A novel method of using continuous tribo-electrification variations for monitoring the tribological properties between pure metal films

The traditional method of using the continuous variation of the friction coefficient with sliding distance to monitor the tribological properties between the contacts of soft metal films is generally low in sensitivity. This paper proposed the novel method of using instead the continuous variation of tribo-electrification voltage. This method was investigated experimentally for the dry friction sliding of iron on copper coated with a thin film of tin and was shown to be much superior to the traditional method in terms of sensitivity and ease of implementation. Moreover, it was observed that the continuous variations of the friction coefficient with sliding distance was very unstable but remained positive, making it indiscriminative for monitoring the tribological properties between the hard metal films. The continuous variations of the tribo-electrification voltage, on the other hand, showed either positive or negative polarity depending on the metal pairs, which allowed the identification of the surface where friction had occurred as well as the sliding surface. Finally, two continuous models to represent the tribo-electrification mechanisms for iron sliding against copper coated with a thin film of tin or nickel at different normal loads were proposed.