Abstract
Multiple-exposure holographic interferometry is combined with photoelasticity to obtain complete, direct, full-field determinations of dynamic stress distributions in two-dimensional problems. The method is independent of assumptions associated with theories of wave propagation. Three independent measurements are used: isochromatics, isoclinics, and isopachics (families of interference fringes that are measures of the difference, directions, and sum, respectively, of the principal stresses at each point). Isochromatics and isoclinics are obtained by synchronizing the (repeatable) loading of a model with a short-duration flash through a continuously variable delay circuit. Interference fringes observed when elements of a polariscope are placed on each side of the photoelastic model are photographed with a still camera. Isopachics are obtained with a form of holographic interferometer that has particular advantages for static and dynamic optical stress analysis (large field of view, automatic elimination of the effect of rigid-body motions of model). The method is applied to the study of: (1) flexural waves in a bar; (2) transverse waves in a prestressed bar; and (3) flow induced in a surrounding, birefringent fluid by flexural waves in a bar. The results are extended by the application of scaling laws to predict stresses in vibrating steel and nylon cables.
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