0
Research Papers: Elastohydrodynamic Lubrication

A Multiscale Study on the Wall Slip Effect in a Ceramic–Steel Contact With Nanometer-Thick Lubricant Film by a Nano-to-Elastohydrodynamic Lubrication Approach

[+] Author and Article Information
D. Savio

Université de Lyon,
CNRS, UMR5259,
INSA-Lyon, LaMCoS,
Villeurbanne F-69621, France
SKF Aeroengine France,
Z. I. no. 2, Rouvignies,
Valenciennes 59309, France

N. Fillot

Université de Lyon,
CNRS, UMR5259,
INSA-Lyon, LaMCoS,
Villeurbanne F-69621, France
e-mail: nicolas.fillot@insa-lyon.fr

P. Vergne

Université de Lyon,
CNRS, UMR5259,
INSA-Lyon, LaMCoS,
Villeurbanne F-69621, France

H. Hetzler, W. Seemann

Institute of Engineering Mechanics (ITM),
Karlsruhe Institute of Technology (KIT),
Karlsruhe 76131, Germany

G. E. Morales Espejel

Université de Lyon,
CNRS, UMR5259,
INSA-Lyon, LaMCoS,
Villeurbanne F-69621, France
SKF Engineering and Research Centre,
Nieuwegein 3430 DT, The Netherlands

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received July 15, 2014; final manuscript received February 23, 2015; published online April 15, 2015. Assoc. Editor: Zhong Min Jin.

J. Tribol 137(3), 031502 (Jul 01, 2015) (13 pages) Paper No: TRIB-14-1166; doi: 10.1115/1.4029937 History: Received July 15, 2014; Revised February 23, 2015; Online April 15, 2015

A novel nano-to-elastohydrodynamic lubrication (EHL) multiscale approach, developed to integrate molecular-scale phenomena into macroscopic lubrication models based on the continuum hypothesis, is applied to a lubricated contact problem with a ceramic–steel interface and a nanometric film thickness. Molecular dynamics (MD) simulations are used to quantify wall slip occurring under severe confinement. Its dependence on the sliding velocity, film thickness, pressure, and different wall materials is described through representative analytical laws. These are then coupled to a modified Reynolds equation, where a no-slip condition applies to the ceramic surface and slip occurring on the steel wall is described through a Navier-type boundary condition. The results of this nano-to-EHL approach can contradict the well-established lubrication theory for thin films. In fact, slip can occur over the whole contact length, leading to a significant modification of the lubricant flow and consequently of the film thickness. If both walls move at the same velocity, the flow is reduced at the contact inlet and the film thickness decreases. If the nonslipping wall entrains the fluid, this one is accelerated resulting in a larger mass flow; nevertheless, the surface separation is reduced as the lubricant flows even faster in the contact center. The opposite effect occurs if the slipping surface entrains the fluid, causing a lower mass flow but higher film thickness. Finally, friction is generally smaller compared to the classical no-slip case and becomes independent of the sliding velocity as total slip is approached.

Copyright © 2015 by ASME
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Fig. 1

Snapshot of a MD system featuring a hybrid interface. In this reference configuration, n-octane is confined between ferrite and silicon nitride walls under typical EHD operating conditions (u2 = −u1 = 1 m/s, P = 1 GPa).

Grahic Jump Location
Fig. 2

Velocity profile across a n-octane film confined between an upper Si3N4 and a lower Fe surfaces under typical EHD operating conditions. The imposed wall speeds u1 = −1 m/s and u2 = 1 m/s along the x-direction are represented by the blue arrows, whereas the fluid velocity is shown by the gray dots. P = 1 GPa, h = 5 nm, and Twall = 303 K.

Grahic Jump Location
Fig. 3

Dependence of the dimensionless slip length Ls/Ls,ref with the wall speeds difference Δu. α-Fe [110] and Si3N4 [001] surfaces, n-octane, P = 1 GPa, h = 5 nm, and Twall = 303 K.

Grahic Jump Location
Fig. 4

Dependence of the dimensionless slip parameter s (a) and slip length Ls/Ls,ref, and (b) with the inverse of the film thickness 1/h. α-Fe [110] and Si3N4 [001] surfaces, n-octane, Δu = 2 m/s, P = 1 GPa, and Twall = 303 K.

Grahic Jump Location
Fig. 5

Dependence of the dimensionless slip parameter s (a) and slip length Ls/Ls,ref, and (b) with pressure P. α-Fe [110] and Si3N4 [001] surfaces, n-octane, Δu = 2 m/s, h = 5 nm, and Twall = 303 K.

Grahic Jump Location
Fig. 6

Combined dependence of the dimensionless slip length Ls/Ls,ref with the operating conditions. (a) Wall velocity difference Δu and inverse of film thickness (1/h). (b) Wall velocity difference Δu and pressure P. (c) Inverse of film thickness (1/h) and pressure P.

Grahic Jump Location
Fig. 7

Viscosity increase with the film thickness for confined n-octane in comparison with the bulk viscosity value. α-Fe [110] and Si3N4 [001] surfaces, Δu = 2 m/s, P = 1 GPa, and Twall = 303 K.

Grahic Jump Location
Fig. 8

Schematic representation of the EHD contact geometry. (a) Line contact between a plane and a cylinder. (b) Equivalent formulation for the numerical resolution.

Grahic Jump Location
Fig. 9

Flow chart of the multiscale approach for the coupling of nanoscale and macroscopic models

Grahic Jump Location
Fig. 10

Film thickness (a) and pressure (b) distributions from the nano-to-EHL approach compared to the classical no-slip solution, for the hybrid contact in a pure rolling configuration

Grahic Jump Location
Fig. 11

Velocity profiles at the contact inlet (a) and center (b) for the steel–ceramic hybrid contact at SRR = 0: nano-to-EHL model with slip on the lower wall (solid curves) compared to the classical no-slip solution (dashed curves)

Grahic Jump Location
Fig. 12

Film thickness dependence on the SRR for the hybrid contact. Variations in h are observed for the nano-to-EHL model with slip, in contrast with the standard no-slip Reynolds solution where the film thickness is independent on SRR.

Grahic Jump Location
Fig. 13

Velocity profiles at the inlet and center of the hybrid contact for the nano-to-EHL model with slip compared to the classical no-slip solution. (a) and (b) SRR = 2: the lower (slipping) wall is stationary. (c) and (d) SRR = −2: the upper (nonslipping) wall is immobile.

Grahic Jump Location
Fig. 14

Mass flow of the lubricant as a function of the SRR in an hybrid contact. Comparison between the nano-to-EHL model with slip on the lower wall with the standard no-slip Reynolds solution.

Grahic Jump Location
Fig. 15

Friction coefficient as a function of the SRR in an hybrid contact. Comparison between the nano-to-EHL model with slip on the lower wall and standard no-slip Reynolds solution.

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In