Frequency response of a photo-viscoelastic material

An electromagnetic shaker was used to apply sinusoidal axial displacements to one end of a column of Hysol 4364, an optically sensitive urethane rubber compound of low modulus. The nondriven end of the column was free. The column was excited at frequencies of 81, 244, 424, 603 and 783 cps, corresponding to the first five resonant frequencies of longitudinal vibration. Measurements were made of displacement mode shapes and phase angles, and birefringence modes and phase angles. Measured displacement modes and phase angles were shown to agree with predictions based on a linear one-dimensional viscoelastic theory. The measurements and theory were used to determine the mechanical and optical frequency response of the material for the experimental frequencies. This consisted of determining:

1. 1.
   the dynamic elastic modulus,