Micro-Elastohydrodynamic Lubrication and its Relationship with Running-in

1986 ◽  
Vol 200 (6) ◽  
pp. 415-424 ◽  
Author(s):  
K P Baglin
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
High Load ◽  
The Way ◽  
Pressure Ripples

The paper determines the conditions under which sinusoidal asperities with a circumferential lay become elastically deformed by hydrodynamic pressure ripples within an elastohydrodynamic conjunction. The information is presented on a non-dimensional plot and it is found that such micro-elastohydrodynamic lubrication (micro-EHL) occurs at relatively low loads and/or with thin macroelastohydrodynamic films. Consideration is given to the way in which the plot may be extended to deal with real surfaces. Its use is demonstrated by the presentation of the lubrication histories of two scuffing tests, one of which ‘ran-in’ prior to failure. It is shown that the test which ‘ran-in’ operated throughout under micro-EHL conditions; in contrast, the second test, which started at a high load and with a thick EHL film, failed practically as soon as there was nominal contact between the surfaces. It is suggested that micro-EHL is a necessary prerequisite for ‘running-in’ and a mechanism is outlined.

Demarcation boundary between region dominated by elastohydrodynamic lubrication and that by the surface force action for different elliptical ratios

2017 ◽  
Vol 69 (2) ◽  
pp. 215-224
Author(s):  
Mohamed Abd Al-Samieh
Keyword(s):  
Van Der Waals ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Surface Force ◽  
Van Der Waals Force ◽  
Line Contact ◽  
Force Action ◽  
Content Type ◽  
Combined Action ◽  
Ellipticity Ratio

Purpose This paper aims to investigate the effect of changing speed of the entraining motion on the formation of ultra-thin lubricating films under different elliptical ratios. The ellipticity parameter (K) varied from 1 (a ball-on-plate configuration) to 6 (a configuration approaching line contact). The influence of the ellipticity parameters, the dimensionless speed and the effects of surface forces on the formation of the minimum film thickness has been demonstrated. The demarcation boundary between region dominated by elastohydrodynamic lubrication (EHL) and that by the surface force action has been demonstrated for different elliptical ratios. Design/methodology/approach The numerical solution has been carried out, using the Newton–Raphson iteration technique, applied for the convergence of the hydrodynamic pressure. The film thickness and pressure distribution are obtained by simultaneous solution of the Reynolds’ equation, the elastic deformation (caused by hydrodynamic pressure, surface force of solvation and Van der Waals force) and the load balance equation. The operating conditions, load and speed of entraining motion, promote formation of ultra-thin films that are formed under the combined action of EHL, surface contact force of solvation and molecular interactions due to presence of Van der Waals force. Findings The paper provides insights about the transition between region dominated by EHL and that by the surface force action for changing ellipticity ratio (K) from 1 (a ball-on-plate configuration) to 6 (a configuration approaching line contact). Originality/value This paper fulfils an identified need to study the effect of changing ellipticity ratio on the formation of ultra-thin films that are formed under the combined action of EHL, surface contact force of solvation and molecular interactions due to presence of Van der Waals force.

A numerical method to investigate the mixed lubrication performances of journal-thrust coupled bearings

2019 ◽  
Vol 71 (9) ◽  
pp. 1099-1107
Author(s):  
Guo Xiang Guo Xiang ◽  
Yanfeng Han ◽  
Renxiang Chen ◽  
Jiaxu Wang Jiaxu Wang ◽  
Ni Xiaokang
Keyword(s):  
Thrust Bearing ◽  
Load Capacity ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Mixed Lubrication ◽  
Hydrodynamic Effect ◽  
Asperity Contact ◽  
Content Type ◽  
Lubrication Regime ◽  
Coupled Effect

