On the Roughness Effect in Hydrodynamic Lubrication

Abstract

Considerable work is being devoted to the influence of surface roughness on load carrying capacity of a bearing in hydrodynamic lubrication. These efforts are mainly concerned with the deviation of the mean pressure from that developed when the surfaces are smooth. These calculations are based on the Reynolds equation with assumptions which by various methods reduce the problem to one with one-dimensional randomness. In this paper it is shown that these current procedures are not valid unless certain stringent conditions are met. To estimate the magnitude of the roughness effect on the load carrying capacity, the upper bounds to the absolute mean deviation and the root mean square deviation of a normalized load carrying capacity from the smooth case is obtained for a general one-dimensional problem valid for an arbitrary distribution. It is found that the upper bound depends critically on the behavior of the autocorrelation of the roughness. The result for the mean deviation is illustrated by a slider bearing with plane mean surfaces.