Elastohydrodynamic Line-Contact of Compressible Shear Thinning Fluids With Consideration of the Surface Roughness

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
J. Y. Jang ◽  
M. M. Khonsari
Keyword(s):  
Surface Roughness ◽  
Total Pressure ◽  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Shear Thinning ◽  
Line Contact ◽  
Lubricating Film ◽  
Shear Thinning Fluids ◽  
Modified Reynolds Equation

Applications involving highly loaded elastohydrodynamic lubrication (EHL), particularly when the lubricant experiences shear thinning, operating with small film thicknesses may necessitate consideration of surface asperities. A modified Reynolds equation with provision for surface roughness and shear thinning is treated to predict the pressure and surface asperity effect in an EHL line-contact. The unknown in the Reynolds equation is the hydrodynamic pressure instead of the total pressure to ensure that the pressure boundary condition at the outlet is properly posed. The Carreau viscosity model is used for characterizing the shear thinning behavior, Patir and Cheng flow factors for taking into the influence of roughness on the lubricating film, and Greenwood–Trip for determination of pressure at the asperity level. The modified Reynolds equation is solved for the hydrodynamic pressure instead of the total pressure with appropriately defined boundary conditions.

Film Thickness and Asperity Load Formulas for Line-Contact Elastohydrodynamic Lubrication With Provision for Surface Roughness

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
M. Masjedi ◽  
M. M. Khonsari
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Surface Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Load Ratio ◽  
Material Surface ◽  
Line Contact ◽  
Wide Range ◽  
Minimum Film Thickness

Three formulas are derived for predicting the central and the minimum film thickness as well as the asperity load ratio in line-contact EHL with provision for surface roughness. These expressions are based on the simultaneous solution to the modified Reynolds equation and surface deformation with consideration of elastic, plastic and elasto-plastic deformation of the surface asperities. The formulas cover a wide range of input and they are of the form f(W, U, G, σ¯, V), where the parameters represented are dimensionless load, speed, material, surface roughness and hardness, respectively.

On the elastohydrodynamic analysis of shear-thinning fluids

2007 ◽  
Vol 463 (2088) ◽  
pp. 3271-3290 ◽  
Author(s):  
J.Y Jang ◽  
M.M Khonsari ◽  
S Bair
Keyword(s):  
Film Thickness ◽  
Numerical Solutions ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Line Contact ◽  
Carreau Model ◽  
Shear Thinning Fluids ◽  
Realistic Prediction ◽  
Comparison With Experiments ◽  
Ehl Contact

Realistic prediction of the characteristics of the elastohydrodynamic lubrication (EHL) contact requires consideration of the appropriate constitutive equation for the lubricant. In many applications, the lubricant exhibits a shear-thinning behaviour which significantly affects the film thickness. In this paper, we present a generalized formulation that can efficiently treat shear-thinning fluids with provision for compressibility in the EHL line contact. Specifically, the Carreau model and the sinh-law model are investigated. An extensive set of numerical solutions and comparison with experiments reveal that the Carreau equation properly captures the film thickness behaviour under both rolling and sliding conditions.

Elastohydrodynamic Lubrication of Rough Surfaces Under Oscillatory Line Contact With Non-Newtonian Lubricant

2007 ◽  
Author(s):  
Mongkol Mongkolwongrojn ◽  
Khanittha Wongseedakaew ◽  
Francis E. Kennedy
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Power Law ◽  
Reynolds Equation ◽  
Initial Conditions ◽  
Rough Surfaces ◽  
Elastohydrodynamic Lubrication ◽  
Oscillatory Motion ◽  
Line Contact ◽  
Minimum Film Thickness

This paper presents the analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with non-Newtonian fluids under oscillatory motion. The effects of transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using multi-grid multi-level method with full approximation technique. Film thickness and pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders, the minimum film thickness calculated numerically becomes smaller. The predicted film thickness is slightly higher than the film thickness obtained experimentally, owing to cavitation that occurred in the experiments. For both hard and soft EHL contacts, the minimum film thickness under oscillatory motion is very thin near the trailing edge of the contact, especially for stiffer surfaces. The surface roughness and power law index of the non-Newtonian lubricant both have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.

Simulation of Plasto-Elastohydrodynamic Lubrication in Line Contacts of Infinite and Finite Length

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Tao He ◽  
Jiaxu Wang ◽  
Zhanjiang Wang ◽  
Dong Zhu
Keyword(s):  
Surface Roughness ◽  
Finite Length ◽  
3D Model ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Axial Direction ◽  
Contact Length ◽  
Line Contact ◽  
Line Contacts ◽  
3D Surface Topography

Line contact is common in many machine components, such as various gears, roller and needle bearings, and cams and followers. Traditionally, line contact is modeled as a two-dimensional (2D) problem when the surfaces are assumed to be smooth or treated stochastically. In reality, however, surface roughness is usually three-dimensional (3D) in nature, so that a 3D model is needed when analyzing contact and lubrication deterministically. Moreover, contact length is often finite, and realistic geometry may possibly include a crowning in the axial direction and round corners or chamfers at two ends. In the present study, plasto-elastohydrodynamic lubrication (PEHL) simulations for line contacts of both infinite and finite length have been conducted, taking into account the effects of surface roughness and possible plastic deformation, with a 3D model that is needed when taking into account the realistic contact geometry and the 3D surface topography. With this newly developed PEHL model, numerical cases are analyzed in order to reveal the PEHL characteristics in different types of line contact.

