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

在过去的十年里，人们合成了具有1-100纳米特征尺寸的===========================ABSTRACT=============================Nanocrystalline材料，并对其进行了广泛的研究。小尺寸的颗粒和大体积分数的原子位于颗粒或界面边界上是这些材料的特征。它们表现出许多不同寻常的机械性能，使它们成为迄今为止少数几个具有在民用、机械、交通和工业应用中作为大规模结构材料的潜在应用的纳米材料系统之一。然而，随着颗粒尺寸被压低到纳米级，确定和理解力学性能及其与微观结构的关系的难度成倍增加。因此，各种力学性能的定量本构关系及其与显微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材料的细观力学本构关系来填补这一空白。为了实现这一目标，我们计划对纳米环境中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模拟。并对模型纳米晶样品中的变形过程进行连续介质模拟。从原子模拟得到的详细本构关系和组织-性能关系将被用于相关颗粒建模。提出的课题是及时的，材料和力学界迫切需要对这些问题的答案。这项拟议工作的成功实施有望有助于建立建模微结构的系统方法，并为纳米多晶材料的机械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.