(1,N) spatial phase-shifting technique in digital speckle pattern interferometry and digital shearography for nondestructive evaluation

Digital speckle pattern interferometry (DSPI) and digital shearography (DS) are two independent useful whole-field noncontacting optical methods for nondestructive flaw detection and precision measurements. We describe a (1, N) spatial phase-shifting technique in DSPI and DS for nondestructive evaluation (NDE) of quasidynamic behavior of objects subject to slowly varying loads. The technique employs a double-aperture arrangement in front of the imaging system to introduce spatial carrier fringes within the speckle. The prominent advantage of the proposed technique is it requires only a single frame prior to the object deformation and a number N of frames during the object deformation for NDE. Quantitative measurement of a defect and its behavior in loading conditions are studied by recording spatially phase shifted frames before and during thermal stressing of the object for continuous deformation variation with time. Experimental results on a polymethyl methacrylate (PMMA) panel using an error-compensating five-phase-step algorithm for quantitative NDE using both DSPI and DS are demonstrated. © 2007 Society of Photo-Optical Instrumentation Engineers.