Elastohydrodynamic Lubrication of Heavily Loaded Circular Contacts

1989 ◽  
Vol 203 (2) ◽  
pp. 133-148 ◽  
Author(s):  
C C Kweh ◽  
H P Evans ◽  
R W Snidle
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Engineering Practice ◽  
Experimental Measurements ◽  
Lubricant Film Thickness ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Steel Surfaces ◽  
Maximum Contact ◽  
Contact Pressures

The paper is concerned with theoretical analysis and experimental measurement of lubricant film thickness in heavily loaded elastohydrodynamic contacts in which the area of elastic deformation is approximately circular. The inverse elastohydrodynamic technique for numerical analysis of contacts of this type described by Evans and Snidle(9) has been used to produce solutions covering a wide range of conditions representative of engineering practice. Detailed solutions for film thickness and pressure have been obtained for conditions giving rise to maximum contact pressures of up to 4.1 GPa with steel surfaces and a mineral oil lubricant. On the basis of these results charts for film thickness have been constructed using the non-dimensional groups proposed by Moes and Bosma(12). Experimental measurements of film thickness have been made using the optical interferometry technique. The conditions used in the experiments have been numerically analysed to provide a direct comparison between theory and experiment. The comparison shows excellent agreement between the theoretical predictions and corresponding experimental measurements.

Elastohydrodynamic Film Thickness in Concentrated Contacts: Part 2: Correlation of Experimental Results with Elastohydrodynamic Theory

1986 ◽  
Vol 200 (3) ◽  
pp. 219-226 ◽  
Author(s):  
R J Chittenden ◽  
D Dowson ◽  
C M Taylor
Keyword(s):  
Film Thickness ◽  
Experimental Studies ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Experimental Results ◽  
Experimental Techniques ◽  
Dimensionless Parameters ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Computational Procedures

The existence of a coherent film of lubricant between highly loaded machine elements has been recognized for many years. Over this period of time measurements of film thickness have gone hand in hand with theoretical analyses in the field now known as elastohydrodynamic lubrication. The experimental techniques of capacitance, electrical resistance and X-ray measurement have been supplemented by the use of optical interferometry while the analytical expressions obtained with the use of elegant simplifications have been superseded by those developed from extensive and comprehensive computational procedures. These developments in experimental techniques have yielded a substantial number of measurements of both minimum and central film thickness. Likewise, the advent of the digital computer has allowed the derivation of a large number of solutions to the problem of elastohydrodynamic lubrication of concentrated contacts. All these results, covering a wide range of geometrical conditions, are to be found in the literature, yet little attempt appears to have been made to assemble a representative set of experimental data to permit a detailed evaluation of the theoretical formulae for elliptical contacts. The second part of this paper therefore considers the correlation between a number of experimental studies covering a wide range of operating conditions and geometries, and the predictions of recent elastohydrodynamic theory. Some of the important aspects of each set of experimental results are then considered and examples are provided which illustrate the following points: 1. Good estimates of lubricant film thickness may be obtained from the theoretical expressions recently derived, even when the dimensionless parameters involved are outside the ranges considered in the derivation of the formulae. 2. The discrepancies which exist between theoretical predictions and some of the measured film thicknesses are nevertheless quite large, even when the dimensionless parameters are within their usual limits. On the whole there is good agreement between experiment and theory, while the general trend of the results indicates that theoretical predictions may underestimate the minimum film thickness by about 10 per cent and the central film thickness by about 25 per cent. This measure of agreement is quite remarkable when the extreme difficulty of interpreting the magnitudes of effective and very thin mean film thicknesses between machined components in various forms of experimental equipment is considered.

scholarly journals Optical Analysis of Ball Bearing Starvation

1971 ◽  
Vol 93 (3) ◽  
pp. 349-361 ◽  
Author(s):  
L. D. Wedeven ◽  
D. Evans ◽  
A. Cameron
Keyword(s):  
Film Thickness ◽  
Ball Bearing ◽  
Point Contact ◽  
Experimental Measurements ◽  
Line Contact ◽  
Optical Analysis ◽  
Grease Lubrication ◽  
Theoretical Predictions ◽  
Pressure Stress ◽  
Starvation Conditions

Elastohydrodynamic oil film measurements for rolling point contact under starvation conditions are obtained using optical interferometry. The experimental measurements present a reasonably clear picture of the starvation phenomenon and are shown to agree with theoretical predictions. Starvation inhibits the generation of pressure and, therefore, reduces film thickness. It also causes the overall pressure, stress, and elastic deformation to become more Hertzian. Additional experiments using interferometry illustrate: the cavitation pattern, lubricant entrapment, grease lubrication, ball spin, and edge effects in line contact.

