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Research Papers: Elastohydrodynamic Lubrication

Scale Effects in Generalized Newtonian Elastohydrodynamic Films

[+] Author and Article Information
Ilya I. Kudish

Department of Mathematics, Kettering University, 1700 West Third Avenue, Flint, MI 48504-4898

P. Kumar, M. M. Khonsari

Department of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803

Scott Bair

Center for High-Pressure Rheology, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

J. Tribol 130(4), 041504 (Aug 05, 2008) (8 pages) doi:10.1115/1.2959104 History: Received December 17, 2007; Revised June 16, 2008; Published August 05, 2008

The estimation or prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the lubricant properties have been obtained from a measurement of the central film thickness and the assumption of a classical Newtonian film-thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient, which compensates for shear-thinning. We have shown by a perturbation analysis of limiting cases for fluid with Carreau rheology (represented by Newtonian and power fluid) and by a full EHL numerical solution for Carreau fluid that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning within the inlet zone. The intention here is to show that errors result from extrapolation of Newtonian formulas to different scale and not to provide advice regarding quantitative engineering calculations.

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Copyright © 2008 by American Society of Mechanical Engineers
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