Numerical investigation on the elastic-plastic transition of a cylindrical coating/substrate composite under normal compression

In order to study the yielding resistance of a coated component in line contact, a cylindrical coating/substrate system contacting a rigid plane was simulated via a plane-strain model. For super-thick coatings, the critical load, contact width and interference were derived for the onset of plastic yielding on the axis of symmetry by a function approximation method. The results indicated the geometrical and mechanical properties of the loaded coating displayed an important influence on these threshold values. For thinner coatings, the Von Mises stress distribution along the axis of symmetry was investigated using a finite element method, of which a pronounced discontinuity at the interface was found by increasing the elasticity modulus of the coating relative to the substrate. Furthermore, an additional stress was induced by the binding constraints imposed at the coating/substrate interface, thus resulting in a weakened resistance to the plastic initiation in relatively thin coatings. In light of finite element results, the initial yield position may be located either within the coating, in the substrate or at the interface between them with the ratio t/R of coating thickness over the substrate radius changing. Besides, when t/R was very small, the total interference of the coated cylinder was mainly attributed to the substrate deformation. With t/R ratio becoming larger, the coating compression became comparable to the substrate value. When t/R had large values, the coating contraction served as a dominant contributor to the composite interference.