A Model for Predicting the Mechanical Properties of Bimodal Nanocrystalline Materials

Giving a bimodal grain size distribution in nanocrystalline materials can effectively achieve both high strength and high ductility. Here we proposed a theoretical model to study the mechanical properties of nanocrystalline materials with bimodal grain size distribution. The Taylor evolution law and the contribution of back stress introduced by dislocation emission from nano-crack tip were used to describe the flow stress. The dependence of mechanical properties on grain size distribution was calculated. Numerical results show that grain refinement can provide higher strength while grain coarsening can enhance strain hardening to enhance ductility. The calculations are consistent with the experimental data.