The Potential of Guided Waves for Monitoring Large Areas of Metallic Aircraft Fuselage Structure
01 Mar 2001-Journal of Nondestructive Evaluation (Kluwer Academic Publishers-Plenum Publishers)-Vol. 20, Iss: 1, pp 29-46
TL;DR: In this article, the potential for long-range propagation of ultrasonic guided waves through metallic aircraft fuselage structure has been investigated using dispersion analysis and numerical modelling, validated by experiment, and it was concluded that an active aircraft system that relies on guided wave propagation of more than 1m is not feasible, whereas localised guided wave monitoring of structurally significant areas is a more practical approach.
Abstract: The potential for long-range propagation of ultrasonic guided waves through metallic aircraft fuselage structure has been investigated using dispersion analysis and numerical modelling, validated by experiment. In order to satisfy the pressing need for integrated structural health monitoring of ageing metallic aircraft, it is likely that an active guided wave system based on current technology must feature efficient propagation over distances of at least 1m with an attenuation of not more than about 40dB/m. Propagation was examined across free skin, tapering skin, skin loaded with sealant and paint, double skin jointed with either sealant or adhesive, and lap and stringer joints, which together adequately characterise metallic monocoque fuselage construction. Whilst the simple and tapering skins allow long range propagation of non-dispersive modes with little reflection at the transition to tapering skin, the attenuation caused by application of a sealant layer generally leaves no viable modes. Guided wave propagation through double skin features the inevitable generation of twin modes with similar phase velocity, which interact with each other during propagation. This interaction crucially determines the efficiency of propagation across narrow joints and effectively precludes propagation across a succession of joints. This work leads to the conclusion that an active aircraft system that relies on guided wave propagation of more than 1m is not feasible, whereas localised guided wave monitoring of structurally significant areas is a more practical approach.
Citations
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TL;DR: In this paper, the capability of embedded piezoelectric wafer active sensors (PWAS) to excite and detect tuned Lamb waves for structural health monitoring is explored.
Abstract: The capability of embedded piezoelectric wafer active sensors (PWAS) to excite and detect tuned Lamb waves for structural health monitoring is explored. First, a brief review of Lamb waves theory is presented. Second, the PWAS operating principles and their structural coupling through a thin adhesive layer are analyzed. Then, a model of the Lamb waves tuning mechanism with PWAS transducers is described. The model uses the space domain Fourier transform. The analysis is performed in the wavenumber space. The inverse Fourier transform is used to return into the physical space. The integrals are evaluated with the residues theorem. A general solution is obtained for a generic expression of the interface shear stress distribution. The general solution is reduced to a closed-form expression for the case of ideal bonding which admits a closed-form Fourier transform of the interfacial shear stress. It is shown that the strain wave response varies like sin a, whereas the displacement response varies like sinc a. ...
890Â citations
Cites background from "The Potential of Guided Waves for M..."
...Among ultrasonic waves, the Lamb waves are particularly advantageous because they can propagate over large distances in plates and shells (Rose 1995, 2002; Krautkramer, 1998; Seale et al., 1998; Alleyne et al., 2001; Dalton et al., 2001; Thomson and Chimenti, 2002)....
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05 Aug 2003
TL;DR: In this article, the capability of embedded piezoelectric wafer active sensors (PWAS) to perform in-situ nondestructive evaluation (NDE) is explored.
Abstract: The capability of embedded piezoelectric wafer active sensors (PWAS) to perform in-situ nondestructive evaluation (NDE) is explored. Theoretical developments and laboratory tests are used to prove that PWAS transducers can satisfactorily perform Lamb wave transmission and reception, pulse-echo, pitch-catch, and phased array functions of conventional ultrasonics thus opening the road for embedded ultrasonics. Subsequently, crack detection in an aircraft panel with the pulse-echo method is illustrated. For large area scanning, a PWAS phased array is used to create the embedded ultrasonics structural radar (EUSR). For quality assurance, PWAS self-tests with the electromechanical impedance method are discussed.
254Â citations
Cites background from "The Potential of Guided Waves for M..."
...Guided Lamb waves have opened new opportunities for cost-effective detection of damage in aircraft structures [7], and a large number of papers have recently been published on this subject [8]....
