Contact, Adhesion and Friction: From Atomic Interactions to Macroscopic Behavior

接触、粘附和摩擦：从原子相互作用到宏观行为

• 批准号: 1411144
• 负责人: Mark Robbins
• 金额: $ 52万
• 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: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1411144&HistoricalAwards=false
• 关键词: Contact; Adhesion; Friction; Atomic; Interactions

Nontechnical SummaryFriction and adhesion affect almost all aspects of technology and everyday life. Despite their importance, our fundamental understanding of their origins and our ability to predict them in practical applications has remained limited. In large part, this is because of the wide range of length scales that are important. Adhesion and friction forces between surfaces result from interactions in regions where atoms are separated by less than a nanometer, but the geometry of these contact regions and the forces within them are determined by subsurface deformations on micrometer and longer scales. Over the last decade, advances in computational algorithms and hardware have begun to allow us to capture all of these length scales for the first time. The results have revealed qualitative shortcomings of traditional engineering models and resulted in simple equations that predict the area and stiffness of the contacts between rough surfaces. The proposed research will extend these studies to calculate friction and adhesive forces. The goal is to provide new understanding of fundamental processes that will allow predictive models for the relation between surface roughness and macroscopic friction and adhesion to be developed. New computational tools will be developed and shared as open source software. Technical SummaryContact, adhesion and friction are complex problems that involve a wide range of length scales. Atomic-scale interfacial interactions determine adhesive and frictional forces, but the area where these forces operate is determined by surface roughness and substrate deformation on nanometer to micrometer or longer scales. Traditional models of contact, adhesion and friction are based on macroscopic continuum equations with phenomenological constitutive relations for the interfacial interactions and macroscopic deformations. By their very nature, continuum equations do not include effects associated with discrete atoms, but most of the adhesive energy comes from changes in separation by a few angstroms and lateral frictional forces on a crystal are periodic with displacements by a lattice constant. The proposed research will address fundamental questions associated with the gaps between atomistic and continuum descriptions. These include the relation between atomic structure and detachment forces, the origins of friction and its connection to roughness, plasticity and disorder, and the extent of correlations in the dynamics at the interface. The goal is to provide new understanding of the physical processes at different scales and develop macroscopic models that incorporate atomic level processes.Efficient multiscale methods that retain atomistic detail at the interface and capture the long-range response of the substrate will be extended, ported to open source simulation packages, and used to simulate contact and friction. The simulations will examine contact of planes and spheres with self-affine or experimentally measured surface roughness. The response of crystals, polymer glasses and elastomers will be studied in elastic and plastic limits with different atomic-scale roughness and adhesive interactions. Studies of contact and adhesion will determine how the contact area and detachment force are related to interfacial interactions, material properties and surface roughness. Studies of friction will address how interactions within these contacts lead to static and kinetic friction, how roughness and plasticity contribute to friction, and examine precursors to steady sliding where only part of the surface slips forward.

非技术摘要摩擦和粘附几乎影响技术和日常生活的所有方面。尽管它们很重要，但我们对它们起源的基本理解以及在实际应用中预测它们的能力仍然有限。在很大程度上，这是因为重要的长度尺度范围广泛。表面之间的粘附力和摩擦力是由原子间隔小于一纳米的区域中的相互作用产生的，但这些接触区域的几何形状及其内部的力是由微米和更长尺度的地下变形决定的。在过去的十年中，计算算法和硬件的进步已经开始使我们第一次能够捕获所有这些长度尺度。结果揭示了传统工程模型的定性缺陷，并得出了预测粗糙表面之间接触面积和刚度的简单方程。拟议的研究将扩展这些研究以计算摩擦力和粘附力。 目标是提供对基本过程的新理解，从而开发表面粗糙度与宏观摩擦和粘附力之间关系的预测模型。新的计算工具将作为开源软件开发和共享。技术摘要接触、粘附和摩擦是涉及各种长度尺度的复杂问题。原子尺度的界面相互作用决定了粘附力和摩擦力，但这些力作用的区域是由表面粗糙度和纳米到微米或更长时间尺度上的基材变形决定的。传统的接触、粘附和摩擦模型基于宏观连续方程，具有界面相互作用和宏观变形的唯象本构关系。就其本质而言，连续介质方程不包括与离散原子相关的效应，但大部分粘附能来自几埃间距的变化，并且晶体上的横向摩擦力随着晶格常数的位移而呈周期性变化。拟议的研究将解决与原子描述和连续描述之间的差距相关的基本问题。这些包括原子结构和分离力之间的关系，摩擦的起源及其与粗糙度、可塑性和无序性的联系，以及界面动力学的相关程度。目标是提供对不同尺度物理过程的新理解，并开发包含原子级过程的宏观模型。保留界面原子细节并捕获基板远程响应的有效多尺度方法将得到扩展，移植到开源模拟包中，并用于模拟接触和摩擦。模拟将检查具有自仿射或实验测量的表面粗糙度的平面和球体的接触。将在具有不同原子级粗糙度和粘合相互作用的弹性和塑性极限下研究晶体、聚合物玻璃和弹性体的响应。对接触和粘附的研究将确定接触面积和分离力与界面相互作用、材料特性和表面粗糙度之间的关系。摩擦研究将解决这些接触内的相互作用如何导致静摩擦和动摩擦、粗糙度和塑性如何导致摩擦，并检查只有部分表面向前滑动的稳定滑动的前兆。