A new theoretical model is proposed to describe the mechanical properties of bimodal nanocrystalline (BNC) materials.In this paper, we have studied the effect of grain size on the constitutive behavior and fracture of BNC materials. During the plastic deformation, dislocations emission from crack tips on the constitutive behavior of BNC materials are also analyzed, it is found that the nanocracks make a positive effect on the strain hardening instead of leading catastrophic failure. Numerical calculations have been carried out according to the model, the results show that the model can describe the enhanced strength and ductility of BNC materials successfully.

Giving a bimodal grain size distribution in nanocrystalline materials can effectively achieve both high strength and high ductility. Here we propose a theoretical model to study the failure behavior of nc materials with bimodal grain size distribution. The dependence of failure properties on grain size distribution were calculated. Numerical results show the strength and ductility of bimodal nanocrystalline materials are sensitive to grain size and the volume fraction of coarse grains.