Modern machine elements are required to work under increasingly severe conditions (thinner lubricating films, higher temperatures, less lubricant, etc.). Therefore, in heavily loaded lubricated contacts the effect of surface topography is now more relevant than say, 40 years ago. Yet, in the year 1977 the 4th Leeds-Lyon Symposium on Tribology was held with the theme ‘Surface Roughness Effects in Lubrication’! How much have we learnt since then? The objective of this paper is to discuss in detail the progress in micro-elastohydrodynamic lubrication (micro-EHL) and to give an overview of mainly modelling progress and understanding in the last 40 years. The paper starts with a quick review of the main methods, models and challenges in micro-elastohydrodynamic lubrication, from the days of the 4th Leeds-Lyon Symposium to current times. Then the focus shifts towards discussing in more detail the existing semi-analytical methodologies developed in recent times to model the micro-elastohydrodynamic lubrication problem. The global and local effects of roughness, the effects of sliding and the transition to dry contact will be included. Finally, examples of industrial applications will be presented where roughness plays a major role in function; at the end, new challenges in the modelling of surface roughness effects in elastohydrodynamic lubrication will be outlined, e.g. interactions with the subsurface material.
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