Purpose This paper aims to present a numerical model to investigate the mixed lubrication performances of journal-thrust coupled bearings (or coupled bearings). Design/methodology/approach The coupled hydrodynamic effect (or coupled effect) between the journal and the thrust bearing is considered by ensuring the continuity of the hydrodynamic pressure and the flow field at the common boundary. The mixed lubrication performances of the coupled bearing are comparatively studied for the cases of considering and not considering coupled effect. Findings The simulated results show that the hydrodynamic pressure distributions for both the journal and thrust bearing are modified due to the coupled effect. The decreased load capacity of the journal bearing and the increased load capacity of the thrust bearing can be observed when the coupled effect is considered. And the coupled effect can facilitate in reducing the asperity contact load for both the journal and thrust bearing. Additionally, the interaction between the mixed lubrication behaviors, especially for the friction coefficient, of the journal and the thrust bearing is significant in the elastohydrodynamic lubrication regime, while it becomes weak in the mixed lubrication regime. Originality/value The developed model can reveal the mutual effects of the mixed lubrication behavior between the journal and the thrust bearing.

The Isothermal Elastohydrodynamic Lubrication of Spheres

1981 ◽  
Vol 103 (4) ◽  
pp. 547-557 ◽  
Author(s):  
H. P. Evans ◽  
R. W. Snidle
Keyword(s):  
Iterative Method ◽  
Reynolds Equation ◽  
Point Contact ◽  
Numerical Procedure ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Analysis Of Results ◽  
Approximate Formulas ◽  
Pressure Analysis

The paper describes a numerical procedure for solving the point-contact elastohydrodynamic lubrication problem under isothermal conditions at moderate loads. Results are presented showing the shape of the film and variation of hydrodynamic pressure. Analysis of results for a range of operating conditions gives the following approximate formulas for minimum and central film thickness, repsectively: Hm = 1.9 M−0.17 L0.34 and Ho = 1.7 M−0.026 L0.40 where H, M, and L are the Moes and Bosma nondimensional groups. In common with earlier solutions based upon the forward-iterative method the solution breaks down under moderately heavily loaded conditions. Ways of extending the solution to heavier loads using the authors’ inverse solution of Reynolds’ equation under point-contact elastohydrodynamic conditions are discussed.

Mathematical Model of Hydrodynamic Fluid Pressure on Smooth and Real Surface

2010 ◽  
Vol 135 ◽  
pp. 429-434
Author(s):  
Chang He Li ◽  
Li Li Wang ◽  
Guo Yu Liu
Keyword(s):  
Fluid Pressure ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Coolant Fluid ◽  
Grinding Wheel ◽  
Maximum Pressure ◽  
Real Surface ◽  
Work Surface ◽  
Peripheral Surface ◽  
Wedge Effect

Conventional method of flood delivering coolant fluid by a nozzle in order to achieve high process performance. However, hydrodynamic fluid pressure can be generated ahead of the contact zone due to the wedge effect between wheel peripheral surface and work surface. In the paper, theoretical hydrodynamic pressure modeling were presented for flow of coolant fluid through the grinding zone in flood delivery grinding using smooth and roughness surface grinding wheel respectively. The simulation results show that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and work surface and the maximum pressure value was generated just in the minimum gap region in which higher fluid pressure gradient occuring. It can also be concluded the surface roughness of grinding wheel and workpiece makes the contact zone’s hydrodynamic pressure rough and unstable, i.e. the value curve considering roughness is not smooth, leading to the micro-elastohydrodynamic lubrication phenomenon.

A mixed elastohydrodynamic lubrication model based on virtual rough surface for studying the tribological effect of asperities

2018 ◽  
Vol 70 (2) ◽  
pp. 408-417 ◽  
Author(s):  
Hui Zhang ◽  
Guangneng Dong ◽  
Guozhong Dong
Keyword(s):  
Film Thickness ◽  
Rough Surface ◽  
Current Model ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Surface Pattern ◽  
Curvature Radius ◽  
Content Type ◽  
Stribeck Curves ◽  
Effect Of Surface

