An experimental study on the scattering of edgeguided waves by a small edge crack in an isotropic plate

Benjamin S. Vien, L. R. Francis Rose, Wing Kong Chiu

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearch

3 Citations (Scopus)

Abstract

Quantitative non-destructive evaluation for small fatigue cracks still remains a significant challenge for structural integrity management, especially for cracks in hidden or hard-To-inspect locations. Recently, Lamb waves have attracted considerable research interest in structural health monitoring (SHM) due to their desirable properties, which includes slow geometrical decay of amplitude with propagation and hence a potential for rapid wide-Area inspection. This paper presents a 3D laser vibrometry experimental study of the interaction between edge-guided waves and a small through-Thickness edge crack in a 3mm thick aluminium (isotropic) plate. A piezoelectric transducer is bonded on the edge of the plate to generate the incident wave. The excitation signal consisted of a 5.5 cycle Hann-windowed toneburst of centre frequency 200 kHz, which is well below the cut-off for the first order Lamb wave modes (A1 and SH1). A 2D FFT procedure is applied to the incident and scattered field along radial lines emanating from the crack mouth so as to obtain both the amplitude of the incident field and the amplitude of the scattered field as a function of scattering angle. In principle, edge waves are one dimensional and therefore their amplitude should not decay with propagation distance, which makes them well suited for SHM. In practice, a small decay with propagation distance was observed, especially for the antisymmetric edge wave, which may be attributed to difficulties in distinguishing between the edge wave and the bulk A0 mode in the 2D FFT plots. Nevertheless, it is shown that the scattered wave field due to a small crack length, a, (compared to the wavelength of incident wave, λ) can be considered to be equivalent to a point source consisting of particular combinations of body-force doublets. It is found that the amplitude of the scattered field increases as a power function of a/λ, whereas the scattered wave pattern is independent of crack length for small cracks a λ. This forward problem of determining the scattered wave field from a known crack size is an essential study to guide a judicious approach to the inverse problem of crack detection and sizing.

Original languageEnglish
Title of host publication8th European Workshop on Structural Health Monitoring, EWSHM 2016
Subtitle of host publicationBilbao, Spain; 5-8 July 2016
Place of PublicationBad Breisig, Germany
PublisherNDT Internet Publishing
Pages1097-1106
Number of pages10
Volume2
ISBN (Print)9781510827936
Publication statusPublished - 2016
Event8th European Workshop on Structural Health Monitoring - Bilbao, Spain
Duration: 5 Jul 20168 Jul 2016
Conference number: 8

Conference

Conference8th European Workshop on Structural Health Monitoring
Abbreviated titleEWSHM 2016
CountrySpain
CityBilbao
Period5/07/168/07/16

Keywords

  • Fatigue crack
  • Lamb waves
  • Laser vibrometry
  • Structural health monitoring.

Cite this

Vien, B. S., Francis Rose, L. R., & Chiu, W. K. (2016). An experimental study on the scattering of edgeguided waves by a small edge crack in an isotropic plate. In 8th European Workshop on Structural Health Monitoring, EWSHM 2016: Bilbao, Spain; 5-8 July 2016 (Vol. 2, pp. 1097-1106). Bad Breisig, Germany: NDT Internet Publishing.
Vien, Benjamin S. ; Francis Rose, L. R. ; Chiu, Wing Kong. / An experimental study on the scattering of edgeguided waves by a small edge crack in an isotropic plate. 8th European Workshop on Structural Health Monitoring, EWSHM 2016: Bilbao, Spain; 5-8 July 2016. Vol. 2 Bad Breisig, Germany : NDT Internet Publishing, 2016. pp. 1097-1106
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abstract = "Quantitative non-destructive evaluation for small fatigue cracks still remains a significant challenge for structural integrity management, especially for cracks in hidden or hard-To-inspect locations. Recently, Lamb waves have attracted considerable research interest in structural health monitoring (SHM) due to their desirable properties, which includes slow geometrical decay of amplitude with propagation and hence a potential for rapid wide-Area inspection. This paper presents a 3D laser vibrometry experimental study of the interaction between edge-guided waves and a small through-Thickness edge crack in a 3mm thick aluminium (isotropic) plate. A piezoelectric transducer is bonded on the edge of the plate to generate the incident wave. The excitation signal consisted of a 5.5 cycle Hann-windowed toneburst of centre frequency 200 kHz, which is well below the cut-off for the first order Lamb wave modes (A1 and SH1). A 2D FFT procedure is applied to the incident and scattered field along radial lines emanating from the crack mouth so as to obtain both the amplitude of the incident field and the amplitude of the scattered field as a function of scattering angle. In principle, edge waves are one dimensional and therefore their amplitude should not decay with propagation distance, which makes them well suited for SHM. In practice, a small decay with propagation distance was observed, especially for the antisymmetric edge wave, which may be attributed to difficulties in distinguishing between the edge wave and the bulk A0 mode in the 2D FFT plots. Nevertheless, it is shown that the scattered wave field due to a small crack length, a, (compared to the wavelength of incident wave, λ) can be considered to be equivalent to a point source consisting of particular combinations of body-force doublets. It is found that the amplitude of the scattered field increases as a power function of a/λ, whereas the scattered wave pattern is independent of crack length for small cracks a λ. This forward problem of determining the scattered wave field from a known crack size is an essential study to guide a judicious approach to the inverse problem of crack detection and sizing.",
keywords = "Fatigue crack, Lamb waves, Laser vibrometry, Structural health monitoring.",
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Vien, BS, Francis Rose, LR & Chiu, WK 2016, An experimental study on the scattering of edgeguided waves by a small edge crack in an isotropic plate. in 8th European Workshop on Structural Health Monitoring, EWSHM 2016: Bilbao, Spain; 5-8 July 2016. vol. 2, NDT Internet Publishing, Bad Breisig, Germany, pp. 1097-1106, 8th European Workshop on Structural Health Monitoring, Bilbao, Spain, 5/07/16.

