In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. The Lamb wave velocity is directly related to the material parameters, so an effective method exists to ascertain the stiffness of composites by measuring the velocity of these waves. In this study, a Lamb wave measurement system was used to measure the bending and out-of-plane stiff...

Spatially distributed arrays of piezoelectric disks are being applied to monitor structural integrity using Lamb waves. Applied loads directly affect waves propagating between array elements because of dimensional changes and the acoustoelastic effect. Resulting changes in phase velocity depend upon the propagation direction as well as the Lamb wave mode and frequency. This paper shows from num...

Platelike structures, made of composites, are being increasingly used for fabricating aircraft wings and other aircraft substructures. Continuous monitoring of the health of these structures would aid the reliable operation of aircrafts. This paper considers the use of a Lamb wave based structural health monitoring SHM system to identify and locate defects in large multilayered composite plates...

In this paper we present the results of a systematic theoretical and experimental investigation of the fundamental aspects of using piezoelectric wafer active sensors (PWASs) to achieve embedded ultrasonics in thin-gage beam and plate structures. This investigation opens the path for systematic application of PWASs for in situ health monitoring. After a comprehensive review of the literature, w...

During the last three years the Swedish Institute for Metals Research (SIMR) has done extensive work on applications of laser generated ultrasound (LUS). This paper reports results from several experiments mainly aimed at industrial on-line applications. LUS has been used to determine grain sizes in commercial low-carbon (LC) and stainless steels. The analysis method employs a scattering theory...

Lamb modes exhibit a resonant behavior at frequencies where the group velocity vanishes while the phase velocity remains finite. This type of zero group velocity (ZGV) point exists in most isotropic materials at the minimum frequency-thickness product of the first order symmetric (S1) Lamb mode. Laser sources couple efficiently into this resonance and a sharp peak is observed with source and re...

| Damage detection using guided Lamb waves is an important tool in Structural health Monitoring. In this paper, we outline a method of obtaining Lamb wave modes in composite structures using two dimensional Spectral Finite Elements. Using this approach, Lamb wave dispersion curves are obtained for laminated composite structures with different fibre orientation. These propagating Lamb wave modes...

Lamb wave time reversal method is a new and tempting baseline-free damage detection technique for structural health monitoring. With this method, certain types of damage can be detected without baseline data. However, the application of this method to thin-wall structures is complicated by the existence of at least two Lamb wave modes at any given frequency, and by the dispersion nature of the ...