Mechanical properties and multi-scale modeling of nanocrystalline materials

A generalized self-consistent scheme based on the coated inclusion method and using interfacial operators is developed and used to describe the grain-size-dependent viscoplastic behavior of pure fcc nanocrystalline materials. The material is represented by an equivalent three-phase material composed of coated inclusions embedded into an equivalent homogeneous medium. Inclusions represent grain cores and behave viscoplastically via dislocation glide while the coating represents both grain boundaries and triple junctions. A recently introduced constitutive law accounting for grain boundary dislocation emission and penetration is used to model the behavior of the coating. The model is applied to pure copper and enables the quantification of the macroscopic effect of interface dislocation emission. The analysis is completed with a set of finite element simulations revealing high stress concentrations at triple junctions.