Two photoviscoelasticity experiments using analog data reduction

A tensile analog may conveniently be used to determine the history of the principal-stress difference from the results of some photoviscoelastic model tests. With this method, the model test is run, and the fringe-order history at the point (s) of interest in the model is recorded. A tensile specimen of the same material is placed in a loading frame and loaded with a stress history which forces it through the fringe-order history observed in the model. This stress history is then the desired principal-stress-difference history occurring in the model. The stress history at points in two nonhomogeneous models was determined with a tensile analog. The uses and limitations of the analog technique are discussed.