A Mathematical Model for the Mixed Lubrication of Non-Conformable Contacts With Asperity Friction, Plastic Deformation, Flash Temperature, and Tribo-Chemistry

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
L. Chang ◽  
Yeau-Ren Jeng
Keyword(s):  
Mathematical Model ◽  
Plastic Flow ◽  
Fluid Pressure ◽  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Flash Temperature ◽  
Power Intensity ◽  
Mixed Regime ◽  
Asperity Contacts ◽  
Mixed Lubrication Regime

A mathematical model is presented in this paper for rolling-sliding contacts operating in a mixed regime of elastohydrodynamic lubrication and boundary lubrication. The model is based on the framework of Johnson et al. (1972, “A Simple Theory of Asperity Contacts in Elastohydrodynamic Lubrication,” Wear, 19, pp. 91–108). It incorporates into this framework a number of important asperity-level variables including asperity friction, friction-induced plastic flow, flash temperature, and boundary-film tribo-chemistry. The model yields a number of variables useful for the assessment of the state of the mixed lubrication. They include the load sharing between fluid and asperities, area of asperity contacts, and fraction area of asperity contacts undergoing plastic flow along with experimentally measurable variables such as the traction coefficient, friction power intensity, and temperature of the overall contact. The model is limited to mixed-lubrication problems in which the load is mainly carried by the fluid pressure and the total area of asperity contacts is a small percentage of the Hertz area. Further development is possible to formulate a model into a wider mixed-lubrication regime using some modeling concepts developed in this paper in conjunction with other modeling techniques.

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.

Soft Elastohydrodynamic Lubrication With Roughness

2003 ◽  
Vol 125 (2) ◽  
pp. 448-451 ◽  
Author(s):  
Andrew T. Kim ◽  
Jongwon Seok ◽  
John A. Tichy ◽  
Timothy S. Cale
Keyword(s):  
Iterative Process ◽  
Fluid Pressure ◽  
Elastohydrodynamic Lubrication ◽  
Surface Interactions ◽  
Mixed Lubrication ◽  
Elastic Displacement ◽  
One Dimensional ◽  
Low Elastic Modulus ◽  
The Mean ◽  
Bounding Surfaces

A “soft” elastohydrodynamic lubrication model for a conformal one-dimensional sliding contact is presented. We describe surface-surface and fluid-surface interactions in conditions where asperities are in direct contact (mixed lubrication), and the effective film thickness is comparable in size to the roughness of the bounding surfaces. In the conditions considered, surfaces have a low elastic modulus, and fluid pressures have a low magnitude, relative to those found in most tribology applications. An interesting coupling is exhibited between the surface roughness, the global elasticity, and the fluid pressure. As opposed to typical tribological applications in conformal mixed lubrication contact, fluid pressure is strong enough to cause significant elastic displacement of the mean boundary surfaces. The deformation is taken into account in an iterative process to compute the resulting spatially dependent stresses, deformations and fluid pressures.

An Experimental Investigation of Grease-Lubricated Journal Bearings

2006 ◽  
Vol 129 (1) ◽  
pp. 84-90 ◽  
Author(s):  
Xiaobin Lu ◽  
M. M. Khonsari
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Stribeck Curve ◽  
Grease Lubrication ◽  
Lubrication Regime ◽  
Bearing Load ◽  
Line Contacts ◽  
The Coefficient Of Friction ◽  
Mixed Lubrication Regime ◽  
Basic Characteristics

A series of experimental results is presented to explore the frictional characteristics of a grease-lubricated journal bearing. Load, grease type, and bushing material are varied to examine their effects on the friction coefficient. The results attest to the existence of distinctive regimes in grease lubrication akin to the oil-lubricated Stribeck curve. A mixed elastohydrodynamic lubrication model for line contacts is employed to estimate the coefficient of friction in mixed lubrication regime. The simulation results capture the basic characteristics of mixed lubrication.

Mixed Elastohydrodynamic Lubrication in a Partial Journal Bearing—Comparison Between Deterministic and Stochastic Models

2006 ◽  
Vol 128 (4) ◽  
pp. 778-788 ◽  
Author(s):  
Mihai B. Dobrica ◽  
Michel Fillon ◽  
Patrick Maspeyrot
Keyword(s):  
Large Scale ◽  
Deterministic Model ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Mixed Lubrication ◽  
Operating Conditions ◽  
Small Scale ◽  
Depth Analysis ◽  
Stochastic Solution ◽  
Mixed Lubrication Regime

The analysis of the mixed lubrication phenomena in journal and axial bearings represents nowadays the next step towards a better understanding of these devices, subjected to more and more severe operating conditions. While the theoretical bases required for an in-depth analysis of the mixed-lubrication regime have long been established, only small-scale numerical modeling was possible due to computing power limitations. This led to the appearance of averaging models, thus making it possible to generalize the trends observed in very small contacts, and to include them in large-scale numerical analyses. Unfortunately, a lack of experimental or numerical validations of these averaging models is observed, so that their reliability remains to be demonstrated. This paper proposes a deterministic numerical solution for the hydrodynamic component of the mixed-lubrication problem. The model is applicable to small partial journal bearings, having a few centimeters in width and diameter. Reynolds’ equation is solved on a very thin mesh, and pad deformation due to hydrodynamic pressure is taken into account. Deformation due to contact pressure is neglected, which limits the applicability of the model in those cases where extended contact is present. The results obtained with this deterministic model are compared to the stochastic solution proposed by Patir and Cheng, in both hydrodynamic and elastohydrodynamic regimes. The rough surfaces used in this study are numerically generated (Gaussian) and are either isotropic or oriented, having different correlation lengths. It is shown that the stochastic model of Patir and Cheng correctly anticipates the influence of roughness over the pressure field, for different types of roughness. However, when compared to the smooth surface solution, the correction introduced by this model only partially compensates for the differences observed with a deterministic analysis.

