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Viscosity measurement in thin lubricant films using shear ultrasonic reflection

Kasolang, S. and Dwyer-Joyce, R.S. (2008) Viscosity measurement in thin lubricant films using shear ultrasonic reflection. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 222 (3). pp. 423-429. ISSN 13506501

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Abstract

When a shear ultrasonic wave is incident on a solid and liquid boundary, the proportion that is reflected depends on the liquid viscosity. This is the basis for some instruments for on-line measurement of bulk liquid viscosity. In machine elements, the lubricant is usually present in a thin layer between two rubbing solid surfaces. The thin film has a different response to an ultrasonic shear wave than liquid in bulk. In this work, this response is investigated with the aim of measuring viscosity in situ in a lubricating film. The proportion of the wave reflected at a thin layer depends on the layer stiffness. A shear wave is reflected by the shear stiffness of the thin layer. For a thin viscous liquid layer, the stiffness is a complex quantity dependent on the viscosity, wave frequency, and film thickness. This stiffness is incorporated into a quasi-static spring model of ultrasonic reflection. In this way, the viscosity can be determined from shear-wave reflection if the oil-film thickness is known. The approach has been experimentally evaluated on some static oil film between Perspex plates. Predictions of the spring model gave good measurement up to layer thicknesses of around 15 μm. For thicker layers, the shear stiffness reduces to such an extent that almost all the wave is reflected and the difference associated with the layer response is hard to distinguish from background noise.

Item Type: Article
Copyright, Publisher and Additional Information: Copyright (c) 2008 Professional Engineering Publishing. This is an author produced version of a paper published in ' Journal of Engineering Tribology '. Uploaded in accordance with the publisher's self-archiving policy.
Keywords: Oil-film measurement Shear wave Ultrasonic reflection Ultrasound Viscosity measurement Mathematical models Shear waves Stiffness Thin films Ultrasonic waves Viscosity Shear ultrasonic wave Shear-wave reflection Solid lubricants
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Mechanical Engineering (Sheffield)
Depositing User: Mr Christopher Hardwick
Date Deposited: 18 Aug 2009 14:33
Last Modified: 08 Feb 2013 16:58
Published Version: http://dx.doi.org/10.1243/13506501jet382
Status: Published
Publisher: Professional Engineering Publishing
Refereed: Yes
Identification Number: 10.1243/13506501jet382
URI: http://eprints.whiterose.ac.uk/id/eprint/9165

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