The physical factors affecting the reliability of ultrasonic non-destructive testing a review of current research

The formation of a beam and the deflection of this relative to a boundary is being investigated to determine the reliability with which one can specify the radiation of stress waves in a solid. Ultimately it is hoped to produce an electronically scanned beam which will be free from transverse waves. Little information is available regarding the propagation of stress waves in metals and much of the literature gives conflicting results. Before the frequency of operation of an ultrasonic testing device can be decided, the metallurgical characteristics of the material should be related to the scattering and absorption which may be expected over a wide frequency range. The means for doing this are not available and an attempt is being made to provide them in a suitable form. Signal processing seems to play a very small part in ultrasonic testing. Nothing appears to have been attempted to increase the probability of detection of a defect when viewed against a background of spurious returns. The problem is made difficult when compared with radar or sonar since the medium is stationary, but means are available theoretically whereby the background due to a large number of small signal returns can be made to change relative to an echo from a larger discontinuity in a stationary medium. This is being investigated experimentally.