The effect of dimple shapes on friction of parallel surfaces

In this study, the effect of different dimple shapes on the tribological performance of surface texture has been investigated. First, a numerical model was developed to study the effect of dimple shapes on hydrodynamic pressure generation. The selected dimple shapes include circle, square, and ellipse, and the flow direction of lubricant is perpendicular to the major axis of elliptical dimples or the sides of square dimples. The results showed that the dimple shape can be optimized for greater hydrodynamic pressure generation. Then, the reciprocating sliding tests were carried out under oil lubrication and face-contact conditions. Tests were conducted for rotational speeds in the range 50-500 r/min and test loads of 200 and 400 N. Surface texture patterns with different dimple shapes were used, the dimple shapes and orientations were the same as those used in the numerical model, and the dimple depth and dimple area ratio were varied under fixed dimple area conditions. The test results indicated that a better friction reduction effect compared with untextured specimens can be obtained by selecting a suitable dimple area ratio and dimple depth for each dimple shape. Comparing the friction reduction effect, the elliptical dimples showed the best performance, the square dimples showed the second best results, and the circular dimples performed worst. However, as the test load increased, the friction reduction effect of all dimple shapes decreased; moreover, the differences between the shapes became smaller.