Many polymeric meterials such as rubbers and plastics show strong dependencies on strain rate and temperature, optically as well as mechanically. Therefore, it is difficult, in general, to perform the complete analysis of mechanical and optical behaviors of these materials mathematically. In this study, a method was proposed on the optical determination of strain energy stored in a linear viscoelastic material, based on the fact that the optical properties may be represented by such a

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... -dashpot model, as the generalized Maxwell or Voigt model, in the same way as the mechanical properties. Then, the experimental strain energy analysis of polyurethane rubber under uniaxial tension was carried out by the use of both mechanical and optical coefficients. The results obtained from both experiments agreed qualitatively as well as quantitatively. Consequently, it is concluded that the optical method would be useful for the experimental determination of strain energy in the viscoelastic materials.