The Elastohydrodynamic Lubrication of Heavily Loaded Contacts

1977 ◽  
Vol 19 (4) ◽  
pp. 149-156 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Analytical Solution ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Dimensional Parameter ◽  
Effect Of Pressure ◽  
General Line ◽  
Minimum Film Thickness ◽  
Line Contacts

An analytical solution is presented to the problem of the lubrication of highly deformed contacts, including the effect of pressure on viscosity. It is shown that the character of the lubrication process depends on the value of a single non-dimensional parameter, and that for each value of this parameter there is a unique non-dimensional value for minimum film thickness. Results are presented for general line contacts and for cylindrical contacts.

Thermal Elastohydrodynamic Lubrication of Axially Crowned Rollers

2021 ◽  
pp. 1-21
Author(s):  
Wassim Habchi
Keyword(s):  
Film Thickness ◽  
Design Parameter ◽  
Numerical Study ◽  
Elastohydrodynamic Lubrication ◽  
Negative Influence ◽  
Reference Case ◽  
Critical Design ◽  
Lubrication Performance ◽  
Minimum Film Thickness ◽  
Line Contacts

Abstract This work presents a comprehensive numerical study of thermal elastohydrodynamic lubrication performance in axially crowned rollers, based on a full-system finite element approach. Axial crowning has always been introduced to finite line contacts, as a mean for improving film thickness. Its influence on friction has often been overlooked though. The current work reveals that axial crowning has a negative influence on friction, increasing it significantly with respect to the reference case of straight rollers. It is shown that, with increased crowning height (or reduced crowning radius), minimum film thickness is increased, but so is friction. Therefore, film thickness enhancement comes at the expense of a deterioration in friction. Besides, achieving sufficient enhancements in minimum film thickness would require using relatively low crowning radii, which would lead to a substantial increase in friction. The frictional increase is traced back to an overall increase in contact pressures and effective contact area within the lubricating conjunction. It is also shown that, when film thickness is the most critical design parameter, the best compromise between enhanced film thickness and deteriorated friction would be to combine axial crowning with roller-end profiling. However, when friction is the most critical design parameter, a simple roller-end profiling would offer the best compromise.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Rolling Line Contacts

1991 ◽  
Vol 113 (3) ◽  
pp. 481-491 ◽  
Author(s):  
H. Salehizadeh ◽  
N. Saka
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Shear Stresses ◽  
Hertz Contact ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Pressure Spike ◽  
Heavy Loads

The two-dimensional thermal elastohydrodynamic equations were numerically solved for a Ree-Eyring type lubricant under pure rolling conditions. Profiles of lubricant pressure, film thickness, and temperature were obtained for medium to heavy loads and moderate to high rolling speeds. The pressure results generally show a small secondary peak near the outlet, but at the highest load considered no pressure spike is obtained and the pressure profile is almost Hertzian. The film thickness results show an increase in minimum film thickness with increasing rolling speeds, but at a lesser rate than those predicted for a Newtonian fluid under isothermal conditions. It is found that unless the lubricant becomes non-Newtonian in the inlet region, the reduction in minimum film thickness at high rolling speeds is completely due to thermal effect. The lubricant temperature profile and the amount of heat generated and dissipated in the contact region were also calculated. The lubricant temperature reaches a maximum just before the entrance to the Hertz contact region. Both shear and compression heating are found to be important in raising the lubricant temperature in the inlet. As the lubricant enters the Hertz contact zone, the temperature first drops rapidly, because of the rapid heat conduction to the rollers, and then remains almost constant for most of the Hertz contact. Near the exit where the pressure gradients are large, the lubricant temperature drops rapidly below the ambient because of lubricant expansion. The lubricant then heats up rapidly before leaving the contact area as a result of heat generated by shear stresses.

