MULTISCALE MODELING OF DAMAGE PROCESSES IN fcc ALUMINUM: FROM ATOMS TO GRAINS

Molecular dynamics (MD) methods are opening new opportunities for simulating the fundamental processes of material behavior at the atomistic level. However, current analysis is limited to small domains and increasing the size of the MD domain quickly presents intractable computational demands. A preferred approach to surmount this computational limitation has been to combine continuum mechanics-based modeling procedures, such as the finite element method (FEM), with MD analyses thereby reducing the region of atomic scale refinement. Such multiscale modeling strategies can be divided into two broad classifications: concurrent multiscale methods that directly incorporate an atomistic domain within a continuum domain and sequential multiscale methods that extract an averaged response from the atomistic simulation for later use as a constitutive model in a continuum analysis. In the present work, new approaches to both concurrent and sequential multiscale modeling are developed. A new approach to concurrent MD-FEM coupling uses statistical averaging of the atomistic MD domain to provide displacement interface boundary conditions to the surrounding continuum FEM domain, which, in return, generates interface reaction forces applied as piecewise constant traction boundary conditions to the MD region. Additionally, a new approach to sequential multiscale modeling is developed and based on the definition of a cohesive zone volume element (CZVE). The CZVE is an atomistic analog to the cohesive zone models that are often used to model material degradation in continuum finite element analyses. Taken together, these two approaches are an attempt to recast atomistic processes within a format suitable for inclusion in grain-scale finite element analyses and are providing a necessary step toward true physics-based analysis of damage processes.