Spectrum Estimation in Autocalibration of Ultrasonic Reflectometry Methods for Lubrication Film Thickness Measurements

The pressure—viscosity coefficient is an indispensable property in the elastohydrodynamic (EHD) lubrication of hard contacts, but often not known. A guess will easily lead to enormous errors in the film thickness. This article describes a method to deduct this coefficient by adapting the value of the pressure—viscosity coefficient until the differences between accurate film thickness approxi-mation values and accurate film thickness measurements over a wide range of values are at a minimum. Eleven film thickness approximation formulas are compared in describing the film thickness of a test fluid with known value of the pressure—viscosity coefficient. The measurement method is based on spacer layer interferometry. It is concluded that for circular contacts the newer more versatile expressions are not better than some older approximations, which are limited to a smaller region of conditions, and that the older fits are as least as appropriate to find the pressure—viscosity coefficient of fluids, in spite of the limited data where they have been based on.

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Some Limitations in Applying Classical EHD Film Thickness Formulas to a High-Speed Bearing

Journal of Lubrication Technology ◽

10.1115/1.3251650 ◽

1981 ◽

Vol 103 (2) ◽

pp. 295-301 ◽

Cited By ~ 11

Author(s):

J. J. Coy ◽

E. V. Zaretsky

Keyword(s):

Film Thickness ◽

High Speed ◽

Heating Effects ◽

Theoretical Predictions ◽

Traction Fluid ◽

Shear Heating ◽

Thickness Measurements ◽

Inner Race ◽

Maximum Stresses ◽

Good Agreement

Elastohydrodynamic film thickness was measured for a 20-mm ball bearing using the capacitance technique. The bearing was thrust loaded to 90, 448, and 778 N (20, 100, and 175 lb). The corresponding maximum stresses on the inner race were 1.28, 2.09, and 2.45 GPa (185,000, 303,000, and 356,000 psi). Test speeds ranged from 400 to 14,000 rpm. Film thickness measurements were taken with four different lubricants: (a) synthetic paraffinic, (b) synthetic paraffinic with additives, (c) neopentylpolyol (tetra) ester meeting MIL-L-23699A specifications, and (d) synthetic cycloaliphatic hydrocarbon traction fluid. The test bearing was mist lubricated. Test temperatures were 300, 338, and 393 K. The measured results were compared to theoretical predictions using the formulae of Grubin, Archard and Cowking, Dowson and Higginson, and Hamrock and Dowson. There was good agreement with theory at low dimensionless speed, but the film was much smaller than theory predicts at higher speeds. This was due to kinematic starvation and inlet shear heating effects. Comparisons with Chiu’s theory on starvation and Cheng’s theory on inlet shear heating were made.

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A New Postulation of Viscosity and Its Application in Computation of Film Thickness in TFL1

Journal of Tribology ◽

10.1115/1.1456090 ◽

2002 ◽

Vol 124 (4) ◽

pp. 811-814 ◽

Cited By ~ 16

Author(s):

Chaohui Zhang ◽

Jianbin Luo ◽

Shizhu Wen

Keyword(s):

Thin Film ◽

Experimental Data ◽

Film Thickness ◽

Solid Surface ◽

Contact Area ◽

Elastohydrodynamic Lubrication ◽

Thin Film Lubrication ◽

Lubrication Film ◽

Viscosity Modification ◽

Film Lubrication

In this paper, a viscosity modification model is developed which can be applied to describe the thin film lubrication problems. The viscosity distribution along the direction normal to solid surface is approached by a function proposed in this paper. Based on the formula, lubricating problem of thin film lubrication (TFL) in isothermal and incompressible condition is solved and the outcome is compared to the experimental data. In thin film lubrication, according to the computation outcomes, the lubrication film thickness is much greater than that in elastohydrodynamic lubrication (EHL). When the velocity is adequately low (i.e., film thickness is thin enough), the pressure distribution in the contact area is close to Hertzian distribution in which the second ridge of pressure is not obvious enough. The film shape demonstrates the earlobe-like form in thin film lubrication, which is similar to EHL while the film is comparatively thicker. The transformation relationships between film thickness and loads, velocities or atmosphere viscosity in thin film lubrication differ from those in EHL so that the transition from thin film lubrication to EHL can be clearly seen.

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