The frictional contact of coated bodies. Part I – The sliding contact

Abstract

Hard coatings provide low friction, high wear resistance and corrosion protection that improve the tribological performances of the machine elements undergoing contact load. In lack of analytical solutions, a numerical study is performed in this paper for a better understanding of the engineering applications of hard coatings with consideration of friction. A previous study on the frictionless contact of bi-layered materials is extended by considering the effect of friction on the contact stress state. The assumption of a sliding contact in which the shear tractions do not affect the pressure distribution is adopted. This simplification, often present in the literature, decouples the contact problems in the normal and in the tangential direction and allows for a pressure distribution solution that is independent of the frictional regime. The shear tractions are subsequently obtained from a kinetic Coulomb-type friction law, under the assumption that the normal load is kept constant. The stress state in the coated system results by superposition of stresses due to the normal and the shear tractions. The frequency response functions needed for the calculation of the six stress tensor components induced by the shear tractions are presented for clarity and completeness. The convolution between these functions and the contact stresses is performed in the frequency domain for improved algorithmic efficiency. The performed contact analysis proves the ability of the numerical method to provide insight on the critical contact condition for plasticity failure, and to assist the optimal design of hard coatings.