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Roughness in EHL
The breakdown of EHL films is not understood; but one possibility is that it is an interaction between
the non-Newtonian behaviour of oils when under very high pressures and shear rates and surface roughness
[1,2]. Much effort is on understanding what happens to roughness in an EHL contact, and it can be shown
theoretically that long wavelength roughness disappears (but generates corresponding pressure fluctuations)
while short wavelength roughness is largely undeformed. The effect is that roughness can pass through an EHL
channel which is too narrow to accommodate it! But the behaviour is more complex still; because disturbances
are transmitted down the EHL channel at the mean surface speed, while the roughness moves with the individual
surface speeds, one can find pressure fluctuations and film thicknesses which appear quite uncorrelated
[3-8].
Relevant/recent publications
- Johnson, K. L. 'Non-newtonian effects in EHL' in Thin Films in Tribology (ed. Dowson, D et al) Elsevier
(1993). Johnson, K. L. and Higginson, J. G. 'A non-newtonian effect of sliding in micro-EHL' Wear,
128, pp249-264 (1988).
- Greenwood, J. A. and Johnson, K. L. 'The behaviour of transverse roughness in sliding EHL contacts'
Wear, 153, pp107-117 (1992).
- Greenwood, J. A. and Morales-Espejel, G. E. 'The behaviour of real transverse roughness in a sliding ehl
contact' in Thin Films in Tribology (ed. Dowson, D. et al) Elsevier (1993)
- Greenwood, J. A. and Morales-Espejel, G. E. 'The behaviour of transverse roughness in ehl contacts' J.
Engineering Tribology, 208, pp121-132 (1994).
- Venner, C. H., Couhier, F., Lubrecht, A. A. and Greenwood, J. A. 'Amplitude reduction of waviness in
transient EHL line contacts' Proc. 23rd Leeds-Lyon Symposium on Tribology, Leeds, Sept 1996.
- Lubrecht, A . A., Graille, D., Venner, C.H., and Greenwood, J. A. 'Waviness amplitude reduction in EHL
line contacts under rolling-sliding' ASME J. Tribology, 120, pp705 -709 (1998).
- Greenwood, J. A . 'Transverse roughness in EHL' J. Engineering Tribology, 213, pp383-396
(1999).
Contact Details
For further information on the work summarised above contact Dr J A Greenwood at Cambridge University
Engineering Department, Trumpington St, Cambridge, CB2 1PZ, UK. Tel: 01223 332733, Fax: 01223 332662. E-mail:
jag@eng.cam.ac.uk
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