The Effect of Kinematic Conditions on Film Thickness in Compliant Lubricated Contact

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
David Nečas ◽  
Tomáš Jaroš ◽  
Kryštof Dočkal ◽  
Petr Šperka ◽  
Martin Vrbka ◽  
...  
Keyword(s):  
Film Thickness ◽  
Optical Glass ◽  
Film Formation ◽  
Fluorescent Microscopy ◽  
Elastohydrodynamic Lubrication ◽  
Constant Load ◽  
Fluid Viscosity ◽  
Lubricating Film ◽  
Theoretical Predictions ◽  
Lubricated Contact

The present paper deals with an investigation of film formation in compliant lubricated contact. Despite these contacts can be found in many applications of daily life including both biological and technical fields, so far little is known about the lubrication mechanisms inside the contacts. The main attention is paid to the effect of kinematic conditions on central film thickness. For this purpose, fluorescent microscopy method was employed. Experiments were realized in ball-on-disk configuration, while the ball was made from rubber and the disk was from optical glass. The contact was lubricated by glycerol and polyglycol to examine the effect of fluid viscosity. The measurements were conducted under pure rolling and rolling/sliding conditions. The entrainment speed varied from 10 to 400 mm/s and constant load of 0.2 N was applied. Experimental results were compared with two theoretical predictions derived for isoviscous-elastohydrodynamic lubrication (I-EHL) regime. It was found that the thickness of lubricating film gradually increases with increasing entrainment speed, which corresponds to theoretical assumptions. Against expectations, evident influence of slide-to-roll ratio (SRR) on film formation was observed. In the last part of the paper, some limitations of this study are discussed and several recommendations for further methodology improvement are suggested.

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.

Measurement of Lubricating Film Thickness in Low Elastic Modulus Lined Bearings, with Particular Reference to Models of Cushion Form Bearings for Total Joint Replacements: Part 1: Steady State Entraining Motion

1994 ◽  
Vol 208 (3) ◽  
pp. 207-212 ◽  
Author(s):  
Z M Jin ◽  
D Dowson ◽  
J Fisher ◽  
D Rimmer ◽  
R Wilkinson ◽  
...  
Keyword(s):  
Film Thickness ◽  
Glass Plate ◽  
Elastohydrodynamic Lubrication ◽  
Normal Incidence ◽  
Joint Replacements ◽  
Total Joint Replacements ◽  
Silicone Fluid ◽  
Lubricating Film ◽  
Theoretical Predictions ◽  
Lubricating Film Thickness

The lubricating film thickness in a model of compliant layered bearings for total joint replacements has been measured by means of optical interferometry under entraining motion. The essential features of the present interferometry technique were off-normal incidence light, a combination of polyurethane elastomer and a crown glass plate as bearing surfaces and the use of silicone fluid or water as lubricants. The film thickness in the lubricated contact was measured for both water and silicone fluid under a range of entraining velocities. Reasonable agreement was found between the experimental measurements of the lubricating film thickness and the theoretical predictions based upon elastohydrodynamic lubrication analysis.

Effects of a thickener structure on grease elastohydrodynamic lubrication films

2000 ◽  
Vol 214 (4) ◽  
pp. 327-336 ◽  
Author(s):  
M Kaneta ◽  
T Ogata ◽  
Y Takubo ◽  
M Naka
Keyword(s):  
Film Thickness ◽  
Direct Observation ◽  
Film Formation ◽  
Elastohydrodynamic Lubrication ◽  
Rolling Speed ◽  
Molecular Structures ◽  
Optimum Temperature ◽  
Oil Viscosity ◽  
Base Oil ◽  
Different Types

The effects of the thickener structure and base oil viscosity on the grease film formation in rolling point elastohydrodynamic contacts have been discussed on the basis of direct observation using the optical interferometry technique. Three different types of diurea greases without additives have been used as test greases. As the base oils three kinds of ether-type synthetic oils having similar molecular structures but different viscosities were used. The film behaviour of fresh greases has also been compared with that of the degraded greases. It has been found that the behaviour of grease elastohydrodynamic lubrication films is basically influenced by the thickener structure and base oil viscosity. The adhesion or deposition of the thickener on the contacting surfaces and oil starvation which affect film formation depend on the thickener structure, base oil viscosity and rolling speed. Furthermore, it has been suggested that there is an optimum temperature which gives a maximum film thickness according to the consistency of the grease.

