Calculation of Clearances in Soft Point Contacts

1988 ◽  
Vol 110 (1) ◽  
pp. 167-173 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Film Thickness ◽  
Point Contacts ◽  
Upstream Side ◽  
Narrow Region ◽  
Minimum Film Thickness ◽  
Soft Point

The clearances in highly deformed contacts are formed in a narrow region on the upstream side, are convected through the contact with little change and emerge downstream where a restriction forms in a narrow exit zone. The paper describes how this behavior simplifies the lubrication analysis. Expressions for the minimum film thickness under point contacts are obtained for the elastic isoviscous regime.

Roughness Amplitude Reduction Under Non-Newtonian EHL Conditions

2005 ◽  
Author(s):  
A. D. Chapkov ◽  
C. H. Venner ◽  
A. A. Lubrecht
Keyword(s):  
Film Thickness ◽  
Pressure Fluctuations ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Quantitative Prediction ◽  
Point Contacts ◽  
Minimum Film Thickness ◽  
Roughness Amplitude ◽  
Average Film Thickness ◽  
Ehl Contact

The influence of surface roughness on the performance of bearings and gears operating under ElastoHydrodynamic Lubrication (EHL) conditions has become increasingly important over the last decade, as the average film thickness decreased due to various influences. Surface features can reduce the minimum film thickness and thus increase the wear. They can also increase the temperature and the pressure fluctuations, which directly affects the component life. In order to describe the roughness geometry inside an EHL contact, the amplitude reduction of harmonic waviness has been studied over the last ten years. This theory currently allows a quantitative prediction of the waviness amplitude and includes the influence of wavelength and contact operating conditions. However, the model assumes a Newtonian behaviour of the lubricant. The current paper makes a first contribution to the extension of the roughness amplitude reduction for EHL point contacts including non-Newtonian effects.

An Interpolation Procedure for the Minimum Film Thickness in Point Contacts

1990 ◽  
Vol 204 (3) ◽  
pp. 199-206 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Contact Geometry ◽  
High Accuracy ◽  
Operating Conditions ◽  
Experimental Results ◽  
Point Contacts ◽  
Design Charts ◽  
Minimum Film Thickness ◽  
Interpolation Procedure

Most engineering point contacts operate in, or close to, the elastic piezoviscous regime. A general interpolation procedure is presented by which the minimum film thickness in any such contact may be estimated. This procedure matches all existing numerical and experimental results with high accuracy. Design charts are provided and these enable the minimum film thickness to be read directly and also allow the effect of changes in contact geometry and operating conditions to be assessed.

An Experimental Evaluation of the Hamrock and Dowson Minimum Film Thickness Equation for Fully Flooded EHD Point Contacts

1981 ◽  
Vol 103 (2) ◽  
pp. 284-294 ◽  
Author(s):  
K. A. Koye ◽  
W. O. Winer
Keyword(s):  
Experimental Data ◽  
Statistical Analysis ◽  
Film Thickness ◽  
Experimental Evaluation ◽  
Point Contact ◽  
Major Axis ◽  
Point Contacts ◽  
Lubricant Film Thickness ◽  
Minimum Film Thickness ◽  
Ellipticity Ratio

Fifty-seven measurements of the minimum lubricant film thickness separating the elastohydrodynamically lubricated point contact of a steel crowned roller and a flat sapphire disk were made by an optical interferometry technique. The data collected were used to evaluate the Hamrock and Dowson minimum EHD film thickness model over a practical range of contact ellipticity ratio where the major axis of the contact ellipse is aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that the experimental data averaged 30 percent greater film thickness than the Hamrock and Dowson model predicts.

Effect of Stiff Coatings on EHL Film Thickness in Point Contacts

2007 ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Dong Zhu
Keyword(s):  
Film Thickness ◽  
Working Conditions ◽  
Coating Thickness ◽  
Point Contact ◽  
Thickness Variation ◽  
Point Contacts ◽  
Lubricant Film Thickness ◽  
Wide Range ◽  
Minimum Film Thickness ◽  
Coating Material Properties

This study investigates the influences of coating material properties and coating thickness on lubricant film thickness based on a point-contact isothermal EHL model developed recently by the authors. The results present the trend of minimum film thickness variation as a function of coating thickness and elastic modulus under a wide range of working conditions. Numerical results indicates that the increase in minimum film thickness, Imax, and the corresponding optimal dimensionless coating thickness, H2, can be expressed in the following formulas: Imax=0.766M0.0248R20.0296L0.1379exp(−0.0245ln2L)H2=0.049M0.4557R2−0.1722L0.7611exp(−0.0504ln2M−0.0921ln2L) These formulas can be used to estimate the effect of a coating on EHL film thickness.

