Comparative holographic interferometry: A nondestructive inspection system for detection of flaws |
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Authors: | Pramod K Rastogi |
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Institution: | (1) Laboratory of Stress Analysis, Swiss Federal Institute of Technology, CH-1015 Lausanne, Switzerland |
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Abstract: | Comparative holographic interferometry addresses a key problem of nondestructive evaluation: comparison of the resistance
to strength in real time of two nominally identical specimens. After outlining the basis of comparative holography in flaw
detection, the present paper reports on some new and complementary developments in comparative holographic interferometry.
The proposed systems stand out by their ability to store the master displacement field in the interferometric setup. The integration
of the storage capacity in the instrument considerably augments its potential in nondestructive routine inspection tasks.
The visual display of the fringes contouring the difference in mechanical response is shown to improve considerably with the
addition of auxiliary phase difference satisfying certain conditions. Methods for the generation of corresponding fringes
are considered and their localization investigated in brief. Particular attention is devoted to the formation of the holographic
moiré fringes. The influence of system misalignment on the moiré fringe interpretation is examined. A potential application
of comparative holography to the quantitative evaluation of fatigue is described. Experimental evidence supporting the operational
feasibility of the technique along with the results obtained in application to flaw detection are finally presented. |
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