Optimum dimple diameter for friction reduction with laser surface texturing: the effect of velocity gradient

The morphological texturing of surfaces has demonstrated high potential to reduce friction and wear. In order to understand the effect of different velocity gradients over the textured area on the optimum dimple diameter, we textured brass pins with round dimples having diameters between 20 and 200 μm. The dimple depth and packing density were kept constant. The samples were tested in a pin-on-disc fashion against sapphire discs and experiments were conducted under mixed lubrication and for two different sliding radii. Our results show that larger velocity gradients favor smaller dimples, whereas for the smaller velocity gradients, larger dimple diameters were beneficial. The effect of there being an influence of the velocity gradient was also found in computational fluid dynamics (CFD) simulations. Experimentally, friction forces could be reduced by up to 80%, demonstrating the tremendous potential of laser surface texturing (LST) to lower friction forces and reduce CO2 emissions.