FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

Results
- 119 -
Figure *l shows the signals diffracted from opposite edges of a circular seatterer.
Constructive interference of the sound wavelets can be seen lying
between the two signals. Figures 5-10 show the frequency spectrum of sound
waves diffracted from the 7 mm brass rod at different orientations. Plotting
fn vs n, the slope yields if as illustrated in Figs. 11 and 12. A frequency
analysis plot and a time analysis plot yielding d and y are shown in
Figs. 13 and It. The actual diameters of the brass rod were measured with a
pair of vernier calipers to ± .02 mm. The values are compared in Table 1.
The axes of the brass rods were vertical (i.e., y = 0) in all cases because
no mechanical system providing accurate control of y was available at the
time of experimentation, but there was no loss of generality in the method
presented here as experimentally, the transducer sees only the relative orientation
of the circular rod with respect to itself.
Figure 15 compares the diameters deduced from frequency analysis and time analysis
with those measured from the vernier calipers. Figure 16 compares y
deduced from frequency analysis and time analysis with the known y. The
average of the error is ~1°. Table 2 illustrates that Ataf~l. The 5.02 mm
diam brass rod was taken as an example.
CONCLUSIONS AND DISCUSSIONS
The time-of-flight method and ultrasonic frequency analysis have been used to
measure the diameters and orientation of circular rods. Commercially available
equipment has been used. In the present experiment, both methods yield
the same information. However it is possible that in other cases, the two
methods can yield information which complement each other. It should be noted
that time measurement can be deduced from the rectified rf signal (Fig. 17).
When the signal is rectified, a lot of information is lost. For unrectified
rf signals frequency analysis can be used to find the bulk and surface properties
of the flaws.
Time and frequency are mutually complementary variables. The two parameters
can reinforce and supplement each other in terms of information each one produces.
The properties of a physical system can be described in terms of pairs
of mutually complementary variables or properties. Other examples of complementary
aspects are the position and linear momentum of a particle, the angular
orientation of a system and its angular momentum, and so on.
The time-of-flight method and ultrasonic frequency analysis have become important
research tools in characterizing flaws for the last ten years. The merger
of the two methods will become a powerful tool for nondestructive testing
in the next twenty years. And hopefully, Canada will play an important role
in their marriage.
ACKNOWLEDGEMENT
The author thanks Mr. M. Hafer for help with plotting the graphs.