Mixed Elastohydrodynamic Lubrication in Finite Roller Contacts Involving Realistic Geometry and Surface Roughness

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Dong Zhu ◽  
Jiaxu Wang ◽  
Ning Ren ◽  
Q. Jane Wang
Keyword(s):  
Stress Concentration ◽  
Elastohydrodynamic Lubrication ◽  
Contact Length ◽  
Operating Conditions ◽  
Engineering Practice ◽  
Dry Contact ◽  
Line Contacts ◽  
Length Direction ◽  
Principal Directions ◽  
Realistic Geometry

Concentrated (or counterformal) contacts are found in many mechanical components that transmit significant power. Traditionally, concentrated contacts can be roughly categorized to point and line contacts. In point contacts, the contact area is small in both principal directions, while in line contacts, it is small in one direction but assumed to be infinitely long in the other direction. However, these two types of geometry are results of simplification that does not precisely cover all the contact conditions in engineering practice. Actually most line contact components are purposely designed to have a crown in the contact length direction in order to accommodate possible non-uniform load distribution and misalignment. Moreover, the contact length is always finite, and at two ends of the contact there usually exist round corners or chamfers to reduce stress concentration. In the present work, the deterministic mixed EHL model developed previously has been modified to take into account the realistic geometry. Sample cases have been analyzed to investigate the effects of contact length, crowning, and end corners (or chamfers) on the EHL film thickness and the stress concentration, and also to demonstrate the entire transition from full-film and mixed EHL down to a practically dry contact under severe operating conditions with real machined roughness. It appears that this modified model can be used as an engineering tool for roller design optimization through in-depth mixed EHL performance evaluation.

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.

Traction in EHL Line Contacts Using Free-Volume Pressure-Viscosity Relationship With Thermal and Shear-Thinning Effects

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Punit Kumar ◽  
M. M. Khonsari
Keyword(s):  
Free Volume ◽  
Elastohydrodynamic Lubrication ◽  
Approximate Equation ◽  
Shear Thinning ◽  
Operating Conditions ◽  
Limiting Shear Stress ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Simulation Results ◽  
Volume Equation

This paper investigates the traction behavior in heavily loaded thermo-elastohydrodynamic lubrication (EHL) line contacts using the Doolittle free-volume equation, which closely represents the experimental viscosity-pressure-temperature relationship and has recently gained attention in the field of EHL, along with Tait’s equation of state for compressibility. The well-established Carreau viscosity model has been used to describe the simple shear-thinning encountered in EHL. The simulation results have been used to develop an approximate equation for traction coefficient as a function of operating conditions and material properties. This equation successfully captures the decreasing trend with increasing slide to roll ratio caused by the thermal effect. The traction-slip characteristics are expected to be influenced by the limiting shear stress and pressure dependence of lubricant thermal conductivity, which need to be incorporated in the future.

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).

Traction in Thermal Elastohydrodynamic Lubrication of Rough Surfaces

1992 ◽  
Vol 114 (1) ◽  
pp. 186-191 ◽  
Author(s):  
L. Chang
Keyword(s):  
Numerical Solutions ◽  
Rough Surfaces ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Wide Range ◽  
Line Contacts ◽  
Simulation Results

This paper studies the traction behavior of elastohydrodynamically lubricated line contacts between two rough surfaces. The study uses a thermal micro-elastohydrodynamic-lubrication (micro-EHL) model and obtains traction coefficients for a wide range of operating conditions and for film parameters as small as 1.50. The simulation results suggest that the traction is generally insensitive to the roughness structure and magnitude as long as the contact maintains a full EHL film. The results also indicate clearly that the lubricant squeeze induced by the motion and interaction of rough surfaces significantly affects the numerical solutions to thermal micro-elastohydrodynamic lubrication.

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.

