Measurement of surface displacements due to ultrasonic wave propagation in elastic solids has traditionally been studied using single-point measurement techniques such as ultrasonic transducers or interferometers. Full-field methods, excluding scanning techniques, are uncommon; examples include holographic interferometry and Schlieren imaging. In many cases, these techniques have been used to yield qualitative results due to inherent difficulties in processing the data. Laser-modulated phase-stepping digital shearography is a full-field, common-path, interferometric method which can be used to quickly visualize ultrasonic wave fields. A shearography system will be described that provides not only whole-field images of ultrasonic waves, but quantitative displacement data within these fields. Images are shown of propagating plate and bar waves, and mathematics relating the calculated optical phase to the ultrasonic wave parameters are presented.
Shearography has been shown to be a powerful tool for on-site non-destructive evaluation applications, especially in aircraft component inspections. However, current commercially available portable shearography systems are qualitative, low signal to noise ratio, and low flaw detection sensitivity. In this paper, we will introduce a real-time, high-resolution, portable, phase-stepping shearography system developed at the Applied Research Lab of The Pennsylvania State University. The system can fit into a wheeled cart and run at a speed of 1-2 inspections/sec for a 7"x5" field of view. It provides full quantitative analysis ability and substantially improves flaw detection sensitivity. The applicability and portability of the system to on-site field NDE applications have been tested by a successful field demonstration conducted at a naval air station.
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