Shrinking of photo-elastic sensitive polymers during fixation of isochromatic pattern using Gamma-radiation

To fix the fringe pattern in a deformed model consisting of photo-elastic sensitive polymer using gamma radiation it is necessary that at the beginning of the fixation procedure a certain amount of polymerisation potential is left as shown in [1, 2]. However, during the fixation process an accompanying shrinking of the used material occurs. In this paper it is shown that for an isotropic polymer model in a gamma chamber of uniformly distributed intensity of the radiation this shrinking does not lead to anisotropic behaviour. That means that the material remains mechanically as well as optically isotropic. Calculating the stress-optical coefficients at the loading step as well as at the unloading step during a calibration experiment using a loaded disk a certain difference occurs.