This paper introduces an analytical approach to study the textured surfaces in hydrodynamic lubrication regime. For this purpose, a method of integrating the Reynolds equation for slider bearings with surface discontinuities is presented. By introducing appropriate dimensionless parameters, analytical relations for various texture profiles in both indented and projected forms are delivered. These relations express the nature of mathematical dependence between textured bearing performance measures and geometrical/operational parameters. An optimisation procedure is employed to achieve the optimum texturing parameters promoting maximum load capacity, load capacity to lubricant flow rate ratio and minimum friction coefficient for asymmetric partially textured slider bearings. Keywords IntroductionIt is now widely accepted that introducing artificially created micro-features onto sliding surfaces can significantly affect friction and wear of the sliding bearings. It is further believed that the textured surfaces provide the best performance amongst all other mechanical surface treatments [1]. The positive effect of artificial surface texturing on enhancing the load capacity, wear resistance and/or friction coefficient of mechanical seals [2], piston-ring/cylinder liner mechanism in internal combustion engines [3,4,5] and roller/piston in hydraulic motors [6] as some of the application examples are shown through numerical and/or experimental studies.Considering the associated theoretical studies, in a pioneering work by Salama [7], the effect of macro-roughness induced by manufacturing process in the form of surface waviness on the slider bearing performances was studied. As a result, existence of an optimum waviness length to amplitude was reported. By developing a theoretical model to obtain pressure distribution for a single micro-asperity and then, spreading the results for a population of asperities mounted on a radial face seal, Hamilton et al [8] notified existence of an optimum range for asperity height and asperity area fraction providing the maximum loads support. They suggested further research on the effect of interactions amongst asperities. On the other hand, an analytical/experimental study on microasperity lubrication by Anno et al [9] proposed that the poorer correlation between experimental and theoretical results in [8] could be improved by considering the hydrodynamic load support induced by small tilts on the tops of asperities. Later on, Anno et al [10] extended the study to 'negative asperities' and concluded that although all shape of asperities (whether positive or negative) of comparable dimension produce similar load support, to avoid leakage, one must utilise negative asperities.The study of tribological effects obtained by introducing surface microfeatures was brought to the centre of attention again by Etsion and Burstein [11] who focused on the study of the effect of shallow pores on the operational behaviour of the mechanical face seals. They solved the Reynolds equation numer...

In this study we attempt to find the optimum geometrical parameters of square-shape micro-dimples imposed on parallel flat bearing surfaces which give the best tribological performance, including load capacity and friction coefficient. An analytical solution of Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of number of dimples as well as dimple length and height ratios for a constant dimpled length, it is tended to get the optimum value of parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remain nearly constant.

In this study we attempt to find the optimum geometrical parameters of square-shape micro-dimples imposed on parallel flat bearing surfaces which give the best tribological performance, including load capacity and friction coefficient. An analytical solution of Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of number of dimples as well as dimple length and height ratios for a constant dimpled length, it is tended to get the optimum value of parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remain nearly constant.

• This is the author's version of a work that was accepted for publication in the journal, Tribology International. Changes resulting from the publishing process, such as peer review, editing, corrections, structural format- AbstractIn tribology, the Rayleigh step is known as a bearing with the highest load capacity amongst all other possible bearing geometries. In classical resources on tribology, it is also shown that there is an optimum geometry for the Rayleigh step providing the highest load capacity. However, the analyses are confined to a special case where the effect of hydrostatic pressure is neglected. Furthermore, the possible optimum parameters in terms of the friction force and/or friction coefficient as well as the lubricant flow rate have not been discussed. In this study, the Rayleigh step is comprehensively analysed including the effect of variations of pressure at the boundaries on the optimum parameters. In addition, the bearing is also optimised considering lubricant flow rate, friction force and friction coefficient. It is shown that the optimum bearing parameters are strictly dependent on the variations of the pressure at the boundaries. It is also verified that the optimum point(s) in terms of load capacity are not necessarily equal to the optimum point(s) considering friction coefficient and/or lubricant flow rate even though if there is no pressure difference between bearing endings.

This item was submitted to Loughborough's Institutional Repository (https://dspace.lboro.ac.uk/) by the author and is made available under the following Creative Commons Licence conditions.For the full text of this licence, please go to: http://creativecommons.org/licenses/by-nc-nd/2.5/ In: Tribology and Dynamics of Engine and Powertrain: Fundamentals, Applications and Future Trends, Edited by H. Rahnejat, Woodhead Publishing, 2010, pp. 470-517, ISBN: 978-1-84569-993-2 Chapter 14 Optimised Textured Surfaces with Application in Piston-Ring/Cylinder Liner Contact R. RAHMANI, Loughborough University, UK A. SHIRVANI and H. SHIRVANI, Anglia Ruskin University, UK Abstract: The application of textured surfaces in tribology has recently gained a huge momentum. In this chapter, a systematic approach to investigate the maximum outcomes from employing such surfaces is introduced with an insight into their application in internal combustion engines. A combination of various affecting parameters on the tribological performance of such surfaces is studied and the optimum results were introduced. The effect of employing such optimised textures in enhancing the lubrication condition in piston ring/cylinder liner contact is also studied.Key words: surface texturing, piston ring/cylinder liner contact, optimisation, slider bearings IntroductionIn general, friction is inherent to and is produced between bodies in contact with relative motion. Friction tends to oppose this relative motion between the bodies through loss of energy mostly in the form of heat, mechanical vibration and noise. Therefore, in most cases, friction is an unfavourable phenomenon. In some cases introduction of friction is desired, for example in order to slow down a moving car, the brakes are used to reduce the existing kinetic energy in the wheels by means of producing frictional losses. However, in most of the cases, facilitating this relative motion between bodies is of concern and as a result, one needs to overcome friction so that the relative motion pursues with a minimal loss of energy.Excessive friction can cause damage to the surfaces in contact in several ways and as a result make them wear. Since the surfaces are damaged due to wear, the rate of energy dissipation due to friction increases and consequently amplifies the rate of wear itself (see Chapter 2).The reason for the existence of friction is mainly that in reality, there is no perfect smooth surface. In fact, surfaces have a degree of roughness in the form of small 'hills' and 'valleys' no matter how well they are prepared. When two surfaces, which are in contact with each other, are put into relative motion, the asperities on the In: Tribology and Dynamics of Engine and Powertrain: Fundamentals, Applications and Future Trends, Edited by H. Rahnejat, Woodhead Publishing, 2010, pp. 470-517, ISBN: 978-1-84569-993-2 opposing surfaces become locked hence inducing friction as initially proposed by Amontons for onset of motion and later under kinetic conditions by Coulomb (see Chapter 2). W...