Surface texturing and its influence on tribological systems performances represent one of the main research topics nowadays. Textures functionality is initially ensured by correct optimization of its geometrical parameters, but the influence of textures quality is not to be neglected. Therefore, a proper selection of fabrication methods appropriate for each individual application is imperative. The process of selection is somehow exhaustive due to abundance of parameters and selection criterions. Hence, this paper proposes a general classification of texture manufacturing techniques, used nowadays within industrial manufacturing and research platforms, with pertinent description of each process including key advantages and drawbacks concerning their application within mechanical systems.
This article is focused on the comparison between experimental and numerical friction forces obtained for a typical hydraulic 'U' rod seal. The numerical results are obtained by the inverse hydrodynamic lubrication method. The experimental results have been obtained on an original experimental device capable of measuring the friction force between a rod and two seals. The reciprocating rod speed, the temperature and pressure in the test cell are controlled. Despite the fact that the numerical results correspond to an idealized hydrodynamic problem for smooth surfaces, it was found that the numerical model agrees with experimental data when the predicted film thickness is higher than the rod roughness but largely lower than the seal roughness. This suggests that the roughness of the seal disappears under the pressure in the sealed contact and do not play an essential role in the lubrication mechanisms. However, it is clear that for very small film thickness, the full film lubrication theory for smooth surfaces is not convenient. This may imply that in these conditions mixed lubrication cannot be ignored or that adhesion phenomena, not taken into account by the lubrication theory, can appear in the contact areas.
This article describes a methodology used to achieve a numerical analysis of hydraulic seals by the inverse hydrodynamic lubrication method. The main novelties consist of taking into account the influence of the shear stresses in the lubricant film and in the treatment of hydrodynamic effects on the seal inlet. Each step is detailed and discussed in terms of possible error over the predicted seal performances. It has been shown that the pressure field computed directly from the structure model does not give a realistic approximation of the hydrodynamic pressure in the inlet zone, and a hydrodynamic correction is necessary. Furthermore, it has been shown that if the tangential friction due to the shear stress in the lubricant film is not taken into account, error of about 5 per cent can be made, concerning the predictions of leakage and friction force.
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