Effects of residual stresses on interfacial adhesion measurement

In this work, effects of the residual stresses on the energy release rate (G) that characterizes the adhesion strength of coatings to substrates are studied with elasticity theory and finite element analysis (FEA). The cases studied are that the interfacial crack is induced by a lateral force from within the substrate on a circular central block that is separated from the substrate, and the crack front is supposed to be in circular shape. Closed-form solutions for G were obtained by elasticity theory for small deflections of coatings and an FEA model was set up that is appropriate for any deflection. The results show that the residual stresses can influence considerably both the energy release rate and the phase angle, therefore should be included in the measurements. The features of variation of the energy release rate with respect to the residual stresses are influenced by the critical buckling stress, and the geometry of the cracked system that includes the sizes of the crack and the central deflection. It is also shown that the present model with a central block of finite radius is necessary when the central block size is larger than the coating thickness. In addition, the elasticity solution yields a measurement of the residual stress from the material parameters and the geometry of the cracked system.