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As the grain boundary region has a rather large volume fraction and dislocation glide becomes more difficult for ultra-fine-grain materials, grain boundary sliding and damage accumulation near triple junctions are urgently needed to be understood and formulated in form of constitutive relations. For this purpose we have built one representative volume element (RVE) where a dislocation density based crystal plasticity model and a cohesive zone model have been used to study the plastic deformation of the bulk material in the presence of grain boundary sliding.

In the crystal plasticity model besides considering the evolution of densities of statistically stored dislocations and geometrically necessary dislocations during plastic deformation, dislocation-grain boundary interaction such as building up and relaxing dislocation pile-ups also needs to be taken into account in form of constitutive relations. The cohesive zone model contains parameters which are functions of grain boundary misorientation and can be determined on the atomistic level.

These RVE simulations of deformation of polycrystalline materials with different grain sizes at different temperatures are carried out to study the size effect, competing mechanisms between the dislocation slip and grain boundary sliding, and micro crack nucleation near grain boundary triple junctions.