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.

A multi-helical ultrasonic imaging approach for the structural health monitoring of cylindrical structures

“…Furthermore, since in the proposed MHUI the higher order helical paths cross the damaged area at different angles, smearing effects will be reduced. 22 Figure 12 shows the results of the image reconstruction obtained for the defect case 1 when the first, third, and ninth helical orders related to the A 0 mode were used. It can be seen that the quality of both the image and damage detection improves as the number of helical orders considered in the algorithm increases.…”

“…GUW measurements combined with image reconstruction algorithms have emerged as a potential technology for increasing the resolution in this direction. 15–28 For example, Leonard and Hinders 25,26 implemented GUW tomography on pipes by treating the GUWs as Lamb waves that propagate along various helical paths (Figure 1). They designed an experimental apparatus to mimic two circumferential belts of transducers 25 (helical ultrasound tomography (HUT)) and a single line of transducers along the meridian of the cylindrical surface 26 (meridional ultrasonic tomography (MUT)).…”

Linear and Nonlinear Guided Wave Imaging of Impact Damage in CFRP Using a Probabilistic Approach

“…Although several attempts to visualize defects using the filtered back-projection tomographic algorithm were done [ 19 , 20 , 21 , 22 , 23 , 24 , 25 ], the most popular alternative methods are the sum-and-delay methods and the probability-based algorithms. Both approaches rely on information obtained from a sparse array or network of ultrasonic transducers that are in most cases permanently attached to the inspected sample.…”

A New Omni-Directional EMAT for Ultrasonic Lamb Wave Tomography Imaging of Metallic Plate Defects

“…One group is the series expansion methods that use algebraic reconstruction techniques (ARTs) [ 10 ] and simultaneous iterative reconstruction techniques (SIRTs) [ 11 ]. The other group is the Fourier-based methods like filtered back projection (FBP) [ 7 , 8 , 12 ] and interpolated filtered back projection (IFBP) [ 13 ]. The geometries of the transducer arrays include the circular array configuration with parallel or fan beam projection [ 14 ], the linear array configuration such as cross-hole [ 10 ] and double cross-hole [ 15 ] and so on.…”