Experimental study of real roughness attenuation in rolling/sliding concentrated contacts

A surface roughness attenuation approach based on the Fourier decomposition of surface roughness into harmonic components may allow predictions of the behavior of real rough surfaces within concentrated lubricated contacts. Recent experiments performed under pure rolling conditions have shown an amplitude reduction of different components that agreed well with the data predicted by the theory. This study represents the next step in the experimental verification of the surface roughness attenuation approach under rolling–sliding conditions. Obviously, the behavior of roughness in the rolling–sliding elastohydrodynamic (EHD) contacts is more complex than for pure rolling. It has been theoretically suggested by other researchers that the modification of the original roughness alone cannot explain all of the major effects that significantly affect film thickness, and a model was proposed in which, along with the roughness attenuation, a complementary wave was generated in the inlet region and moved at the entrainment speed. This paper is focused on the possibility of extracting complementary waves from experiments with real rough surfaces conducted under rolling–sliding conditions and of determining whether the amplitudes of the complementary wave can be determined. This represents the first attempt to study both effects of rough surface behavior separately. The complementary wave was extracted from the measured data by subtracting the attenuated original roughness from the measured film thickness. Although the experimental results were quite scattered, a trend similar to that of the theoretical curves was observed. Based on the results, it can be suggested that the significance of the complementary wave is comparable to the attenuation principle.