Abstract
The load-bearing behaviour of lubricated contacts depends primarily on the normal force, the relative velocity, and the geometry. Thus, with the aid of the Stribeck curve, it is usually well possible to characterize whether hydrodynamics, mixed friction, or boundary friction is more likely to be present. The fact that the load regime can also depend on the fluid quantity is obvious, but has hardly been systematically investigated so far. Especially for contacts with microscopic roughness, the defined application of a very small amount of fluid is a very challenging requirement. In this paper, a very fundamental study shows how a pin-on-disc tribometer can be used to achieve the transition from dry friction via mixed friction to predominant hydrodynamics by the amount of supplied fluid. The experiments are carried out on samples filed with different coarseness. In addition, the simultaneous influence of partial filling and normal force as well as relative velocity is also shown. Very good reproducibility has been practically reached over the entire range of the tests. Regarding the quantities for the coefficient of friction (COF), it was concluded that close to full filling, a reduction of the fluid quantity has a similar effect on the COF as the reduction of the velocity. This property goes along with the common theory of starved lubricated systems. Such behaviour was not observed to the same extent for the normal force. In the vicinity of smaller fluid quantities, the COF increases very rapidly with further reduction in fluid quantity, far more disproportionately than that with reduction in velocity. With a deeper understanding of this problem, various practical issues such as idling or the run-up process in bearings can also be studied in a more focused manner.
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The authors thank the German Research Foundation for funding this project (No. 390252106, “Fundamental Studies on Tribological Contacts with Partially Filled Gaps”)
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Lukas STAHL. He received his bachelor’s and master’s degrees in mechanical engineering from Technische Universität Braunschweig, Germany, in 2016 and 2018 respectively. He joined the Institute of Dynamics and Vibration at the same university afterwards. He finished his Ph.D. degree in mechanical engineering in 2022. His research interests include tribology, lubricated friction, and starved lubrication.
Michael MÜLLER. He received his Ph.D. degree from Technische Universität Braunschweig, Germany, in 2007, on the subject of friction in brakes. In 2020, he was appointed Associate Professor. Since 2011, he leads a research group on lubricated contacts at the Institute for Dynamics and Vibrations. In addition to these fundamental problems, he researches gap flows in general, such as in wet grinding processes or compression flows of adhesives.
Georg-Peter OSTERMEYER. He is a professor and till 2022 head of the Institute of Dynamics and Vibrations (IDS) at Technische Universität Braunschweig, Germany. Formerly he held the Chair of Mechanics and Friction Physics at Technische Universität Berlin, Germany. He has about 30 years of experience in industry and universities on modeling and simulation of complex systems. He received numerous national and international awards for his friction research and serves on numerous international steering committees and advisory boards.
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Stahl, L., Müller, M. & Ostermeyer, GP. On the experimental characterization of the fluid volume influence on the friction between rough surfaces. Friction 11, 1334–1348 (2023). https://doi.org/10.1007/s40544-022-0683-9
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DOI: https://doi.org/10.1007/s40544-022-0683-9