Study On The Contact Property Of Rough Surface During Loading-Unloading Process

The contact behavior between rough surfaces has important influence on friction,abrasion,lubrication,conduction,thermal conductivity and so on,which has been one of the main subjects of tribology.Based on fractal theory,this paper establishes a loading-unloading contact mechanics model of rough surfaces combining with the influence of frequency indexes on the size of the asperities,and studies the contact characteristics of rough surface.Firstly,based on Weierstrass-Mandelbrot function,this paper simulates two-dimensional and three-dimensional fractal rough surface.With analyzing the function of fractal parameters,we get that the larger the fractal dimension of the rough surface,the smaller the roughness and the smoother the rough surface.The effect of the profile scaling parameter G on the rough surface is opposite to the fractal dimension D and the frequency index range also has a significant effect on the rough surface.Secondly,based on fractal theory,a loading-unloading contact mechanics model of two-dimensional and three-dimensional rough surfaces has been established.The existing conditions of elastic deformation,elastoplastic deformation and fully plastic deformation of the single asperity are deduced.And the mechanical expressions of asperity under loading and unloading are obtained for different conditions of deformation.The traditional size distribution function of asperity is modified according to a rule that the real contact area and the total contact load at the end of loading equal area and load in the inception of unloading.And the size distribution function of each frequency index asperity is developed under loading and unloading.Eventually,the relations between the total contact load and the real contact area are obtained under loading and unloading.The results show that the contact mechanical properties of-the rouglh surface depend on the range of asperity frequency indexes in a loading-unloading cycle.When asperity frequency index nmin +5 is less than elastic critical frequency index,the rough surface appears to elastic deformation property in a loading-unloading cycle.When asperity frequency index nmin is greater than elastic critical frequency index,the real contact area in unloading process is greater than the real contact in loading process.As interference increases,the difference between the real area of loading and the real area of unloading is increasing.Finally,the morphology parameters of rough surface are obtained by using Leica DCM 3D.And converting the parameters into the corresponding values which are input to the theoretical model.Then the rough surface contact performance test was conducted,and the experimental result is compared with the calculation result of theoretical model to verify the rationality and feasibility of this model.