The Pressure-Viscosity Coefficient for Newtonian EHL Film Thickness With General Piezoviscous Response

[+] Author and Article Information
Scott Bair

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

Yuchuan Liu, Q. Jane Wang

MCC Mechanical Engineering, Northwestern University, 2145 Sheridan RD, #B224, Evanston, IL 60208

J. Tribol 128(3), 624-631 (Mar 03, 2006) (8 pages) doi:10.1115/1.2197846 History: Received November 14, 2005; Revised March 03, 2006

There has been a long-standing need for a piezoviscous parameter αfilm that, together with the ambient viscosity μ0, will completely quantify the Newtonian rheology so that the film thickness for liquids that do not shear-thin in the inlet may be calculated as h=h(μ0,αfilm,), regardless of the details of the pressure-viscosity response. It seems that Blok’s reciprocal asymptotic isoviscous pressure has certain advantages over the conventional pressure-viscosity coefficient, which is poorly suited for this purpose. The first detailed review of piezoviscous models for low pressures is provided. A simulation code that is apparently stable for all realistic pressure-viscosity response was utilized with diverse piezoviscous models and model liquids to develop a satisfactory definition of αfilm that reads αfilm=[1exp(3)][03α*μ(0)dpμ(p)]; 1α*=0μ(0)dpμ(p). In the case of μ=μ0exp(αp),αfilm=α and formulas are provided for other models.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematic of the general pressure-log viscosity response of a glass-forming liquid. Isotherms with temperature increasing to the right (viscosity decreasing with increasing temperature).

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Figure 2

Viscosity of the model liquids, bis(phenoxyphenoxy)benzene, 5P4E, and dipentaerythritol hexaisostearate, DPAS, at temperatures that cause the ambient viscosity and the conventional pressure-viscosity coefficients to converge. The curves represent the Tait-Doolittle free volume model. The low pressure behavior of (a) is shown enlarged in (b).

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Figure 3

Film thickness of the model liquids, measured and simulated

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Figure 4

Pressure profile in the inlet and the maximum inlet pressure depend on the pressure-viscosity response

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Figure 5

Diverse empirical models employed for testing αfilm. Parameters are given in Table 6. These models yield essentially the same film thickness.



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