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Nano and microscale contact characteristics of tribofilms derived from fully formulated engine oil

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journal contribution
posted on 16.11.2018, 14:47 by Jamal Umer, Nick MorrisNick Morris, Michael Leighton, Ramin RahmaniRamin Rahmani, Sashi Balakrishnan, Homer Rahnejat
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.


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.



  • Mechanical, Electrical and Manufacturing Engineering

Published in

Tribology International


UMER, J. ... et al, 2018. Nano and microscale contact characteristics of tribofilms derived from fully formulated engine oil. Tribology International, 131, pp.620-630.


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This paper was accepted for publication in the journal Tribology International and the definitive published version is available at

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