Susumu Isono

Mechanism of Levitation of a Slider with a Micro/Nanoscale Surface Structure on a Rotating Disk

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.

Numerical analysis of micro-/nanoscale gas-film lubrication of sliding surface with complicated structure

It has been reported that the friction between a partially polished diamond-coated surface and a metal surface was drastically reduced to zero when they are slid at a few m/s. Since the sliding was noiseless, it seems that the diamond-coated surface was levitated over the counter surface and the sliding mechanism was the gas film lubrication. Recently, the mechanism of levitation of a slider with a micro/nanoscale surface structure on a rotating disk was theoretically clarified [S. Yonemura et al., Tribol. Lett., (2014), doi:10.1007/s11249-014-0368-2]. Probably, the partially polished diamond-coated surface may be levitated by high gas pressure generated by the micro/nanoscale surface structure on it. In this study, in order to verify our deduction, we performed numerical simulations of sliding of partially polished diamond-coated surface by reproducing its complicated surface structure using the data measured by an atomic force microscope (AFM). As a result, we obtained the lift force which is large enough to levitate the slider used in the experiment.

Effect of Configuration of Micro‐/Nanoscale Structure on Sliding Surface on Molecular Gas‐Film Lubrication

Nakamori et al. found experimentally that the friction between a partly polished diamond coating and a metal surface was drastically reduced to zero as relative speed increased to a few m/s [Diamond Relat. Mater. 14, (2005), 2122]. It seems that diamond coating took off the counter surface because sliding was noiseless in their experiment. However, the mechanism of this phenomenon was unknown. In the previous work, we performed the numerical simulation of micro‐/nanoscale gas flow between two sliding surfaces, i. e., the slider surface with microscale surface roughness like partly polished diamond coating and the flat counter surface. And then, we successfully reproduced lift force large enough to suspend the slider used in the experiment and found that this effect became notable only for micro‐/nanoscale gas flow. In the present paper, we investigate the effect of configuration of micro‐/nanoscale structure on sliding surface on molecular gas‐film lubrication. Since micro‐/nanoscale gas flows between two...