Abstract: Aiming at the lack of theoretical research with the surface morphology characteristics affect the stability of modal coupling system by friction and the structure of the system caused. An attempt is to explain the dynamic characteristics of the macroscopic system from the microscopic view. The more accurate model of normal and tangential contact stiffness of surface topography is established based on fractal theory. With the vehicle brake disc as the object, a typical mode coupling

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... el with two degrees of freedom is presented and the fractal contact stiffness model is introduced. The influence of the tangential and normal stiffness ratio, friction coefficient, and the natural frequency ratio on the stability of system and the conditions of the different frequency noise arise are studied. It is concluded that these contact topography parameters are the main factors to influence the vibration noise ; the vibration noise condition and the frequency of the system are different with the different characteristics of the surface topography. The conclusions obtained may help us more deeply understand the influence of the surface topography on the macroscopic system. At the same time, it can provide reference for engineering design and manufacture, and has a certain engineering significance. Key words:fractal theory;joint surface topography;mode coupling;instability;friction-induced vibration