Theoretical and experimental investigation of normal contact forces-deformation relationship of rough surfaces during loading and unloading processes

The bolted joint is indispensable in mechanical systems for connecting structures, and the normal contact force is a key parameter for evaluating interfacial behaviors. In this paper, a normal contact model of the bolted joint with a rough interface is established. Considering the loading and unloading process of the rough interface, the analytical expressions for the normal contact force are derived, incorporating information about micro-topography, material properties, and displacement. The effects of surface morphology and material properties on the normal contact force-interfacial displacement relationship are discussed through extended mathematical analysis. The results indicate that the contact force for a rougher surface is larger than that for a relatively smooth surface during the loading process. In the unloading process, the contact force for the relatively rough surface is initially slightly larger than that for the relatively smooth surface. Finally, through experimental comparison and verification, the dimensionless normal contact force theoretical calculation values are basically consistent with the experimental values, which validates the accuracy of the model proposed in this study.