New equations for enhanced film thickness in line contacts under pressurized ambient conditions

2016 ◽  
Vol 231 (5) ◽  
pp. 616-622 ◽  
Author(s):  
Niraj Kumar ◽  
Punit Kumar
Keyword(s):  
Film Thickness ◽  
Ambient Pressure ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Ambient Conditions ◽  
Alternative Approach ◽  
Film Forming ◽  
Highly Sensitive ◽  
Minimum Film Thickness ◽  
Line Contacts

An elastohydrodynamic lubrication model is proposed for line contacts under pressurized ambient conditions often encountered in hydraulic pumps, submarine machinery and many other submerged systems. It has been demonstrated that the film forming behavior under such conditions is essentially different from that in conventional elastohydrodynamic lubrication contacts. The numerical simulation results are regressed to develop new central and minimum film thickness equations for Newtonian fluids as functions of ambient pressure, speed, load, and material parameters. An alternative approach is also discussed which involves the use of existing film thickness formulas with ambient viscosity and pressure–viscosity coefficient pertaining to the desired pressure range. A film thickness enhancement of more than 100% over conventional elastohydrodynamic lubrication case is observed. This enhancement is shown to be highly sensitive to the pressure–viscosity coefficient. Besides, the effect of shear-thinning behavior is also investigated and it is found to lower the film thickness enhancement, especially at high ambient pressures.

The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—Piezoviscous Behaviour

1992 ◽  
Vol 206 (6) ◽  
pp. 417-424 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubrication Theory ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Entrainment Velocity ◽  
Residual Film ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Important Exception

In many line contacts the operating conditions, such as load, entrainment velocity and contact radii, vary with time. Generally, the results from standard elastohydrodynamic lubrication theory, derived for constant conditions, can be used to obtain a quasi-steady prediction of film thickness that is sufficiently accurate for design purposes. An important exception to this is where the entrainment direction changes because, under those conditions, the quasi-steady approach predicts that there will be no clearance between the surfaces while in practice a residual film will persist. A previous paper showed that the minimum film thickness during entrainment reversal depends primarily on the rate of change of entrainment velocity. Limit expressions for the minimum clearance in the four regimes of lubrication were obtained. The present paper is part of a programme to develop a minimum film thickness chart for entrainment reversal and deals with the transition between the rigid-piezoviscous and the elastic-piezoviscous regimes.

Thermal Elastohydrodynamic Lubrication of Heavily Loaded Line Contacts—An Efficient Inlet Zone Analysis

1998 ◽  
Vol 120 (1) ◽  
pp. 119-125 ◽  
Author(s):  
Mihir K. Ghosh ◽  
Raj K. Pandey
Keyword(s):  
Film Thickness ◽  
Thermal Loading ◽  
Elastohydrodynamic Lubrication ◽  
Thermal Reduction ◽  
Reduction Factor ◽  
Computationally Efficient ◽  
Rolling Velocity ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Inlet Zone

An inlet zone analysis of TEHD lubrication of heavily loaded line contacts has been done using a computationally efficient and accurate numerical method based on Lobatto quadrature developed by Elrod and Brewe (1986). The results under extremely heavy conditions of dimensionless load W = 5.2*10−4 (pH = 2.0 GPa) and dimensionless rolling velocity U = 2.0*10−10(50 m/s) are presented. Significant reduction in thermal reduction factor (film thickness) at high rolling speeds relative to isothermal conditions have been observed. The results of the present work have been compared with the results of Wilson and Sheu (1983) and Hsu and Lee (1994). A correction formula of the thermal reduction factor for the minimum film thickness has been derived for a range of thermal loading parameters, loads, and slip ratios.