Lubricating Grease Replenishment in an Elastohydrodynamic Point Contact

1993 ◽  
Vol 115 (3) ◽  
pp. 501-506 ◽  
Author(s):  
Henrik A˚stro¨m ◽  
Jan Ove O¨stensen ◽  
Erik Ho¨glund
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Video Recording ◽  
Point Contact ◽  
Video Camera ◽  
Lubricating Oil ◽  
Spin Motion ◽  
Lubricating Grease ◽  
Lubricating Film ◽  
Theoretical Predictions

A ball and disk apparatus was used to investigate the lubricant replenishment of an elastohydrodynamically lubricated point contact. This replenishment of the contact is crucial for building up a lubricating film. Whereas lubricating oil manages to achieve replenishment, lubricating grease appears not to achieve this, with lubricant starvation and a dramatic decrease in film thickness as a result. The distribution of grease around the contact was studied using normal and high-speed video. The movements of grease in the vicinity of the contact could be seen by adding molybdenum disulfide particles to the grease. A recording was then made, using highspeed video recording. The overall cavitation regions were studied using an ordinary video camera and grease without particles. On the basis of the results, possible lubricating grease replenishment mechanisms are discussed. The resulting film thickness was also compared with theoretical predictions using the Hamrock and Dowson starvation criterion, assuming negligible replenishment. The measured film thickness was larger than the predicted, which indicated that some replenishment occurs. In the case of an ordinary thrust ball bearing, replenishment was found to rely on the spin motion of the balls.

Analysis of EHL Circular Contact Start Up: Part I—Mixed Contact Model With Pressure and Film Thickness Results

2000 ◽  
Vol 123 (1) ◽  
pp. 67-74 ◽  
Author(s):  
Jiaxin Zhao ◽  
Farshid Sadeghi ◽  
Michael H. Hoeprich
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Contact Problems ◽  
Iteration Scheme ◽  
Mixed Lubrication ◽  
Contact Forces ◽  
Solid Contact ◽  
Start Up ◽  
Lubricated Contact

In this paper a model is presented to investigate the start up condition in elastohydrodynamic lubrication. During start up the lubrication condition falls into the mixed lubrication regime. The transition from solid contact to lubricated contact is of importance when investigating the start up process and its effects on bearing performance. The model presented uses the multigrid multilevel method to solve the lubricated region of the contact and a minimization of complementary energy approach to solve the solid contact region. The FFT method is incorporated to speed up the film thickness calculation. An iteration scheme between the lubrication and the solid contact problems is used to achieve the solution of the mixed lubrication contact problem. The results of start up with smooth surfaces are provided for the case when speed increases from zero to desired speed in one step and the case when speed is linearly increased to desired speed. The details of the transition from full solid contact to full lubricated contact in EHL start up are presented. The change of pressure and film thickness as well as contact forces and contact areas are discussed.

Measurement of Lubricating Film Thickness in Low Elastic Modulus Lined Bearings, with Particular Reference to Models of Cushion Form Bearings for Total Joint Replacements: Part 2: Squeeze-Film Motion

1994 ◽  
Vol 208 (3) ◽  
pp. 213-217 ◽  
Author(s):  
Z M Jin ◽  
G McClure ◽  
D Dowson ◽  
J Fisher ◽  
B Jobbins
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Thick Layer ◽  
Squeeze Film ◽  
Synovial Joint ◽  
Joint Replacements ◽  
Total Joint Replacements ◽  
Lubricating Film ◽  
Low Elastic Modulus ◽  
Theoretical Predictions

An optical interferometry technique has been successfully used to study the lubricant film thickness in a compliant layered bearing model for total joint replacements under squeeze-film motion. Experiments have been carried out for both thin and thick layers of compliant bearing material. It has been demonstrated that the film thickness patterns depend significantly upon the layer thickness if other parameters are kept constant. For the thin layer, the film thickness in the contact region was found to be essentially uniform and quite good agreement was found with the theoretical predictions based upon a simplified analysis due to Dowson et al. (13) and Higginson (14). However, for the thick layer, a central dimple or pocket was formed and a relatively large difference was found between the experimentally determined central film thickness and the simple parallel circular disc theoretical predictions. The practical implications of the present results are discussed in relation to the lubrication mechanism in the natural synovial joint and its replacement.

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.

