Report Paper 3: Elastohydrodynamic Lubrication of ‘O’ Ring Seals

1969 ◽  
Vol 184 (12) ◽  
pp. 197-200
Author(s):  
I. A. Gibson ◽  
C. J. Hooke ◽  
J. P. O'Donoghue
Keyword(s):  
Theoretical Analysis ◽  
Film Thickness ◽  
Pressure Gradient ◽  
Contact Zone ◽  
Elastohydrodynamic Lubrication ◽  
Iterative Solution ◽  
Contact Conditions ◽  
Dry Contact

This report gives details of a theoretical analysis of the lubrication of ‘O’ ring seals. Under dry contact conditions the pressure gradient at inlet to the contact zone is infinite, and an iterative solution has been developed to determine the inlet sweep of pressure under conditions of elastohydrodynamic lubrication. The exit film thickness and pressures have also been determined for conditions of variable outlet viscosity and pressure gradient. Typical results for an ‘O’ ring are given for a standard seal section.

Effect of oil starvation on the isothermal impact problem

2017 ◽  
Vol 232 (10) ◽  
pp. 1332-1339
Author(s):  
Duohuan Wu ◽  
Jing Wang ◽  
Peiran Yang ◽  
Ton Lubrecht
Keyword(s):  
Film Thickness ◽  
Pressure Gradient ◽  
Thickness Distribution ◽  
Elastohydrodynamic Lubrication ◽  
Maximum Pressure ◽  
Numerical Techniques ◽  
Minimum Film Thickness ◽  
The Impact ◽  
Impact Motion ◽  
Impact Problem

In this study, the effect of oil starvation on isothermal elastohydrodynamic lubrication of an impact motion is explored with the aid of numerical techniques. During the impact process, on comparison with the fully lubricated results, the pressure and film thickness are much lower and the entrapped film shape does not happen. The rebound is delayed by the oil starvation assumption. During the rebound process, a periphery entrapment is seen in the starved film thickness distribution. Under the starved condition, the maximum pressure gradient is higher. The central film thickness and minimum film thickness exhibit different variations compared with the results by fully flooded assumption.

Effect of Roughness Orientation on the Elastohydrodynamic Lubrication Film Thickness

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Dong Zhu ◽  
Q. Jane Wang
Keyword(s):  
Film Thickness ◽  
Stochastic Models ◽  
Deterministic Model ◽  
Elastohydrodynamic Lubrication ◽  
Contact Problems ◽  
Operating Conditions ◽  
Orientation Effect ◽  
Line Contact ◽  
Lubrication Film ◽  
Dry Contact

Effect of roughness orientation on lubricant film thickness has been an important issue of surface design, attracting much attention since the 1970 s. A systematical study, however, is still needed for various contact types in an extended range of operating conditions, especially in mixed lubrication cases with film thickness to roughness ratio (λ ratio) smaller than 0.5. The present study employs a deterministic mixed elastohydrodynamic lubrication (EHL) model to investigate the performance of lubricating films in different types of contact geometry, including the line contact, circular contact, and elliptical contacts of various ellipticity ratios. The speed range for analyzed cases covers 11 orders of magnitude so that the entire transition from full-film and mixed EHL down to dry contact (corresponding λ ratio from about 3.5 down to 0.001 or so) is simulated. Three types of machined surfaces are used, representing transverse, longitudinal, and isotropic roughness, respectively. The line contact results are compared with those from the stochastic models by Patir and Cheng (“Effect of Surface Roughness Orientation on the Central Film Thickness in EHD Contacts,” Proc. 5th Leeds-Lyon Symp. on Tribol., 1978, pp. 15–21) and the influence of roughness orientation predicted by the deterministic model is found to be less significant than that by the stochastic models, although the basic trends are about the same when λ > 0.5. The orientation effect for circular or elliptical contact problems appears to be more complicated than that for line contacts due to the existence of significant lateral flows. In circular contacts, or elliptical contacts with the ellipticity ratio smaller than one, the longitudinal roughness may become more favorable than the isotropic and transverse. Overall, the orientation effect is significant in the mixed EHL regime where theλratio is roughly in the range from 0.05 to 1.0. It is relatively insignificant for both the full-film EHL (λ > 1.2 or so) and the boundary lubrication/dry contact (λ < 0.025 ∼ 0.05).

Optical Interferometric Observations of the Effects of a Bump on Point Contact EHL

1992 ◽  
Vol 114 (4) ◽  
pp. 779-784 ◽  
Author(s):  
M. Kaneta ◽  
T. Sakai ◽  
H. Nishikawa
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Numerical Simulations ◽  
Contact Region ◽  
Thickness Distribution ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Interesting Phenomenon ◽  
Contact Conditions ◽  
Average Speed

The effects of surface kinematic conditions on micro-elastohydrodynamic lubrication (micro-EHL) are investigated under rolling and/or sliding point contact conditions using the optical interferometry technique. A long bump of chromium sputtered on the surface of a highly polished ball is used as a model asperity. It is shown that the film thickness distribution or the elastic deformation of the bump is influenced significantly by the surface kinematic conditions and the orientation of the bump. An interesting phenomenon is also found when contacting surfaces move with different speeds; the thin film formed on a transversely oriented bump existing at the entrance of the contact travels through the contact region at the average speed of the surfaces. The experimental results obtained qualitatively confirm published numerical simulations.

