The Statistical Application of a Thermal EHL Theory for Individual Asperity-Asperity Collisions to the Sliding Contact of Rough Surfaces

1975 ◽  
Vol 97 (2) ◽  
pp. 311-318 ◽  
Author(s):  
P. E. Fowles
Keyword(s):  
Friction Coefficient ◽  
Hydrodynamic Lubrication ◽  
Sliding Contact ◽  
Unit Load ◽  
Lubrication Regime ◽  
Statistical Application ◽  
Model Surfaces ◽  
Mixed Lubrication Regime ◽  
Thermal Ehl ◽  
20 Nm

The numerical results of a previously developed thermal EHL theory describing the collisions between idealized asperities are analyzed statistically to obtain macroscopic values of unit load, traction, and friction coefficient for two model surfaces in sliding contact under a range of conditions. It is shown that significant unit loads and tractions can be generated as a result of the microsopic EHL contacts alone. The variation of friction coefficient with load and sliding speed corresponds qualitatively with experiment in the mixed lubrication regime between boundary and hydrodynamic lubrication, but quantitatively the friction coefficients are two to three times too high. The results imply that the lubricant becomes non-Newtonian and/or exhibits a limiting shear strength in virtually all asperity interactions, even those in which the thickness of the intervening lubricant film is maintained in the 20-nm range.

A Theory of Mixed Lubrication

1972 ◽  
Vol 186 (1) ◽  
pp. 421-430 ◽  
Author(s):  
H. Christensen
Keyword(s):  
Hydrodynamic Lubrication ◽  
Dynamic Properties ◽  
Mixed Lubrication ◽  
Rapid Rise ◽  
Operating Characteristics ◽  
Lubrication Regime ◽  
Lubricated Contact ◽  
Mixed Lubrication Regime ◽  
Lubrication Conditions ◽  
Lubrication Properties

The phenomena observed when a lubricated contact or bearing is operating under mixed lubrication conditions are assumed to arise from an interaction of the surface asperities or roughness as well as from hydro-dynamic action of the sliding surfaces. It is shown how one of the previously published stochastic models of hydrodynamic lubrication can be extended or generalized to deal with mixed lubricating conditions. As an illustration of the application of the theory to a concrete example the influence on the operating characteristics of a plane pad, no side-leakage bearing is analysed. It is found that in the mixed lubrication regime friction is mainly controlled by the boundary lubrication properties of the liquid–solid interface. Load, on the other hand, is almost entirely controlled by the hydro-dynamic properties of the bearing. It is demonstrated how transition to mixed lubrication conditions will cause a rapid rise in friction thereby producing a minimum point in the Stribeck type diagram.

scholarly journals Friction coefficient in mixed lubrication: A simplified analytical approach for highly loaded non-conformal contacts

2017 ◽  
Vol 9 (7) ◽  
pp. 168781401770626 ◽  
Author(s):  
Javier Echávarri Otero ◽  
Eduardo de la Guerra Ochoa ◽  
Enrique Chacón Tanarro ◽  
Benito del Río López
Keyword(s):  
Friction Coefficient ◽  
Thermal Effects ◽  
Mixed Lubrication ◽  
Good Precision ◽  
Experimental Conditions ◽  
Lubrication Regime ◽  
Line Contacts ◽  
Mixed Lubrication Regime ◽  
Lubrication Conditions ◽  
Highly Loaded

This article presents an analytical model for predicting friction in mixed lubrication regime. The calculations consider load shared between roughness asperities and the lubricant film, as well as the appearance of thermal effects in the contact and the influence of the lubricant rheology. Tests using tribometers have been performed to measure the friction coefficient in non-conformal surfaces for both point and line contacts. This allows verifying the results of the model under a broad range of experimental conditions with an influence on the lubrication conditions. Reasonably good precision has been found in the results obtained, which combined with a simplicity of use confers the model a high practical utility for rough estimates of the friction coefficient under mixed lubrication.

A Friction Model for Cold Strip Rolling With Two-Wavelength Surface Roughness in the “Mixed” Lubrication Regime

2003 ◽  
Vol 125 (3) ◽  
pp. 670-677 ◽  
Author(s):  
H. R. Le ◽  
M. P. F. Sutcliffe
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Rolling Direction ◽  
Hydrodynamic Pressure ◽  
Friction Model ◽  
Mixed Lubrication ◽  
Strip Rolling ◽  
Lubrication Regime ◽  
Mixed Lubrication Regime ◽  
Cold Metal

A two-dimensional friction model has been developed for cold metal rolling in the “mixed” lubrication regime. Roughness is modelled using superimposed short and long wavelength asperities with a lay orientated along the rolling direction. The hydrodynamic pressure in the lubricant is solved using Reynolds’ equation, coupled with the crushing process of the two-wavelength roughness. This allows for the solution of film thickness and contact area ratio and hence friction coefficient through the roll-bite. The model extends the authors’ earlier model [15] by allowing for a variation in hydrodynamic pressure across the width of the contact. Predictions for both the surface roughness and the friction coefficient are in reasonable agreement with published measurements.

