Does a Sum of Hyperelastic and Single-Integral Viscoelastic Terms Describe Nonlinear Mechanical Behavior of Elastomers?

An extensive set of linear and nonlinear mechanical experiments, including nonlinear stress-strain behavior, stress relaxation, and creep/recovery, have been carried out on lightly crosslinked styrene-butadiene rubber (23.5 wt% styrene) for a wide range of temperatures, extension rates and extension ratios. The linear viscoelastic response determined via tensile creep and dynamic shear experiments was time temperature superposed to obtain the relaxation spectrum. The nonlinear data set is used for validating a class of constitutive models consisting of an additive combination of a hyperelastic term and a single integral quasilinear viscoelastic term. For moderate deformations and temperatures corresponding to the ‘rubbery regime’ (i.e. T > T_g + 50 ⁰C), the model with the Doyle-Eriksen strain measure index of n = -0.5 quantitatively described all the features of the observed mechanical behavior. The dependence of the model parameters on temperature and crosslink density was also analyzed.