Fan beam and double crosshole Lamb wave tomography for mapping flaws in aging aircraft structures

Abstract

As the worldwide aviation fleet continues to age, methods for accurately predicting the presence of structural flaws-such as hidden corrosion and disbonds-that compromise airworthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. The work summarized here focuses on a variety of different tomographic reconstruction techniques to graphically represent the Lamb wave data in quantitative maps that can be easily interpreted by technicians. Because the velocity of Lamb waves depends on thickness, for example, the traveltimes of the fundamental Lamb modes can be converted into a thickness map of the inspection region. This article describes two potentially practical implementations of Lamb wave tomographic imaging techniques that can be optimized for in-the-field testing of large-area aircraft structures. Laboratory measurements discussed here demonstrate that Lamb wave tomography using either a ring of transducers with fan beam reconstructions, or a square array of transducers with algebraic reconstruction tomography, is appropriate for detecting flaws in multilayer aircraft materials. The speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems are discussed in this article.

On the development and testing of a guided ultrasonic wave array for structural integrity monitoring

“…Significant work has been reported on the first symmetrical mode S 0 and the lowest shear mode SH 0 , as their displacement, stress distribution, and propagation velocity at low frequencies are similar to the bulk ultrasonic wave modes [6]. In particular, the S 0 mode has been used for tomography applications [7], as at low frequency-thickness it has the highest group velocity, i.e., the fastest arrival time. The scattering at typical structural features and defects has been studied for a variety of applications [8], [9].…”

Study on Guided Wave Imaging Methods for SOLID Rocket Motor Shell Material

“…In 1994, Jansen spread the LWT technology to the field of composite materials nondestructive testing [10]. In 2000, Malyarenko studied the filtered method for fan beam projection and double crosshole geometry [11]. In 2002, Leonard presented a sample of parallel projection and fan beam projection [12].…”

Lamb Wave Detection of Delaminations in Large Diameter Pipe Coatings

“…Since they propagate relatively long distances within pipe, plate and shell structures, guided waves allow inspection of greater areas with fewer sensors, making this technique attractive for a variety of applications [6,7]. This paper builds on a previous line of research we've developed over the past decade [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Here, we will point out some of the major breakthroughs over the decades as well as recent advancements in the specific areas discussed in this work.…”