Abstract: Based on the contact model of coated sphere and 7 assumptions, the contact stiffness model for coated asperity is derived firstly, and then the contact fractal model and normal contact stiffness fractal model for rough surfaces with elastic-perfectly plastic hard coatings are proposed. The proposed models are simulated for investigating the effects of coating thickness ratio, coating and substrate material properties, and substrate surface roughness on the contact behavior and the normal contact stiffness of rough surfaces with hard coating. The simulating results demonstrated the following conclusions. Under a given load rough surfaces with hard coatings exhibits a smaller actual contact area and a greater normal contact stiffness compared to those of uncoated rough surfaces. The thicker the hard coating, the smaller the actual contact area of coated rough surfaces. The influence of the elastic modulus ratio between the coating and substrate on the contact behavior and normal contact stiffness diminishes as the fractal dimension increases. Rough surfaces with harder coatings exhibit a smaller actual contact area and greater normal contact stiffness. Rough surfaces with hard coatings on smoother substrate surfaces display a larger actual contact area and greater normal contact stiffness. The simulation results also demonstrate that the proposed models closely approximate the general rough surface contact fractal MB model and the normal contact stiffness fractal model for uncoated rough surfaces (based on the MB model). The consistency between the conclusions of the proposed fractal model and those of the statistical contact model for hard-coated rough surfaces validates the feasibility of the proposed modeling approach and the correctness of the developed models.

Key words: coating asperities, rough surface with hard coating, contact load, contact area, contact stiffness, fractal model