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Tribology Letters

, 67:16 | Cite as

Effects of Nanoscale Ripple Texture on Friction and Film Thickness in EHL Contacts

  • Tomasz WoloszynskiEmail author
  • Thomas Touche
  • Pawel Podsiadlo
  • Gwidon W. Stachowiak
  • Juliette Cayer-Barrioz
  • Denis Mazuyer
Original Paper
  • 66 Downloads

Abstract

The effects of nanoscale ripple texture on the film thickness and friction in elastohydrodynamically lubricated (EHL) contacts were investigated through ball-on-disc experiments and numerical simulations of line contacts. The texturing was produced by femtosecond LASER irradiations and the ripple texture was in the form of sinusoidal waviness with nanoscale amplitudes and wavelengths. The experimental and numerical results indicate that the orientation of the ripples with respect to the entrainment direction has little to no effect on their capability to form a lubricating film. In the EHL regime, the ripples were found to reduce the central and minimum film thickness by half of their peak-to-peak amplitude as compared to a smooth contact. The transition from EHL to mixed lubrication regime was attributed to micro-EHL effects although the subsequent friction increase was found to be largely due to the onset of asperity contacts. In the mixed lubrication regime, the coefficient of friction was mainly determined by surface roughness and its value increased with an increase in the ripple amplitude.

Keywords

Elastohydrodynamic lubrication Film thickness Friction Ripple Waviness 

List of Symbols

\(a\)

Contact radius

\(A\)

Waviness/ripple amplitude

\(A_{\text{d}}\)

Waviness/ripple deformed amplitude

\(d\)

Groove depth

\(h,H\)

Film thickness

\({H_0}\)

Distance between ball and disc neglecting elastic deformation

\({h_{{\text{av}}}}\)

Average central film thickness

\({h_{\text{c}}},{H_{\text{c}}}\)

Central film thickness

\({h_{\text{m}}},{H_{\text{m}}}\)

Minimum film thickness

\(p,P\)

Pressure

\({p_{\text{h}}}\)

Maximum Hertzian pressure

\({p_{{\text{m}},{\text{Hertz}}}}\)

Mean Hertzian pressure

\({p_{\text{m}}}\)

Mean contact pressure

\({R_{\text{q}}}\)

RMS roughness

\({R_{\text{x}}}\)

Reduced curvature radius

\({\text{SRR}}\)

\({\text{Sliding}}/{\text{rolling ratio}}=100\% \cdot {u_{\text{s}}}/{u_{\text{e}}}\)

\(t,T\)

Time

\({\Delta}T\)

Time step

\(TE\)

Temperature

\({u_1}\)

Disc speed

\({u_2}\)

Ball speed

\({u_{\text{e}}}\)

\({\text{Entrainment speed}}=({u_1}+{u_2})/2\)

\({u_s}\)

Sliding speed \(={u_1} - {u_2}\)

\(W\)

Load

\(w\)

Groove width

\(x,X\)

Position along the contact

\({\varvec{\Delta}}X\)

Mesh spacing

\({\Lambda}_{\text{T}}\)

Tallian parameter

\(\varepsilon\)

Cavitation penalty parameter

\({\eta _0}\)

Ambient viscosity

\(\eta ,\bar {\eta }\)

Dynamic viscosity

\(\dot {\gamma }\)

Shear rate

\(\lambda\)

Groove/waviness/ripple wavelength

\(\mu\)

Friction coefficient

\({\rho _0}\)

Ambient density

\(\rho ,\bar {\rho }\)

Density

\(\sigma\)

Composite RMS roughness

\(\tau\)

Shear stress

\(\theta\)

Ripple orientation

\(\mathcal{H}\)

Modified Hersey number

Notes

Acknowledgements

The authors would like to thank the School of Civil and Mechanical Engineering, Curtin University for the support of this study and acknowledge IREIS Company (France) for active collaboration and fabricating surface textures.

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.School of Civil and Mechanical EngineeringCurtin UniversityPerthAustralia
  2. 2.Ecole Centrale de Lyon, LTDS UMR 5513Ecully CedexFrance

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