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Reflectivity Estimation using an Expectation Maximization Algorithm for Ultrasonic Testing of Adhesive Bonds

This paper discusses the use of the pulse-echo technique of ultrasonic testing (UT) for nondestructive testing (NDT) of adhesive bonds of thin metal sheets (less than 1 mm thick) in which the thickness of the adhesive layer and the metal sheets, as well as the acoustical properties of the adhesive, are unknown. The aim of UT of adhesive joints is to assess the integrity of the front (interface close to the interrogating transducer) and rear adherent/adhesive interfaces. To achieve this goal, accurate estimation of the reflectivity is required. In this study, a model-based approach was applied to signals obtained from adhesively bonded joints in order to estimate their reflectivity. The transducer wavelet was modeled by gaussian echoes and the reflectivity (the desired system response) was estimated by using the expectation maximization algorithm. The decay rate of reverberations in the front metal sheet calculated from the estimated amplitudes of the sequence was used as a basis for detection of disbond in the front interface. By applying the proposed technique, it was possible to detect void-disbonds and the presence of anomalies, such as grease and water in the front interface of a joint made by 0.5 mm thick aluminum plates. Disbonds in the rear interface of this joint were also detected by examining the phase inversion of the echo reflected from the rear interface.

Adams, R. D. and B. W. Drinkwater, “Non-destructive Testing of Adhesively -bonded Joints,” International Journal of Materials and Product Technology, Vol. 14, Nos. 5 – 6, November 1999, pp. 385–398. Allin, J. M., P. Cawley and M. J. S. Lowe, “Adhesive Disbond Detection of Automotive Components using First Mode Ultrasonic Resonance,” NDT & E International, Vol. 36, No. 7, October 2003, pp. 503–514. Banks, W. M, D. Hayward, S. B. Joshi, Z. Li, K. Jeffrey and R. A. Pethrick, “High Frequency Dielectric Investigations of Adhesive Bonded Structures,” Insight, Vol. 37, No. 12, 1995, pp. 964–968. Cawley, P., “Low Frequency NDT Techniques for the Detection of Disbonds and Delaminations,” British Journal of NDT, Vol. 32, No. 9, 1990, pp. 454–461. Cawley, P. and R. Adams, “The Mechanics of the Coin-tap Method of Nondestructive Testing,” Journal of Sound and Vibration, Vol. 122, No. 2, 1998, pp. 299–316. Cawley, P., “The Rapid Non-destructive Inspection of Large Composite Structures,” Composites, Vol. 25, No. 5, May 1994, pp. 351–357. Cawley, P., “The Sensitivity of the Mechanical Impedance Method of Nondestructive Testing,” NDT International, Vol. 20, No. 4, August 1987, pp. 209–215. Challis, R. E., R. J. Freemantle, J. D. H. White and G. P. Wilkinson, “Ultrasonic Compression Wave NDT of Adhered Metal Lap Joints of Uncertain Dimensions,” Insight, Vol. 37, No. 12, 1995, pp. 954–963. Challis, R. E., R. J. Freemantle, G. P. Wilkinson, and J. D. H. White, “Compression Wave NDE of Adhered Metal Lap Joints: Uncertainties and Echo Feature Extraction,” Ultrasonics, Vol. 34, No. 2 – 5. June 1996, pp. 315–319. Demirli R. and J. Saniie, “Model-based Estimation of Ultrasonic Echoes Part I: Analysis and Algorithms,” IEEE Transactions on Ultrasononics, Ferroelectrics and Frequency Control, Vol. 48, No. 3, 2001, pp. 787–802. Demirli R. and J. Saniie, “Model-based Estimation of Ultrasonic Echoes Part II: Nondestructive Evaluation Application,” IEEE Transactions