Multi-scale modeling of shear banding in fully dense nanocrystalline Ni sheet

A multi-scale model for predicting shear localization under quasi-static strain rate was constructed on the basis of experimental observations on the evolution of shear banding in fully dense nanocrystalline Ni sheet. In the framework of the model, the grain geometry, strain rate and temperature-dependent transition between the GB dislocation slip and the GB diffusion were established during process of the shear banding. First, the GB dislocation slip was dominant at small plastic strain stage, and homogeneous deformation was exhibited in this stage. With the increasing strain, the contribution of the GB diffusion increased and the shear banding developed rapidly. To quantitatively analyze this chain mechanism of shear banding, an important dynamic parameter, which indicates the contributions of the two microscopic mechanisms to the shear banding, was introduced effectively. Thus constitutive relation of the shear banding based on the varied microscopic physical mechanisms can be determined. Further, a meso-scale theoretical model was established with gradient theory and tangent modulus approach to predict evolution of characteristic properties of the shear band, such as shear band width and the distribution of shear strain. After the implementation of the multi-scale theoretical modeling, the shear banding behavior in the nanocrystalline Ni sheet can be properly understood and described.