Direct determination of second-order derivatives in plate bending using multiple-exposure shearography

Abstract

A technique, called multiple-exposure shearography, is presented in this paper for direct determination of second-order derivatives of displacements in a plate. The optical set-up is similar to that of conventional shearography. Four exposures of the illuminated test specimen on the same photographic film are made. The first exposure is made when the specimen is in its unloaded state, and the second after an incremental load is applied. The third exposure is made when the specimen is shifted slightly whilst it is still under load. Finally, the fourth exposure is made after the specimen is unloaded. The fringe pattern, reconstructed in the same way as in conventional shearography, is related to the second-order derivative of displacements. Hence, the curvatures and twist of the deflected surface are computed directly from the fringe orders. © 1994.