Project: FOREMOST: Fullerene-based opportunities for robust engineering: Making optimised surfaces for tribology. Work packages 2.2 (Tribological mapping of rolling contacts) and 2.4 (Tribological mapping of fretting contacts).
A consortium of 31 companies and Universities in Europe. Among the participants are IonBond (UK and Switzerland), Fuchs (Germany), Nanomaterials (Israel), Renault (France), EADS (Germany), Rolls-Royce (UK), Goodrich (UK), CEA (France), VITO (Belgium), BAM (Germany), FZR (Germany), CNRS (France), Josef Stefan Institute (Slovenia), MFA (Hungary), NPL (UK), Stockholm University (Sweden), Uppsala University (Sweden), Linköpings University (Sweden), Newcastle University (UK), and Leeds University (UK). The project is co-ordinated by the Tekniker Technological Centre (Spain) and has a total cost of about 19 million Euros.
Sponsor: European Union (project details on the EU website).
Researcher from Imperial College London: Dr George K. Nikas (Mechanical Engineering Department)
Supervisors for the part of the project at Imperial College London:
Dr Richard Sayles (Imperial College London, Mechanical Engineering Department).
Mr Alberto Alberdi (Tekniker, Spain).
Professor Staffan Jacobson (Uppsala University, Sweden).
Project duration (for the author's part): 18 months (2005-2007).
Project cost payable to Imperial College London: £209,000.
Technical report: A technical report was written by Dr Nikas for the European Union. The 117-page report contains 73 figures (including 225 diagrams), 16 tables, 13 detailed equations and 7 appendices. Of the 225 performance diagrams, 90 are for the rolling contact analysis and 135 are for the fretting contact analysis.
Dr Nikas' project commenced in December 2005. The main objective of the author's work, which involves mathematical analysis and computational modelling, is the tribological performance mapping of rolling and fretting contacts of coated solids under dry and lubricated conditions.
The tribological mapping involves the following tasks.
Contact and subsurface stress analysis of rolling and fretting contacts of coated solids.
Computation of frictional effects in dry and in simulated lubricated conditions.
Study of failure and reliability issues.
Estimation of the fatigue life of the coated components and comparison of the coated and uncoated surfaces to highlight the improvements.
Finite Element (FE) models have been developed using the commercial software ADINA. The models deal with smooth surfaces and apply two-dimensional analysis (plane strain). For rolling contacts, this involves the contact between two coated solid cylinders and the contact of a coated cylinder with a flat coated substrate. For fretting contacts, the model deals with a flat pad with rounded edges on a coated flat substrate. Some examples are shown next, purely for demonstration purposes.
Figure 1 shows the FE mesh for the 2-d rolling contact of a coated cylinder on a coated substrate in plane strain. The mesh is intelligently constructed to be dense in the areas of interest and coarse in areas where accuracy is of less importance, such that computational speed is not compromised. This model contains approximately 21,000 to 33,000 solid elements with the minimum element size in the coatings equal to approximately 1 µm.
Fig. 1. FE mesh for the 2-d rolling contact of coated cylinder on coated substrate.
Figure 2 next shows the lateral displacement (Y) at some point during the loading of the roller.
Fig. 2. Distribution of lateral displacement (Y) at some point during loading of the roller.
Another model developed deals with the 2-d rolling contact of two coated solid cylinders in plane strain. Figure 3 shows the lateral (Y) displacement at some point during the loading of the cylinders.
Fig. 3. Distribution of lateral displacement (Y) at some point during loading of the cylinders.
This model contains approximately 50,000 solid elements with the minimum element size in the coatings equal to 1 µm. The FE mesh is intelligently constructed to put more nodes in areas of importance, such as near the coatings. This fine coating discretization is demonstrated in Fig. 4. The thickness of the coatings is 5 µm and the FE elements in the vicinity of the contact are approximately 1 µm × 1 µm in size.
Fig. 4. FE mesh for the rollers contact, showing the fine discretization of the coatings.
Publications of the author related to this work
Nikas, G. K., Sayles, R. S. Surface coatings and finite-element analysis of layered fretting contacts. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2009, 223(2), 159-181.
Nikas, G. K., Sayles, R. S. Finite-element analysis of layered rolling contacts. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2008, 222(7), 865-886.
Homepage of Dr Nikas