A Critical Assessment of the Role of Viscometers in Quantitative Elastohydrodynamics

Abstract

Until very recently, viscometers have not had a significant role in the development of the field of elastohydrodynamic lubrication (EHL). Viscosity has generally been treated as an adjustable parameter that assumed the values at elevated pressure necessary to validate whatever model was proposed. The description of the pressure dependence of viscosity in EHL requires the choice of a model that reproduces the way that viscosity changes with pressure and requires values for the parameters of the chosen model. Viscometers are necessary for both requirements if a quantitative understanding of the mechanisms of film generation and friction is sought. Four types of pressurized viscometers, two based on Poiseuille flow and two on Couette flow, are investigated here. They yield remarkably similar pressure responses. There is therefore no ambiguity in the measurement of the pressure dependence of viscosity in pressurized viscometers. A significant challenge for engineers wishing to apply the results archived in the EHL literature is the assessment of the extent to which the results would be altered if an accurate viscosity had been employed. An important step toward establishing EHL as a quantitative science would be the designation of reference liquids for the pressure–viscosity effect and the use of these liquids in experimental and analytical investigations of EHL.

KEYWORDS:

• Elastohydrodynamics
• EHL
• Rheology
• Viscosity
• High-Pressure

ACKNOWLEDGEMENT

This work was supported by the National Science Foundation under grant number EEC#0540834.

Review led by Michael Khonsari