Independent estimation of interfacial stiffnesses at two interfaces in a three-layered laminated structure

Abstract

In multilayered structures, the mechanical properties of one of the interfaces were degraded due to inadequate surface treatment or processing. In this study, we performed a numerical analysis on a double-spring interface model with different interfacial stiffnesses. For the normal incidence of longitudinal waves, the reflection spectra of the three-layered laminated structure with different vertical interfacial stiffnesses did not change for the exchange of the stiffnesses of the two interfaces. Therefore, it is difficult to estimate the interfacial stiffnesses of the two interfaces independently only from the reflection spectra of vertically incident longitudinal waves. In contrast, the reflection coefficient corresponding to some notches in the reflection spectrum of longitudinal waves incident at an incidence angle of 45° shows a monotonic variation with the ratio between upper and lower interfacial stiffnesses. This result suggests that the interfacial stiffnesses of the two interfaces can be estimated independently by using the longitudinal component of the reflection spectrum obtained by the oblique incidence of longitudinal waves.