The Role of Asperity Geometry and Roughness Orientation for the Friction-Reducing Effect of Adsorbed Molecular Films

Abstract

The influence of roughness orientation on the friction-speed characteristics of adsorbed films was investigated by changing the angle of the anisotropically striated roughness to the sliding direction of the counter surface. As the angle of the striated roughness becomes perpendicular to the sliding direction, the friction coefficient is decreased. The friction-speed characteristics of the adsorbed film in the transverse direction of the striated roughness having different height or shape of asperities were also investigated. The friction coefficient obtained in the low speed region decreased with increasing arithmetic mean peak curvature (Spc) when stearic acid-formulated oil was used as a lubricant oil. The results demonstrated that the roughness orientation and the asperity shape of the transverse roughness were key factors for generating additional load-bearing pressure so that the adsorbed films could exert their intrinsic friction-reducing effects.

Keywords

• boundary lubrication
• surface roughness
• striated roughness
• adsorbed film
• micro-ehl