Effects of Speed on Scuffing in Mixed Lubrication

1994 ◽  
Vol 208 (4) ◽  
pp. 269-279 ◽  
Author(s):  
D A Kelly ◽  
C G Barnes
Keyword(s):  
Thermal Model ◽  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Engineering Practice ◽  
General Criterion ◽  
Sliding Direction ◽  
Lubrication Regime ◽  
Surface Finishes ◽  
Mixed Lubrication Regime ◽  
Lubrication Conditions

Theories of failure of elastohydrodynamic lubrication are briefly reviewed, but none that relate to scuffing per se and no general criterion that accounts for the sensitivity of scuffing to rolling as well as sliding speed are found. A theoretical investigation of micro-EHL by Baglin, for surface finishes with a lay parallel to the sliding direction, predicts boundaries in the operating condition domain to a regime of mixed lubrication in which little elastic deformation of asperities by micro-EHL is expected. A new thermal model incorporating salient features of scuffing in mixed lubrication conditions is described. It is shown to give the form of a boundary in the sliding/rolling speed domain above which localized temperatures close to melting may be expected and below which lower temperatures suggest running-in without scuffing may be expected. Results of scuffing tests on circumferentially ground discs, at sliding and rolling speeds in the range 3-10 m/s, are reported and shown for surfaces with a distinguishable mainscale wavelength in their topography, (a) to provide further support for the location of the boundaries to the mixed lubrication regime in the operating domain predicted by Baglin and (b) to match the form of the thermal model in the speed domain. Implications for engineering practice are briefly discussed.

scholarly journals Modelling tribochemistry in the mixed lubrication regime

2019 ◽  
Vol 132 ◽  
pp. 265-274 ◽  
Author(s):  
Abdullah Azam ◽  
Ali Ghanbarzadeh ◽  
Anne Neville ◽  
Ardian Morina ◽  
Mark C.T. Wilson
Keyword(s):  
Mixed Lubrication ◽  
Lubrication Regime ◽  
Mixed Lubrication Regime

Numerical Modeling of Mixed Lubrication and Flash Temperature in EHL Elliptical Contacts

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Neelesh Deolalikar ◽  
Farshid Sadeghi ◽  
Sean Marble
Keyword(s):  
Surface Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Asperity Contact ◽  
Lubrication Regime ◽  
Predicting Performance ◽  
Pure Rolling ◽  
Rolling Element ◽  
Contact Pressures ◽  
Film Lubrication

Highly loaded ball and rolling element bearings are often required to operate in the mixed elastohydrodynamic lubrication regime in which surface asperity contact occurs simultaneously during the lubrication process. Predicting performance (i.e., pressure, temperature) of components operating in this regime is important as the high asperity contact pressures can significantly reduce the fatigue life of the interacting components. In this study, a deterministic mixed lubrication model was developed to determine the pressure and temperature of mixed lubricated circular and elliptic contacts for measured and simulated surfaces operating under pure rolling and rolling/sliding condition. In this model, we simultaneously solve for lubricant and asperity contact pressures. The model allows investigation of the condition and transition from boundary to full-film lubrication. The variation of contact area and load ratios is examined for various velocities and slide-to-roll ratios. The mixed lubricated model is also used to predict the transient flash temperatures occurring in contacts due to asperity contact interactions and friction. In order to significantly reduce the computational efforts associated with surface deformation and temperature calculation, the fast Fourier transform algorithm is implemented.

A Starved Mixed Elastohydrodynamic Lubrication Model for the Prediction of Lubrication Performance, Friction and Flash Temperature With Arbitrary Entrainment Angle

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Wei Pu ◽  
Dong Zhu ◽  
Jiaxu Wang
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Flash Temperature ◽  
Machined Surface ◽  
Lubrication Performance ◽  
Wide Range ◽  
Starved Lubrication

In this study, a modified mixed lubrication model is developed with consideration of machined surface roughness, arbitrary entraining velocity angle, starvation, and cavitation. Model validation is executed by means of comparison between the obtained numerical results and the available starved elastohydrodynamic lubrication (EHL) data found from some previous studies. A comprehensive analysis for the effect of inlet oil supply condition on starvation and cavitation, mixed EHL characteristics, friction and flash temperature in elliptical contacts is conducted in a wide range of operating conditions. In addition, the influence of roughness orientation on film thickness and friction is discussed under different starved lubrication conditions. Obtained results reveal that inlet starvation leads to an obvious reduction of average film thickness and an increase in interasperity cavitation area due to surface roughness, which results in significant increment of asperity contacts, friction, and flash temperature. Besides, the effect of entrainment angle on film thickness will be weakened if the two surfaces operate under starved lubrication condition. Furthermore, the results show that the transverse roughness may yield thicker EHL films and lower friction than the isotropic and longitudinal if starvation is taken into account. Therefore, the starved mixed EHL model can be considered as a useful engineering tool for industrial applications.

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