Influence of Surface Waviness on the Thermal Elastohydrodynamic Lubrication of an Eccentric-Tappet Pair

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
J. Wang ◽  
C. H. Venner ◽  
A. A. Lubrecht
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Surface Waviness ◽  
Film Pressure ◽  
Oil Film ◽  
Working Cycle ◽  
Temperature Oscillations ◽  
Minimum Film Thickness ◽  
Traction Coefficient ◽  
Oil Film Pressure

The effect of single-sided and double-sided harmonic surface waviness on the film thickness, pressure, and temperature oscillations in an elastohydrodynamically lubricated eccentric-tappet pair has been investigated in relation to the eccentricity and the waviness wavelength. The results show that, during one working cycle, the waviness causes significant fluctuations of the oil film, pressure, and temperature, as well as a reduction in minimum film thickness. Smaller wavelength causes more dramatic variations in oil film. The fluctuations of the pressure, film thickness, temperature, and traction coefficient caused by double-sided waviness are nearly the same compared with the single-sided waviness, but the variations are less intense.

Film thickness in elastohydrodynamically lubricated slender elliptic contacts: Part I – numerical studies of central film thickness

2021 ◽  
pp. 135065012110477
Author(s):  
Marius Wolf ◽  
Sergey Solovyev ◽  
Fatemi Arshia
Keyword(s):  
Film Thickness ◽  
State Of The Art ◽  
Experimental Studies ◽  
Elastohydrodynamic Lubrication ◽  
Large Parameter ◽  
Numerical Studies ◽  
Minimum Film Thickness ◽  
Subsequent Publication ◽  
New Formula ◽  
Increasing Load

In this paper, analytical equations for the central film thickness in slender elliptic contacts are investigated. A comparison of state-of-the-art formulas with simulation results of a multilevel elastohydrodynamic lubrication solver is conducted and shows considerable deviation. Therefore, a new film thickness formula for slender elliptic contacts with variable ellipticity is derived. It incorporates asymptotic solutions, which results in validity over a large parameter domain. It captures the behaviour of increasing film thickness with increasing load for specific very slender contacts. The new formula proves to be significantly more accurate than current equations. Experimental studies and discussions on minimum film thickness will be presented in a subsequent publication.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Line Contacts Under Simple Sliding Conditions

1992 ◽  
Vol 114 (2) ◽  
pp. 317-327 ◽  
Author(s):  
Shao Wang ◽  
T. F. Conry ◽  
C. Cusano
Keyword(s):  
Film Thickness ◽  
Surface Temperature ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Reduction Factor ◽  
Simple Formulation ◽  
Maximum Surface ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Maximum Surface Temperature

A computationally simple formulation for the stationary surface temperature is developed to examine the thermal non-Newtonian EHD problem for line contacts under simple sliding conditions. Numerical results obtained are used to develop a formula for a thermal and non-Newtonian (Ree-Eyring) film thickness reduction factor. Results for the maximum surface temperature and traction coefficient are also presented. The thermal effects on film thickness and traction are found to be more pronounced for simple sliding than for combined sliding and rolling conditions.

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.

The Effects of Surface Irregularities on the Elastohydrodynamic Lubrication of Sliding Line Contacts. Part II—Wavy Surfaces

1984 ◽  
Vol 106 (1) ◽  
pp. 113-119 ◽  
Author(s):  
P. R. Goglia ◽  
C. Cusano ◽  
T. F. Conry
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Smooth Surface ◽  
Wave Amplitude ◽  
Elastohydrodynamic Lubrication ◽  
Wavy Surface ◽  
Line Contacts ◽  
Surface Irregularities ◽  
Wavy Surfaces ◽  
Octahedral Shear Stress

The micro-EHD effects caused by wavy surfaces have been analytically investigated. The investigation includes the effects of phase, wavelength, and wave amplitude on film thickness, pressure distribution and subsurface octahedral shear stress field. The presence of a wavy surface with a given wavelength produces pressure oscillations of the same wavelength. With increasing wave amplitude and decreasing wavelength, the micro-EHD action increases. This results in a maximum value of the octahedral shear stress which is greater in magnitude and closer to the surface than the corresponding smooth surface case. The slope of the wavy surface in the inlet region determines whether the average film thickness is smaller or larger than the smooth surface value.

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