Research On The Plastic Contact Model Of Cylindrical Asperities

The contact of rough surfaces is very critical to the analysis of tribology, lubrication, thermal conductivity and electrical properties between two surfaces. In microscope scale, a rough surface can be regarded as a series of asperities with certain stochastic distributions of asperity height, size and geometry. Therefore, it is very important to study the contact between asperities.Based on the theoretical analysis and finite element solution, an overview of the researches on the elastic contact, elastoplastic contact and fully plastic contact between asperities are conducted in this thesis, and the advantages and disadvantages of the mentioned models are compared in detail.The most widely adopted shapes of the asperities in engineering applications are sphere, ellipsoid and cylinder. However, most of the previous researches are concerned on the contact of spherical or ellipsoid asperities, whereas only a few researches have been reported on the elastic contact of cylindrical asperities, which is also important in engineering surfaces. In this thesis, finite element method is used to study the elastic contact, elastoplastic contact and fully plastic contact between a cylindrical asperity and a rigid plane. The relationships between contact load, contact half-width and contact interference displacement are fully analyzed. The effects of material properties and the radius of the cylindrical asperity on these relationships are discussed in detail, and empirical formulas are obtained to describe the relations between dimensionless parameters through curve fitting. It is also found that the relationships between the dimensionless parameters are almost independent on the material yield stress and asperity radius.As to the contact of cylindrical multi asperities, the interaction between the deformations of two neighbor asperities is conducted in detail, as well as the interaction and mergence of the plastic zones belong to the corresponding asperities. The effect of wavelength on the relationships between the contact load, contact interference displacement and contact area are also explored. The researches in this thesis should be very helpful to the complete solution of the contact between surfaces owing cylindrical roughness.