New Film Thickness Equation for Elastohydrodynamic Lubrication of Isothermal Smooth Line Contacts Under Heavy Loads for Newtonian Fluids

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.

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

Journal of Tribology ◽

10.1115/1.2920890 ◽

1992 ◽

Vol 114 (2) ◽

pp. 317-327 ◽

Cited By ~ 16

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.

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

Journal of Tribology ◽

10.1115/1.3260846 ◽

1984 ◽

Vol 106 (1) ◽

pp. 113-119 ◽

Cited By ~ 62

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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Uniform Equations in the Inlet and Exit Zones of Heavily Loaded Point and Line Elastohydrodynamically Lubricated Contacts Involved in Various Steady Motions

Journal of Tribology ◽

10.1115/1.4029448 ◽

2015 ◽

Vol 137 (2) ◽

Author(s):

Ilya I. Kudish

Keyword(s):

Film Thickness ◽

Point Contact ◽

Elastohydrodynamic Lubrication ◽

Point Contacts ◽

Lubrication Film ◽

Lubricated Contacts ◽

Asymptotic Equations ◽

Line Contacts ◽

Steady Motions ◽

Numerical Approaches

Heavily loaded point elastohydrodynamically lubricated (EHL) contacts involved in steady purely transitional, skewed transitional, and transitional with spinning motions are considered. It is shown that in the central parts of the inlet and exit zones of such heavily loaded point EHL contacts the asymptotic equations governing the EHL problem along the lubricant flow streamlines for the above types of contact motions can be reduced to two sets of asymptotic equations: one in the inlet and one in the exit zones. The latter sets of equations are identical to the asymptotic equations describing lubrication process in the inlet and exit zones of the corresponding heavily loaded line EHL contact (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For each specific motion of a point contact, a separate set of formulas for the lubrication film thickness is obtained. For different types of contact motions, these film thickness formulas differ significantly (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For heavily loaded contacts, the discovered relationship between point and line EHL problems allows to apply to point contacts most of the results obtained for line contacts (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC; Kudish, I. I., and Covitch, M. J., 2010, Modeling and Analytical Methods in Tribology, Chapman and Hall/CRC).

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Analysis of Soft-Elastohydrodynamic Lubrication Line Contacts on Finite Thickness

Journal of Tribology ◽

10.1115/1.4039161 ◽

2018 ◽

Vol 140 (4) ◽

Cited By ~ 1

Author(s):

Qie-Da Chen ◽

Wang-Long Li

Keyword(s):

Film Thickness ◽

Finite Deformation ◽

Contact Region ◽

Finite Thickness ◽

Elastohydrodynamic Lubrication ◽

Soft Materials ◽

Systematic Analysis ◽

Pressure Distributions ◽

Green Strain ◽

Line Contacts

Soft elastohydrodynamic lubrication (soft-EHL) is an important mechanism in biotribological systems. The soft-EHL has some distinct differences from the traditional hard-EHL, and a systematic analysis factoring in key features of the “softness” appears to be lacking. In this paper, a complete soft-EHL line-contact model is developed. In the model, the half-space approximation is replaced by the finite thickness analysis; the geometrical and material nonlinearity due to finite deformation is factored in; the surface velocities altered by the curvature effect are considered, and the load balance equation is formulated based on the deformed configuration. Solutions are obtained using a finite element method (FEM). The film thickness, pressure distributions, and material deformation are analyzed and discussed under various entraining velocities, elastic modulus, and material thickness of the soft layer. Comparisons are made between soft-EHL and hard-EHL modeling assumptions. The analyses show that the classical EHL modeling is not suitable for soft materials with high loads. The results show that the finite deformation (Green strain) should be considered in soft-EHL analysis. In the contact region, the hard EHL solver overestimates the pressure distribution and underestimates the film thickness and deformation.

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The Effects of Surface Irregularities on the Elastohydrodynamic Lubrication of Sliding Line Contacts. Part I—Single Irregularities

Journal of Tribology ◽

10.1115/1.3260845 ◽

1984 ◽

Vol 106 (1) ◽

pp. 104-112 ◽

Cited By ~ 84

Author(s):

P. R. Goglia ◽

T. F. Conry ◽

C. Cusano

Keyword(s):

Shear Stress ◽

Film Thickness ◽

Smooth Surface ◽

Maximum Stress ◽

Elastohydrodynamic Lubrication ◽

Maximum Value ◽

Ehd Lubrication ◽

Line Contacts ◽

Surface Irregularities ◽

Octahedral Shear Stress

A full line contact solution, under isothermal conditions, is obtained in which the effects of single stationary surface irregularities on the EHD lubrication process are studied under pure sliding conditions. The irregularities studied are furrows, furrows with built-up edges, and asperities. The effects of these irregularities on film thickness, pressure, and subsurface octahedral shear stress are presented. The pressure and film thickness resulting from such surface irregularities are significantly changed from their smooth surface values. These changes alter the state of stress in the subsurface region by increasing the maximum value of octahedral shear stress and bringing the location of this maximum stress closer to the surface. The film thickness in the contact is significantly changed from the smooth surface value only when the irregularities are located in the inlet region while the maximum value of the octahedral shear stress increases to the greatest extent when the irregularities are located in the outlet half of the contact.

