The relationship between friction and film thickness in EHD point contacts in the presence of longitudinal roughness
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Published version
Author(s)
Guegan, J
Kadiric, A
Gabelli, A
Spikes, H
Type
Journal Article
Abstract
This study investigates friction and film thickness in elastohydrodynamic contacts of machined, rough surfaces, where roughness is dominated by longitudinal ridges parallel to the rolling/sliding direction. A ball-on-disc tribometer was used to simultaneously measure friction and film thickness in rough contacts as well as with nominally smooth specimens for comparison. The studied rough surfaces were selected so that the influence of the root-mean-square roughness and roughness wavelength can be assessed. Friction and film measurements were taken over a range of slide–roll ratios and speeds and with two lubricating oils with different viscosities, hence covering a wide range of specific film thicknesses. The measurements with the nominally smooth specimens show that friction is strongly influenced by thermal effects at high SRRs and that the transition from mixed/boundary to full EHD lubrication occurs at lambda ratios greater than three. At low speeds, the rough specimens are found to generate higher friction than the smooth ones for all the roughness structures considered, and this is shown to be related to the thinner minimum film thickness. Comparison of friction in rough and smooth contacts shows that the total friction in rough contacts can be divided into two components: one that is equivalent to friction in smooth contacts under the same conditions and is dependent on the slide–roll ratio, and the other that is due to the presence of roughness and is independent of the slide–roll ratio under the conditions tested. Further analysis of the minimum film thickness on tops of roughness ridges indicates that even after the full lift-off, an effect of the roughness on friction persists and is most likely related to the local shear stress in the micro-EHD contacts on the top of roughness ridges. At even higher speeds, the difference in friction between the rough and smooth specimens vanishes.
Date Issued
2016-10-17
Date Acceptance
2016-10-05
ISSN
1573-2711
Publisher
Springer Verlag (Germany)
Journal / Book Title
Tribology Letters
Volume
64
Copyright Statement
© The Author(s) 2016
Open Access
This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Open Access
This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Subjects
Mechanical Engineering & Transports
0912 Materials Engineering
0913 Mechanical Engineering
Publication Status
Published
Article Number
ARTN 33