Experimental Study of Lubricant Film Thickness Behavior in the Vicinity of Real Asperities Passing through Lubricated Contact

Abstract

This article presents an experimental study of the influence of real surface micro-geometry on the film thickness in a circular elastohydrodynamic (EHD) contact formed between a real, random, rough surface of steel ball and smooth glass disk. Phase shifting interferometry was used to measure in situ initial undeformed rough surface profiles, whereas thin film colorimetric interferometry provided accurate information about micro-EHD film thickness behavior over a wide range of rolling speeds. Two real roughness features were studied in detail—a 56-nm-high ridge and a 90-nm-deep groove, both transversely oriented to the direction of surface motion. It was shown that the ridge is heavily deformed in a loaded contact and its height increases with increasing rolling speed. The asperity tip film thickness behavior is quite similar to the contact average film thickness when the film thickness is higher than the undeformed ridge height. However, below this limit the film is thicker than what the EHD theory predicts. For the groove, a local reduction in film thickness at the leading edge was observed. When the groove is passing through the EHD conjunction, it maintains its undeformed shape. The behavior of both roughness features studied shows good agreement with previous experimental observations conducted using an artificially produced ridge and groove.

Keywords:

• Elastohydrodynamic Lubrication (EHL)
• Micro-EHL
• Mixed Lubrication
• Surface Roughness

ACKNOWLEDGMENTS

This research was supported by the Grant Agency of the Czech Republic and the Ministry of Education, Youth and Sports of the Czech Republic under grants Nos. 101/03/0525, J22/98:262100002, ME607, and ME631. The test oil was supplied by the Sun Oil Company Belgium. The assistance of Mr. Radek Poliščuk of Shiny Computing CZ, in interferogram processing software development, is gratefully acknowledged.

Presented at the 58th STLE Annual Meeting in New York City, New York April 28-May 1, 2003

Final manuscript approved February 12, 2004

Review led by Dong Zhu