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Inverse Solution of Reynolds’ Equation of Lubrication Under Point-Contact Elastohydrodynamic Conditions

Journal of Lubrication Technology ◽

10.1115/1.3251733 ◽

1981 ◽

Vol 103 (4) ◽

pp. 539-546 ◽

Cited By ~ 40

Author(s):

H. P. Evans ◽

R. W. Snidle

Keyword(s):

Film Thickness ◽

Pressure Distribution ◽

Reynolds Equation ◽

Point Contact ◽

Elastohydrodynamic Lubrication ◽

Hydrodynamic Pressure ◽

Inverse Solution ◽

Heavy Loads

The paper describes a technique for solving the inverse lubrication problem under point contact elastohydrodynamic conditions, i.e. the calculation of a film thickness and shape corresponding to a given hydrodynamic pressure distribution by an inverse solution of Reynolds’ equation. The effect of compressibility and influence of pressure upon viscosity are included in the analysis. The technique will be of use in solving the point contact elastohydrodynamic lubrication problem at heavy loads.

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Elastohydrodynamic Lubrication Between Rolling and Sliding Ceramic Cylinders: An Experimental Investigation1

Journal of Tribology ◽

10.1115/1.1310332 ◽

2000 ◽

Vol 122 (4) ◽

pp. 721-724 ◽

Cited By ~ 5

Author(s):

T. Sperrfechter ◽

R. Haller

Keyword(s):

Thermal Conductivity ◽

Film Thickness ◽

Young’S Modulus ◽

Young's Modulus ◽

Elastohydrodynamic Lubrication ◽

Ceramic Materials ◽

Oil Film ◽

Thin Film Sensors ◽

Line Contacts ◽

Clear Increase

The present work focuses on the investigation of the influence of bulk ceramic materials on the behavior of elastohydrodynamically (EHD) lubricated line contacts. The materials alumina Al2O3, zirconium oxide ZrO2 and aluminum nitride (AIN) are used. Comparative measurements were taken with steel disks made of 42CrMo4. Of primary importance are the material parameters Young’s modulus and thermal conductivity. The experimental variables pressure, temperature and oil film thickness in the EHD contact of a two disk test rig were measured with the aid of evaporated thin film sensors. As the results show, an increase in the Young’s modulus causes a clear increase of the pressure level. The oil film thickness distributions show a decline of the flattening width and of the constriction occurring at the contact outlet. The influence of the material with respect to its thermal conductivity dominates, above all, in the region of the load transmitting contact zone. The transition from a good to a bad conductor of heat causes a rise in temperature, more prominent for materials with lower thermal conductivities. This leads to viscosity decrease causing clearly reduced oil film thicknesses in the contact. [S0742-4787(00)01404-1]

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Influence of Different Viscosity Lubricant to Finite Line Contacts on Elastohydrodynamic Lubrication (EHL) under Oscillating

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.538-541.1939 ◽

2012 ◽

Vol 538-541 ◽

pp. 1939-1944

Author(s):

Yan Fei Wang ◽

Tong Shu Hua ◽

Hao Yang Sun

Keyword(s):

Film Thickness ◽

Elastohydrodynamic Lubrication ◽

Oil Film ◽

Entrainment Velocity ◽

Finite Line Contact ◽

Line Contacts ◽

Finite Line ◽

Contact Roller ◽

Two Parameters ◽

Experimental Rig

To make further researches into the elastohydrodynamic lubrication properties of a finite line contact roller, oscillating experiments were carried out on made overload experimental rig for oil film measurement using optical interference technique. Film thickness and shape were measured in two kinds of viscosity polyisobutylene. This study indicates that both lubricant viscosity and roller entrainment velocity play an important role on EHL of finite line contacts. On motion, the more increase in viscosity or speed, the thicker the oil film thickness, simultaneity edge effect is distinctly intensified and film thickness increases less on roller end, difference of the film thickness is increased between roller end and the central. Above two parameters are significant for logarithmic profile roller in crowning design.

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Thermal Elastohydrodynamic Lubrication of Axially Crowned Rollers

Journal of Tribology ◽

10.1115/1.4053094 ◽

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.

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