Techniques for the generation of quantitative ultrasonic images in non-dest
ructive testing have generally involved a substantial cost in terms of data
storage and computational time, and thus have found limited application. P
reference has therefore been given to the more straightforward imaging meth
ods, such as main beam projection, that detect the presence of defects and
provide a limited flaw sizing capability.
The relatively small number of flaws requiring detailed examination, couple
d with substantial increases in available data storage and computational po
wer, has made it possible to use a number of straightforward tomographic re
construction methods to produce images of flaws contained within the materi
al under examination. These can then be fused together into a single image
from which more accurate measurements of flaw size, shape and orientation c
an be made. The three tomographic methods that have been implemented in thi
s work are reflection tomography, time-of-flight diffraction tomography and
transmission tomography. Selection of images used in the fusion process de
pends on the nature of the flaw, as each of these methods identifies differ
ent characteristics of the flaw shape. The reconstruction methods have been
used to generate images from a variety of flaws contained within aluminum
cylinders, some or all of the images being fused to produce the final flaw
image. Time domain measurements used in the reconstruction were then applie
d to simulate the application of multi-element arrays for data acquisition
and the subsequent tomographic images evaluated. (C) 1999 Published by Else
vier Science B.V. All rights reserved.