Contact scanning Lamb wave tomography

Abstract

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in platelike structures such as airframe skins, storage tanks, and pressure vessels. Their propagation depends on frequency thickness and material properties, and, because structural flaws present changes in effective thickness and/or material properties, Lamb waves can be employed to assess the integrity of these structures. For structures with large surface areas, a full integrity evaluation can be a time-consuming operation, but with Lamb wave techniques, this evaluation can be performed with waves propagating along one dimension of the inspection area as the probing transducers are moved in the perpendicular dimension. Such an approach yields information about the presence of flaws within the scanned area. Then, in order to quantitatively characterize the flaws, Lamb wave measurements can be made for a number of projections and an image of the flawed region can be reconstructed tomographically. Contact scanning Lamb wave tomography for metallic and composite structures with flaws is discussed as a practical technique for quantitative nondestructive evaluation.