FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

CONCLUSION
Classical bulk and surface wave pulse-echo techniques were evaluated in their
ability to detect and size surface breaking cracks in the base of rails.
Although both of these techniques give good results for EDM slots, echo
amplitudes from real cracks depend on crack closure and the presence of
filling material. Rayleigh waves offer considerable advantages in terms of
singal to noise and ease of detection [22] but their high sensitivity to
factors other than crack depth make them unusable for sizing. Classical shear
wave pulse-echo techniques were found to be in good agreement with the open
flaw depth when calibrated on EDM slots. For proper sizing of the full depth,
the techniques used were found inadequate. Since the closed or filled part of
cracks are partially transparent to ultrasound, it is likely that more
advanced NDT techniques using feature extraction in the time or frequency
domain would also be inadequate without adaptation. This work points out the
need for theoretical modelling and experimentation on the interaction of
ultrasound with closed cracks and in particular of the scattering phenomena
occuring at the tip [23],
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[2] H.J. Mayer; Mater. Eval., j42, 793 (1984)
[3] J. Drury; Brit. J. NDT, p 200, July (1979)
[4] E.A. Kraut; IEEE Trans. Sonics Ultrasonics, Su-^3_, 162 (1976)
[5] P.A. Doyle, CM. Scala; Ultrasonics, 16, 164 (1978)
[6] R.B. Thompson, D.O. Thompson; J. Metals, p. 29, July (1981)
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[8] S. Serabian; Mater. Eval., J39_, 1243 (1981)
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[13] R.B. Thompson, C.J. Fiedler; "Review of Progress in Quantitative
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[14] I.A. Viktorov; "Rayleigh and Lamb Waves", (Plenum Press, NY 1967)
[15] J.M. Carson, J.L. Rose; Mater. Eval. p. 27, April (1980)
[16] L. Adler, M. de Billy, G. Quentin; J. Appl. Phys. j)3, 8756 (1982)
[17] M. Hirao, H. Fukuoda, Y. Mirura; J. Acoust. Soc. Ara. 7^, 602 (1980)
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[21] W.M. Visscher; ibid [15]
[22] H. Seiger; NDT Intl., p. 131, June (1982)
[23] R.B. Thompson; Applied Mechanics Division of ASME, Symposium on Wave
Propagation in Inhomogeneous Media, San Antonio, Texas, June 1984