A new application of laser vibrometric wave field propagation measurements: Grain structure visualization

Laser vibrometry is used routinely to visualize the process of ultrasonic wave propagation on solid sample surfaces. It was discovered recently, that the material microstructure of metals can be obtained from a sequence of high resolution laser vibrometric snapshots of the wave field. This information is usually hidden by the larger amplitudes of the propagating wave, but can be extracted by appropriate evaluation of the measured data. We call this method Grazing Incidence Ultrasound Microscopy (GIUM). Applying the method to an austenitic weld, it is proved that the resulting grain structure does not depend on the incident angle of the ultrasonic wave. This confirms the interpretation of the images as material structures and also our explanation of the contrast mechanism.