A single exposure reflection moiré interferometric technique for complete curvature analysis of bent plates

Most known moiré methods need to be repeated three times for getting curvature information in three different in plane directions, for the complete analysis. To overcome this difficulty, a new single exposure moiré interferometric technique is proposed that maps completely partial curvature contours in three different directions of laterally loaded specularly reflecting plate models. Converging HeNe laser light is diffracted by a lens plane cross grating. The 00, + 10 and the +01 diffraction orders are permitted through the Fourier transform (FT) plane and collimated to illuminate the plate model. The reflected light from the loaded model records the model with the inherent deformed interferometric cross grating superimposed on it. A posteriori Fourier filtering of the developed recording (moirégram) gives partial curvature contours pertaining to three different in plane directions from which the principal curvatures and the principal directions are obtained. Also, this technique, being a single exposure technique, has the potential for complete bending analysis of plates subjected to lateral impact loading and destructive loading applications, where the repeatability of the event may not be possible.     

A selective diffraction order based lens plane grating shearing interferometer for the study of bent plates

A simple, elegant and flexible technique for the determination of partial slope, curvature and twist contours of bent plates is proposed. A single frequency cross-grating (SFCG) placed just ahead of the field lens collects the light reflected by the smooth plate model. From the resultant diffraction pattern formed at the Fourier transform (FT) plane, based on the desired contours, only a few orders are permitted selectively to pass through to the recording plane. This manner of real time in-situ filtering of the diffraction orders is new. While slope contours require double exposures, curvature and twist contours are obtained from single exposures.     

The measurement of deformation of a bridge by moiré photography and photogrammetry

Optical techniques offer advantages over mechanical methods for displacement measurement. A comparative study has been made between photogrammetry and moiré photography during a destructive test applied to a bridge. The first provided accurate values for point displacements whereas the second revealed the whole field movements and indicated the region of eventual failure.