Experimental study on nonlinear friction behavior of granular flow lubrication

Solid granules have good lubrication performance and load-bearing capacity, which has been concerned by researchers. However, the correlation mechanism between lubrication performance and granular medium dynamics is hardly focused on. In this study, the characteristics of two parallel friction pairs lubricated by the granular medium are experimentally investigated to study the nonlinear friction behavior during this process. The experimental results showed that the fluctuation behavior of friction force and friction coefficient with time shows a more flat nonlinear trend with the increase of the shear velocity and the pressure load. The discrete element simulation results corresponding to the experiment revealed that the change of nonlinear behavior of measured friction and friction coefficient is closely related to the evolution of force chains and dynamic characteristics of this granular flow lubrication system. The shear dilatancy amplitude of this granular flow lubrication system decreases obviously with the increase of the shear velocity and the pressure load. The flow states of granular medium is the main reason influencing the nonlinearity of shear gap. This study reveals the key factors affecting the friction nonlinearity and provides an evidence for the formation of granular shear dilatancy between two friction pairs lubricated by granular medium.