Study on the determination of interfacial binding strength of coatings (Ⅰ): theorctical analysis of stress in thin film binding interface

Abstract

The theoretical model of stress in film binding interface is established with the help of laser scratch testing (LST) and the theory of bending stress, the distribution formulae of stress such as shear stress, normal stress and stripping stress are deduced, and the mechanism of stress forming in binding interface is analyzed. It is shown that the normal stress of interface is mainly concentrated on interface center region, it decreases quickly near the interface edge, becomes zero at the interface edge. Shear stress and stripping stress are mainly concentrated in the interface edge, they decrease quickly away from the edge. Normal stress of film is not related with film thickness, matrix thickness and Young's modulus,the shear stress and stripping stress increase with film thickness, and they are determined by thickness of film and matrix and Young's modulus.