Blind test of Lamb wave diffraction tomography

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in plates and 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 and fatigue cracks represent changes in effective thickness and local 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 to give a quantitative map of a quantity of interest, e.g. thickness loss due to corrosion. As a test of the Lamb wave scanning apparatus and diffraction tomography reconstruction algorithms, we have undertaken an experiment which is double-blind in the medi...