A Starved Mixed Elastohydrodynamic Lubrication Model for the Prediction of Lubrication Performance, Friction and Flash Temperature With Arbitrary Entrainment Angle

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Wei Pu ◽  
Dong Zhu ◽  
Jiaxu Wang
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Flash Temperature ◽  
Machined Surface ◽  
Lubrication Performance ◽  
Wide Range ◽  
Starved Lubrication

In this study, a modified mixed lubrication model is developed with consideration of machined surface roughness, arbitrary entraining velocity angle, starvation, and cavitation. Model validation is executed by means of comparison between the obtained numerical results and the available starved elastohydrodynamic lubrication (EHL) data found from some previous studies. A comprehensive analysis for the effect of inlet oil supply condition on starvation and cavitation, mixed EHL characteristics, friction and flash temperature in elliptical contacts is conducted in a wide range of operating conditions. In addition, the influence of roughness orientation on film thickness and friction is discussed under different starved lubrication conditions. Obtained results reveal that inlet starvation leads to an obvious reduction of average film thickness and an increase in interasperity cavitation area due to surface roughness, which results in significant increment of asperity contacts, friction, and flash temperature. Besides, the effect of entrainment angle on film thickness will be weakened if the two surfaces operate under starved lubrication condition. Furthermore, the results show that the transverse roughness may yield thicker EHL films and lower friction than the isotropic and longitudinal if starvation is taken into account. Therefore, the starved mixed EHL model can be considered as a useful engineering tool for industrial applications.

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.

Effects of Differential Scheme and Mesh Density on EHL Film Thickness in Point Contacts

2006 ◽  
Vol 128 (3) ◽  
pp. 641-653 ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Wenzhong Wang ◽  
Yuanzhong Hu ◽  
Dong Zhu
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
System Approach ◽  
Elastohydrodynamic Lubrication ◽  
Mesh Size ◽  
Point Contacts ◽  
Wide Range ◽  
Mesh Density ◽  
Differential Scheme

This paper investigates the effects of differential scheme and mesh density on elastohydrodynamic lubrication (EHL) film thickness based on a full numerical solution with a semi-system approach. The solution variation with different schemes and mesh sizes is revealed based on a set of numerical cases in a wide range of central film thickness from several hundred nanometers down to a few nanometers. It is observed that when the film is thick, the effects of differential schemes and mesh density are not significant. However, if the film becomes ultra-thin, e.g., below 10–20 nanometers, the influence of mesh density and differential schemes becomes more significant, and a proper dense mesh and differential scheme may be highly desirable. The present study also indicates that the solutions from the 1st-order backward scheme give the largest film thickness among all the solutions from different schemes at the same mesh size.

A Three-Dimensional Model of Line-Contact Elastohydrodynamic Lubrication for Heterogeneous Materials with Inclusions

2016 ◽  
Vol 08 (02) ◽  
pp. 1650014 ◽  
Author(s):  
Kun Zhou ◽  
Qingbing Dong
Keyword(s):  
Film Thickness ◽  
Half Space ◽  
Surface Deformation ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Line Contact ◽  
Lubricant Film Thickness ◽  
Equivalent Inclusion Method ◽  
Surface Contact

This paper develops a three-dimensional (3D) model for a heterogeneous half-space with inclusions distributed periodically beneath its surface subject to elastohydrodynamic lubrication (EHL) line-contact applied by a cylindrical loading body. The model takes into account the interactions between the loading body, the fluid lubricant and the heterogeneous half-space. In the absence of subsurface inclusions, the surface contact pressure distribution, the half-space surface deformation and the lubricant film thickness profile are obtained through solving a unified Reynolds equation system. The inclusions are homogenized according to Eshelby’s equivalent inclusion method (EIM) with unknown eigenstrains to be determined. The disturbed half-space surface deformations induced by the subsurface inclusions or eigenstrains are iteratively introduced into the lubricant film thickness until the surface deformation finally converges. Both time-independent smooth surface contact and time-dependent rough surface contact are considered for the lubricated contact problem.

