PTFEMD2009 - IOP PUBLISHING JOURNAL OF PHYSICS CONDENSED MATTER J Phys Condens Matter 21(2009 144201(8pp doi:10.1088/0953/144201 The effect of

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IOP P UBLISHING J OURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 21 (2009) 144201 (8pp) doi:10.1088/0953-8984/21/14/144201 The effect of normal load on polytetraFuoroethylene tribology Peter R Barry 1 , Patrick Y Chiu 1 , Scott S Perry 1 , W Gregory Sawyer 1 , 2 , Simon R Phillpot 1 and Susan B Sinnott 1 , 3 1 Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611-6400, USA 2 Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611-6250, USA E-mail: [email protected]±.edu Received 27 July 2008, in ²nal form 7 October 2008 Published 18 March 2009 Online at Abstract The tribological behavior of oriented poly(tetra±uoroethylene) (PTFE) sliding surfaces is examined as a function of sliding direction and applied normal load in classical molecular dynamics (MD) simulations. The forces are calculated with the second-generation reactive empirical bond-order potential for short-range interactions, and with a Lennard-Jones potential for long-range interactions. The range of applied normal loads considered is 5–30 nN. The displacement of interfacial atoms from their initial positions during sliding is found to vary by a factor of seven, depending on the relative orientation of the sliding chains. However, within each sliding con²guration the magnitude of the interfacial atomic displacements exhibits little dependence on load over the range considered. The predicted friction coef²cients are also found to vary with chain orientation and are in excellent quantitative agreement with experimental measurements. (Some ²gures in this article are in colour only in the electronic version) 1. Introduction Poly(tetra±uoroethylene) (PTFE) is known to have a low friction coef²cient [ 1–3 ] and has been used in applications ranging from low friction bearings to nonstick frying pan coatings. It is also known for its excessively high wear rates compared to many common bulk polymers [ 4 ]. Consequently there is a concerted effort to design composites [ 5–7 ]th a t enhance the wear properties of PTFE while maintaining its low friction. A key tool in the collective effort to clarify the origins of friction is atomic-level simulation, which has the ability to provide insight into potential atomic-level mechanisms that may be correlated to macroscopic friction phenomena. Many of the insights recently obtained by atomistic simulation are in good agreement, at least qualitatively, with prior experimental results [ 8–11 ]. For example, in their atomic- scale molecular dynamics friction simulations of hydrogen- terminated diamond (111) against diamond (111) surface 3 Author to whom any correspondence should be addressed. coated with amorphous, hydrogen-free carbon ²lms, Gao et al [ 12 ] predicted similar friction forces for different amorphous ²lm thickness. Their ²ndings on the friction response due to counterface saturation by varying the hydrogen terminations of interfacial carbons are in good qualitative agreement with what is known about diamond-like carbon ²lms [ 13 ]. A more
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.

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PTFEMD2009 - IOP PUBLISHING JOURNAL OF PHYSICS CONDENSED MATTER J Phys Condens Matter 21(2009 144201(8pp doi:10.1088/0953/144201 The effect of

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