Quantification of the imperfect interface impact on guided wave dispersion in anisotropic multilayers composite using Stroh formalism and stiffness matrix method

The integrity of multilayer structures is fundamentally governed by the quality of their interfacial bonds. In reality, these interfaces are seldom perfect; they often contain micro-cracks, porosity, or weak adhesion, leading to what is modelled as an “imperfect” or “soft” interface. These interfacial defects can significantly alter the wave propagation characteristics, thereby affecting the accuracy of non-destructive testing techniques and the predictions of the behavior of multilayers composite structures. Consequently, developing robust models that accurately capture the physics of wave interaction with imperfect interfaces is a critical step towards reliable damage quantification and life-cycle prediction. In this article, we study an anisotropic multilayer structure with imperfect interfaces using a general formulation based on Stroh formalism combined with the stiffness matrix method. To model defects in multilayer structures, we applied effective spring boundary conditions. After validating the proposed formulation using the semi-analytical finite element method in the case of a perfect interface, the present formulation was applied to analyze the dispersion curves of a three-layers composite with imperfect interfaces. The results quantitatively demonstrate that the presence of imperfect interfaces leads to a significant decrease in phase velocity between 1.97% and 52.19% across all modes with the S0 mode being particularly susceptible to severe velocity reduction. We further elucidate the definitive influence of the interface stiffness parameter ‘m’, showing that a reduction by one order of magnitude can lead to velocity increases of up to 99.95%. This study, therefore, provides clear, quantifiable evidence of the critical impact of interfacial defects and structure thickness on guided wave vibration modes.