NDTnet 1998 Aug, Vol.3 No.8

Abstract

There has been considerable interest in computed tomography with ultrasound, since the successful introduction of computed tomography with X-rays. This is mainly due to the fact that ultrasonic computed tomography (UCT) may generate cross-sectional images (tomograms) of three different material properties: (i) an attenuation tomogram representing the ultrasonic energy loss due to scatter and absorption in the material; (ii) a speed-of-sound tomogram representing a measure of the elastic constants in the material [1]; and, (iii) a reflection tomogram representing a map of ultrasonic impedance mismatch from boundaries and inhomogeneities.
In particular, the reflection tomogram is of interest for the nondestructive evaluation (NDE) community because most industrial relevant materials, like e.g. pipelines, rods, axles, only allows access from one side of the material.

In this study, ultrasonic three-dimensional information was obtained of defects in cylindrical AlSi-alloys and Plexiglass specimens. This information was established by constructing twodimensional reflection tomograms in multiple planes, in the third dimension, and stacking them serially. For this purpose, a circular aperture array (see e.g. [21) was used to measure Bscan profiles within the cylinder. From these profiles two-dimensional tomograms were reconstructed using a filtered backprojection technique [31. Examples of real defects are presented. Furthermore, artificial defects in the AlSi-alloy were compared with similar artificial defects in Plexiglas specimens.The results indicate that defect characterization in cylindrical specimens, may be substantially improved through the use of the proposed NDE method (see e.g. [4] for a comprehensive review of NDE methods).

1. .Nielsen, S.A. and Andersen, S.I.: 18th Riso Intern. Symp. on Materials Science, 1997,1:455-464.
2. Nielsen, S.A. and Bjorno, L.; Acoustical Imaging, 1997, 23 (In press).
3. Nielsen, S.A.; Borum, K.K. and Gundtoft, H.E.; Ist World Congress on Ultrasonics, Berlin, 1995, 1: 446-450.
4. Rheinländer, J.T., Nielsen, S.A.; Borum, K.K. and Gundtoft, H.E.; 18th Riso Intern. Symp. on Materials Science, 1997, 1:101-125.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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