An experimental study on the scattering of edgeguided waves by a small edge crack in an isotropic plate. / Vien, Benjamin S.; Francis Rose, L. R.; Chiu, Wing Kong.

8th European Workshop on Structural Health Monitoring, EWSHM 2016: Bilbao, Spain; 5-8 July 2016. Vol. 2 Bad Breisig, Germany : NDT Internet Publishing, 2016. p. 1097-1106.

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearch

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T1 - An experimental study on the scattering of edgeguided waves by a small edge crack in an isotropic plate

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AU - Francis Rose, L. R.

AU - Chiu, Wing Kong

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N2 - Quantitative non-destructive evaluation for small fatigue cracks still remains a significant challenge for structural integrity management, especially for cracks in hidden or hard-To-inspect locations. Recently, Lamb waves have attracted considerable research interest in structural health monitoring (SHM) due to their desirable properties, which includes slow geometrical decay of amplitude with propagation and hence a potential for rapid wide-Area inspection. This paper presents a 3D laser vibrometry experimental study of the interaction between edge-guided waves and a small through-Thickness edge crack in a 3mm thick aluminium (isotropic) plate. A piezoelectric transducer is bonded on the edge of the plate to generate the incident wave. The excitation signal consisted of a 5.5 cycle Hann-windowed toneburst of centre frequency 200 kHz, which is well below the cut-off for the first order Lamb wave modes (A1 and SH1). A 2D FFT procedure is applied to the incident and scattered field along radial lines emanating from the crack mouth so as to obtain both the amplitude of the incident field and the amplitude of the scattered field as a function of scattering angle. In principle, edge waves are one dimensional and therefore their amplitude should not decay with propagation distance, which makes them well suited for SHM. In practice, a small decay with propagation distance was observed, especially for the antisymmetric edge wave, which may be attributed to difficulties in distinguishing between the edge wave and the bulk A0 mode in the 2D FFT plots. Nevertheless, it is shown that the scattered wave field due to a small crack length, a, (compared to the wavelength of incident wave, λ) can be considered to be equivalent to a point source consisting of particular combinations of body-force doublets. It is found that the amplitude of the scattered field increases as a power function of a/λ, whereas the scattered wave pattern is independent of crack length for small cracks a λ. This forward problem of determining the scattered wave field from a known crack size is an essential study to guide a judicious approach to the inverse problem of crack detection and sizing.

AB - Quantitative non-destructive evaluation for small fatigue cracks still remains a significant challenge for structural integrity management, especially for cracks in hidden or hard-To-inspect locations. Recently, Lamb waves have attracted considerable research interest in structural health monitoring (SHM) due to their desirable properties, which includes slow geometrical decay of amplitude with propagation and hence a potential for rapid wide-Area inspection. This paper presents a 3D laser vibrometry experimental study of the interaction between edge-guided waves and a small through-Thickness edge crack in a 3mm thick aluminium (isotropic) plate. A piezoelectric transducer is bonded on the edge of the plate to generate the incident wave. The excitation signal consisted of a 5.5 cycle Hann-windowed toneburst of centre frequency 200 kHz, which is well below the cut-off for the first order Lamb wave modes (A1 and SH1). A 2D FFT procedure is applied to the incident and scattered field along radial lines emanating from the crack mouth so as to obtain both the amplitude of the incident field and the amplitude of the scattered field as a function of scattering angle. In principle, edge waves are one dimensional and therefore their amplitude should not decay with propagation distance, which makes them well suited for SHM. In practice, a small decay with propagation distance was observed, especially for the antisymmetric edge wave, which may be attributed to difficulties in distinguishing between the edge wave and the bulk A0 mode in the 2D FFT plots. Nevertheless, it is shown that the scattered wave field due to a small crack length, a, (compared to the wavelength of incident wave, λ) can be considered to be equivalent to a point source consisting of particular combinations of body-force doublets. It is found that the amplitude of the scattered field increases as a power function of a/λ, whereas the scattered wave pattern is independent of crack length for small cracks a λ. This forward problem of determining the scattered wave field from a known crack size is an essential study to guide a judicious approach to the inverse problem of crack detection and sizing.

KW - Fatigue crack

KW - Lamb waves

KW - Laser vibrometry

KW - Structural health monitoring.

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Vien BS, Francis Rose LR, Chiu WK. An experimental study on the scattering of edgeguided waves by a small edge crack in an isotropic plate. In 8th European Workshop on Structural Health Monitoring, EWSHM 2016: Bilbao, Spain; 5-8 July 2016. Vol. 2. Bad Breisig, Germany: NDT Internet Publishing. 2016. p. 1097-1106