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Research Papers: Elastohydrodynamic Lubrication

The Shear-Thinning Elastohydrodynamic Film Thickness of a Two-Component Mixture

[+] Author and Article Information
Yuchuan Liu, Q. Jane Wang

Center for Surface Engineering and Tribology, Northwestern University, 2145 Sheridan Road, B224, Evanston, IL 60208

Ivan Krupka, Martin Hartl

Institute of Machine and Industrial Design, Faculty of Mechanical Engineering, Brno University of Technology, 61669 Brno, Czech Republic

Scott Bair1

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

1

Corresponding author

J. Tribol 130(2), 021502 (Mar 20, 2008) (7 pages) doi:10.1115/1.2842298 History: Received September 07, 2007; Revised October 31, 2007; Published March 20, 2008

Lubricant base oils are often blends of different molecular weight cuts to arrive at a specified ambient pressure viscosity and, to improve the temperature-viscosity behavior or to simply increase the viscosity, viscosity-modifying polymer additives are often added to the base oil. This paper investigates the effect of mixture rheology on elastohydrodynamic lubrication (EHL) film thickness using EHL contact measurements and a full numerical analysis for three synthetic lubricants including two single-component lubricants PAO650 and PAO100 and a mixture of these. The pressure and shear dependences of the viscosity of these lubricants were measured with high-pressure viscometers; viscosities were not adjusted to fit experiment. The point contact film thicknesses for these lubricants in pure rolling were measured using a thin-film colorimetric interferometry apparatus. Numerical simulations based on the measured rheology show very good agreement with the measurements of film thickness while the Newtonian prediction is up to twice the measurement. These results validate the use of realistic shear-thinning and pressure-viscosity models, which originate from viscosity measurements. It is conceivable that simulation may provide a means to “engineer” lubricants with the optimum balance of film thickness and friction through intelligent mixing of components.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison of the viscosity function for the base oil, PAO100, and original and new viscosity functions for the mixture, PAO100+PAO650. New viscosity measurements at 22°C generated with the 12.67mm cylinder set are indicated by points.

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Figure 2

Comparison of film thickness for PAO650 at 75°C

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Figure 3

Comparison of film thickness for PAO100 at 50°C

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Figure 4

Comparison of film thickness for 20%PAO650+PAO100 at 50°C

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Figure 5

Film thinning ratio for PAO650 at 75°C

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Figure 6

Film thinning ratio for PAO100 at 50°C

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Figure 7

Film thinning ratio for 20%PAO650+PAO100 at 50°C

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Figure 8

Comparison of film thickness between single-component PAO100 and mixture 20% PAO650 in PAO100

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Figure 9

Shear stress profiles for PAO100 and the mixture at different speeds of u=0.003m∕s, 0.03m∕s, and 0.3m∕s

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