A Model for Elastohydrodynamic Film Failure in Contacts Between Rough Surfaces Having Transverse Finish

1996 ◽  
Vol 118 (4) ◽  
pp. 847-857 ◽  
Author(s):  
H. P. Evans ◽  
R. W. Snidle
Keyword(s):  
Physical Mechanism ◽  
Elastohydrodynamic Lubrication ◽  
Significant Loss ◽  
Complete Loss ◽  
Finite Width ◽  
Real Contact ◽  
Asperity Contacts ◽  
Conventional Grinding ◽  
Elliptical Contact ◽  
Failure Models

The paper describes an elastohydrodynamic lubrication (EHL) model for collapse of the film in a contact of finite width between surfaces which have roughness aligned transverse to that of lubricant entrainment. The failure mechanism proposed is that of sideways leakage of the lubricant in the gaps that are present between the surfaces due to the valley features of the surface roughness. Under typical high temperature conditions with surfaces finished by conventional grinding, it is shown that the gap between the surfaces when lubricated is almost identical to that between the same dry surfaces in contact with the addition of a small land clearance equivalent to the nominal EHL film thickness. Analysis of idealized valley geometries leads to criteria for complete cavitation or significant loss of pressure between asperity contacts, but application of these criteria to a real contact suggests that scuffing occurs under conditions which are less severe than predicted by either of these simple failure models. Detailed analysis of leakage from the valley features in the transverse direction at the edges of a real elliptical contact shows that this can explain the complete loss of the film in a real contact, and this suggests a physical mechanism of scuffing.

scholarly journals Elastohydrodynamic Lubrication between Two Rollers : Finite Width Analysis

1985 ◽  
Vol 28 (241) ◽  
pp. 1367-1372 ◽  
Author(s):  
Shigeaki KURODA ◽  
Kazuyoshi ARAI
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Finite Width

Plasto-Elastohydrodynamic Lubrication in Point Contacts for Surfaces With Three-Dimensional Sinusoidal Waviness and Real Machined Roughness

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Tao He ◽  
Ning Ren ◽  
Dong Zhu ◽  
Jiaxu Wang
Keyword(s):  
Plastic Deformation ◽  
Rough Surface ◽  
Mechanical Design ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Von Mises Stress ◽  
Asperity Contacts ◽  
Lubrication Characteristics ◽  
Von Mises

Efficiency and durability are among the top concerns in mechanical design to minimize environmental impact and conserve natural resources while fulfilling performance requirements. Today mechanical systems are more compact, lightweight, and transmit more power than ever before, which imposes great challenges to designers. Under the circumstances, some simplified analyses may no longer be satisfactory, and in-depth studies on mixed lubrication characteristics, taking into account the effects of 3D surface roughness and possible plastic deformation, are certainly needed. In this paper, the recently developed plasto-elastohydrodynamic lubrication (PEHL) model is employed, and numerous cases with both sinusoidal waviness and real machined roughness are analyzed. It is observed that plastic deformation may occur due to localized high pressure peaks caused by the rough surface asperity contacts, even though the external load is still considerably below the critical load determined at the onset of plastic deformation in the corresponding smooth surface contact. It is also found, based on a series of cases analyzed, that the roughness height, wavelength, material hardening property, and operating conditions may all have significant influences on the PEHL performance, subsurface von Mises stress field, residual stresses, and plastic strains. Generally, the presence of plastic deformation may significantly reduce some of the pressure spikes and peak values of subsurface stresses and make the load support more evenly distributed among all the rough surface asperities in contact.

scholarly journals Transient elastohydrodynamic point contact analysis using a new coupled differential deflection method Part 2: Results

2003 ◽  
Vol 217 (4) ◽  
pp. 305-322 ◽  
Author(s):  
M. J. A. Holmes ◽  
H. P. Evans ◽  
T. G. Hughes ◽  
R. W. Snidle
Keyword(s):  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Contact Analysis ◽  
Asperity Contact ◽  
Lubrication Equation ◽  
Analysis Technique ◽  
Elliptical Contact ◽  
Surface Profiles ◽  
Film Thinning ◽  
Film Collapse

