Electronic Speckle Pattern Interferometry (ESPI) and Digital Shearography have been shown to be of great value for the Non-destructive Evaluation of the integrity of materials and manufactured components. The NDT Laboratory in the Department of Mechanical Engineering at the University of Cape Town has an active research group focused on the research, development and the various applications of ESPI and Digital Shearography. This work culminated in the development of portable prototype inspection systems based on Digital Shearography and ESPI. The current portable systems, mentioned above, generate intensity based fringe patterns. By introducing a known phase shift into the speckle pattern during the image recording process, displacement fringe patterns, based on the change in phase of the laser light, can be generated. These fringe patterns differ in that they reveal distinct 2π discontinuities and are thus suited for automated inspection techniques and are also suited for object surface displacement mapping techniques. This paper reports on the progress made in developing phase stepped ESPI and Digital Shearography. The techniques are described and applied to selected flawed composite samples. The findings are presented and comparisons are drawn between the results obtained from both phase stepping and conventional intensity based optical interference techniques. The possibility of applying phase stepping techniques to portable inspection systems is also discussed.
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