Development of a Breadboard Instrument for the Ultrasonic Measurement of Stress

The measurement of stress is a generic problem which constantly occurs in nondestructive evaluation applications. X-ray diffraction provides the most successful approach, but suffers from the limitation that only a very near surface layer is sensed. Ultrasonic measurements, based on the stress dependence of the wave speed, have the capability of sampling bulk material. However, they suffer from some practical problems, including degradations in accuracy due to competing sources of wave speed shifts and difficulties of making measurements in complex geometries. The former problem has, in principle, been overcome by an approach recently developed as discussed below