The mechanism and the parameters influencing friction and film thickness for single-surface boundary slip in thermal EHL contacts

Ajeeb, Rayan (author), Požar, Tomaž (author), Kalin, Mitjan (author)

This study presents a new and fundamental mechanism together with the parameters that affect elastohydrodynamic lubrication (EHL) boundary slip using Navier–Stokes formulations and implementing the shear-limited slip model proposed by Spikes and Granick, which captures the onset and evolution of the slip at the fluid–solid interface. Thermal EHL line contact using a fully coupled fluid–solid solver was employed. The results show that forward-slip, backward-slip, and no-slip regimes can arise within and outside an EHL contact, depending on the slide-to-roll ratio (SRR) and the slip yield stress, which change the position where slip initiates. When the wall shear stress magnitude before the Hertzian contact is larger than the slip yield stress, backward slip occurs before the Hertzian contact, reducing lubricant entrainment and leading to film thinning. In contrast, when the wall shear stress magnitude before the Hertzian contact is lower than the slip yield stress, slip occurs within the Hertzian contact and may lead to either increased or decreased central film thickness, depending on the SRR at a given contact pressure. For the most benefit of boundary slip it is essential that slip starts exactly at the Hertzian contact inlet, which ensures effect across the whole Couette-dominated contact region. A specific wall shear stress value is defined in this work, i.e. pre-Hertzian slip-suppression threshold (τ▫$_{w,}^{pH}$▫max), which enables such condition. Moreover, when slip is active within the Hertzian contact, slip on the faster surface promotes greater friction reduction and central film thickness increase than slip on the slower surface. By imposing slip, under the analysed conditions, the largest friction reduction was about 30%, and the central film thickness increase about 66%.

• Language: English
• Keywords: modelling, elastohydrodynamic lubrication (EHL), slip, friction, film thickness
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2027
• Number of pages: 20 str.
• Numbering: Vol. 226, pt. 3, art. 112719
• PID: 20.500.12556/RUL-188686
• UDC: 539.92:621.89
• ISSN on article: 0301-679X
• DOI: 10.1016/j.triboint.2026.112719
• COBISS.SI-ID: 292557827
• Publication date in RUL: 25.09.2026

Record is a part of a journal

• Title: Tribology international
• Shortened title: Tribol. int.
• Publisher: Elsevier, Butterworth Scientific
• ISSN: 0301-679X
• COBISS.SI-ID: 26558976

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: modeliranje, elastohidrodinamično mazanje, drsenje, trenje, debelina filma

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0231
• Name: Tribologija

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: J2-60050
• Name: Zmanjšanje trenja z naprednimi kontakti - FRAC