A systematic approach is required in order to determine the frictional characteristics of a contacting pair in the presence of a tribofilm. Despite the clear benefits in functionality and in reducing wear, the generation of ZDDP-based tribofilms often lead to increased frictional losses. Such an increase is also observed in the tribometric tests reported here, as well as in open literature. This paper investigates the underlying mechanics for the rise in friction using an integrated methodology, based upon Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The use of an analytical contact mechanics model demonstrates that the pressure coefficient of boundary shear strength, measured using lateral force microscopy, provides an explanation for the observed increase in measured friction at micro-scale.
Funding
The authors would like to express their gratitude to the Engineering and Physical Sciences Research Council, Castrol Ltd. and UET Lahore under the Faculty Development Program, for the financial support provided to this reported research.
History
School
Mechanical, Electrical and Manufacturing Engineering
Published in
Tribology International
Citation
UMER, J. ... et al, 2018. Nano and microscale contact characteristics of tribofilms derived from fully formulated engine oil. Tribology International, 131, pp.620-630.
This paper was accepted for publication in the journal Tribology International and the definitive published version is available at https://doi.org/10.1016/j.triboint.2018.11.007.