Modeling the strain-hardening effect and plastic deformation of nanocrystalline FCC metals dispersed with the finest grains

A mechanism-based plasticity model focusing on deformation and failure behavior of nanocrystalline (NC) FCC metals dispersed the finest grains (FGs) is proposed. The stress-strain relationship is derived by invoking the impeding effect of the FGs on the movement of grain boundary dislocations along the grain boundaries and the unique role of nanocracks into the constitutive model. A strain-based cumulative distribution function is also included in the present model to account for the contribution of grain boundaries to the local flow stress due to grain refinement during plastic deformation. It is found that the interaction between dislocations and the FGs contributes to the strain-hardening property and the failure behavior is attributed to the nanocrack evolution. Numerical results show that the proposed model can successfully describe the enhanced strength and ductility of the NC metals in previous experimental literatures. It is further noted that the strength and ductility are sensitive to the volume fraction of the FGs and the density of nanocracks. This quantitative continuum plasticity model can be utilized to optimize the mechanical properties of the nanostructured metals by tuning the material structure parameters.