Influence of material viscoelasticity on the scattering of guided waves by defects

Guided waves are potential candidates for the nondestructive evaluation of viscoelastic structures due to their relatively long range of propagation. The major drawback is the difficulty in interpreting the scattered waves especially at high frequency-thickness values since many modes then exist. Moreover, in damping material waveguides, each mode of the scattered field has its own attenuation. Viscoelastic material characterization has been widely investigated by many authors in the past, but very few are treating multimodal scattering by discontinuities in viscoelastic guide. The scattering of a pure fundamental mode incident on a trough in a viscoelastic plate is investigated in this paper, over a relatively large frequency range, with up to five scattered modes. A hybrid two-dimensional finite element and modal projection method is used, based on modal orthogonality, to obtain the relative energy fluxes of each mode. Experiments are also made to validate the numerical predictions.