Validation of the basic friction equation on Real contact surface based on macro and nano properties of Tribo-film

Abstract

The formation of tribofilm by lubricant additives plays an important role in improving the performance of boundary lubrication. In previous studies, it has been discussed that the frictional force due to adhesion can be expressed as a product of the real contact area and the shear strength of the contact junction. Therefore, to evaluate the friction mechanism dominated by the tribofilm in detail, it is important to divide and identify the effects of the shear strength and real contact area. However, there are few studies that have verified the relationship between shear strength and macro friction coefficient with experimental data. In this study, nanofrictional property and real contact area of tribofilm was investigated using nanoindentation equipment and contact analysis. The results show that the shear strength of base material and tribofilms are correlated with the macro friction coefficients. In addition, the friction coefficients are calculated by applying the shear strength to the basic friction equation. The result shows that the friction coefficients calculated from the basic friction equation coincide with those measured by the macro friction test at a certain contact ratio of tribofilms formed in Tricresyl phosphate and over based calcium sulfonate.