Calibration of nanocrystal grain boundary model based on polycrystal plasticity using molecular dynamics simulations

Decohesion parameters are computed for the tilt grain boundaries through molecular simulations and the parameters are employed in a elastoplastic deformation model of a face centered cubic (FCC) nanocrystal. The calibrated continuum grain boundary model accounts for reversible elastic and irreversible inelastic separation sliding deformations. The intragranular plasticity was modeled using a rate independent single crystal plasticity model. Atomistic calculations are presented for a planar, copper grain boundary interface with a tilt lattice misorientation for cases of loading and unloading. The interface models are deformed to full separation and then relaxed to study inelastic behavior. Plots of stress versus displacement show a distinctly different deformation response between normal and tangential interface loading conditions. Two dimensional microstructures uniaxially loaded using the calibrated cohesive model indicate that the macroscopically observed nonlinearity in the mechanical response is mainly due to the inelastic response of the grain boundaries. Plastic deformation in the interior of the grains prior to the initiation of grain boundary cracks was not observed. Although key features of the molecular simulation results have been introduced in the cohesive model, a few discrepancies between the behavior of cohesive model when compared to molecular simulations are noted.