TV-HOLOGRAPHY AND HOLOGRAPHIC-INTERFEROMETRY - INDUSTRIAL APPLICATIONS

A detailed vibration analysis is vital for industry. However, in parti cular in the automotive industry, one is interested in the acoustical field or in the determination of strain and stress. The acoustical fie ld can easily be measured by microphones or intensity microprobes; how ever, it is also important to understand by which vibration modes the noise is emanating. TV-Holography, also called electronic speckle inte rferometry (ESPI), and double or multipulse (three or four) holography are two famous techniques of holography (Marwitz, H., Praxis der Holo graphie, Expert Verlag, 1990). In speckle interferometry two images of the speckle field at different times are recorded directly with a CCD camera and then subtracted from each other by an image processing sys tem. The resulting interference fringes are available in real time. In double pulse holography a ruby laser is triggered such that the inter esting object vibration is recorded by two consecutive laser pulses. T he interference fringes can be evaluated at reconstruction time by the phase shift technique, if two reference beams are used. The multi-pul se method is very useful for the investigation of operational vibratio n modes or of transient processes like shock waves. The calculation of the acoustical field and frequency spectrum requires the knowledge of the contour for the generation of boundary elements. The contour data can be taken either from CAD or FEM data or by measurement with optic al 3D measurement systems. The acoustical field is calculated by solvi ng the Helmholtz integral. For experimental strain and stress analysis the 3D shape and the 3D displacement are also necessary. For acoustic al prediction the component of the displacement, which is perpendicula r to the surface, is determined. On the other hand, for strain/stress calculation the tangential components to the surface are used.