Micro-Elastohydrodynamic Lubrication and its Relationship with Running-in

Abstract

The paper determines the conditions under which sinusoidal asperities with a circumferential lay become elastically deformed by hydrodynamic pressure ripples within an elastohydrodynamic conjunction. The information is presented on a non-dimensional plot and it is found that such micro-elastohydrodynamic lubrication (micro-EHL) occurs at relatively low loads and/or with thin macroelastohydrodynamic films. Consideration is given to the way in which the plot may be extended to deal with real surfaces. Its use is demonstrated by the presentation of the lubrication histories of two scuffing tests, one of which ‘ran-in’ prior to failure. It is shown that the test which ‘ran-in’ operated throughout under micro-EHL conditions; in contrast, the second test, which started at a high load and with a thick EHL film, failed practically as soon as there was nominal contact between the surfaces. It is suggested that micro-EHL is a necessary prerequisite for ‘running-in’ and a mechanism is outlined.