An ultrasonic interface layer model for bond evaluation

An interface layer model for adhesive bonding weakness evaluation is described to assist in ultrasonic oblique incidence analysis of waves traveling across the interface. This model assumes that the interface between the substrate and adhesive can be treated from a wave propagation point of view as a homogenous isotropic interface layer. The interface bonding quality can then be estimated by predetermined properties of the interface layer. The smooth bond can be formed by a thin nonviscous liquid layer between the two solid media. Numerical results show a frequency dependence of the reflection factors as well as a direct influence of the interface layer properties on reflection. Experiments on bonded structures were conducted to confirm the theoretical prediction. Experiments on smooth bond simulation structures showed the same trends as the theoretical curves of longitudinal wave reflection vs. frequency. Higher sensitivities of shear waves at oblique incidence for bonding weakness detection were found compared with longitudinal waves at normal incidence.