Multiwavelength shearography for evaluation of in-plane strain distributions

摘要

Abstract: We report on a novel set-up using image shearing speckle pattern interferometry for the determination of 2D strain distributions of an object surface. This system is based on simultaneous illumination of the object with three diode lasers that emit at different wavelengths between 810 nm and 850 nm. Their speckle images are separated within the shearographic set-up, consisting of a variable shear element, a special color separation optics and 3 b/w CCD cameras, in such a way that each camera records the speckle image corresponding to one laser source only. The shearographic camera in combination with the appropriate illumination geometry allowed us to isolate all six displacement derivatives from phase stepped fringe patterns. The good suitability and accuracy of the system for the determinant of 2D strain distributions are demonstrated on the basis of shearographic measurements during tensile and comparison with strain gage measurements. !7