The Problem: To Analyze Surface Contours and Large Deformations

The K100/PJM optical head using the HoloFringe300 interferometry program provides a projected fringe moiré interferometer that can contour objects and measure large-scale deformations. Fringes are projected onto the object at an angle to the line of observation. The changes in location of the fringes measure the out-of-plane deformation of the object. The projected fringes do not appear in the output image because of the phase-step imaging technique employed and the processing performed by the interferometry program. Unlike holography, shearography and speckle correlation, projected fringe moiré can compare different object surfaces, or compare surfaces to a stored analytical reference pattern. Phase imaging and phase unwrapping can give sub-fringe resolution in the order of 10^-4 of the object width.

5b

5a

5c

Figure 5. Expansion of Cardboard due to moisture. A sheet of thin cardboard was moistened on its back with a drop of water and compared to its profile before the wetting occurred. The fringe projection angle was calibrated to 45^o and the fringe density was calibrated to 100 fringes across the horizontal image. Fig. 5a shows the wrapped phase fringes, displayed in real-time, of the deformation. Fig. 5b shows the fringe locus function obtained by unwrapping the fringes of 5a. Fig. 5c shows a 3D plot of the deformation.