on Ultrasononics, Ferroelectrics and Frequency Control, Vol. 48, No. 3, 2001, pp. 803–811. Engholm, M., and T. Stepinski, “Designing and Evaluating Transducers for Narrowband Ultrasonic Spectroscopy,” Ultrasonics Symposium, 2005 IEEE, 18 – 21 September 2005, pp. 2085–2088. Feder, M., Statistical Signal Processing using a class of Iterative Estimation Algorithm, Ph.D. Thesis, Massachusetts Institute of Technology, 1987. Feder, M. and E. Weinstein, “Parameter Estimation of Superimposed Signals using the EM Algorithm,” IEEE Transactions on Acoustics, Speech and Signal Processing, Vol. 36, No. 4, April 1998, pp. 477–489. Gladden, L. F. and P. Alexander, “Applications of Nuclear Magnetic Resonance Imaging in Process Engineering,” Measurement Science and Technology, Vol. 7, No. 3, 1996, pp. 423–435. Goglio, L. and M. Rossetto, “Ultrasonic Testing of Adhesive Bonds of Thin Metal Sheets,” NDT & E International, Vol. 32, No. 6, September 1999, pp. 323–331. Guyott, C. and P. Cawley, “Evaluation of the Cohesive Properties of Adhesive Joints using Ultrasonic Spectroscopy,” NDT & E International, Vol. 21, No. 4, August 1988, pp. 233–240. Hagemaier, D. J., “Automated Ultrasonic Inspection of Adhesive Bonded Structure,” Materials Evaluation, Vol. 40, No. 4, 1982, pp. 572–578. Herrera, R. H., R. Orozco and M. Rodriguez, “Wavelet-based Deconvolution of Ultrasonic Signals in Nondestructive Evaluation,” Journal of the Zhejiang University, Science A, Vol. 7, No. 10, 2006, pp. 1748–1756. Honarvar, F., H. Sheikhzadeh, M. Moles and A. N. Sinclair, “Improving the Time-resolution and Signal-to-noise Ratio of Ultrasonic NDE Signals,” Ultrasonics, Vol. 41, 2004, pp. 755–763. Maeva, E., I. Severina, S. Bondarenko, G. Hapman, B. O’Neil, F. Severin and Gr. Maev, “Acoustical Methods for the Investigation of Adhesively Bonded Structures: A Review,” Canadian Journal of Physics, Vol. 82, No. 12, 2004, pp. 981–1025. Mendel, J. M., Optimal Seismic Deconvolution: An Estimation-based Approach. Academic Press, New York, 1983. Munns, I. J. and G. A. Georgiou, “Non-destructive Testing Methods for Adhesively Bonded Joint Inspection – A Review,” Insight, Vol. 37, No. 12, 1995, pp. 941–52. Neal, S. P., P. L. Speckman and M. A. Enright, “Flaw Signature Estimation in Ultrasonic Nondestructive Evaluation using the Wiener Filter with Limited Prior Information,” IEEE Transactions on Ultrasononics, Ferroelectrics and Frequency Control, Vol. 40, No. 4, 1993, pp. 347–353. Newman, J. W., “Shearographic Inspection of Aircraft Structure,” Materials Evaluation, Vol. 49, 1991, pp. 1106–1109. Sin, S. K., and C. H. Chen, “A Comparison of Deconvolution Techniques for the Ultrasonic Nondestructive Evaluation of Materials,” IEEE Transactions on Image Processing, Vol. 1, No. 1, 1992. Stepinski, T. amd M. Jonsson, “Narrowband Ultrasonic Spectroscopy for NDE of Layered Structures,” Insight, Vol. 47, 2005, pp. 220–224. Titov, S. A., R. G. Maev and A. N. Bogachenkov, “Pulse-echo NDT of Adhesively Bonded Joints in Automotive Assemblies,” Ultrasonics, Vol. 48, Nos. 6–7, 2008, pp. 537–546. Wang, W. and S. I. Rokhlin, “Evaluation of Interfacial Properties in Adhesive Joints of Aluminum using Angle-beam Ultrasonic Spectroscopy,” Journal of Adhesion Science and Technology, Vol. 5, No. 8, 1991, pp. 647–666. Zeighami, M. and F. Honarvar, “New Approaches for Testing of Adhesive Joints by Ultrasonic C-scan Imaging Technique,” Materials Evaluation, Vol. 67, No. 8, 2009, pp. 935–45.
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