Deformation, Strength, Fatigue and Fracture of Gradient Nanostructured Metals

非技术摘要：金属在我们社会的基础设施和整体经济发展中发挥着至关重要的作用，这一点从金属的年全球市场价值接近1万亿美元的事实中可见一斑。在过去的五年中，一种被称为梯度纳米结构金属的新型纳米材料作为一种材料类别出现了，它具有超高强度、良好的拉伸延展性、增强的应变硬化、优异的断裂韧性和抗疲劳性能。然而，目前对控制这些材料性能的基本机制的缺乏严重限制了我们针对特定应用定制或优化它们的性能的能力。另一方面，计算建模和模拟能力的最新进展为我们在微米和纳米尺度上理解材料的力学性质提供了前所未有的机会来推进知识前沿。这项拟议的研究将利用尖端的多尺度建模和模拟方法来解决与梯度纳米结构金属的机械性能和行为有关的基本问题。该项目将对研究生和本科生进行最先进的计算技术培训。技术摘要拟议的研究将解决以下问题：控制梯度纳米结构金属力学性能的变形机制是什么？如何设计梯度微纳米结构来优化梯度纳米结构金属的力学响应？研究中的问题将通过结合有限元方法、应变梯度塑性、内聚力模型、晶体塑性、位错动力学和分子动力学模拟的多尺度模拟方法来解决，以研究梯度纳米结构金属的变形和破坏机制。技术方法将以PI开发的经验和理论/模拟能力为基础。这项工作将通过超大规模和高分辨率的原子和位错动力学模拟来阐明变形控制机制，通过连续应变梯度塑性和疲劳和断裂行为的内聚模拟来解释实验数据和现象，并指导结构优化和加工的进一步研究。拟议工作中的超大规模模拟将在国家计算科学研究所进行，其余拟议的计算工作将在布朗大学计算和可视化中心进行。该项目将对研究生和本科生进行最先进的计算技术培训。

Non-technical Abstract:Metals play essential roles in infrastructural and overall economic developments of our society, as reflected by the fact that the annual global market value of metals is close to a trillion US dollars. During the last five years, a new class of nano materials called gradient nanostructured metals have emerged as a material class which exhibits an unusual combination of ultrahigh strength, good tensile ductility, enhanced strain hardening, superior fracture toughness and fatigue resistance. However, the current lack of understanding of the underlying mechanisms that control the properties of these materials severely limits our ability to tailor or optimize their properties for specific applications. On the other hand, recent advances in computational modeling and simulation capabilities are providing unprecedented opportunities to advance the knowledge frontier in our understanding of mechanical properties of materials at micro- and nano-scales. The proposed research will take advantage of the cutting-edge multiscale modeling and simulation methods to address the fundamental issues with regard to the mechanical properties and behavior of gradient nanostructured metals. The project will train graduate and undergraduate students in state of the art computational techniques. Technical AbstractThe proposed research will address the following questions: What are the deformation mechanisms that control the mechanical properties of gradient nanostructured metals? How to design the gradient micro- and nanostructures to optimize the mechanical responses of gradient nanostructured metals? The problems under study will be tackled via a multiscale modeling approach that combines finite element method, strain gradient plasticity, cohesive modeling, crystal plasticity, dislocation dynamics and molecular dynamics simulations will be used to investigate the deformation and failure mechanisms of gradient nanostructured metals. The technical approach will be based on the experience and theoretical/simulation capabilities developed by the PI. The proposed work will clarify the controlling deformation mechanisms through ultra-large-scale and high-resolution atomistic and dislocation dynamics simulations, interpret the experimental data and phenomena through continuum strain gradient plasticity and cohesive modeling of fatigue and fracture behavior, and guide further research in structural optimization and processing. The ultra-large scale simulations in the proposed work will be performed on the National Institute for Computational Sciences, and the rest of the proposed computational work will be performed at the Center for Computing and Visualization at Brown University. The project will train graduate and undergraduate students in state of the art computational techniques.