A normal contact stiffness fractal prediction model of dry-friction rough surface and experimental verification

The normal contact stiffness is one of important dynamic parameters and the accurate construction of its model is conducive to subsequent modeling and analysis of dynamics on whole machine. However, in most of previous normal contact stiffness models, the influence of friction factor of rough surfaces is neglected. Given that the friction factor of rough surfaces has a significant influence on the structural dynamic characteristics, in this paper, a normal contact stiffness fractal prediction model of dry-friction rough surface considering friction factor based on three-dimensional fractal function is established. And the given (power spectrum density) PSD function is used to identify two important fractal parameters, three-dimensional fractal dimension D and the fractal roughness G. The analysis of numerical simulation indicates that the normal contact stiffness monotonically increases and decreases respectively with the three-dimensional fractal dimension and fractal roughness increasing; it increases with the actual contact area and the maximum contact area of asperity increasing; it tends to decrease on the whole with the friction factor increasing, which turns out to be linear decrease firstly and then exponential decrease. In addition, the friction factor has an important influence on natural frequency of the whole structure. In this paper, the validity of the established model is verified by experiment and the normal contact stiffness of surface should be considered in the dynamics modeling of the whole machine.