Abstract
A robust electronic shearography technique is described that is immune to ambinet noise. In this technique, additive speckle-interference images containing information about the same two states of deformation of a test object undergoing acoustic stressing are acquired in each video frame. When a spatially nonuniform phase modulation is introduced in every other frame during the video sequence (using a tilting mirror) and the additive interference images are subtracted sequentially using a real-time image processor, the self-interference component of sheared-speckle interference pattern is removed. The susceptibility of this method to environmental noise caused by induced thermal noise and low frequency vibration is demonstrated to be lower than that of conventional substractive shearography methods; fringe visibility and contrast are significantly improved as well. The ability of this technique to work in a turbulent environment is demonstrated, and application to detection of structural defects in adhesively bonded structures, a problem of interest in nondestructive evaluation of structures, is shown.
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References
Hung, Y.Y., “A Speckle-Shearing Interferometer,”Optics Comm.,11,732 (1974).
Sirohi, R.S., International Proceedings for Holography and Speckle Phenomena and their Industrial Applications, World Scientific Inc., 393 (1988).
Newman, J.W., “Shearographic Inspection of Aircraft Structure,” Mat. Eval., 1106 (1991).
Achenbach, J.D. andThompson, D.O., “Towards Quantitative Nondestructive Evaluation of Aging Aircraft,”Structural Integrity of Aging Airplanes, ed., S.N. Atluri, S.G. Sampath andP. Tong, Springer Verlag, Berlin (1991).
Bobo, S.N., “The Aging Aircraft Fleet—A Challenge for Nondestructive Inspection,”Review of Progress in Quantitative Nondestructive Evaluation,9B,ed. D.O. Thompson and D.E. Chimenti,2097,Plenum Press (1990).
Owner-Petersen, M., “Decorrelation and Fringe Visibility: on the Limiting Behavior of Various Electronic Speckle-pattern Correlation Interferometers,”J. Opt. Soc. of Amer. A,8 (7),1082 (1991).
Lokberg, O.J. andMalmo, J.T., “Long-distance Electronic Speckle Pattern Interferometry,”Opt. Eng.,27 (2),150 (1988).
Spooren, R., “Double-pulse subtraction TV holography,”Opt. Eng.,31 (5),1000 (1992).
Pouet, B.F., Chatters, T.C. and Krishnaswamy, S., “Synchronized Reference Updating Technique for Electronic Speckle Interferometry,” J. Nondestructive Testing (1992).
Chatters, T.C., Pouet, B.F. and Krishnaswamy, S., “Shearographic Interferometry with Synchronized Pressure Stressing,” Conf. Proc.: Review of Progress in Quantitative Nondestructive Evaluation, Plenum Press (1992).
Pouet, B.F. andKrishnaswamy, S., “Additive-subtractive Decorrelated Electronic Speckle Pattern Interferometry,”Opt. Eng.,32 (6),1360 (1993).
Creath, K. andSlettemoen, G.A., “Vibration Observation Techniques for Digital Speckle Pattern Interferometry,”J. Opt. Soc. Amer. A,2 (2),1629 (1985).
Jones, R. andWykes, C., Holography and Speckle Interferometry, Cambridge University Press, Cambridge (1989).
Slettemoen, G.A., “General Analysis Fringe Contrast in Electronic Speckle Pattern Interferometry,”Opt. Acta,26 (3),313 (1979).
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Chatters, T.C., Pouet, B.F. & Krishnaswamy, S. Additive-subtractive phase-modulated shearography with synchronized acoustic stressing. Experimental Mechanics 35, 159–165 (1995). https://doi.org/10.1007/BF02326475
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DOI: https://doi.org/10.1007/BF02326475