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Abstract: In this paper we review the state of the art in an emerging new technology: embedded ultrasonic non-destructive evaluation (NDE). Embedded ultrasonic NDE permits active structural health monitoring, i.e. the on-demand interrogation of the structure to determine its current state of structural health. The enabling element of embedded ultrasonic NDE is the piezoelectric wafer active sensor (PWAS). We begin by reviewing the guided wave theory in plate, tube, and shell structures, with special attention to Lamb waves. The mechanisms of Lamb wave excitation and detection with embeddable PWAS transducers is presented. It is shown analytically and verified experimentally that Lamb wave mode tuning can be achieved by the judicious combination of PWAS dimensions, frequency value, and Lamb mode characteristics. Subsequently, we address in turn the use of pitch-catch, pulse-echo, and phased array ultrasonic methods for Lambwave damage detection. In each case, the conventional ultrasonic NDE results are contrasted with embedded NDE results. Detection of cracks, disbonds, delaminations, and diffuse damage in metallic and composite structures are exemplified. Other techniques, such as the time reversal method and the migration technique, are also presented. The paper ends with conclusions and suggestions for further work.
243Â citations
Cites background from "The Potential of Guided Waves for M..."
...The potential use of guided waves for monitoring metallic aircraft structures was investigated by Alleyne and Cawley (1992) and Dalton et al. (2001)....
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TL;DR: Full wavefield measurements obtained with either an air-coupled transducer mounted on a scanning stage or a scanning laser vibrometer can be combined with effective signal and imaging processing algorithms to support characterization of guided waves as well as detection, localization and quantification of structural damage.
236Â citations
TL;DR: Given better focused research and development considering the key factors identified here, structural health monitoring has the potential to follow the path of rotating machine condition monitoring and become a widely deployed technology.
Abstract: There has been a large volume of research on structural health monitoring since the 1970s but this research effort has yielded relatively few routine industrial applications. Structural health monitoring can include applications on very different structures with very different requirements; this article splits the subject into four broad categories: rotating machine condition monitoring, global monitoring of large structures (structural identification), large area monitoring where the area covered is part of a larger structure, and local monitoring. The capabilities and potential applications of techniques in each category are discussed. Condition monitoring of rotating machine components is very different to the other categories since it is not strictly concerned with structural health. However, it is often linked with structural health monitoring and is a relatively mature field with many routine applications, so useful lessons can be read across to mainstream structural health monitoring where there ar...
236Â citations
Cites background from "The Potential of Guided Waves for M..."
...Here, there are multiple reflections from the relatively closely spaced ribs and stiffeners that greatly complicate the received signals and reduce the feasible test range; Dalton et al.(65) showed that testing over distances greater than 1 m was unlikely to be feasible at the ....
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...Here, there are multiple reflections from the relatively closely spaced ribs and stiffeners that greatly complicate the received signals and reduce the feasible test range; Dalton et al.65 showed that testing over distances greater than 1 m was unlikely to be feasible at the .100 kHz frequencies required for adequate spatial resolution in these structures....
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TL;DR: The results indicate that Lamb waves may be used to find notches when the wavelength to notch depth ratio is on the order of 40, and the 2-D Fourier transform method is used to quantify Lamb wave interactions with defects.
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TL;DR: In this article, a two-dimensional Fourier transform (2D FFT) was used to measure the amplitudes and velocities of the Lamb waves propagating in a plate, the output of the transform being presented using an isometric projection which gives a three-dimensional view of the wave-number dispersion curves.
Abstract: A technique for the analysis of propagating multimode signals is presented. The method involves a two-dimensional Fourier transformation of the time history of the waves received at a series of equally spaced positions along the propagation path. The technique has been used to measure the amplitudes and velocities of the Lamb waves propagating in a plate, the output of the transform being presented using an isometric projection which gives a three-dimensional view of the wave-number dispersion curves. The results of numerical and experimental studies to measure the dispersion curves of Lamb waves propagating in 0.5-, 2.0-, and 3.0-mm-thick steel plates are presented. The results are in good agreement with analytical predictions and show the effectiveness of using the two-dimensional Fourier transform (2-D FFT) method to identify and measure the amplitudes of individual Lamb modes.
889Â citations