scholarly journals Roughness in lubricated rolling contact: The dry contact limit

2007 ◽  
Vol 221 (7) ◽  
pp. 787-791 ◽  
Author(s):  
A. V. Olver ◽  
D Dini
Keyword(s):  
Thin Films ◽  
Fourier Transform ◽  
Film Thickness ◽  
Fast Fourier Transform ◽  
Elastohydrodynamic Lubrication ◽  
Fourier Component ◽  
Rolling Contact ◽  
Perturbation Model ◽  
Rolling Contacts ◽  
Dry Contact

A difficulty with the standard fast Fourier transform (FFT) perturbation model of roughness in lubricated rolling contacts is that it does not necessarily converge towards the elastic case as the film thickness is reduced; rather it leads to a situation in which all the roughness is completely flattened. This is rarely the case for real engineering surfaces. Here, it is shown that this difficulty can be avoided by carrying out a Fourier transform of the elastostatically flattened roughness and using the resulting (complex) amplitude as the low-film thickness limit of each Fourier component in the elastohydrodynamic lubrication (EHL) analysis. Results give a plausible convergence to the elastostatic solution, which is nevertheless consistent with the expected near-full-film EHL behaviour and which becomes identical to the earlier model for roughness that, statically, can be fully flattened. As expected, hydrodynamic action persists at the finest scale, even for very thin films.

A Study of Elastohydrodynamic Lubrication of Rough Surfaces

1991 ◽  
Vol 113 (1) ◽  
pp. 110-115 ◽  
Author(s):  
L. Chang ◽  
M. N. Webster
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Rough Surface ◽  
Contact Zone ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Micro Deformation ◽  
Sinusoidal Functions ◽  
Sensitive Parameters ◽  
Pressure Perturbations

This paper reports some results of rough-surface, elastohydrodynamically lubricated (EHD) contacts obtained using a previously developed transient EHD model. The surface roughness is modeled with sinusoidal functions of small wavelength compared to the contact zone. Results are presented showing how the operating conditions affect the film thickness, micro-deformation of the roughness, and the pressure perturbations due to motion and interaction of roughness within the contact. This preliminary work suggests that the entraining velocity and the slide-to-roll ratio are the most sensitive parameters influencing the lubrication process of rough-surface EHD contacts.

The Contribution of a Sliding Velocity to EHL Film Thickness Distribution

2012 ◽  
Author(s):  
Milan Omasta ◽  
Ivan Krupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Thickness Distribution ◽  
Central Area ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Sliding Velocity ◽  
Contact Conditions ◽  
Entrainment Velocity ◽  
Pure Rolling ◽  
Circular Contact

In general contact conditions, the surface velocities are variously oriented, thus the entrainment and sliding velocity act at different directions. The effects of magnitude and direction of the sliding velocity in elastohydrodynamic lubrication (EHL) circular contact have been investigated. Film thickness distribution has been obtained using thin-film colorimetric interferometry. It has been found that direction of sliding velocity with respect to entrainment velocity play a role in film thickness distribution, particularly at high slide-to-roll ratios. A superposition of the effects of a pure rolling and of an opposite sliding has been considered. The pure rolling condition creates typical horse-shoe shaped film, whereas under the opposite sliding condition (i.e. zero entrainment velocity) conical depression in the central area of Hertzian contact called “dimple” has been observed.

Computation of Fluid Film Pressures by Measuring the Elastohydrodynamic Lubrication Film Thickness with Nano-Scale Resolution

2006 ◽  
Vol 326-328 ◽  
pp. 413-416
Author(s):  
Si Youl Jang
Keyword(s):  
Image Processing ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Processing Technique ◽  
Fluid Film ◽  
Image Processing Technique ◽  
Contact Conditions ◽  
Lubrication Film ◽  
Nano Scale ◽  
Thickness Variations

Many EHL (elastohydrodynamic lubrication) experiments have been performed with the regard to measuring the film thickness variations according to contact conditions, such as contact load, sliding-rolling ratio, contact accelerations for the verification purpose of lubricant characteristics. The measured images of film thickness by the interferometry system are easily converted into film thickness values even both in nanometer scale and resolution with the help of image processing technology. However, only the measurement of the EHL film thickness is not enough to verify the lubricant characteristics under the various contact conditions, because the lubricant is under very high contact pressures above 500MPa, where the lubricant is suddenly solidified and is no longer considered as a fluid itself. In this work, the EHL fluid film pressures are computed from the measured interferometric image of contact film thickness ranging from 10nm to several hundred nano meter, which should be taken with nano-scale resolution. The image processing technique makes it possible to convert the measured film thickness into contact fluid film pressures if the contact geometry and material properties are known. Without the nano-scale resolution for the measured film thickness, the converting computation from the measured film thickness to fluid film pressure is not possible due to the severe noises of interferometric image over the contact area. Measuring technology of the EHL film thickness with nano-scale is also explained with regards to nano scale resolution.

