Modelling thin film lubrication: Scientific versus engineering approaches

Abstract

There have been many recent advances in lubrication experimentation from a scientific perspective - the ability to perform meaningful measurements on molecular-scale films. Likewise, impressive strides have been made in the modelling of thin film (nanometer-scale) lubrication, from molecular dynamics and other theoretical techniques, again emanating from scientific domains. Selected recent experimental and theoretical results are discussed, particularly the ‘state variable’ theories applied to simple stick-slip configuration. Continuum-based methods are traditionally thought to be of little value in describing the modes of lubrication occurring at molecular scale. However, there is considerable experimental evidence suggesting that elements of the continuum theory may be valid, in the case of films as thin as several nanometres. The behaviour of rheological models and their applicability to thin film lubrication is described. Approaching these problems from the fluid film constitutive equation perspective is less often used but appears to be promising. Such continuum methods can take advantage of the extensive existing research methodologies such as the finite-element method of the engineering tribology community.