elastohydrodynamisk

Elastohydrodynamisk, or elastohydrodynamic lubrication (EHL), is a regime in tribology where contacting bodies deform elastically under high Hertzian pressures while a lubricating film is maintained by hydrodynamic action. In EHL, the film thickness is small relative to the contact geometry, and the load is supported predominantly by a pressurized lubricant film rather than rough asperities.

Key features of EHL include high contact stresses—often hundreds of megapascals—elastic deformation of the surfaces, and a thin lubricant film whose viscosity increases with pressure (the pressure-viscosity effect). Temperature rise from viscous heating and, in some cases, non-Newtonian lubricant behavior may accompany the regime. The problem is inherently coupled: surface deformation alters the film, and the film pressure further deforms the surfaces.

Theory and modeling of elastohydrodynamics combine the Reynolds equation for thin-film flow with elastic contact theory (e.g., Hertzian contacts). Solutions, developed mid-20th century and refined since, predict film thicknesses from nanometers to a few micrometers, as well as central and minimum film contours and pressure distributions. Numerical methods and semi-empirical film-thickness formulas are used to design and diagnose EHL contacts.

Applications of elastohydrodynamic lubrication are common in high-load, low- to moderate-speed contacts such as gears, rolling-element bearings, cam-follower mechanisms, and constant-velocity joints. EHL helps explain wear reduction, noise control, and reliability in these components by accounting for elastic deformation, high-pressure film formation, and lubricant rheology under load.