<title>Vibration analysis and nondestructive testing by digital shearography</title>

Abstract

TV-Holography has been applied for NDT and vibration measurement of engineering components and structures in the last few years. The main limitation of the technique arises from its sensitivity against rigid body movement and the rapid increases in fringes depending on the displacement, which makes it difficult to interpret the fringe pattern. An approach which is insensitive against rigid body motion and provides a wider and more controllable sensitivity range is performed by digital shearography. Instead of measuring displacement, digital shearography measures directly displacement derivatives. With the support of the digital image processing and phase shifting techniques, digital shearography allows the shearogram to be observed in real time and to be evaluated quantitatively and automatically. Thus, this technique is suited well for nondestructive testing and strain measurement. For the vibration measurement, shearogram depicts the full-field information of dynamic deformation derivatives. By applying the phase shifting technique in conjunction with the laser light modulator, the shearogram can be evaluated quantitatively. Thus, the dynamic deformation field (w) and dynamic flexural strain field can be also obtained by integrating or differentiating the phase map of shearogram. This paper presents the principle of the method. Its applications in nondestructive testing, strain measurement and dynamic analysis are shown.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.