Contact analysis of thin films bonded to graded coatings

In this study, the contact mechanics of thin films bonded to graded coatings is investigated both analytically and numerically. In these problems, the stresses may be arisen due to uniform temperature changes and temperature excursions, far field mechanical loading, and residual stresses resulting from film processing or manufacturing process of the graded coatings. The primary interest in this study is the examination of the stress concentrations or singularities near the film ends. The underlying mechanics problem is formulated by assuming the film acts as a “membrane” and the graded coating as a functionally graded material (FGM). In the analytical formulation, the problem is reduced to a singular integral equation for the unknown interfacial shear stresses through an asymptotic expansion and then solved numerically using a suitable collocation technique. Finite Element Method (FEM) is utilized in the computational studies. The calculated results include interfacial shear stress between the film and the graded coating, strength of stress singularity at the film ends and the axial normal stress in the film. This study reveals that both mechanical and geometrical parameters of the system as well as the loading type have a great effect on the stress distribution and the strength of shear stress singularity at the film ends. Adjusting these parameters and selecting the appropriate type of grading will reduce these stresses that may have a bearing on the failure of the coating.