Hydrodynamic Lubrication in Axisymmetric Stretch Forming—Part 2: Experimental Investigation

1991 ◽  
Vol 113 (4) ◽  
pp. 667-674 ◽  
Author(s):  
L. G. Hector ◽  
W. R. D. Wilson
Keyword(s):  
Experimental Investigation ◽  
Film Thickness ◽  
Hydrodynamic Lubrication ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Stretch Forming ◽  
Workpiece Material ◽  
Contour Map ◽  
Theoretical Predictions ◽  
Interference Studies

In order to test the validity of the theoretical model discussed in Part 1, an experimental technique, employing optical interferometry, has been developed to measure lubricant film thickness during axisymmetric stretch forming. Specially fabricated, transparent punches are used for both double and multiple beam interference studies. The choice of workpiece material, lubricant, and forming speed ensures that the punch/sheet conjunction will be hydrodynamically lubricated during most of the process. Interference patterns, due to the variable film of lubricant separating the punch and sheet surfaces, are formed as the sheet wraps around the punch. These patterns provide a contour map of the lubricant film thickness along the punch/sheet conjunction. The measured film thickness, as taken from an interpretation of the patterns, is compared with the theoretical predictions of Part 1.

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 Analysis of Chromium Molybdenum Coatings Under Mixed Elastohydrodynamic Lubrication for Film Thickness, Friction, and Wear Characterizations

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
David Pickens ◽  
Zhong Liu ◽  
Takayuki Nishino ◽  
Q. Jane Wang
Keyword(s):  
Film Thickness ◽  
Friction And Wear ◽  
Elastohydrodynamic Lubrication ◽  
Tribological Performance ◽  
Root Mean Square Roughness ◽  
Boundary Lubrication Friction ◽  
Lubricant Film Thickness ◽  
Free Surfaces ◽  
Surface Topographies ◽  
Coated Surfaces

This research aims to evaluate the tribological performance of chromium molybdenum (CrMo) coatings under point and line-contact mixed elastohydrodynamic lubrication. This article studies the coatings made from two different methods and treated in an electrifying process of different durations, which produced microchannels and micropockets in the surfaces. The resulting surface topographies had varying impacts on lubricant film thickness, friction, and wear. Root-mean-square roughness (Sq) and porosity are used to characterize the surfaces and their performances in terms of film thickness, friction, and wear. The results suggest that the coated surfaces with a lower Sq and porosity density tended to yield higher film thickness. However, their influence on friction is complicated; lower roughness and porosity are preferred for lower wear, but certain levels of small roughness and surface pores may help to reduce boundary lubrication friction when compared with the frictional behaviors of porosity-free surfaces and those with higher roughness and higher porosity.

Prediction of transient lubricating film thickness in knee prostheses with compliant layers

1998 ◽  
Vol 212 (3) ◽  
pp. 157-164 ◽  
Author(s):  
Z M Jin ◽  
D Dowson ◽  
J Fisher ◽  
N Ohtsuki ◽  
T Murakami ◽  
...  
Keyword(s):  
Knee Joint ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Contact Radius ◽  
Knee Prostheses ◽  
Stroke Length ◽  
Additional Advantage ◽  
Lubricating Film ◽  
Theoretical Predictions ◽  
Lubricating Film Thickness

The transient lubricating film thickness in knee prostheses using compliant layers has been predicted under simulated walking conditions based upon the elastohydrodynamic lubrication theory. Qualitative agreement has been found between the present theoretical predictions and the experimental measurements using an electric resistance technique reported earlier. It has been shown that the contact geometry plays an important role in the generation of fluid film lubrication in knee prostheses using compliant layers. The maximum lubricating film thickness is predicted for the maximized contact area of a transverse conjunction where the semi-minor contact radius lies in the direction of entraining. The additional advantage of the transverse contact conjunction is that the possibility of lubricant starvation due to small stroke length can be minimized. All these factors, together with the kinematic requirements in the natural knee joint, should be taken into consideration when designing artificial knee joint replacements.

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