Guided acoustic emission waves in a thick composite plate

Abstract

In this paper, an efficient and accurate semi-analytical method based on the wavenumber integral representation of the elastodynamic field is described to calculate the surface responses produced by localized dynamic loads in a relatively thick composite plate. Two types of loads are considered: a pencil lead break source located on the surface and a localized shear delamination within the interior of the plate. In the case of the pencil lead break source, the calculated results for the surface motion are compared with those obtained in laboratory experiments on a 4.4 mm thick 32 layered cross-ply graphite/epoxy using high-fidelity broad band transducers. The waveforms consist of both flexural and extensional modes; the amplitude variations of these modes are found to be strongly dependent on their propagation direction. For the delamination source at the mid plane, the results from the exact calculation are compared with those from an approximate laminate theory with shear correction factor and moment tensor representation of the source. The results obtained by the two methods are shown to have excellent agreement in the low frequency ranges. Although, the motion due to the delamination is dominated by flexural waves of lower frequency in both thin and thick plates, the presence of extensional waves are observed in thicker laminates. The acoustic emission waveforms from the initiation of a shear delamintaion source at various interfaces are also calculated. It is found that the amplitude of the flexural modes decreases and that of the extensional modes increases as the source moves farther away from the mid plane.