Transverse roughness in elastohydrodynamic lubrication

The astonishing progress of numerical solutions of the rough surface elastohydrodynamic problem over the last thirty years is reviewed. The state of theoretical understanding of the numerical results is described, and it is shown how from the behaviour of sinusoidal waviness of different wavelengths it is possible to deduce an approximation to the behaviour of real roughness and of isolated ridges and scratches, at least for a Newtonian lubricant. However, it is argued that the lubricant behaviour needed to ensure that theoretical traction coefficients remain of realistic size casts doubt on the use of a Newtonian lubricant for the analysis of rough surfaces, so that the applicability of these predictions to a real elastohydrodynamic lubrication (EHL) contact is somewhat suspect.