===========================ABSTRACT============================= Nanocrystalline materials with characteristic grain size of 1-100 nanometers have been synthesized and investigated extensively in the last decade. Small sized grains and large volume fraction of atoms sitting on grain or interface boundaries characterize these materials. They exhibit many unusual mechanical properties, making them by far one of only a few nanoscale material systems that have potential to be used as large-scale structural material in civil, mechanical, transport, and industrial applications. However, as the dimensions of the grain size are pushed down to nanometer scale, the degrees of difficulty multiply in determining and understanding the mechanical properties and their relations with microstructures. As a result, quantitative constitutive relations for various mechanical properties and their relation with microstructures have not been fully established. This work aims at filling this gap by searching for micromechanical constitutive relations in nanocrystalline materials using large-scale atomistic simulations. To achieve this goal, we plan to perform large-scale atomistic modeling of various detailed microstructures and their contributions to constitutive relations in nanoscale environment. And to perform continuum modeling of deformation process in model nanocrystalline samples. The detailed constitutive relation and microstructure- property relation obtained from atomistic simulations will be used in corse- grained modeling. The proposed topics are timely and answers to these questions are urgently needed for materials and mechanics community. Successful execution of this proposed work is expected to contribute to establishing systematic approaches for modeling microstructures and laying a solid foundation for constitutive modeling of mechanical deformation in nanoscale polycrystalline materials.
