Application of optical shape measurement for the nondestructive evaluationof complex objects

Holographic interferometry makes it possible to measure high-precision disp lacement data in the range of the wavelength of the laser light used. Howev er, for a precise determination of 3-D displacement vectors of complex obje cts the 3-D shape of the surface is required. Modern optical shape measurem ent technologies enable a very effective approach to finding the Cartesian coordinates of complex surfaces, These data are used to calculate the spati ally variable sensitivity vectors for the displacement measurement, The sha pe data are measured with white-light fringe projection using a multiwavele ngth technique to acquire absolute phase values. To make the shape data ava ilable for 3-D displacement measurement they have to be transferred into a reference coordinate system of the interferometric setup, where the deforma tion of the object caused by operational load is measured precisely. For th is purpose a registration procedure is applied. For engineering application s it is useful to make the data available for computer-aided engineering sy stems, The object surface has to be approximated analytically from the meas ured point cloud to generate a surface mesh. The displacement vectors can b e assigned to the nodes of this surface mesh for visualization of the defor mation 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 f urther numerical investigations. The described procedure is demonstrated on an automotive component. Thus more accurate and effective measurement tech niques make it possible to bring experimental and numerical displacement an alysis closer together. (C) 2000 Society of Photo-Optical Instrumentation E ngineers. [S0091-3286(00)02801-4].