Universal ultrasonic goniometer for Rayleigh and surface skimming longitudinal wave dispersion measurements

Abstract

There are several approaches for determining the Rayleigh wave dispersion of surface treated materials. Most of them are based either on ultrasonic probes in contact technique or on laser excitation or detection of ultrasound. Disadvantages of these methods for in-service use are coupling problems (contact methods) and very high device costs (laser based methods). The paper presents an immersion technique trying to avoid the disadvantages of the previous approaches for practical use. The High precision Ultrasound Goniometer (HUGO) allows to vary both: the sound beam angles and the distance between the excitation and detection sound beams. Thus, the Rayleigh wave velocity and its dispersion can be determined by two independent methods: by the drop in the reflexion coefficient at the Rayleigh angle and by change in travel time for a given change in travel distance. The dispersion can also be determined for surface skimming longitudinal waves. The application for stress determination in surface treated aero-engine materials is discussed.