Purpose The main purpose of this paper is to present the effort on developing a mixed elastohydrodynamic lubrication (EHL) model to study the tribological effect of asperities on rough surface. Design/methodology/approach The model, with the use of the average flow Reynolds equation and the K-E elasto-plastic contact model, allows predictions of hydrodynamic pressure and contact pressure on the virtual rough surface, respectively. Then, the substrate elastic deformation is calculated by discrete convolution fast-Fourier transform (DC-FFT) method to modify the film thickness recursively. Afterwards, corresponding ball-on-disk tests are conducted and the validity of the model demonstrated. Moreover, the effects of asperity features, such as roughness, curvature radius and asperity pattern factor, on the tribological properties of EHL, are also discussed though plotting corresponding Stribeck curves and film thickness shapes. Findings It is demonstrated that the current model predicts very close data compared with corresponding experimental results. And it has the advantage of high accuracy comparing with other typical models. Furthermore, smaller roughness, bigger asperity radius and transverse rough surface pattern are found to have lower friction coefficients in mixed EHL models. Originality/value This paper contributes toward developing a mixed EHL model to investigate the effect of surface roughness, which may be helpful to better understand partial EHL.

Soft micro-elastohydrodynamic lubrication and friction at rough conformal contacts

2016 ◽  
Vol 231 (3) ◽  
pp. 302-315 ◽  
Author(s):  
B Wennehorst ◽  
GWG Poll
Keyword(s):  
Solid Body ◽  
Film Formation ◽  
Normal Load ◽  
Elastohydrodynamic Lubrication ◽  
Elastic Solid ◽  
Hydrodynamic Pressure ◽  
Mixed Lubrication ◽  
Fluid Film ◽  
Shear Stresses ◽  
Asperity Contacts

Conformal surfaces in parallel sliding lack a macroscopic hydrodynamic pressure and fluid film formation mechanism. However, such a mechanism still exists on a microscopic level due to roughness. It is common to translate roughness into a variation of fluid film thickness which in turn yields a hydrodynamic pressure distribution resulting in a net hydrodynamic lift. Reynolds equation and a suitable cavitation algorithm suffice to describe this effect mathematically. In case one surface consists of a compliant material with low modulus of elasticity, the deformation of asperities due to pressures and shear stresses in the fluid cannot be neglected—in fact, besides cavitation, it significantly contributes to the net hydrodynamic lift. Therefore, a coupling between fluid dynamics and elastic solid body deformations needs to be introduced. An additional complication arises when the hydrodynamic lift and the subsequent separation of the mean lines of the contacting rough surfaces is not enough to prevent asperity contacts completely. This situation is known as mixed lubrication where part of the normal load is transmitted at asperity contacts. These contacts are commonly treated as solid body contacts with a Coulomb-like friction law or more sophisticated solid friction models. However, when considering asperities as contraformal Hertzian contacts, elastic deformation may allow for the existence of thin micro-elastohydrodynamic lubricant films preventing direct solid body contact even at speeds which otherwise would be regarded as deep within the mixed lubrication regime close to boundary lubrication. These films may not be able to prevent wear completely, but may reduce friction significantly in comparison to dry friction. In this paper, the existence of such effects is demonstrated both by simulation and by experiments with elastomeric radial lip seals.

Elastohydrodynamic Lubrication in an Instrument Ball-Bearing

1976 ◽  
Vol 98 (2) ◽  
pp. 244-248 ◽  
Author(s):  
J. W. Kannel ◽  
D. K. Snediker
Keyword(s):  
Film Thickness ◽  
Experimental Measurement ◽  
Ball Bearing ◽  
Elastohydrodynamic Lubrication ◽  
Primary Parameter ◽  
X Ray ◽  
The Way

The paper deals with experimental measurement of bearing torque and “percentage of lubrication” in instrument size (R6) bearings. The primary parameter found to affect bearing performance for several lubricant investigations is base viscosity. Inference of EHD film thickness is made from the percentage of film measurements which are compared with X-ray data. A reasonable correlation between the two types of data is presented, thereby, paving the way toward the use of the more universally applicable percentage of film measurements for the determination of EHD conditions in real bearing systems.

