Parallel projection and crosshole Lamb wave contact scanning tomography

Abstract

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in thin plates and thin laminated structures, such as airframe skins, storage tanks, and pressure vessels. Their propagation properties in these media depend on the vibrational frequency as well as on the thickness and material properties of the structure. Structural flaws such as disbonds, corrosion, fatigue cracks, and voids represent changes in effective thickness and material properties, and therefore measurement of variations in Lamb wave propagation can be employed to assess the integrity of these structures. Lamb wave measurements can be made for a number of relative transducer positions (projections) and an image of the flawed region can be reconstructed tomographically. This paper presents a new technique in which two contact piezoelectric transducers are independently scanned along parallel lines in a fashion analogous to that commonly used in seismic crosshole tomography. These results are compared to those for parallel projection Lamb wave tomography data collected with an automated contact scanning apparatus. The advantages and drawbacks of these two methods in the development of automated tomographic Lamb wave scanners for quantitative mapping of thickness variation in platelike materials are discussed.

Guided wave tomography with an improved scattering model

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Lamb Wave Detection of Delaminations in Large Diameter Pipe Coatings

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Profile imaging of actual defects in steel plate based on electromagnetic ultrasonic SH guided wave scattering

“…ln recent years, ElJGW imaging technique has been developed to obtain more detailed information about defects [15-1 6]. Guided wave tomography imagi ng exploits an array of transducers to transmit and receive a group of guided wave rays and reconstructs the defect image using the projection data [17][18][19]. When guided wave e ncounters defects and strong scattering happens, the effect of scatteri ng will dominate a nd lead to much artifacts on the reconstructio n image of defects, w hi ch severely d egrades the positioning acc uracy and image quality of defects obtained by traditional guided wave imaging m ethods [20].…”