Numerical Analysis of Transient Elastohydrodynamic Lubrication During Startup and Shutdown Processes

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Xiqun Lu ◽  
Qingbing Dong ◽  
Kun Zhou ◽  
Bin Zhao ◽  
Bo Zhao
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Steady State Solution ◽  
Time Dependent ◽  
Initial Value ◽  
Transient Conditions ◽  
Lubrication Film ◽  
Dry Contact ◽  
Good Consistency ◽  
Mechanical Elements

In this study, a numerical model is developed for the analysis of elastohydrodynamic lubrication (EHL) at transient conditions during startup and shutdown processes. The time-dependent solutions are derived from an iterative algorithm with surface roughness involved, and the initial value is specified as the solution of the dry contact for the startup or steady-state solution of the lubrication contact at the starting velocity for the shutdown. The technique of discrete convolution and fast Fourier transform (DC-FFT) is employed to improve the computational efficiency. Solutions for smooth surfaces are compared with those obtained numerically and experimentally, and good consistency can be found. Profiles of pressure and film thickness and contours of subsurface stresses are analyzed to reveal the effects of acceleration/deceleration on the lubrication evolution. An isotropic roughness is then taken into account for the analysis. It is concluded that the coupling effects of the lubricant cavitation and oriented roughness would result in complex profiles of pressure and film thickness due to their disturbances to the lubrication film. A machined rough surface is presented to demonstrate the generality of the model. The analysis may potentially provide guidance to estimate the behavior of mechanical elements.

Some Aspects of the Micro-Elastohydrodynamic Lubrication of Rough Cylinders Finished with a Circumferential Lay

1990 ◽  
Vol 204 (3) ◽  
pp. 145-158 ◽  
Author(s):  
K P Baglin
Keyword(s):  
Film Thickness ◽  
A Priori ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Total Load ◽  
Lubrication Film ◽  
Operating Variables ◽  
Dry Contact ◽  
Pressure Ripple ◽  
Asperity Deformation

Earlier work has shown that sinusoidal asperities with a circumferential lay give rise to transverse pressure ripples within the nominally smooth elastohydrodynamic pressure distribution. The ripples can become sufficiently large to cause elastic deformation of the generating asperities. This paper assumes that the deformed shape can be described using the Westergaard ‘dry contact’ analysis with the load (that, fraction of the total load contained within the pressure ripple) being unknown a priori. Solution of the Reynolds equation leads to the production of non-dimensional plots which give the extent of asperity deformation and the micro-elastohydrodynamic lubrication film thickness underneath the asperities as functions of the operating variables. It is shown that sensible lubricant films can exist between rough surfaces even as the nominal ratio of undeformed roughness/macro film thickness approaches 10. Different non-dimensional plots exist for different ‘sharpness’ asperities, defined as the ratio of amplitude/wavelength. For low values of the ratio, appropriate to roller bearings for example, Westergaard-type flat formation is appropriate over the total range of operating conditions considered. With sharper asperities, such as occur with W-N gears, the Westergaard flat is appropriate for relatively small deformations but, with increasing deformation, side lobes must form within the predicted ‘flat’. It is argued that this analysis will remain appropriate while the system is capable of producing high pressure in the valleys of the sinusoid but will become inappropriate as asperity deformation approaches the value it would have when bearing the total load.

Kinematics of the MATCO™ hip simulator and issues related to wear testing of metal-metal implants

1997 ◽  
Vol 211 (1) ◽  
pp. 89-99 ◽  
Author(s):  
J B Medley ◽  
J J Krygier ◽  
J D Bobyn ◽  
F W Chan ◽  
A Lippincott ◽  
...  
Keyword(s):  
Film Thickness ◽  
Contact Zone ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Wear Testing ◽  
Circular Path ◽  
Hip Implants ◽  
Hip Simulator ◽  
Metal Metal

Metal-metal hip implants have been used clinically in Europe to reduce the risk of wear particle induced osteolysis. Joint simulator devices could provide useful information for design improvement of the modern generation of metal-metal hip implants. Early wear results for metal-metal hip specimens were obtained using a MATCO™ hip simulator. A detailed kinematic analysis was developed for the MATCO™ simulator and applied to two of the wear experiments to predict the starting surface motion, contact zone and lubricant film thickness. It was shown that points on cup surfaces were not subjected to a reciprocating interaction with the head during wear at the beginning of testing but as wear proceeded, it was suggested that, in some cases, reciprocating interaction did occur on the cup surface. Comparison between simulator and in vivo kinematics suggested a more realistic representation for cup than for head wear. In the simulator, the Hertzian contact zone moved in a circular path over the cup surface and changed in size in correspondence with the applied load. Elastohydrodynamic lubrication was considered to be possible in the simulator, with estimated fluid film thickness as great as 0.1 μm. However, such thick films were not likely to have occurred at the start of the two wear tests which were examined in detail, although some mixed film lubrication might have accounted for the relatively low wear of one of the specimens. The inclusion of kinematic details, contact mechanics and elastohydrodynamic lubrication analysis in simulator testing protocols and in design of metal-metal hip implants was recommended.

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