A Hybrid method for transient wave scattering by flaws in composite plates

hybrid technique is developed to analyse the plane-strain elastic wave propagation and scattering by flaws in laminated composite plates. The problem is solved first in transformed frequency domain. The incident fields due to a line load are computed through combining a stiffness method and modal summation technique. The hybrid method employed here combines finite element formulation in a bounded interior region containing all the flaws of the plate with an approximate wave modal representation for the scattered field in the exterior region. The time-domain response is recovered by Fourier inverse transformation. The results for a uniaxial graphite-epoxy plate with a line load are presented to check the accuracy of the incident field. The reliability of the proposed method is confirmed by comparing scattering results, for the uniaxial graphite-epoxy plate with surface-breaking crack, with those obtained by a boundary element technique. The study is motivated by the need to develop a quantitative ultrasonic technique to identify the integrity of the joints (interphases) between two plates. In this paper, an illustrative example, two laminated composite plates jointed together by an isotropic interphase with and without crack on the interphase, is studied in detail. It is shown that dynamic responses of the surface points near the crack are sensitive to crack length. The arrival-time-delay of the Rayleigh wave is linked directly to the crack lengths. 0 1997 Elsevier Science Ltd.