Elastohydrodynamic lubrication analysis of metal-on-metal hip prostheses under steady state entraining motion

2001 ◽  
Vol 215 (6) ◽  
pp. 531-541 ◽  
Author(s):  
M Jagatia ◽  
Z M Jin
Keyword(s):  
Film Thickness ◽  
Elastic Deformation ◽  
Hip Prosthesis ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Acetabular Cup ◽  
Spherical Coordinate ◽  
Hip Prostheses ◽  
General Methodology ◽  
Metal On Metal

The elastohydrodynamic lubrication problem of metal-on-metal hip joint replacements was considered in this study. A simple ball-in-socket configuration was used to represent the hip prosthesis. The Reynolds equation in a spherical coordinate was adopted for the fluid-film lubrication analysis, to account for the ball-in-socket geometry. The corresponding elastic deformation was calculated by means of the finite element method in order to consider the complex ball-in-socket geometry as well as the backing materials underneath the acetabular cup. Both the Reynolds and the elasticity equations were solved simultaneously using the Newton-Raphson finite difference method. The general methodology developed was then applied to a recent experimental prototype metal-on-metal hip implant. It was shown that the backing materials underneath the acetabular cup had little influence on the predicted contact pressure and the elastic deformation at the bearing surfaces for this particular example. Both the film thickness and the hydrodynamic pressure distributions were obtained under various loads up to 2500 N. The predicted minimum lubricating film thickness from the present study was compared with a simple estimation using the Hamrock and Dowson formulae based upon an equivalent ball-on-plane model and excellent agreement was found. However, it was pointed out that for some forms of metal-on-metal hip prostheses with a thin acetabular cup, a polyethylene inlay underneath a metallic bearing insert or a taper connection between a bearing insert and a fixation shell, the general methodology developed in the present study should be used and this will be considered in future studies.

Comparison of tribological performance of roller follower and flat follower under mixed elastohydrodynamic lubrication regime

2016 ◽  
Vol 231 (8) ◽  
pp. 986-996 ◽  
Author(s):  
Amir Torabi ◽  
Saleh Akbarzadeh ◽  
Mohammadreza Salimpour
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Numerical Model ◽  
Film Thickness ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Minimum Film Thickness ◽  
Cam Follower ◽  
Key Parameter

In this study, a numerical model is developed to show the performance improvement of a cam–follower mechanism when using a roller type follower compared to the flat-faced follower. Nonconformal geometry besides the thermal effects due to the shearing of the lubricant film results in formation of a thin film in which the asperities contribute in carrying the load. The numerical model is developed in which the geometry, load, speed, lubricant properties, and the surface roughness profile is taken as input and the film thickness and friction coefficient as a function of cam angle are predicted. The asperities are assumed to have elastic, elasto-plastic, and plastic deformation. Simulation results indicated that the thermal effects cannot be neglected. Surface roughness is also a key parameter that affects the pressure distribution, film thickness, and friction coefficient. Finally, asperity and hydrodynamic pressure is reported and the performance of the two mechanisms is compared. Roller follower has a considerable preference in terms of friction coefficient compared to flat-faced follower. The minimum film thickness, however, is slightly larger in the flat follower.

Third Paper: Elastohydrodynamic Lubrication of O-Ring Seals

1966 ◽  
Vol 181 (1) ◽  
pp. 205-223 ◽  
Author(s):  
C. J. Hooke ◽  
D. J. Lines ◽  
J. P. O'Donoghue
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Hydrodynamic Theory ◽  
Maximum Pressure ◽  
Circular Section ◽  
Ring Seal ◽  
Elastic Distortion ◽  
Standard Solution ◽  
The Difference ◽  
Sealing Pressure

The paper presents a theoretical solution to the ideal problem of an O-ring seal constructed of an isotropic elastic material moving at a constant axial velocity along a cylinder. By means of a standard solution for the elastic distortion of a circular section, and the inverse hydrodynamic theory proposed by Dowson and Higginson, compatible solutions for the hydrodynamic pressure and film shape between the seal and cylinder walls are obtained. It is shown that with a typical seal section taken from British Standard, with standard groove dimensions and ‘nip’, the sealing pressure, which is defined as the difference between the maximum pressure under the seal contact and the sealed pressure, remains independent of the sealed pressure. The net leakage past the seal, which is the difference between the fluid flow across the seal when it is ‘pumping’ against the pressure and that when the seal is ‘motoring’ or moving with the pressure, is shown to increase with sealed pressure. The results are presented in non-dimensional form to generalize their application.

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