Lubrication mechanisms with laser-surface-textured surfaces in elastohydrodynamic regime
Résumé
Micro-texturing is very efficient to make surfaces super-hydrophobic according to a physical process known as 'lotus effect'. In the recent past, tribologists have also investigated surface texturing because it could be a promising way to increase the lifetime of contacts or to make its working conditions more severe. Moreover, significant friction coefficient reductions have been obtained with textured surfaces in different lubrication regimes. In this presentation, transient lubrication phenomena induced by laser-made circular dimples passing through an elastohydrodynamic lubrication point contact are analysed both experimentally and numerically. Under rolling-sliding conditions, the passage of an isolated dimple modifies the film thickness distribution. Deep dimples induce an oil film failure. On the contrary, a shallow dimple locally generates a large increase in the film thickness. Dimples geometry and the slide/roll ratio modify the pressure distribution and then control the level and extension of the local film reinforcement. Experiments are simulated numerically with a two-dimensional multi-grid solver. This allows one to have a better understanding of the lubrication mechanism with a textured surface as a function of dimple geometry, entrainment speed, and contact pressure. The key point is the control of tribological conditions to maintain the viscosity of the lubricant high enough inside the dimple in order that the shearing can expel it to locally enhance the film thickness.