the indented substrate contribute their own dislocation activity, sending dislocations directly from the surface into the crystal, but those activities mostly remain localized near the indented surface. Force-displacement curves and the hysteresis which occurs due to inelastic deformation and heating of the substrate are studied for each cycle, and correlated with sub-surface and surface nucleation of defects

Finite temperature multiscale computational modeling of materials at nanoscale

The A multiscale computational method (CADD) is presented for modeling of materials at nanoscale whereby a continuum region containing defects is coupled to a fully atomistic region. The method reduces the degree of freedom in simulations of mechanical behavior of nanomaterials without sacrificing important physics. Applications to nanoindentation are used to validate and demonstrate the capabilities of the model

Multiscale modeling of solids at the nanoscale: Dynamic approach

One major class of multiscale models directly couples a region described with full atomistic detail to a surrounding region modeled using continuum concepts and finite element methods. Here, the development of a new dynamic approach to such coupled atomistic-continuum models is discussed with insight into the key ideas and features, with emphasis on fundamental difficulties involved in dynamic multiscale models. Simulations of nanoindentation in single crystals are performed to demonstrate the power of the developed method in capturing both long-range dislocation plasticity and short-range atomistic phenomena during single or cyclic loading without the computational cost of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. The deformation mechanisms and the surface evaluation that occur during a series of single and cyclic indentation simulations are discussed