Strain energy function of styrene butadiene rubber and the effect of temperature

Abstract

AbstractBiaxial and uniaxial tensile stress relaxation tests were made on square sheet specimens of styrene butadiene rubber (SBR), mounted in a universal biaxial tester within a temperature‐controlled box, with the object of studying the effect of temperature on the strain energy function. The stress relaxation responses, usually for times up to 10 min, were obtained for various degrees of biaxiality, various extension ratios, and various temperatures within the limits of +25 to −45°C. The results indicated that if the Valanis–Landel representation of the strain energy function \documentclass{article}\pagestyle{empty}\begin{document}$ W = \sum\nolimits_{i = 1}^3 {w\left( {\lambda _i } \right)} $\end{document} is adopted, then time and strain are factorizable over the indicated temperature range, with time and temperature being related in the usual fashion. That is, changing the temperature does not affect the form of w(λi) but only that of G(t/αT), the temperature‐dependent relaxation modulus, aT being the regular Williams–Landel–Ferry (WLF) shift factor. The results verify the Valanis–Landel theory for various combinations of biaxiality