Elastohydrodynamic lubrication of coated finite line contacts

2017 ◽  
Vol 232 (9) ◽  
pp. 1077-1092 ◽  
Author(s):  
Shivam S Alakhramsing ◽  
Matthijn B de Rooij ◽  
Dirk J Schipper ◽  
Mark van Drogen
Keyword(s):  
Mechanical Properties ◽  
Film Thickness ◽  
Surface Profile ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Maximum Pressure ◽  
Lubrication Performance ◽  
Line Contacts ◽  
Finite Line ◽  
Axial Surface

In this work, a finite element-based model is presented that simulates elastohydrodynamic lubrication in coated finite line contacts. Using this model, the film thickness and pressure distributions, between a straight roller with rounded edges on a plate, were analyzed. The model was successfully validated against representative results reported in literature. Parameter studies were conducted to study the influence of varying operating conditions, axial surface profile parameters and coating mechanical properties on the overall elastohydrodynamic lubrication behavior of the contact. It was found that in contrast with typical elastohydrodynamic lubrication behavior, the maximum pressure and minimum film thickness, which are located at the rear of the contact, are largely influenced by variations in load. Results also reveal that axial surface profile parameters and coating mechanical properties may act as amplifiers to the effect of load on pressure and film thickness distribution and can thus, if smartly chosen, significantly enhance lubrication performance.

Elastohydrodynamic Lubrication of Elastomeric-Coated Surfaces in Line Contact

1995 ◽  
Vol 209 (2) ◽  
pp. 119-130 ◽  
Author(s):  
A A Elsharkawy ◽  
B J Hamrock
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Elastic Cylinder ◽  
Elastic Half Space ◽  
Operating Conditions ◽  
Elasticity Analysis ◽  
Elastic Substrate ◽  
Pressure Profiles ◽  
Dry Contact ◽  
Coated Surfaces ◽  
Raphson Method

Elastohydrodynamic lubrication analysis for an elastomeric layer bonded to an elastic substrate and indented by a rotating elastic cylinder is introduced. The surface elastic deformations are computed from full elasticity analysis of layered elastic half-space. The dry-contact problem was solved first, and the iterative Newton-Raphson method was used to solve the elastohydrodynamic lubrication problem. The lubricant rheological equations were considered in the present analysis. The significant effects of the elastomeric layer thickness on the pressure profiles and film shapes at different operating conditions are presented and discussed.

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.

Waviness Amplitude Reduction in EHL Line Contacts Under Rolling-Sliding

1998 ◽  
Vol 120 (4) ◽  
pp. 705-709 ◽  
Author(s):  
A. A. Lubrecht ◽  
D. Graille ◽  
C. H. Venner ◽  
J. A. Greenwood
Keyword(s):  
Film Thickness ◽  
Financial Constraints ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
The Other ◽  
Foreseeable Future ◽  
Lubricant Film Thickness ◽  
Detailed Understanding ◽  
Line Contacts ◽  
Do So

Due to technological pressures the lubricant film thickness in EHD contacts has decreased over the years and will continue to do so for the foreseeable future. On the other hand, financial constraints cause the surface roughness in these contacts to decrease very slowly, or might even cause an increase. As a result, the ratio of film thickness to composite roughness will continue to decrease. The question that remains to be answered is to what extent this decrease will affect the contact performance. A third development makes this question even more acute, the request of increased reliability. As a consequence, the problem of the detailed understanding of the elastohydrodynamic lubrication with rough surfaces is as urgent as ever. Recent work has shown that the features inside the contact deform, and that the level of deformation is a function of the wavelength of the feature and the contact operating conditions, including slip. This last aspect of the problem, which has not been addressed previously, forms the central topic of the current paper. Instead of studying the deformation of a real roughness profile, the deformation of its sinusoidal Fourier components is investigated.

The behaviour of heavily loaded line contacts with transverse roughness

1999 ◽  
Vol 213 (4) ◽  
pp. 309-320 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Surface Roughness ◽  
Full Range ◽  
Numerical Results ◽  
Operating Conditions ◽  
Entrainment Velocity ◽  
Original Surface ◽  
Line Contacts ◽  
Transverse Roughness ◽  
Inlet Length

In heavily loaded, piezoviscous contacts the surface roughness tends to be flattened inside the conjunction by any relative sliding of the surfaces. However, before it is flattened, the roughness affects the inlet to the contact, producing clearance variations there. These variations are then convected through the contact, at the entrainment velocity, producing a clearance distribution that differs from the original surface. The present paper explores this behaviour and establishes how the amplitude of the convected clearance varies with wavelength and operating conditions. It is shown that the primary influence is the ratio of the wavelength to the inlet length of the conjunction. Where this ratio is large, the roughness is smoothed and there is little variation in clearance under the conjunction. Where the ratio is small, significant variations in clearance may occur but the precise amplitude and phasing depend on the ratio of slide to roll velocities and on the value of a piezoviscous parameter, c. The numerical results agree closely with existing solutions but extend these to cover the full range of operating conditions.

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