Extending the capability of the Greenwood Williamson microcontact model

This paper describes a readily implemented simulation model that extends the Greenwood Williamson microcontact model to include skewness in the distribution of surface summit heights and the presence of a surface coating of prescribed thickness and compliance. Parametric runs were made to explore the effect of these factors on the load, area and mean real pressure at the contacting asperities for a fixed separation of the mean planes of the contacting surfaces such as occurs when the surfaces are separated by a stiff elastohydrodynamic film. It was found that the average asperity load increases with coating thickness when the coating is stiffer than the substrate and decreases when the coating is made more compliant. The opposite is true for the average asperity area of contact. Like load, the average asperity pressure increases with coating thickness when the coating is stiffer than the substrate and decreases when the coating is more compliant. For the same rms summit height the mean asperity pressure in the absence of a coating was found to be higher by a factor of 1.6 when the skewness is + 1 than when it is - 1. The relative effect of skewness on pressure is practically constant as coating thickness increases for the compliant coating while the absolute effect decreases. For the stiff coating the absolute effect is constant while the relative effect diminishes.