Analytically decoupling of friction coefficient between mixed lubricated fractal surfaces

Abstract

Herein, we present a generalized close-formed model of the friction coefficient between fractal surfaces in mixed lubrication. A mathematical transformation from asperity area to oil film thickness is conducted, which changes the fractal method’s traditional basis of the area distribution to establish an analytical fractal model of oil film thickness. A dynamic film thickness model with external load under the determination of the surface roughness is further proposed. Based on the fractal-based oil film thickness, the contact force for each part is solved under the external normal force, and decoupling is achieved presented by contact ratio. Through the contact ratio, the constitutive model of friction coefficient is elucidated. The effects of fractal parameters and important working parameters on friction coefficient are then analyzed, and comparison with experimental data is conducted. This work provides a general analytical expression for friction coefficient in mixed lubrication with explicit form and wide applications.