Application of optical shape measurement for the nondestructive evaluation of complex objects

Holographic interferometry makes it possible to measure high-precision displacement data in the range of the wavelength of the laser light used. However, for a precise determination of 3-D displacement vectors of complex objects the 3-D shape of the surface is required. Modern optical shape measurement technologies enable a very effective approach to finding the Cartesian coordinates of complex surfaces, These data are used to calculate the spatially variable sensitivity vectors for the displacement measurement, The shape data are measured with white-light fringe projection using a multiwavelength technique to acquire absolute phase values. To make the shape data available for 3-D displacement measurement they have to be transferred into a reference coordinate system of the interferometric setup, where the deformation of the object caused by operational load is measured precisely. For this purpose a registration procedure is applied. For engineering applications it is useful to make the data available for computer-aided engineering systems, The object surface has to be approximated analytically from the measured point cloud to generate a surface mesh. The displacement vectors can be assigned to the nodes of this surface mesh for visualization of the deformation of the object under test, They also can be compared with the results of finite-element calculations or can be used as boundary conditions for further numerical investigations. The described procedure is demonstrated on an automotive component. Thus more accurate and effective measurement techniques make it possible to bring experimental and numerical displacement analysis closer together. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02801-4].