Contact ratio and deformation of asperity in nano-partial lubrication

Partial lubrication or mixed lubrication in the nano-scale is discussed, wh ich is constituted from dry contact, boundary lubrication, thin film lubric ation. A dynamic contact ratio has been used to describe such lubrication, and the relationship between the contact ratio and its influence factors wa s investigated. Experimental results indicate that the dynamic contact rati o increases with the decrease of film thickness by the exponential function . The decrease of speed and lubricant viscosity, and the increase of loads will enlarge the value of the contact ratio. When the polar additives are a dded into the basic oil, the contact ratio decreases. In addition, the cont act ratio of the surfaces with small roughness is larger than that of the s urfaces with large roughness at very low speed. However, the contact ratio of smooth surfaces decreases more quickly with speed than that of rough sur faces, and therefore, it will become smaller than that of rough surfaces af ter speed increases over a certain degree.