Elastohydrodynamic

Elastohydrodynamic lubrication is a regime of lubrication that occurs in highly loaded contact zones where the lubricant film is thin enough to cause elastic deformation of the contacting bodies. It is most important for rolling-contact bearings and gear meshes, where high contact pressures and relatively low separation lead to significant surface deformation while maintaining separation by a lubricating film.

The physics of elastohydrodynamic lubrication uses a form of the Reynolds equation for thin-film flow, augmented to account for pressure-induced viscosity changes and for elastic deformation described by Hertzian contact theory. The high pressures raise the lubricant viscosity (the pressure-viscosity effect) and create a pressure distribution that sustains a thin film, with film thickness typically on the order of tens of nanometers to a few micrometers. Non-Newtonian effects may be important for some oils and operating conditions.

Elastohydrodynamic lubrication reduces metal-to-metal contact and wear, but friction can remain substantial under high loads. Analysis often relies on numerical solutions that couple the Reynolds equation with elasticity calculations and accurate lubricant properties, including viscosity and its variation with pressure and temperature, as well as lubricant additives.

Applications of EHL include gear contacts, rolling-element bearings, cam mechanisms, and other high-load, low-clearance mechanisms found in transmissions, engines, and hydraulic systems. The concept underpins the design and analysis of many machine components where extreme pressures and thin lubricant films govern performance and durability.