It has been previously reported that the friction between a partially polished diamond-coated surface and a metal surface was drastically reduced to zero in the atmosphere as relative speed was increased (Nakamori et al. in Diam Relat Mater 14:2122-2126, 2005). On the other hand, it has also been reported that laser-textured surfaces have good tribological performance in the case of gas lubrication (Kligerman and Etsion in Tribol Trans 44:472-478, 2001). The surfaces in the aforementioned two cases have a micro/nanoscale structure. It is expected that both surfaces are levitated by a high-pressure gas film between sliding surfaces by the same mechanism. In the present work, the mechanism of high gas pressure generation is clarified by the performance of numerical simulations and by theoretical analysis. The following two features of pressure distributions on textured surfaces were found to induce high gas pressure. First, gas pressure increases in the direction of the counter surface-s motion over the dimple region. Second, the pressure distribution over the flat region is convex upward, and hence, the high pressure obtained at the outlet of the dimple is maintained for a long distance in the flat region. The causes of such pressure distributions are herein explained analytically. The governing factor of pressure distributions and the optimal dimple location in the period of the repeated surface pattern are also discussed. Furthermore, the knowledge obtained here is utilized to design the surface structure to obtain high gas pressure.
- Direct simulation Monte Carlo method
- High Knudsen number flow
- Molecular gas film lubrication
- Partially polished diamond coating
- Rarefied gas dynamics
- Surface texturing