Ultrasonic testing is used to locate defects in components and determine the size of the defects. In castings for example these can include inhomogeneities, shrinkage cavities and pores. The process is based on the phenomenon that sound is partly or entirely reflected by defects as it passes through the workpiece. This can produce an echo, or the sound is weakened by the shadow effect of the defect. The sound velocity of the object being detected has to be different from that of the base material.
The pulse-echo method is the most common (Figure 1). Here the probe that is used works simultaneously as the emitter and receiver. The ultrasonic impulse is emitted by the probe, reflected by the defect and received again by the probe. Conclusions are drawn about the size of the defect based on the height of the echo amplitude.