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      Single asperity friction in the wear regime

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      Tsinghua University Press
      single-asperity contact, friction, molecular dynamics, atomic wear, plastic wear

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          We used molecular dynamics simulation to investigate the friction of a single asperity against a rigid substrate, while generating debris. In the low wear regime (i.e., non-linear wear rate dependence on the contact stress, via atom-by-atom attrition), the frictional stress is linearly dependent on the normal stress, without any lubrication effect from the wear debris particles. Both the slope (friction coefficient) and friction at zero normal stress depend strongly on asperity-substrate adhesion. In the high wear regime (i.e., linear wear rate dependence on the contact stress, via plastic flow), the friction-normal stress curves deviate from a linear relation merging toward plastic flow of the single asperity which is independent of the interfacial adhesion. One can further link wear and friction by considering debris generation as chemical reaction, driven by both normal and frictional forces. The coupling between wear and friction can then be quantified by a thermodynamic efficiency of the debris generation. While the efficiency is less than 5% in the low wear regime, indicating poor mechanochemical coupling, it increases with normal stress toward 50% in the high wear regime.

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          Most cited references27

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          Earthquakes and friction laws

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            Stick-slip as a mechanism for earthquakes.

            Stick-slip often accompanies frictional sliding in laboratory experi ments with geologic materials. Shallow focus earthquakes may represent stick slip during sliding along old or newly formed faults in the earth In such a situation, observed stress drops repre sent release of a small fraction of the stress supported by the rock surround ing the earthquake focus.
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              Friction laws at the nanoscale.

              Macroscopic laws of friction do not generally apply to nanoscale contacts. Although continuum mechanics models have been predicted to break down at the nanoscale, they continue to be applied for lack of a better theory. An understanding of how friction force depends on applied load and contact area at these scales is essential for the design of miniaturized devices with optimal mechanical performance. Here we use large-scale molecular dynamics simulations with realistic force fields to establish friction laws in dry nanoscale contacts. We show that friction force depends linearly on the number of atoms that chemically interact across the contact. By defining the contact area as being proportional to this number of interacting atoms, we show that the macroscopically observed linear relationship between friction force and contact area can be extended to the nanoscale. Our model predicts that as the adhesion between the contacting surfaces is reduced, a transition takes place from nonlinear to linear dependence of friction force on load. This transition is consistent with the results of several nanoscale friction experiments. We demonstrate that the breakdown of continuum mechanics can be understood as a result of the rough (multi-asperity) nature of the contact, and show that roughness theories of friction can be applied at the nanoscale.

                Author and article information

                Tsinghua Science and Technology
                Tsinghua University Press (Xueyuan Building, Tsinghua University, Beijing 100084, China )
                05 September 2018
                : 06
                : 03
                : 316-322 (pp. )
                [1]Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
                Author notes
                * Corresponding author: Yunfeng SHI, E-mail: shiy2@ 123456rpi.edu

                Yunfeng SHI. He received his Ph.D. degree in materials science from the University of Michigan, Ann Arbor, in 2006. He then spent two years in North Carolina State University as a postdoctoral research associate. Dr. Shi joins the Department of Materials Science and Engineering at Rensselaer Polytechnic Institute in Fall 2008 as an assistant professor and was promoted to associate professor in 2014. His research focuses on simulation and modeling of advanced materials systems. His recent interests include nanoporous carbon, molecular motors, energetic materials, nanotribology and metallic glasses.

                Yongjian YANG. He received his Ph.D. degree in materials engineering from Rensselaer Polytechnic Institute in Troy, New York in 2017. Now he is a postdoctoral scholar at the Penn State University in State College. His research interests include nanotribology, glass science, metal-organic framework, etc., using molecular simulation.


                This work is licensed under a Creative Commons Attribution 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                Page count
                Figures: 6, Tables: 0, References: 32, Pages: 7
                Research Article

                Materials technology,Materials properties,Thin films & surfaces,Mechanical engineering
                friction,atomic wear,plastic wear,single-asperity contact,molecular dynamics


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