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Tribology: From Atomic Interactions to Macroscopic Response

摩擦学：从原子相互作用到宏观响应

基本信息

批准号：
1929467
负责人：
Brian Camley
金额：
$ 57.2万
依托单位：
Johns Hopkins University
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2020
资助国家：
美国
起止时间：
2020-01-01 至 2022-02-28
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1929467&HistoricalAwards=false
关键词：
Tribology Atomic Interactions Macroscopic Response

项目摘要

NONTECHNICALThis award supports theoretical and computational research, and education on the microscopic origins of tribology with an aim toward enabling the design of materials with desired tribological properties. Tribology is the study of sliding surfaces and encompasses adhesion, friction, lubrication and wear. The origins of friction have remained one of the great intellectual challenges since da Vinci, and tribological processes have a tremendous impact on daily life and technology. Indeed, friction is estimated to account for more than 20% of global energy consumption. There is a large gap between traditional macroscopic models of tribology, which must be fit to experiments that closely mimic the application, and recent studies that reveal a wealth of intriguing behavior in molecular scale contacts. The goal of the proposed research is to link behavior at these different scales for systems of practical relevance: polymers like plexiglass, layers of short molecules (surfactants) bound to solid surfaces, and small lubricant molecules under the extremes of pressure and shear found in automobile bearings. These systems have been chosen because there is an unusual amount of data from experiments and models at different scales, and because their behavior should be affected by fewer processes than metals or other crystalline systems. Specific questions that will be addressed are: i) How do adhesive and external forces determine the contact area where surfaces interact to produce friction and adhesion? Ii) How does permanent plastic deformation of the surfaces influence contact and friction? Iii) Why does friction in many systems depend on past history as well as the current velocity? Iv) How are changes in the viscosity of lubricants with pressure, temperature and rate related to changes in molecular configurations and/or thermal activation and what may they teach us about the glass transition? The software developed in the project will be shared with other researchers through public repositories and an online tool that provides users with calculated contact properties and builds a database of rough surfaces for future research. Research will involve students from high school through graduate school levels and demonstrations of tribological behavior will be shared with the public through outreach effortsTECHNICAL This award supports theoretical and computational research, and education on the microscopic origins of tribology with an aim toward enabling the design of materials with desired tribological properties. Our ability to probe tribological processes at the nanometer scale has developed rapidly in the last decades, revealing a wide range of new physics and phenomena. However, connecting this rich behavior to the phenomenological models widely used to describe macroscopic experiments has proved extremely challenging. The goal of the proposed research is to use simulations to make this link for specific systems: polymers, self-assembled monolayers and small molecule lubricants, where new theoretical methods, computational algorithms, and experimental techniques are able to bridge the gap between nanometers and micrometers. Multiscale simulations of elastic surfaces will be used to study how van der Waals interactions and roughness on scales up to tens of micrometers determine the contact geometry and macroscopic adhesive force between surfaces. Then the conditions for substrate plasticity to occur and its effects on contact, adhesion and friction will be evaluated. The history dependence of friction is often described by rate-state models that describe the evolution of the sliding interface with a phenomenological “state” variable. Simulations of polymers and self-assembled monolayers will be performed to search for a quantitative link between the changes in state variable and molecular processes. Simulations of surfaces with roughness on nanometer to micrometer scales will be tested against the growing body of experimental data for contact areas, stresses and macroscopic friction coefficients of polymers and self-assembled monolayers. Elastohydrodynamic lubrication offers a window on rheology extremely far from equilibrium, with extreme pressures that may drive fluids through the glass transition and rates high enough to overlap with molecular relaxation times and simulations. Simulations will be used for quantitative tests of assumptions underlying rheological models that assume viscosity is determined by changes in molecular order or stress-biased hopping in a complex energy landscape. They will also test ideas about the nature and existence of the glass transition.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该奖项支持理论和计算研究，以及摩擦学微观起源方面的教育，目的是使设计出具有所需摩擦学性能的材料成为可能。摩擦学是对滑动表面的研究，包括粘着、摩擦、润滑和磨损。自达芬奇以来，摩擦的起源一直是最大的智力挑战之一，摩擦学过程对日常生活和技术产生了巨大的影响。事实上，据估计，摩擦占全球能源消耗的20%以上。传统的摩擦学宏观模型必须适合于接近应用的实验，而最近的研究揭示了分子尺度接触中的大量有趣行为，两者之间存在着巨大的差距。这项拟议研究的目标是将具有实际意义的系统在这些不同尺度上的行为联系起来：有机玻璃等聚合物、结合在固体表面的短分子(表面活性剂)层，以及汽车轴承中发现的在极端压力和剪切下的小润滑油分子。之所以选择这些系统，是因为从不同规模的实验和模型中获得了不寻常的数据量，而且它们的行为应该受到比金属或其他晶体系统更少的过程的影响。将解决的具体问题是：i)粘附力和外力如何确定表面相互作用以产生摩擦和粘合的接触区域？Ii)表面的永久塑性变形如何影响接触和摩擦？Iii)为什么许多系统中的摩擦力既取决于过去的历史又取决于当前的速度？IV)润滑剂粘度随压力、温度和速率的变化与分子构型和/或热激活的变化有什么关系，它们可以教会我们什么关于玻璃化转变的知识？该项目开发的软件将通过公共存储库和一个在线工具与其他研究人员共享，该工具为用户提供计算的接触属性，并为未来的研究建立一个粗糙表面数据库。该奖项支持理论和计算研究，以及摩擦学微观起源方面的教育，目的是设计出具有所需摩擦学特性的材料。在过去的几十年里，我们在纳米尺度上探索摩擦学过程的能力迅速发展，揭示了一系列新的物理和现象。然而，将这种丰富的行为与被广泛用于描述宏观实验的现象学模型联系起来，被证明是极其具有挑战性的。这项拟议的研究的目标是利用模拟将这种联系用于特定系统：聚合物、自组装单分子膜和小分子润滑剂，在这些系统中，新的理论方法、计算算法和实验技术能够弥合纳米和微米之间的差距。弹性表面的多尺度模拟将被用来研究范德华相互作用和几十微米尺度上的粗糙度如何决定表面之间的接触几何和宏观粘附力。然后将评估发生基材塑性的条件及其对接触、附着力和摩擦的影响。摩擦的历史依赖性通常用速率-状态模型来描述，该模型用一个唯象的“状态”变量描述滑动界面的演化。将进行聚合物和自组装单分子膜的模拟，以寻找状态变量变化和分子过程之间的定量联系。对纳米到微米级粗糙表面的模拟将与越来越多的关于聚合物和自组装单分子膜的接触面积、应力和宏观摩擦系数的实验数据进行测试。弹性流体动力润滑提供了一个非常远离平衡的流变学窗口，具有可能驱动流体通过玻璃化转变的极端压力，并且速度足够高，与分子松弛时间和模拟重叠。模拟将用于对流变模型背后的假设进行定量测试，这些假设假设粘度是由分子顺序的变化或复杂能源环境中的应力偏向跳跃决定的。他们还将测试有关玻璃过渡的性质和存在的想法。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。