Abstract:
Measurement of surface displacements, due to elastic wave propagation, has traditionally been studied using single-point measurement techniques, such as ultrasonic transducers or interferometers. Full-field methods, excluding scanning techniques, are uncommon, especially outside of research environments---examples include optical holography and Schlieren photography. Laser-modulated phase-stepping digital shearography is a full-field, common-path, interferometric method which can be used to quickly visualize ultrasonic wave fields in industrial settings. A shearography system will be described that provides not only whole-field images of the ultrasonic waves, but quantitative displacement data within these fields. Images of the displacement fields produced by Lamb and quasi-Rayleigh waves were recorded as they traveled along surfaces of several plates and bars. Evidence of wave reflections, multimode propagation, and flaw interaction will be discussed. [Work supported by the Penn State University Applied Research Lab and the Navy Manufacturing Science and Technology LINC Program.]