The Influence of Surface Roughness on Thin Film, Mixed Lubrication Presented at the World Tribology Congress 2001, Vienna, Austria, 3 –7 September By J. W. Choo A.V. Olver H.A. Spikes Tribology Section Department of Mechanical Engineering, Imperial College of Science, Technology and Medicine, London

The Influence of Surface Roughness on Thin Film, Mixed Lubrication Introduction World Tribology Congress 2001, Vienna Trend of machine elements (i) Higher loads and temperature → progressively thinner films. (ii) Increased operation in mixed lubrication. In very thin film conditions, Higher proportion of load is carried by asperity contact than by lubricant. Calculate pressure distribution → Improve life predictions

The Influence of Surface Roughness on Thin Film, Mixed Lubrication Method of Study Employ 3D SLIM  3D maps of EHD contact. Study…  model surface roughness features.  effects of (i) surface features (i) asperity height (iii) asperity slope.  corresponding pressure distribution. Correlate with real roughness results.

3D SLIM (Spacer Layer Imaging Method) The Influence of Surface Roughness on Thin Film, Mixed Lubrication 3D SLIM (Spacer Layer Imaging Method) World Tribology Congress 2001, Vienna White Light Glass disk with thin Cr layer and SiO2 spacer layer CCD Camera 3D Map or Profile of Separation

Calibration Procedure The Influence of Surface Roughness on Thin Film, Mixed Lubrication World Tribology Congress 2001, Vienna Calibration Procedure Ultra-thin film interferometry  log( hc ) vs. log( Ū )

The Influence of Surface Roughness on Thin Film, Mixed Lubrication World Tribology Congress 2001, Vienna Calibration Curve [3G/(R+G+B)]2 [3R/(R+G+B)]2 [3B/(R+G+B)]2

The Influence of Surface Roughness on Thin Film, Mixed Lubrication World Tribology Congress 2001, Vienna Reliability of 3D SLIM

The Experimental Set-up The Influence of Surface Roughness on Thin Film, Mixed Lubrication The Experimental Set-up World Tribology Congress 2001, Vienna Steel Ball With Ridge Inlet Outlet Coated Glass Disc Microscope Motor Loading system Ball Encoder CCD Camera White Light Ball Carriage

Improvements to the 3D SLIM technique The Influence of Surface Roughness on Thin Film, Mixed Lubrication Improvements to the 3D SLIM technique World Tribology Congress 2001, Vienna Reduction of spacer layer compression.  0.5 nm per 0.1 GPa Spacer layer thickness mapping.  measurement range 0 to 210 nm  accuracy ±2 nm Location accuracy of ball position is 15m.

The Influence of Surface Roughness on Thin Film, Mixed Lubrication Test Specimens World Tribology Congress 2001, Vienna Ridge Height (nm) Width (μm) Slope (0 ) A 163 55 0.437 B 342 37 1.002 C 145 20 1.359 Height Slope Width

The Influence of Surface Roughness on Thin Film, Mixed Lubrication World Tribology Congress 2001, Vienna Typical Film Profile Steel Ball With Ridge Inlet Outlet Coated Glass Disc

Effects of Single Transverse Ridges on Lubricant Film Thickness The Influence of Surface Roughness on Thin Film, Mixed Lubrication Effects of Single Transverse Ridges on Lubricant Film Thickness World Tribology Congress 2001, Vienna Pure Rolling Condition

Minimum Film Thickness The Influence of Surface Roughness on Thin Film, Mixed Lubrication Minimum Film Thickness World Tribology Congress 2001, Vienna Pure Rolling Condition

Maximum Film Thickness The Influence of Surface Roughness on Thin Film, Mixed Lubrication Maximum Film Thickness World Tribology Congress 2001, Vienna Pure Rolling Condition

+  Pressure Calculation Film Thickness Undeformed Surface World Tribology Congress 2001, Vienna Pressure Calculation Film Thickness Undeformed Surface Pressure Distribution + 

Pressure Ridge A: Slope = 0.437 deg Ridge C: Slope = 1.359 deg World Tribology Congress 2001, Vienna Pressure Ridge A: Slope = 0.437 deg H = 163nm, W = 55 microns Ridge C: Slope = 1.359 deg H = 145nm, W = 20 microns

The Influence of Surface Roughness on Thin Film, Mixed Lubrication Conclusion of Results World Tribology Congress 2001, Vienna In pure rolling, A lubricant film entrapment (film perturbation) is formed in front of the ridge. Ridges with lower slopes generated thicker minimum films. Ridge height and slope influences the amount of entrapped lubricant. Pressure, Film perturbation causes an increase in pressure. Pressure at ridge increased with slope.

Effects of SRR on Inlet Flow Film Perturbation The Influence of Surface Roughness on Thin Film, Mixed Lubrication Effects of SRR on Inlet Flow Film Perturbation World Tribology Congress 2001, Vienna Ridge C (H = 145 nm, S = 1.359 degrees), SRR 69%, Uball = 149mm/s, Udisk = 73mm/s Inlet Outlet Peak of Ridge Inlet Outlet Peak of Ridge

The Influence of Surface Roughness on Thin Film, Mixed Lubrication World Tribology Congress 2001, Vienna Array of Round Bumps Average Surface Speed Pure Rolling Conditions Ū = 19. 60 mms-1 SRR = 0.8 % Ū = 16. 27 mms-1 SRR = 35 % Ū = 54.38 mms-1 Ū = 54.12 mms-1 Ū = 106.67 mms-1 Ū = 106.53 mms-1 Rolling-Sliding Conditions

The Influence of Surface Roughness on Thin Film, Mixed Lubrication World Tribology Congress 2001, Vienna Future Work Isotropic Roughness Starved Conditions Dual Roughness Acknowledgement This work is financially supported by SKF Engineering & Research Centre B.V.