Research on Fractal Modeling of Hard-Coated Rough Surface Contact Considering the Mechanism of Elastic–Plastic Deformation

This study develops an elastoplastic fractal contact model for rough hard-coated surfaces along, with a corresponding contact stiffness model based, on a coated asperity contact model and a statistical rough surface contact model. To establish the contact stiffness model for the coated surface asperities, seven fundamental postulates were developed. Numerical simulations were conducted to systematically analyze the influence of the ratio between the coating thickness and the asperity radius, the material properties of the coating and the substrate, and the substrate surface roughness on the contact behavior and stiffness of the coated surfaces. The results demonstrate that under a given load, hard-coated rough surfaces exhibit a smaller real contact area but higher stiffness compared to uncoated surfaces. Thicker and stiffer coatings further reduce the contact area while increasing stiffness. Smoother substrate surfaces lead to a larger contact area and higher stiffness in the coated systems. These findings align with the existing statistical contact models for hard-coated rough surfaces, and the predicted contact area closely matches the prior simulation results. To validate the model, experimental tests were conducted on the TiN-coated specimens. The theoretically predicted contact stiffness showed strong agreement with the experimental measurements, confirming the accuracy and applicability of the proposed fractal-based stiffness model.