Scattering of guided waves by defective adhesive bonds in multilayer anisotropic plates

We introduce an analytic-numerical method to simulate the interaction between ultrasonic guided waves and defective adhesive bonds in multilayer structures. We replace the thin adhesive layer by equivalent continuous distribution of normal and transversal springs and locally reduce the corresponding spring constants to model localized defects. We then formulate the resulting scattering problem as a linear least squares problem and solve it accordingly. The developed formulation is easy to implement and equally well suited to treating anisotropic as well as isotropic constituent layers. We illustrate the application of the proposed method through the simulation of ultrasound inspection of a three-layer isotropic plate and a sixteen-layer anisotropic plate used in the aeronautical industry, indicating in the simulations the guided modes that will most strongly interact with interfacial defects and computing the scattering resulting from the interaction of these modes with localized defects. We believe that the proposed method will serve both to aid in the design of interface inspections and as a basis for solving inverse scattering problems.