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Introduction
Surface texturing has emerged as a viable technique to significantly enhance the load-carrying capacity, friction coefficient, and wear resistance of vital tribological components such as bearings, mechanical seals, piston rings, and the like. To maximize the effect of surface texturing, many theoretical and experimental studies have been carried out that concentrate on the geometrical parameters of textures. See recent reviews in Gropper et al.[1] and Ahmed et al.[2] One of the often cited literatures on the subject is the work of Etsion et al.,[3] who in 1999 investigated the effects of geometric parameters on the performance of spherical-shaped dimples on laser-textured mechanical seal faces. They reported that the dimple depth-over-diameter (DOD) ratio is the most important design parameter and that there exists an optimum value of this parameter which maximizes the average pressure. They further suggested that the preferable value of the ratio is in the range of 0.01-0.05, and that a higher velocity or a smaller clearance (by higher load) value would yield a smaller value of the optimum ratio. In a subsequent paper in 2013, Etsion[4] stated that to fully benefit from surface texturing, a proper optimization of the geometrical parameters, including the dimple DOD ratio and area density, must be performed in accordance with the application in hand. Therefore, the determination of the optimum dimple DOD ratio has received great deal of attention in recent tribology literature.
The hydrodynamic effect generated by laser surface texturing in liquids, studied in Etsion et al.,[3] is also applicable to gas-lubricated, high-speed seals as shown in the model by Kligerman and Etsion.[5] They found that the main difference is the optimum dimple DOD ratio, which is much smaller in gas than in liquid-lubricated applications. Shi et al.[6] compared the load-carrying capacity performance of mechanical gas seals textured with mircogrooves and microdimples by numerical treatment of the Reynolds equation for compressible Newtonian fluid. The results indicated that the optimum dimple DOD ratio that maximizes gas film stiffness is around 0.005 and found it to be independent of the type of texture patterns, area density, and the seal clearance.
The dimple DOD ratio has been also found to be the most important parameter for enhancing the tribological performance of piston...