The paper presents results obtained using a transient analysis technique for point contact elastohydrodynamic lubrication (EHL) problems based on a formulation that effectively couples the elastic and hydrodynamic equations. Results are presented for transverse ground surfaces in an elliptical contact that show severe film thinning at the transverse limits of the contact area. This thinning is caused by transverse (side) leakage of the lubricant from the contact in the remaining deep valley features. Comparison is made between the elliptical contact results on the entrainment centreline and the equivalent line contact analysis. This confirms the importance of edge effects as a likely cause of film collapse and scuffing failure. The surface profiles used in the analysis are taken from test discs used in scuffing experiments and from gears used in micropitting tests. Side leakage is found to be sufficiently severe to cause microasperity contact in the numerical examples presented. This contact mainly occurs close to the edges of the corresponding Hertzian area and correlates in position with the location at which scuffing is found to first occur in the earlier experiments. Comparisons are made with other numerical results for point contact configurations with sinusoidally varying surface features obtained by Zhu (2000) and considerable differences are seen in the calculated extent of asperity contact. The differences are thought to be due to the simplified treatment of the lubrication equation adopted by Zhu.

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.

EHD Analysis With Distributed Structural Inertia

1999 ◽  
Vol 123 (3) ◽  
pp. 462-468 ◽  
Author(s):  
E. G. Olson ◽  
J. F. Booker
Keyword(s):  
Numerical Stability ◽  
Journal Bearing ◽  
Elastohydrodynamic Lubrication ◽  
Static Model ◽  
Significant Loss ◽  
The Finite Element Method ◽  
Governing Equations ◽  
Inertia Effects ◽  
Coupled Problem ◽  
Structural Inertia

An elastohydrodynamic lubrication model is presented for the coupled problem of a hydrodynamic lubricating fluid in an elastic structure that includes distributed structural inertia. The problem is formulated and the governing equations solved with the finite element method for an illustrative journal bearing subject to dynamic loading. Inertia effects are demonstrated through comparisons with an existing quasi-static model. While it is true that structural inertia can be neglected without significant loss of accuracy for many journal bearing applications, the new model presented does capture effects of distributed structural inertia where such effects are important and exhibits improvements over existing methods with respect to numerical stability.

scholarly journals Ultrasonic Measurement for Film Thickness and Solid Contact in Elastohydrodynamic Lubrication

2010 ◽  
Author(s):  
R. S. Dwyer-Joyce ◽  
J. Zhu ◽  
T. Reddyhoff
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Theoretical Models ◽  
Asperity Contact ◽  
Oil Film ◽  
Real Area Of Contact ◽  
Nominal Thickness ◽  
Asperity Contacts ◽  
Mediated Contact ◽  
Ultrasonic Investigation

The reflection of ultrasound can be used to determine oil film thickness from the stiffness of the separating film. However, boundary or mixed film lubrication is a common occurrence in elastohydrodynamic lubricated (EHL) contacts, as the nominal thickness of the separating film approaches the surface asperity height. In this paper an ultrasonic investigation was carried out on the interface between a steel ball sliding on a flat disc as the speed was reduced into the boundary regime. The ultrasonic reflection then depends on the stiffness of the interface that now consists of an oil layer and asperity contacts. To distinguish the stiffness contribution from asperity contact and oil layer, a mixed lubrication model for circular contacts was established. This predicted the lubricant film thickness and proportions of solid and liquid mediated contact. The total stiffness predicted by theoretical models showed a good agreement with experimental measurement for kinematic cases. The model can then be used to extract the proportion of real area of contact, and the oil film thickness, from ultrasonic results.

