Search for Constitutive Relations for Micromechanics Modeling of Model Nanocrystalline Materials: A Multiscale Approach

===========================摘要=============================在过去的十年中，人们已经合成并广泛研究了1-100纳米的纳米晶材料。这些材料的特点是晶粒尺寸小，原子体积分数大，位于晶粒或界面边界上。它们表现出许多不同寻常的机械性能，使其成为迄今为止仅有的几种纳米级材料系统之一，有可能在民用、机械、运输和工业应用中用作大规模结构材料。然而，随着晶粒尺寸被推到纳米尺度，在确定和理解力学性能及其与微观组织的关系方面的难度成倍增加。因此，各种力学性能的定量本构关系及其与微观组织的关系尚未完全建立。这项工作旨在通过使用大规模原子模拟来寻找纳米晶体材料的微观力学本构关系来填补这一空白。为了实现这一目标，我们计划在纳米尺度环境中对各种详细的微结构及其对本构关系的贡献进行大规模的原子建模。并对模型纳米晶试样的变形过程进行连续模拟。从原子模拟中获得的详细的本构关系和微观结构-性能关系将用于粗粒度建模。提出的主题是及时的，这些问题的答案是材料和力学界迫切需要的。这项工作的成功实施将有助于建立微观结构建模的系统方法，并为纳米尺度多晶材料力学变形的本构建模奠定坚实的基础。

===========================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.