Simple method for direct determination of bending strains by use of digital holography

A computer-based technique is described for direct determination of bending strains in beam and plate structures. First a displacement-related phase-c hange map is constructed by digital holography and computer-vision techniqu es. Subsequently the computer generates an exact replica of the phase-chang e map, then overlays the two identical maps and, finally, rotates one of th e maps through 180 degrees relative to the other in their planes about a po int of interest. The local curvatures and the local twist of the bent surfa ce at the point of interest are determined from the conic sections that are reconstructed from the algebraic sum of the phase changes at the vicinity of this point, thus permitting further calculation for determination of the local bending strains. When the need arises, bending moments and stresses may be determined concurrently. As the optical setup is simple, with comput er-based data acquisition and processing, the entire system is user friendl y, and rapid measurement is achieved. (C) 2001 Optical Society of America.