Elastohvdrodvnamic Lubrication of Elliptical Contacts with Pure Spin

1993 ◽  
Vol 207 (2) ◽  
pp. 83-92 ◽  
Author(s):  
D Dowson ◽  
C M Taylor ◽  
H Xu
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Pure Spin ◽  
Variable Speed ◽  
Bearing Surface ◽  
Variable Speed Drives ◽  
Machine Elements ◽  
Elastic Distortion ◽  
Elliptical Contact ◽  
Surface Deflection ◽  
Bounding Surfaces

In a lubricated, non-conformal conjunction piezoviscous effects associated with the lubricant and elastic distortion of the bounding surfaces can have a significant influence upon the generation of the lubricant film and consequently upon the oil pressure distribution. In many widely studied cases which have been concerned with surface motions of rolling/sliding, it has been shown that these effects enhance the load-generating capability of the oil-film. However, some machine elements experience more complicated bearing surface motions. For example, spinning as well as entraining occurs in the elliptical contact regions of angular contact bearings and some forms of continuously variable speed drives. In this paper, results from a study on the elastohydrodynamic lubrication of elliptical contacts with pure spin are reported. In contrast to the former situation, an unfavourable influence of the surface deflection upon the generation of the fluid film has been observed. Comparison with experimental observation demonstrated encouraging agreement.

A Numerical Solution of the Thermal Elastohydrodynamic Lubrication in an Elliptical Contact

1982 ◽  
Vol 104 (3) ◽  
pp. 392-400 ◽  
Author(s):  
H. Bru¨ggemann ◽  
F. G. Kollmann
Keyword(s):  
Numerical Solution ◽  
Pressure Distribution ◽  
Energy Equation ◽  
Stokes Equations ◽  
Elastohydrodynamic Lubrication ◽  
Navier Stokes ◽  
Time Dependency ◽  
Navier Stokes Equations ◽  
Elliptical Contact ◽  
The Finite Difference Method

A numerical solution for the calculation of thickness and temperature of film and traction coefficients between heavily loaded elliptical contact is developed. To start the calculation a Hertzian pressure distribution modified at the inlet and outlet regions is assumed and the surface deformations are calculated. The Navier-Stokes equations and the energy equation are simultaneously solved by the finite difference method. The pressure distribution introduced is verified with the help of the condition of continuity and, if necessary, corrected. The dependence of the viscosity and the density of the lubricant on pressure and temperature is determined by empirical equations which are derived from experimental data. A time dependency of the viscosity is allowed for high viscosities. The distribution of temperature in the film is obtained for a selected example. The thicknesses of the oil film and the traction coefficients are compared with experimental results.

Temperature Analysis of Involute Gear Based on Mixed Elastohydrodynamic Lubrication Theory Considering Tribo-Dynamic Behaviors

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Hui L. Dong ◽  
Ji B. Hu ◽  
Xue Y. Li
Keyword(s):  
Contact Area ◽  
Temperature Rise ◽  
Gear Tooth ◽  
Elastohydrodynamic Lubrication ◽  
Gear Pair ◽  
Rolling Velocity ◽  
Involute Gear ◽  
Tooth Width ◽  
Asperity Contacts ◽  
Tooth Flank

An integrated model is proposed for involute gear pair combining the mixed elastodhydrodynamic lubrication (EHL) theory for finite line contact with surface temperature rise equations considering tribo-dynamic loading behaviors. The film stiffness and viscous damping as well as the friction force are taken into account. The surface topography of tooth flank measured by 3D surface profiler is also included to solve the local temperature and pressure distribution in the contact area. The results show that the temperature distributions in different meshing positions along the line of action exhibit dissimilar characteristics due to the varying of dynamic load and the changing slip-to-roll ratio, which denotes the relationship between sliding velocity and rolling velocity on the tooth flank. Besides, the maximum of temperature is likely to appear at different sides of the gear tooth width as the gear pair meshes along the line of action. Moreover, with the increasing surface roughness, the ratio of asperity contacts becomes larger, so more heat generates from the contact area and leads to higher temperature rise.

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