The Elastohydrodynamic Lubrication of Elliptical Point Contacts Operating in the Isoviscous Region

1995 ◽  
Vol 209 (4) ◽  
pp. 225-234 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Radius Ratio ◽  
Point Contacts ◽  
Reasonable Estimate ◽  
Wide Range ◽  
Minimum Film Thickness

The elastohydrodynamic lubrication of point contacts is examined and results for the minimum film thickness are presented for a wide range of radius ratios and operating conditions. The results are compared with the predictions of the appropriate regime formulae. Although these formulae give a reasonable estimate of the contact's behaviour, the actual clearances are often substantially different, particularly close to the regime boundaries. Interpolation equations for seven values of radius ratio are given and these should be sufficient to allow the minimum clearance to be estimated for most isoviscous point contacts.

Experimental Evaluation of EHD Film Shape and Its Comparison With Numerical Solution

2000 ◽  
Vol 122 (4) ◽  
pp. 689-696 ◽  
Author(s):  
I. Krˇupka ◽  
M. Hartl ◽  
R. Polisˇcˇuk ◽  
J. Cˇerma´k ◽  
M. Lisˇka
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
Three Dimensional ◽  
Ccd Camera ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Point Contacts ◽  
Ehd Lubrication ◽  
Pure Rolling ◽  
Minimum Film Thickness

Colorimetric interferomentry has been applied to the study of EHD lubrication of point contacts under pure rolling conditions to obtain lubricant film shapes with high accuracy and resolution. An RGB CCD camera together with an extensive image processing software has enabled real time evaluation of chromatic interferograms. The classical numerical isothermal solution of EHD lubrication of point contacts has been used for the comparison with three-dimensional representations of film thickness distributions obtained from experiments. A good agreement was found between experimental and numerical EHD film shapes by comparing lubricant film profiles and positions of minimum film thickness. Both experimental results and numerical solution confirm the ratio between central and minimum film thickness to change significantly with operating conditions. [S0742-4787(00)00404-5]

On the crucial role of ellipticity on elastohydrodynamic film thickness and friction

2016 ◽  
Vol 230 (12) ◽  
pp. 1503-1515 ◽  
Author(s):  
J-D Wheeler ◽  
N Fillot ◽  
P Vergne ◽  
D Philippon ◽  
GE Morales Espejel
Keyword(s):  
Film Thickness ◽  
Maximum Pressure ◽  
Fluid Viscosity ◽  
Point Contacts ◽  
Entrainment Velocity ◽  
Minimum Film Thickness ◽  
Elliptical Contact ◽  
Thickness Variations ◽  
Poiseuille Flows

The study reported here deals with elastohydrodynamic point contacts and it is focused on the influence of contact ellipticity. In five velocity–load reference cases, ellipticity was varied from slender to wide configurations, including the circular contact. For each case, Hertzian pressure, Hertzian area, load, and entrainment velocity were kept constant while the ellipticity was varied by changing the curvature radii. In this context, the maximum central film thickness did not occur for the infinitely wide contact, but for a slender configuration close to the circular case. Moreover, the minimum film thickness reached its optimum for a wide but finite elliptical contact. For low ellipticity ratios, specific film thickness features were obtained. In particular, very high central/minimum film thickness ratios are found. The cause of these behaviors was found in the change of the convergent shape. When the ellipticity was varied, the Poiseuille flows parallel and transverse to the entrainment direction were significantly modified and these modifications were quantitatively analyzed for the different cases. The competition between the Couette and the Poiseuille flows was totally different between the narrow and the wide elliptical contact, and this change was responsible for the film thickness variations with ellipticity. Ellipticity also had an effect on friction as it influenced the maximum pressure which in turn impacts the fluid viscosity.

The Influence of Piezoviscosity on the Minimum Film Thickness in Heavily Loaded Elastohydrodynamic Point Contacts

1990 ◽  
Vol 204 (2) ◽  
pp. 117-125 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Contact Geometry ◽  
Operating Conditions ◽  
Point Contacts ◽  
Centre Line ◽  
Minimum Film Thickness

The lowest film thicknesses in heavily loaded point contacts occur in a band around the rear of the contact. The minimum lies either at the centre of this band or at its ends, near the sides of the conjunction. The clearances in the two regions vary independently with changes in contact geometry and operating conditions, but for relatively narrow contacts and for higher loads the clearance at the contact sides is smaller than on the centre-line. This paper examines how this side clearance alters, under heavily loaded conditions, with changes in piezoviscosity.

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