The effect of surface roughness on friction and film thickness in transition from EHL to mixed lubrication

• Published in: Tribology international 2018-12, Vol.128, p.356-364
• Main Authors: Zapletal, T., Sperka, P., Krupka, I., Hartl, M.
• Format: Article
• Language: English
• Subjects: Elastohydrodynamic lubrication; Film thickness; Friction; Lubricants & lubrication; Lubrication; Mixed lubrication; Surface layers; Surface roughness; Surface roughness effects; Thin films
• ISSN: 0301-679X; 1879-2464
• DOI: 10.1016/j.triboint.2018.07.047

The purpose of this study is to reveal the connection between the film thickness and the friction for a uniform surface texture on transition from full film to mixed lubrication in non-conformal contacts. The current study tries to clarify the processes leading to the friction increase during the transition that is usually seen in the Stribeck curve. The transition to mixed lubrication and the friction increase are usually associated with a direct contact between surface irregularities. However, the experimental results showed that friction increases much earlier before the first contact was detected. It was revealed that a standard mixed friction modeling based on the area in a direct contact has significant limitations. Numerous possible explanations for this phenomenon are discussed. [Display omitted] •The connection between the film thickness and the friction on transition from full film to mixed lubrication was studied.•Average film thickness deviates from the theory due to the first contact between opposite surfaces.•The friction increases much earlier than the first contact between opposite surfaces is detected.•Limitation of friction prediction based on a direct contact between rubbing surfaces are shown.•Numerous possible explanations for friction increase before contact detection are discussed.