Digital Speckle Pattern Interferometry for Studying Surface Deformation and Fracture of Materials

Abstract

In this chapter, a two-stepTwo-step digital speckle pattern interferometry (DSPIDigital speckle pattern interferometry (DSPI)) method with an unknown phase shiftUnknown phase shift of a reference waveReference wave is described. The method implements the recording of two speckle fringe patterns (speckle interferogramsSpeckle interferogram (SI) (SIsSpeckle interferogram (SI))) before deformation of the studied surfaceSurface differing in an arbitrary phase shiftArbitrary phase shift between the reference wavesReference wave and two SIsSpeckle interferogram (SI) after the surface deformationSurface deformations differing in the same arbitrary phase shiftArbitrary phase shift. In this case, the phases of the two initial SIsSpeckle interferogram (SI) recorded before and after surface deformationSurface deformations coincide. As with the phase shifting interferometryPhase shifting interferometry (PSI) methods considered in Chap. 2 , the population Pearson correlation coefficientPopulation Pearson correlation coefficient (PPCC) is used to calculate the unknown phase shiftUnknown phase shift. Computer simulation and experimental verification of this method confirm its reliability to restore in-plane and out-of-plane surface displacementsSurface displacements. Beam and sheet metal specimens, as well as composite specimens containing various defects and damages were studied by using this method performed with the help of 2D and 3D speckle interferometersSpeckle interferometer. The displacement fieldsDisplacement field of the studied specimens were retrieved and the hidden defects were detected. The subtractive synchronized DSPIDigital speckle pattern interferometry (DSPI) method for detection of subsurface defectsSubsurface defect in laminated composites is also represented in this Chapter. Subsurface defectsSubsurface defect were detected using an optical-digital speckle interferometerOptical-digital speckle interferometer (ODSI) (ODSI) and ultrasonic excitationUltrasonic excitation (US excitation) of the studied specimen in the frequency range from 10 to 150 kHz. Experiments performed demonstrate the ability of the ODSIOptical-digital speckle interferometer (ODSI) to detect subsurface delaminations and disbonds in laminated composite panels.