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Abstract: This work is devoted to the characterization of defects in the bonding of two carbon epoxy composite plates using Lamb waves. First, artificial defects are located by a C-scan performed by two air-coupling transducers. Next, Lamb wave propagation is studied with a laser interferometer. The behavior of the incident wave is interpreted and related to the nature of the defect. The size of the flaw area is estimated. [Copyright &y& Elsevier]

The evolution of the experimental frequency width of symmetric modes of an aluminum plate is studied as a function of the angle of incidence below the first critical angle. It is found that the frequency width predicted by resonant scattering theory, corrected for the directivity of emitter and receiver, generally explains the experimental frequency width well. However, large discrepancies remain for the frequency width of the S1 mode at angles of incidence larger than 9°. It is demonstrated that these are caused by not taking into account the complex nature of the slowness of the plate mode. This suggests that there is a need for a theory that models the interaction of a beam of ultrasound, bounded in space and time, with an elastic plate. [Copyright &y& Elsevier]

The paper presents a set of numerical results on the use of surface mounted piezoelectric transducers to analyse the effects of impact damage and delamination of plate-like structures on the Lamb wave mode. The effects of the size, properties and orientation of the damage upon a propagating Lamb wave is qualitatively determined. In this paper, impact damage was simulated by a local change in the stiffness of the material in the structure and a delamination. The effects on the transmission of the incident Lamb wave when it propagates through a region of change in density are analysed. This paper will also demonstrate how the properties of a propagating Lamb wave can be affected by the existence of a delamination in a plate. [Copyright &y& Elsevier]

Abstract: A novel combined spectral estimate (CSE) method for differentiation and estimation the phase velocities of multimode Lamb waves whose wave numbers are much close or overlap one another in multiplayer plates is presented in this paper, which based on auto-regressive (AR) model and 2-D FFT. Simulated signals in brass plate were processed by 2-D FFT and CSE. And experiments are performed by using two conventional angle probes as emitter and receiver on the same surface of three-layered aluminum/xpoxy/aluminum plates, which include symmetrical and unsymmetrical plates. The multimode Lamb waves are excited in these laminates, and the received signal is processed by 2-D FFT and CSE, respectively. The results showed that the phase velocities of multimode signals whose wave numbers are much closed cannot be differentiated by 2-D FFT, but CSE has strong spatial resolution. Compared the measured phase velocities with the theoretical values, the error is smaller than 2% on the whole. It promises to be a useful method in experimental signals processing of multimode Lamb waves. [Copyright &y& Elsevier]