The Mechanical and Optical Characterization of Polyurethane with Application to Photoviscoelastic Analysis

Abstract

The main requirement for practical photo-viscoelastic analysis is optical and mechanical characterization of the material, which has a strong time and temperature dependence of mechanical and optical properties. It is assumed that polyurethane is a linear-photoviscoelastic material and the correspondence rule for mechanical behavior proposed by Alfrey⁽¹⁾ can be also applied to optical behavior. The birefringence and stress or strain were measured simultaneously under two conditions, one being constant strain rate and the other being constant load. From experimental data, the stress-strain and the stress, strain-birefringence relations were obtained and the coefficients on the Laplace transformed plane of time were calculated. Based on this calculation, a new method of approximation of Prony series was proposed. The result calculated using abovementioned technique from constant strain rate data is well corresponding to the directly calculated result from creep testing. Therefore, it is found very good to apply the theory of linear-photo-viscoelasticity to this material.