Effectiveness and design of surface texturing for different lubrication regimes

The aim of the present research work was to investigate the possibilities of designing surface texturing for different lubrication regimes and to evaluate its effectiveness, especially under starved, boundary and mixed lubrication regimes. This was achieved by combining an experimental tribological investigation with a surface-roughness analysis, a 2D FEM simulation and fluid dynamic modelling. The tribological investigation under unidirectional and reciprocating sliding was focused on the effect of the laser-texturing parameters-including the dimple depth and size, the dimple area density and the contact size-on the coefficient of friction under different lubrication regimes, achieved by varying the sliding speed, the normal load and the lubricant viscosity. The results of this investigation show that under starved lubrication conditions the textures resist sliding, resulting in increased friction, as was also indicated by the FEM simulation. Only when a very low dimple density was used could the oil-pocket effect be observed. In boundary lubrication the tribological behaviour of textured surfaces can be related to the surface-roughness parameters (R (sk) and R (ku)), with smaller dimples and lower dimple densities leading to reduced levels of friction. The largest gain in terms of friction reduction was observed when approaching full-film lubrication, where fluid dynamic modelling was used to correlate the effect of the dimple depth, size and shape on friction.