Lubrication Fundamentals Stribeck Diagram The Stribeck diagram illustrates the various lubrication regimes for one surface sliding over another surface: hydrodynamic lubrication – the two surfaces are completely separated by a fluid film (either liquid or gas). mixed lubrication – there is a fluid film between the two surfaces, but there is also mechanical contact between roughness asperities on the surfaces. boundary lubrication – the surfaces are so close together that there is no longer a continuum fluid film between them. The surfaces are protected by lubricant films only a few molecules thick. Slide created by: Richard F. Salant at the Georgia Institute of Technology References: Williams, J. A., Engineering Tribology, Cambridge University Press, 2005.