Elastohydrodynamischer

Elastohydrodynamics (EHD), often referenced in German as elastohydrodynamischer, is a branch of tribology that studies lubrication regimes in which elastic deformation of contacting bodies and hydrodynamic pressure generate a lubricating film that keeps surfaces apart under high load. The term reflects the combination of elastic deformation and hydrodynamic lubrication that occurs in many rolling and sliding contacts.

Key characteristics of elastohydrodynamic lubrication include very high contact pressures, typically up to several gigapascals, and very small film thicknesses, often in the micrometer range or below. Viscosity rises under pressure (piezoviscous effects), and the contacting surfaces deform elastically according to Hertzian contact theory. The result is a thickened lubricant film that supports load without direct metal-to-metal contact.

Modeling elastohydrodynamics involves coupling the Reynolds equation for lubricant flow with elasticity theory to determine pressure distributions, film thickness, and load-carrying capacity. Semi-empirical film-thickness formulas, developed by researchers such as Hamrock and Dowson, are commonly used to predict operating film thickness under given speeds, loads, and temperatures. Key factors include material moduli, surface radii of curvature, lubricant viscosity, temperature, and surface roughness.

Applications of EHL are widespread in high-load, high-pressure components such as gears, rolling-element bearings, cam-follower mechanisms, and certain medical implants. The elastohydrodynamic regime is distinct from pure hydrodynamic lubrication and from boundary or mixed lubrication, and it is often characterized by measurements of film thickness and pressure using optical or interferometric techniques alongside numerical simulations.