A mechanism-based plastic model to simulate the mechanical properties in nanostructured bimodal metals

Engineering a bimodal grain size distribution in nanostructured materials has been proved to effectively achieve both higher strength and higher ductility. In these materials, large grains provide hardening ability and small grains provide larger yield stress. Accounting for the contributions of microcracks which nucleate in the nano/ultrafine grained phase and stop at the boundary of large grains during the plastic deformation, a mechanism-based plastic model is developed to describe the strength and ductility of the bimodal metals. The strain-based Weibull probability distribution function is utilized to predict the failure behavior of the bimodal metals. With the aid of the modified mean field approach, the stress-strain relationship can be derived by combining the constitutive relations of the nano/ultrafine grained phase and the coarse grained phase. Numerical results show that the proposed model can completely describe the mechanical properties of the bimodal metals, including yield strength, strain hardening and uniform elongation. The predictions are in good agreement with the experimental results. These results will benefit the optimization of both strength and ductility by controlling constituent fractions and the size of the microstructures in materials. Copyright © (2013) by International Conference on Fracture.