ABSTRACT
Experiments have shown that a gradient design, in which grain size spans over four orders of magnitude, can make strong nanomaterials ductile. This chapter presents a developed model to identify the constitutive behavior of all the component layers by considering GNDs and HDI stress. The overall mechanical response is then calculated based on the properties of these individual layers through volume averaging. A dislocation density-based theoretical model has been proposed to describe the strain hardening of gradient IF steels by incorporating GNDs that are associated with the non-uniform deformation as experimentally observed on the lateral surface. A principle assumption has been made that all GNDs in the gradient structure are injected by the observed surface non-uniform deformation. The proposed theoretical framework for gradient nanostructures could be implemented into a finite element scheme to improve the accuracy without imposing some assumptions such as zero stress component along the thickness direction.
