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Outline

Title
Abstract
Introduction
Detection and Imaging Procedure
Experimental Set-Up and Results
Total Focusing Method
Conclusion
References

Proceedings of Meetings on Acoustics

Profile image of Alexandre AubryAlexandre Aubry

2013

https://doi.org/10.1121/1.4800759
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6 pages

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Abstract

Flaw detection using ultrasonic evaluation of coarse-grain steels is perturbed by a high structural noise due to scattering. This leads to a decrease of the detection capabilities, particularly at high frequencies and large depths for which multiple scattering dominates. Recent academic studies have shown that the contribution of multiple scattering could be dramatically reduced. These results were obtained on a model random medium made of parallel steel rods immersed in water. The ability to detect a target could be significantly increased using a specific filtering method, based on the full matrix capture (F.M.C.) combined with a smart post-treatment based on random matrix theory, in supplement with the DORT method (i.e., decomposition of the time-reversal operator). Here, the same technique to separate simple and multiple scattering contributions is now applied to a real material. Experimental results were obtained on a nickel-based alloy (Inconel600®) with a thermicallyinduced c...

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heterogeneous materials (steels, welding, composites …) using ultrasonic waves. For this purpose, a continuous wavelet transform is applied to ultrasonic Ascan signals acquired using an ultrasonic Non Destructive Testing (NDT) device. The timescale representation provided, which highlights the temporal evolution of the spectral content of the Ascan signals, is relevant but can lead to misinterpretation. The problem is to identify if each pattern from the wavelet representation is due to the structural noise or a flaw. To solve it, a detection technique based on statistical significance testing in the timescale plane is used. Typical structural noise signals are then described using an autoregressive model which seems relevant according to the spectral content of the signals. The approach is tested on experimental signals, obtained by ultrasonic NDT of metallic materials (austenitic stainless steel) then of a welding in this steel and indeed enables to separate various components from the signal that is two kinds of structural noise and flaw echoes.

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References (13)

  1. J.A. Turner and R.L. Weaver, "Time dependence of multiply scattered diffuse ultrasound in polycrystalline media", J. Acoust. Soc. Am. 97(5), 2639-2644 (1995).
  2. J.A. Turner and R.L. Weaver, "Radiative transfer and multiple scattering of diffuse ultrasound in polycrystalline media", J. Acoust. Soc. Am. 96(6), 3675-3683 (1994).
  3. C. Holmes, B.W. Drinkwater and P.D. Wilcox, "Post-processing of the full matrix of ultrasonic transmit-receive array data for non-destructive evaluation", NDT & E International 38(8), 701-711 (2005).
  4. J. Zhang, B.W. Drinkwater, P.D. Wilcox, A.J. Hunter, "Defect detection using ultrasonic arrays: The multi-mode total focusing method", NDT & E International 43(2), 123-133 (2010).
  5. B. Angelsen, Ultrasound imaging. Waves, signals and signal processing, Emantec Trondheim, Norway, 2000.
  6. M. Fink et al., "Time-reversed acoustics", Rep. Prog. Phys. 63, 1933 (2000).
  7. C. Prada, E. Kerbrat, D. Cassereau and M. Fink, "Time reversal techniques in ultrasonic nondestructive testing of scattering media", Inverse Problems 18, 1761 (2002).
  8. C. Prada, M. Tanter and M. Fink, "Flaw detection in solids with the D.O.R.T. method" in 1997 IEEE Ultrasonics Symposium vol 1, edited by IEEE 1997, 1997, pp. 679-683.
  9. E. Kerbrat, C. Prada, D. Cassereau and M. Fink, "Imaging in the presence of grain noise using the decomposition of the time reversal operator", J. Acoust. Soc. Am. 113, 1230-1240 (2003).
  10. A. Aubry and A. Derode, "Random Matrix Theory Applied to Acoustic Backscattering and Imaging In Complex Media", Phys. Rev. Lett. 102(8), 84301 (2009).
  11. A. Aubry and A. Derode, "Detection and imaging in a random medium: A matrix method to overcome multiple scattering and aberration", J. Appl. Phys. 106(4), 044903 (2009).
  12. C. Prada, S. Manneville, D. Spoliansky and M. Fink., "Decomposition of the time reversal operator: Detection and selective focusing on two scatterers", J. Acoust. Soc. Am. 99, 2067-2076 (1996).
  13. A. Aubry and A. Derode, "Singular value distribution of the propagation matrix in random scattering media", Waves in Random and Complex Media 20(3), 333-363 (2010).

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Flaw detection using ultrasonic evaluation of coarse-grain steels is perturbed by a high structural noise due to scattering. This leads to a decrease of the detection capabilities, particularly at high frequencies and large depths for which multiple scattering dominates. Recent academic studies have shown that the contribution of multiple scattering could be dramatically reduced. These results were obtained on a model random medium made of parallel steel rods immersed in water. The ability to detect a target could be significantly increased using a specific filtering method, based on the full matrix capture (F.M.C.) combined with a smart post-treatment based on random matrix theory, in supplement with the DORT method (i.e., decomposition of the time-reversal operator). Here, the same technique to separate simple and multiple scattering contributions is now applied to a real material. Experimental results were obtained on a nickel-based alloy (Inconel600®) with a thermicallyinduced coarse grain structure and manufactured flaws (side drilled holes) at different depths. The experimental set-up used a multi-element ultrasonic array. Results are presented and compared to other detection techniques, at various depths and frequencies. Despite a dominant multiple scattering noise, a significant improvement of the detection performances is observed.

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In-service inspection of industrial components is e s ential for power plant operators in order to ensu re an optimal and secure operation. In particular, Ultras onic Non Destructive Testing is commonly used for t his purpose. Unfortunately, ultrasonic wave propagation in compl ex components such as coarse-grain steels can be ha mpered by a high backscattered noise mostly due to scattering at rain boundaries. As a result, detecting a defe ct b comes difficult, especially when multiple scattering domi nates single scattering. A deep flaw in a multiplescattering sample can become undetectable by classical ultraso nic techniques: a situation which is more likely to occur at higher frequencies, or in structures exhibiting lar ger grain sizes. To avoid this, one can restrict th e ultrasonic inspection to low-frequency regimes, where multiple scattering is negligible, naturally at the cost of a loss of spatial resolution. Yet a recent study on synthetic scatter ing media, made of randomly...

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