Elastohydrodynamic Lubrication of Circumferentially Finished Rollers having Sinusoidal Roughness

1987 ◽  
Vol 201 (1) ◽  
pp. 29-36 ◽  
Author(s):  
G Karami ◽  
H P Evans ◽  
R W Snidle
Keyword(s):  
Film Thickness ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Axial Direction ◽  
Constant Load ◽  
Asperity Contact ◽  
Asperity Contacts ◽  
Roughness Amplitude ◽  
Large Roughness

The paper describes an isothermal elastohydrodynamic lubrication analysis of rollers having circumferential sinusoidal roughness. Theoretical results are shown which demonstrate the influence of roughness amplitude on the distribution of hydrodynamic pressure and film thickness at constant load and constant roughness wavelength. At a large roughness amplitude the hydrodynamic pressure in the valleys between asperity contacts is insignificant and each asperity contact behaves as an ‘isolated’ elastohydrodynamic point contact. As the roughness is reduced, however, the valley pressures build up, the pressure becomes more uniformly distributed in the axial direction and the minimum film thickness increases.

Effect of Proteins on Film Formation in Bovine Serum Lubricated Contacts Under Rolling/Sliding Conditions

2012 ◽  
Author(s):  
Martin Vrbka ◽  
Tomas Navrat ◽  
Ivan Krupka ◽  
Martin Hartl ◽  
Jiri Gallo
Keyword(s):  
Film Thickness ◽  
Bovine Serum ◽  
High Speed ◽  
Film Formation ◽  
Research Work ◽  
Digital Camera ◽  
Protein Film ◽  
Lubricating Film ◽  
Ceramic Femoral Head ◽  
Optical Test

The aim of this study is to perform detail experimental mapping of the lubricating film thickness of bovine serum (BS) within the contact between an artificial metal or ceramic femoral head and a glass disc and analyze effect of proteins on the film formation under rolling/sliding conditions. The film thickness was studied experimentally using an optical test rig as a function of time under variety of constant mean speeds. Chromatic interferograms were recorded with a high-speed digital camera and evaluated with thin film colorimetric interferometry. Under pure rolling conditions it was observed that the central film thicknesses increased with time for all measurements. When the disc was slower than head then the measured central film thicknesses achieved values only about some few nanometres, whereas when the tests were realized with faster disc then measured central film thicknesses achieved significantly higher values. Distribution of the film thickness within the contact zone is not homogeneous and two different film thickness regions can be found; thicker protein film and thinner base film that both show specific behaviour over time. This study showed that protein formation plays an important role in the lubrication processes of artificial joints of the human. Due to challenging of this study the more complex research work is carried out at the present time.

The line contact problem of elastohydrodynamic lubrication - I. Asymptotic structure for low speeds

1989 ◽  
Vol 424 (1867) ◽  
pp. 393-407 ◽  
Keyword(s):  
Asymptotic Solution ◽  
Contact Problem ◽  
Film Thickness ◽  
Numerical Solutions ◽  
Elastohydrodynamic Lubrication ◽  
Thin Layers ◽  
Line Contact ◽  
Asymptotic Regime ◽  
Lubricating Film ◽  
Pressure Spike

This paper reports the first formal asymptotic solution to the line contact problem of elastohydrodynamic lubrication (EHL), a fundamental problem describing the elastic deformation of lubricated rolling elements such as roller bearings, gear teeth and other contacts of similar geometry. The asymptotic régime considered is that of small λ , a dimensionless parameter proportional to rolling speed, viscosity and the elastic modulus. The solution is shown to possess four regions: a zone where the lubricating film is both thin and slowly narrowing and which is closely related to the contact area that occurs in the absence of lubricant, an upstream inlet zone of low pressure, and two thin layers on either side of the contact zone. The solutions in the first two just-mentioned zones are given by simple analytical expressions. The solutions in the two thin layers are obtained from two universal functions obtained by Bissett & Spence ( Proc. R. Soc. Lond . A 424, 409 (1989)). Although these two functions, related to the local film thickness, are obtained by numerical techniques by Bissett & Spence, it should be emphasized that all cases in the asymptotic régime considered are hereby solved definitively without recourse to further computation. Although some features of this structure have been suggested by other solution approaches, generally, these are numerical or ad hoc approximations. See the texts by Johnson ( Contact Mechanics , pp. 328 (1985)) and Dowson & Higginson ( Elasto-hydrodynamic lubrication (1977)), this work provides a formal mathematical basis for understanding most of the principal features of EHL. The solution provides a simple formula for minimum film thickness and displays the sharp narrowing of the lubricating film in the thin layer near the exit. In the basic asymptotic solution provided here, the dimensionless pressure-viscosity coefficient, α , is assumed to be O (1), and in this parameter régime, no pressure spike will occur. By comparing with the work of Hooke ( J. mech. Engng Sci . 19(4), 149 (1977)), we can show that an incipient pressure spike occurs when α becomes as large as O ( λ -1/5 ). However, asymptotic solutions in this latter parameter régime require new numerical solutions for each case of interest and are not pursued here.

Sign in / Sign up

Export Citation Format

Share Document