Effect of interfacial adhesion on the ultrasonic interaction with adhesive joints: A theoretical study using...

The effect of interfacial properties on the reflection and transmission characteristics of ultrasonic waves at adhesively bonded joints is theoretically investigated. An adhesive joint is modeled as a double-interface model, namely, a homogeneous layer coupled to adherends by two spring-type interfaces with different interfacial stiffnesses. For the normal incidence of a one-dimensional longitudinal wave, theoretical results are obtained and validated by finite element simulation. When the thickness of the adhesive layer is sufficiently small compared to the wavelength, the amplitude reflection and transmission coefficients show monotonic dependence on frequency, which can be explained by the theoretical relation of the double-interface model to a single spring-type interface model. The reflection and transmission behavior is invariant if the values of the two interfacial stiffnesses are interchanged. For a relatively thick adhesive layer, on the other hand, the reflection coefficient shows local minima at multiple frequencies. As one interfacial stiffness decreases, the local minimum frequencies decrease and the local minima increase. If the values of the two interfacial stiffnesses are interchanged, the reflection coefficient remains invariant but the reflection waveform shows different features. The obtained reflection and transmission characteristics are discussed in light of the characterization of the interfacial adhesion.