Plasticity in Polycrystals: Dislocations and Grain Boundaries
In ultra-fine grained and nanocrystalline materials the grain boundary region has a rather large volume fraction and therefore the 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 point 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 for grain boundary and a crystal plasticity model has been adopted for the bulk material to study the grain size effect and competing mechanisms between dislocation slip and grain boundary sliding.With the RVE simulations we study the grain size effect and competing mechanisms between dislocation slip and grain boundary sliding. Furthermore, we also investigate the 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. It is observed in our study that the cohesive zone deformation can contribute significantly to the total plasticity deformation. The figure shows the deformation heterogeneity for RVE with different grain boundary cohesive behaviour.