A New Approach to Determine Lubrication Regimes of Piston-Ring Assemblies

1997 ◽  
Vol 119 (4) ◽  
pp. 808-816 ◽  
Author(s):  
Naeim A. Henein ◽  
Shengqiang Huang ◽  
Walter Bryzik
Keyword(s):  
Piston Ring ◽  
Hydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Spark Ignition Engine ◽  
Frictional Torque ◽  
New Approach ◽  
Lubrication Regimes ◽  
Lubrication Regime ◽  
Mixed Lubrication Regime ◽  
And Shifts

A new approach is developed to determine piston-ring assembly lubrication regimes from the instantaneous frictional torque measured for the whole engine. This is based on the variation of the friction coefficient with the duty parameter in the Stribeck diagram over the mixed and hydrodynamic lubrication regimes. The derived equation determines the lubrication regimes from the slope of the line in the Stribeck diagram. A single cylinder spark ignition engine was instrumented to determine the total instantaneous frictional torque of the engine. Experiments were conducted under different loads at a constant speed. Results show that the regime is mixed lubrication near the top dead center (TDC) and shifts to the hydrodynamic lubrication regime as the piston moves away from TDC. The extent of the mixed lubrication regime depends on engine load and speed.

Numerical Analysis of Laser-Textured Piston-Rings in the Hydrodynamic Lubrication Regime

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Gonzalo Brito Gadeschi ◽  
Katja Backhaus ◽  
Gunther Knoll
Keyword(s):  
Numerical Analysis ◽  
Friction Coefficient ◽  
Distribution Pattern ◽  
Surface Texture ◽  
Piston Ring ◽  
Hydrodynamic Lubrication ◽  
Piston Rings ◽  
Variable Curvature ◽  
Lubrication Regime ◽  
Optimal Surface

In this work, the performance of barrel-shaped laser-textured piston rings is numerically investigated. The surface texture, parameterized by the dimple density, dimple depth, and dimple distribution pattern, is optimized to minimize the friction coefficient for piston rings of variable curvature. We consider fully textured as well as partially textured piston rings with two different dimple distributions patterns: a central dimple distribution, and a distribution along the piston ring edges. Finally, the sensitivity of the optimal surface parameters to the piston ring curvature is assessed.

scholarly journals Identification of Local Lubrication Regimes on Textured Surfaces by 3D Roughness Curvature Radius

2014 ◽  
Vol 966-967 ◽  
pp. 120-125 ◽  
Author(s):  
Cédric Hubert ◽  
Krzysztof J. Kubiak ◽  
Maxence Bigerelle ◽  
Laurent Dubar
Keyword(s):  
Hydrodynamic Lubrication ◽  
Contact Boundary ◽  
Curvature Radius ◽  
Textured Surfaces ◽  
Lubrication Regimes ◽  
Lubrication Regime ◽  
Cross Section Area ◽  
Strip Drawing ◽  
Mixed Lubrication Regime ◽  
Tribological Contact

This paper proposes a new method of 3D roughness peaks curvature radius calculation and its application to tribological contact analysis as a characteristic signature of tribological contact. This method is introduced through the classical approach of calculation of radius of asperity in 2D. Actually, the proposed approach provides a generalization of Nowicki's method [], depending on horizontal lines intercepting the studied profile. Here, the basic idea consists in intercepting the rough surface by a horizontal plane and to calculate the cross section area without including “islands into islands”, i.e. the small peaks enclosed in bigger ones. Then, taking into account the maximal value of the height amplitude of the roughness included into this area, an appropriate algorithm is proposed, without requiring the classical hypothesis of derivability, which may be unstable when applied to engineering surfaces. This methodology is validated on simulated surfaces, and applied to engineering surfaces created experimentally, with a laboratory aluminium strip drawing process. The regions of the textured and lubricated specimens surface are analysed, and the results gives interesting prospects to qualitatively identify the local lubrication regimes: regions with high curvature radii correspond to severe contact (boundary/mixed lubrication regime) while regions with low curvature radii correspond to hydrodynamic lubrication regime.

Parametric Study of the Behavior of a Mechanical Face Seal Operating in Mixed and TEHD Lubrication Regimes

2012 ◽  
Author(s):  
André Parfait Nyemeck ◽  
Noël Brunetière ◽  
Bernard Tournerie
Keyword(s):  
Heat Transfer ◽  
Friction Coefficient ◽  
Mixed Lubrication ◽  
Operating Conditions ◽  
Fluid Viscosity ◽  
Face Seal ◽  
Lubrication Regimes ◽  
Lubrication Regime ◽  
Mechanical Face Seal ◽  
Mixed Lubrication Regime

In this paper, the behavior of a mechanical face seal is analyzed for different operating conditions and designs. For that, a theoretical model including a multiscale approach of the mixed lubrication regime, heat transfer and deformation of the seal rings is used. It has been possible to clearly identify the three different lubrication regimes of a mechanical seal: the mixed lubrication where the friction coefficient decreases, the rough hydrodynamic regime corresponding to an increasing friction and then the thermo-elasto-hydrodynamic (TEHD) regime for which the coefficient of friction is approximately constant. In this work, the influence of the fluid pressure, the seal roughness height, the balance ratio, the rings materials, the dry friction coefficient and viscosity are respectively examined. Generally speaking, the variation of these parameters affects the location of the optimum value of the friction coefficient in the mixed lubrication regime. In the TEHD regime, the temperature is mainly influenced by the materials and the fluid viscosity, which control the amplitude of deformation and heat transfer. A dimensionless parametric analysis has been carried out in order to perform an overall discussion of the results. It is shown that the mixed and rough hydrodynamic lubrication regimes are controlled by the modified duty parameter, while the TEHD regime is controlled by the sealing parameter.

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