An analytical study of the scattering of ultrasonic guided waves at a delamination-like discontinuity in a plate

Interface delaminations between individual plies in a composite, or disbonds of face sheets in honeycomb structures often remain undetected. Using guided ultrasonic waves (Rayleigh and Lamb waves) such hidden defects can be detected. In this work, an analytical framework that considers propagating, nonpropagating and evanescent waves to analyze the scattering of an incident ultrasonic wave at a delamination-like discontinuity is presented. Wave conversion at the interface of the damage is quantified in terms of the power flows of the individual waves. The analytical solutions are compared with results from numerical simulations. For an incident Lamb wave, excellent agreement is found. However, it is shown that the analytical solution for an incident Rayleigh wave has significant differences from the numerical results, due to the incomplete nature of the Rayleigh wave-field in the half-space. Even though this study is performed for isotropic waveguides, the method can be extended to transversely isotropic laminates by substituting the corresponding expressions for the dispersion equations, as well as displacement and stress fields.