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Abstract

In ultra-fine grained and nanocrystalline materials dislocation glide becomes increasingly difficult. Hence, to describe the deformation of such materials, it is important to understand grain boundary sliding and damage accumulation near triple junctions and to formulate valid constitutive relations. For this purpose we have built a representative volume element (RVE) where a cohesive zone model has been developed in which the normal and tangential behavior for special grain boundaries are parameterized based on ab-initio calculations for bi-crystals. This model has been coupled with a dislocation density based crystal plasticity model for the bulk material in order to study the plastic deformation of polycrystalline material in the presence of grain boundary sliding. With the RVE simulations we study competing mechanisms between dislocation slip and grain boundary sliding. Furthermore, we also investigate micro crack nucleation near grain boundary triple junctions. The simulation results reveal that the normal and tangential interface strengths, both, are necessary to obtain a good load carrying capacity of crystal aggregate. Furthermore, grain boundaries with higher interface strength tend to produce stress concentrations and strain heterogeneities and even change the local deformation patterns. This study also finds that grain boundaries with larger misorientations can stably increase the global material strength during the deformation process.