Dynamic multiscale modeling of materials at the nanoscale

Dynamic coupling of atomistic and continuum computational methods of solids at the nanoscale have received much interest recently, because many problems are not addressed well by either model alone. In the dynamic multiscale approaches, much emphasis has been placed on damping spurious reflections at the interface of the coupled regions. We have revised and extended an existing static coupled method to a dynamic concurrent method at finite temperature in which a damping band (or thermostating zone) minimizes spurious reflections. The coupled formulation is composed of a continuum region (modeled via Finite element) and molecular dynamics in a atomistic region. Our investigation on 1D test simulations of the method clearly shows that the damping band not only dissipates the reflected wave energy from the atomistic/continuum interface but also the energy of waves which are reflected off the FE mesh as it coarsens away from the atomistic region.;The developed method has the ability of treating dislocations as either atomistic or continuum entities within a single computational framework at finite temperature. The method captures, at the same time, the atomistic mechanisms and the long-range dislocation effects without the computational cost of full atomistic simulations. This multiscale model is found to be an effective system for both visualization and quantification of dislocation nucleation and motion, including the deformation of the atomistic region resulting from defect nucleation. We have conducted simulations to study several applications such as nanoindentation, nanoscratching and nanomachining. The results reported here provide direct and fundamental mechanistic insights into the processes associated with contact deformation and quantitative predictions of discrete plasticity events that are consistent with experimental observations.