The combined effects of couple stresses and surface roughness patterns on the squeeze film characteristics of curved annular plates are studied. The Stokes (1966) couple stress fluid model is included to account for the couple stresses arising due to the presence of microstructure additives in the lubricant. In the context of Christensen's (1969) stochastic theory for the lubrication of rough surfaces, two types of one-dimensional roughness patterns (circumferential and radial) are considered. The governing modified stochastic Reynolds type equations are derived for these roughness patterns. Expressions for the mean squeeze film characteristics are obtained. Numerical computations of the results show that the circumferential roughness pattern on the curved annular plate results in more pressure buildup whereas performance of the squeeze film suffers due to the radial roughness pattern for both concave and convex pads. Further the squeeze film time is longer (shorter) for the circumferential (radial) roughness patterns. Improved squeeze film characteristics are predicted for the couple stress lubricant. 1. Introduction Squeeze film characteristics play an important role in many applications, namely, lubrication of machine elements and artificial joints. In view of their wide rang of applications, numerous theoretical and experimental studies have been conducted [1–7]. Later, Parkins and Woollam [8] conducted an experimental study of the behavior of an oscillating oil squeeze film. Most of the theoretical studies on squeeze film lubrication between plane parallel plates or between curved circular plates are based on the Newtonian constitutive approximation for the lubricants. However, this approximation is not a satisfactory engineering approach for most of the practical problems in lubrication. The modern lubricants exhibiting non-Newtonian behaviour are the fluids containing long chain polymer additives. The microcontinuum theory derived by Stokes [9] is the simplest generalization of the classical theory of fluids, which allows for polar effects such as the presence of antisymmetrical stresses, couple stress, and body couples. Many investigators have used couple stress fluid theory to analyze the performance of various bearing systems [10–14]. These studies have led to the predictions such as higher load carrying capacity, lower coefficient of friction, and delayed time of approach in comparison with the Newtonian case. In most of the theoretical investigations of hydrodynamic lubrication, it has been assumed that the bearing surfaces are smooth. This
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