Lubrication modes elastohydrodynamic

Elastohydrodynamic lubrication (EHD) occurs when the extent of surface deformation is comparable with the lubricant film thickness, so that a heavy load causes local elastic deformation of the contacting surfaces, but without any significant a.sperity interaction. Taking into account the low lubricant thickness (typically from 0.01 to 10 pm) and the high contact pressures (typically in the GPa range), the lubricant properties differ from tho.se of a traditional bulk liquid. since a strong viscosity increase may occur, when the lubricant behaves more like a solid than a liquid. Moderate temperature rises may occur, thus inducing some thermochemical reactions between the surfaces and the lubricant additives, but no tribochemical phenomena are involved, unlike the next lubrication mode. 

Examples of piston ring experiments can be found in (17)-(23). The rings in these references have a diameter of the order of 100 mm, except the crosshead diesel engine (23), which has a cylinder bore of 570 mm. The ring width is of the order of 2.5 to 10 mm. The mode of the lubrication is often intermediate elastohydrodynamic, which means that loads are moderate (24). 

Piston ring experiments are troublesome because of the many degrees of freedom of the ring, and the number of transducers which can be mounted, thus limiting the number of transducer positions. The mode of lubrication is intermediate or medium elastohydrodynamic. 

A cam-flat follower geometry allows the transducer to be positioned at any wanted location (see section 3), thus permitting many measurements. The mode of lubrication is medium till full elastohydrodynamic, or mixed film. 

It is interesting to note that when we introduced the concept of the lambda ratio into studies of the wear of total replacement joints, the mode of lubrication in such bearings was also ill-understood. In the previous paper the point presented was that steady state wear in metal-on-metal joints appeared to correlate quite well with the calculated elastohydrodynamic film thickness, but not with available information on the lambda ratio. The difficulty appears to arise mainly in relation to the specification of the latter quantity. 

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