Multiscale study of the dynamic friction coefficient due to asperity plowing
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Multiscale study of the dynamic friction coefficient due to asperity plowing Jianqiao HU1,2, Hengxu SONG3,*, Stefan SANDFELD3, Xiaoming LIU1,2,*, Yueguang WEI4 1
State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
2
School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China
3
Institute for Advanced Simulation, IAS-9: Materials Data Science and Informatics Forschungszentrum Juelich GmbH, Juelich
52425, Germany 4
Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China
Received: 25 May 2020 / Revised: 16 July 2020 / Accepted: 31 July 2020
© The author(s) 2020. Abstract: A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities. Therefore, the frictional properties of the macroscale-level rough surface are determined by the mechanical behaviors of nanoasperity contact pairs under shear. In this work, we first used molecular dynamics simulations to study the non-adhesive shear between single contact pairs. Subsequently, to estimate the friction coefficient of rough surfaces, we implemented the frictional behavior of a single contact pair into a Greenwood-Williamson-type statistical model. By employing the present multiscale approach, we used the size, rate, and orientation effects, which originated from nanoscale dislocation plasticity, to determine the dependence of the macroscale friction coefficient on system parameters, such as the surface roughness,separation, loading velocity, and direction. Our model predicts an unconventional dependence of the friction coefficient on the normal contact load, which has been observed in nanoscale frictional tests. Therefore, this model represents one step toward understanding some of the relevant macroscopic phenomena of surface friction at the nanoscale level. Keywords: multiscale friction; asperity plowing; dislocation plasticity; size/velocity effect; crystal orientation; statistical model
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Introduction
The empirical mathematical summary of Amonton’s first (friction force is proportional to the applied normal load) and second (friction force is independent of the apparent contact area) friction laws is the relation F = μN, where F is the friction force, N is the applied normal load, and μ is the coefficient of friction (COF). Even though Amonton’s law works well for dry friction problems in traditional engineering, the reason for this remains unclear for quite a long time. In
Bowden and Tabor’s work [1], Amonton’s law was explained by the fact that rough surfaces in contact with each other consist of numerous smaller contact pairs. Consequently, the actual contact area due to these microscopic and plastically deformed contact pairs is much smaller than the apparent contact area. Both experimental and numerical studies have found that the real contact area is actually proportional (or quasi-proportional) to the nor
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