SGER: Mechanical Behavior of Low Coordination Number Metallic Systems

SGER：低配位数金属系统的机械行为

• 批准号: 0836768
• 负责人: Gary Dargush
• 金额: $ 16万
• 依托单位: SUNY at Buffalo
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-15 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0836768&HistoricalAwards=false
• 关键词: SGER; Mechanical; Behavior; Low; Coordination

TECHNICAL: In this high-risk, high-payoff exploratory research program, the PI investigates the mechanical behavior of low coordination number (LCN) metallic systems and their constitutive equations. The intellectual merit resides in identifying this knowledge gap and in proposing a unique set of experiments and modeling strategies to characterize LCN system mechanical properties. To date, virtually all the research on nano-mechanical properties has focused on systems whose physical dimensions are of the order of tens to hundreds of nanometers. These ?nano? systems share a basic commonality with their bulk counterparts - their atomic coordination number (CN) is the same as that in the bulk (12 for FCC or HCP, 8 for BCC). A fundamental departure in mechanical behavior is expected to occur when the atomic CN changes relative to the bulk. This is because a departure from bulk CN is accompanied by a change in intrinsic properties of the system such as the cohesive energy, modulus, etc. However, little is known about the behavior of systems so small that the total number of atoms constituting the specimen is less than the bulk CN. The transformative nature of these studies can be gauged from the fact that something as elementary as the stress-strain curves for LCN systems remain unknown; the term 'Poisson ratio' makes little sense in LCN systems; modulus (ordinarily an intrinsic property) itself varies with the number of atoms in the system, and surface energy effects are likely dominant. The scientific payoff lies in establishing a new framework for mechanical properties of LCN systems. The high-risk component of this research resides in the ability to reliably make such atomic sized samples and measure their mechanical properties. This is non-trivial. New experimental techniques have to be developed and new concepts have to evolve that currently have no analogs in relatively larger systems. Specific research objectives include: (1) Measure force-displacement curves as a function of CN (12); (2) Infer stiffness as a function of CN from the measured force-displacement curves; (3) Measure force-displacement curves for linear atomic chains and infer the dependence of modulus on chain length; (4) Evaluate the feasibility of detecting transitions between different isomers for a given CN; (5) Develop phenomenological constitutive equations for the above and infer stress-strain curves and moduli. NON-TECHNICAL: This research has significant broader impacts and implications that extend beyond the obvious gains and insight that would be made in understanding the deformation behavior of materials. Results would provide a new intellectual framework for studying not just mechanical behavior of small nano systems, but also an entirely new avenue for treating the problem of deformation in bulk systems. In addition, by establishing basic or elementary constitutive relationships for small coordination systems, the research would impact ongoing studies of mechanics of molecules, biomolecules, and biological cell membranes. The educational broader impacts include training and education of a graduate student who would participate in this cutting edge research at the intersection of metals, mechanical deformation, advanced tools for testing, technique development and modeling.

技术支持：在这个高风险、高回报的探索性研究项目中，PI研究了低配位数（LCN）金属系统的力学行为及其本构方程。智力的优点在于识别这种知识差距，并提出了一套独特的实验和建模策略，以表征LCN系统的机械性能。迄今为止，几乎所有的纳米机械性能的研究都集中在系统的物理尺寸是几十到几百纳米的顺序。这些吗纳米？体系与其本体对应物共享一个基本共性-它们的原子配位数（CN）与本体中的相同（FCC或HCP为12，BCC为8）。当CN原子相对于本体发生变化时，预计会发生机械行为的根本偏离。这是因为偏离散装CN是伴随着系统的固有特性，如内聚能，模量等的变化，然而，很少有人知道系统的行为如此之小，构成试样的原子总数小于散装CN。这些研究的变革性质可以从以下事实来衡量：LCN系统的应力-应变曲线等基本的东西仍然是未知的;“泊松比”一词在LCN系统中几乎没有意义;模量（通常是固有属性）本身随系统中原子的数量而变化，表面能效应可能占主导地位。科学的回报在于建立一个新的框架，力学性能的LCN系统。这项研究的高风险部分在于可靠地制造这种原子大小的样品并测量其机械性能的能力。这不是小事。必须开发新的实验技术，必须发展新的概念，目前在相对较大的系统中没有类似物。 具体的研究目标包括：（1）测量力-位移曲线作为CN（12）的函数;（2）从测得的力-位移曲线推断刚度作为CN的函数;（3）测量线性原子链的力-位移曲线，并推断模量对链长的依赖性;（4）评估检测给定CN的不同异构体之间的转变的可行性;（5）确定不同异构体之间的转变。（5）建立了上述材料的唯象本构方程，并推导出应力-应变曲线和模量。 非技术性：这项研究具有更广泛的影响和意义，超出了理解材料变形行为的明显收获和洞察力。结果将提供一个新的知识框架，不仅研究小纳米系统的力学行为，而且也是一个全新的途径，处理问题的变形在散装系统。此外，通过建立小配位系统的基本或基本本构关系，该研究将影响正在进行的分子，生物分子和生物细胞膜力学研究。教育更广泛的影响包括研究生的培训和教育，他们将参与金属，机械变形，先进的测试工具，技术开发和建模的交叉点的尖端研究。