Use of phased array probes for detecting stress corrosion cracking

The angular spectrum of ultrasonic probes has to be varried in order to adapt the sound fields to azimuthally or horizontally oblique positions of cracks. This is most easily achieved by means of phased away probes. The task of the project was to establish a phased away of probes suitable to solving the problem defined. The sound fields can be focussed through simultaneous lens deflection, which improves the signal-to-noise ratio. Experiments for optimizing the side lobe suppression have been made in order to allow variation at three points if maximum membrane dimensions are derived from the possible delay time and the suitable growing angle: (1) Element size distribution over the membrane; (2) amplitude weighting for edge elements; (3) delay time modulation for the edge elements. Data acquisition and recording (amplitude, detection time) has been automized, and the minicomputer also controlled the swinging of the sonic beams. (orig./HP)