Abstract: Mixed lubrication in the nano-scale is discussed, which is constituted from dry friction, boundary lubrication, thin film lubrication. A dynamic contact ratio which is the contact ration measured in the rolling process is used to describe the nano-mixed lubrication, and the relationship between the contact ratio and its influence factors is investigated. Experimental results indicate that the dynamic contact ratio increases with the decrease of thin film thickness by an exponential function. The decreases of speed and lubricant viscosity, and the increase of loads will enlarge the value of the contact ratio. When polar additives are added into basic oil, the contact ratio decreases. In addition, the contact ratio between smooth surfaces is larger than that between rough surfaces in lower speed. However, the contact ratio between smooth surfaces decreases more quickly with speed than that between rough surfaces, and therefore, it will become smaller than that of rough surfaces after speed increases over a critical value.

Key words: Mixed lubrication Nano-tribology, Thin film lubrication