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In this paper, combined effects of surface roughness and couple stresses on squeeze film lubrication between porous circular stepped plates is analysed. In the context of Christensen stochastic theory for the study of surface roughness two types of one-dimensional surface roughness pattern, viz., azimuthal roughness pattern and radial roughness pattern are considered. The stochastic modified Reynolds equation for these two types of roughness patterns is derived for the couple-stress fluid. The Beavers-Joseph slip boundary condition on the fluid-porous interface is utilized. Closed form expressions for the mean load carrying capacity and squeeze film time are obtained. It is found that the squeeze film characteristics are improved for the azimuthal surface roughness pattern. However, the performance of the squeeze film bearing suffers due to the presence of radial roughness pattern.

This paper describes the theoretical analysis of the effect of micropolar fluid on the lubrication characteristics of porous inclined stepped composite bearing. The lubricant with additives in the film region and also in the porous region is modelled as Eringen's micropolar fluid, which is characterised by the presence of suspended rigid particles with microstructures. The generalised Reynolds type equation is derived for the most general porous bearing configuration (porous composite bearings) lubricated with micropolar fluid. The closed form expressions are obtained for the fluid film pressure, load carrying capacity, frictional force and coefficient of friction. These expressions can be utilised to obtain the performance characteristics of four different bearing systems, namely, porous plane inclined slider, porous composite tapered land bearing, porous stepped bearing and composite porous tapered concave bearing. It is observed that the micropolar fluid lubricants provide an increased load carrying capacity and decreased coefficient of friction as compared to the corresponding Newtonian case.