ABSTRACT
Although lubrication is used in many diµerent applications and under many diµerent conditions, its actual function is o§en not well understood. Lubrication is the usage of a third material between two surfaces. ˜ese two surfaces could be in relative sliding motion or they could be stationary. Lubrication is used to reduce or control friction and wear between these surfaces. ˜e lubricant or third material between the two surfaces is usually either a ¨uid, a solid, or a semisolid (grease, gel, paste) with a low shear strength. Reducing the shear stress between two surfaces has the eµect of reducing the friction and wear. ˜e thickness of the lubricant layer does not have to be substantial as even a single molecular layer can be eµective at reducing the friction and wear (may be classiŸed as a type of boundary Ÿlm lubrication). However, a thick layer of lubricant can be more reliable and resilient. If lubricant is removed from between surfaces due to wear or squeezing, it can sometimes be replenished by a supply inlet or by being imbedded in the bulk surface itself. Surface dimples and textures can also act as an eµective reservoir for lubricants and will be discussed in more detail in Section 14.6.
