To tailor film thickness and friction in oil lubricated contacts by solid-liquid interactions

Project duration

2018 - 2020

Project Category


Contact Information

prof. dr. Mitjan Kalin


Qingdao University of Technology, People's Republic of China  

Lubricated contacts are of great importance for many mechanical systems and often a key component that facilitate smooth operation. In these contacts it is desired that lubricating oil forms enough thick lubricating film that prevents direct contacts between both contact surfaces and thus enable low or no-wear contact conditions. However, full-lubricating film, due to oil viscosity, presents drag in the contact, resulting in friction and consequently increased energy consumption. Design of the lubricated contacts, especially in order to achieve low friction and wear and thus reduced energy consumption, is one of the key role of tribology, scientific field dealing with friction, lubrication and wear of contacts in relative motion.

In recent years there were several studies that show the importance of solid-liquid interface interactions (surface energy, surface tension and wetting) and phenomena (solid-liquid slip) in tailoring full-film lubricated contact properties, i.e. film thickness and friction. What is more, the Slovenian and Chinese groups that propose this bilateral project were one of the leading research groups in this field.

The main issue about the solid-liquid slip phenomenon is the fact that its effect on lubrication performance is still not undoubtedly resolved. Namely, in numerous studies from nano to macro-scale it has been shown that solid-liquid slip mechanism reduces friction, but on the other hand its effect on lubricating film can result either in increase or in decrease in film thickness. The latter fact makes the design of lubricating contacts by employing solid-liquid interactions and phenomena even more demanding. Namely, too large magnitude of solid-liquid slip that would significantly reduce friction, could induce too thin lubricating film, which cannot fully separate contact surfaces, resulting in propagating wear and in worst case in failure of the lubricated contact.

Therefore, it is necessary to fully understand the correlation among solid-liquid interface affinity, friction and film thickness for reducing energy consumption while ensuring the reliability of oil film lubrication. Unfortunately, the comprehensive knowledge has not been well established yet, especially for engineering relevant surfaces, such as DLC coatings.

The proposed bilateral project wants to address these challenges by establishing collaboration between two research groups dealing with the same topic – i.e. effect of solid-liquid interactions and phenomena on lubrication, but each group in their specific field.