Elastohydrodynamic lubrication of rough surfaces

The detailed understanding of elastohydrodynamic lubrication (EHL) with rough surfaces has become an important problem as the ratio of film thickness to surface roughness is decreasing. Recently it has been recognized that the roughness inside an EHL contact might be different from the roughness outside the contact owing to elastic deformation. As will be explained in this paper, a first step in understanding the deformation of a real rough surface is the detailed knowledge of the amplitude reduction of harmonic features, which forms the topic of this paper. For the line contact problem it is shown that the deformed amplitude of a harmonic feature (waviness) depends on the original amplitude of the feature, its wavelength and the contact operating conditions, including the slide-roll ratio. The amplitude reduction can be completely described by a single dimensionless parameter. For the point contact problem it is shown that the deformed amplitude of isotropic waviness depends on the original amplitude of the feature, its wavelength and the contact operating conditions. Once again, the amplitude reduction can be completely described by a single dimensionless parameter. The presented relations for line and circular contact can be used as a basis for a modified Λ parameter predicting the relation between the real ratio of film thickness to amplitude inside the EHL contact. A numerical example of the calculation of the deformation is given.