Two Dimensional Modified Reynolds Equation Including Pressure Dependent Viscosity Effect

2012 ◽  
Author(s):  
Jung Gu Lee ◽  
Alan Palazzolo
Keyword(s):  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Fluid Film ◽  
Maximum Pressure ◽  
Elastic Solids ◽  
Pressure Distributions ◽  
Pressure Dependent Viscosity ◽  
Modified Reynolds Equation ◽  
Dependent Viscosity ◽  
Modified Equation

The Reynolds equation plays an important role for predicting pressure distributions for fluid film bearing analysis, One of the assumptions on the Reynolds equation is that the viscosity is independent of pressure. This assumption is still valid for most fluid film bearing applications, in which the maximum pressure is less than 1 GPa. However, in elastohydrodynamic lubrication (EHL) where the lubricant is subjected to extremely high pressure, this assumption should be reconsidered. The 2D modified Reynolds equation is derived in this study including pressure-dependent viscosity, The solutions of 2D modified Reynolds equation is compared with that of the classical Reynolds equation for the ball bearing case (elastic solids). The pressure distribution obtained from modified equation is slightly higher pressures than the classical Reynolds equations.

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.

On the Pressure Rippling and Roughness Deformation in Elastohydrodynamic Lubrication of Rough Surfaces

1993 ◽  
Vol 115 (3) ◽  
pp. 439-444 ◽  
Author(s):  
L. Chang ◽  
M. N. Webster ◽  
A. Jackson
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Thermal Effects ◽  
Numerical Solutions ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Isothermal Conditions ◽  
Large Pressure ◽  
Shear Heating ◽  
Micro Deformation

The objective of this paper is to conduct a qualitative analysis on the effects of lubricant shear thinning, lubricant shear heating and the roughness-induced transients on the pressure rippling and roughness deformation that occurs under elastohydrodynamic lubrication (EHL) conditions. To facilitate the analysis, the numerical solutions to an example problem of EHL line contact between a perfectly smooth surface and a sinusoidal rough surface are presented. This micro-EHL problem is first solved using the conventional model of a Newtonian lubricant and a stationary rough surface under isothermal conditions. It is then solved by including the non-Newtonian effects, the roughness-induced transients and the thermal effects in sequence, so that the changes in the results brought about by each of these elements can be clearly observed and then analyzed. The analysis, which is not limited to the model problem solved in this paper, suggests that misleading results of large pressure rippling and flattened surface roughness are obtained using the Newtonian lubricant models under steady-state, isothermal conditions. Much less micro-deformation of the surface roughness is actually produced because the magnitude of the pressure ripples is greatly limited by either the lubricant non-Newtonian shear thinning and shear heating or the roughness-induced transients.

Thermohydrodynamic Analysis of Surface Roughness in the Flow Field

2005 ◽  
Vol 127 (2) ◽  
pp. 293-301
Author(s):  
Joon Hyun Kim ◽  
Joo-Hyun Kim
Keyword(s):  
Surface Roughness ◽  
Flow Field ◽  
Film Thickness ◽  
Shear Zone ◽  
Rough Surfaces ◽  
Hydrodynamic Pressure ◽  
Computational Procedure ◽  
Fluid Films ◽  
Lubricating Film ◽  
Fluid Film Thickness

The study deals with the development of a thermohydrodynamic (THD) computational procedure for evaluating the pressure, temperature, and velocity distributions in fluid films with a very rough geometry. A parametric investigation is performed to predict the bearing behaviors in the lubricating film with the absorbed layers and their interfaces as determined by rough surfaces with Gaussian distribution. The layers are expressed as functions of the standard deviations of each surface to characterize flow patterns between both rough surfaces. Velocity variations and heat generation are assumed to occur in the central (shear) zone with the same bearing length and width. The coupled effect of the surface roughness and shear zone dependency on the hydrodynamic pressure and temperature has been found in the noncontact mode. The procedure confirms the numerically determined relationship between the pressure and film gap, provided that its roughness magnitude is smaller than the fluid film thickness.

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.

Study on Photoelastic Method for Measuring Elastohydrodynamic Lubrication Pressure in Line Contact

2013 ◽  
Vol 281 ◽  
pp. 329-334
Author(s):  
Jun He ◽  
Huang Ping ◽  
Qian Qian Yang
Keyword(s):  
Film Thickness ◽  
Pressure Distribution ◽  
Reynolds Equation ◽  
Friction Pair ◽  
Elastohydrodynamic Lubrication ◽  
Ccd Camera ◽  
Measuring System ◽  
Line Contact ◽  
Basic Equations ◽  
Plastic Disk

In the present paper, a new method for measuring elastohydrodynamic lubrication (EHL) pressure in line contact is proposed, which is based on the photoelastic technique. The pressure distribution of EHL film and the inner stresses in the friction pairs are fundamental issues to carry out EHL research. The film thickness, pressure and temperature have been successfully obtained with solving the basic equations such as Reynolds equation and energy equation simultaneously or separately, with numerical model of EHL problem. The film thickness can be also measured with the optical interference technique. However, the pressure measurement is still a problem which has not been well solved yet, so as the inner stresses inside the friction pairs. With the experimental mechanics, the photoelastic technique is a possible method to be used for measuring the pressure distribution of EHL film and inner friction pair in the line contact. Therefore, A flat plastic disk and a steel roller compose the frictional pairs of the photoelastic pressure measuring rig with combining the monochromatic LED light source, polarizer CCD camera and stereomicroscope to form the whole pressure measuring system of the line contact EHL. The experimental results with the rig display the typical features of EHL pressure. This shows that the method is feasible to be used for measuring the pressure of EHL film and the inner stresses of the friction pairs in the line contact.

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