Place: "Mechanics Colloquium", Bergische Universität, Wuppertal, Germany
Grain boundaries (GB) play an important role in the plastic deformation of ultra-fine-grained materials as dislocation glide becomes increasingly difficult. Hence, to describe the deformation of such materials, it is important to understand dislocation-GB interaction, GB glide mechanism and even damage accumulation near triple junctions and to formulate valid nonlocal constitutive relations. For this purpose we have built a representative volume element (RVE) where dislocation density based crystal plasticity (CP) model is used to model the bulk material deformation and cohesive zone models (CZM) are used to model the grain boundary behaviour. 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. A recent result of this research has revealed 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.