Ultrasonic waves and material and defect characterization in composite plates

Analysis of wave propagation and scattering in a composite plate is complic ated by the anisotropic properties of the laminae. An accurate computation of the wave field excited by transient sources in such a plate is required in order to characterize the anisotropic stiffness properties of the lamina e and for ultrasonic evaluation of delamination defects. Here, a variationa l formulation has been used for deriving the dispersion equation governing guided elastic waves in laminated plates. The equation is a matrix eigenval ue problem that can be solved for the wavenumbers at given frequencies or f or the frequencies at given wavenumbers. For accurate evaluation of the eig envalues it is necessary to have a large number of sublayers, which results in large matrices and is not computationally efficient. However, the matri x formulation combined with analytical refinement is shown to give fairly a ccurate results that agree well with experiments. In this article, results for guided wave dispersion and the inverse problem of material characteriza tion are presented. In addition, an analysis of scattering by defects in a laminated plate is given. Two techniques are discussed. One is a hybrid met hod that combines the finite-element representation with the guided-wave mo dal expansion of the global field, and the other is a boundary integral tec hnique.