Viscoelastic properties of a gum vulcanizate at large static deformations

Abstract

AbstractThe loss tangent corresponding to small sinusoidal oscillations superposed on a large static deformation is found to decrease with increasing static deformation ratio for a natural rubber gum vulcanizate. Further, the response functions of the stress–relaxation and the incremental stress–relaxation vs. time and the storage modulus vs. frequency are found not to be separable functions of time and strain effects. These findings are shown to indicate that the elastic contribution to the viscoelastic response of this elastomer increases more rapidly with the static deformation than does the relaxation contribution. The loss modulus, however, is found to be a separable function of time and strain effects. Hence, only one relaxation function is needed in the viscoelastic constitutive theory applied to this elastomer. The finite linear viscoelasticity theory as modified by Morman has a form which can account for these results. Predictions of the incremental stress–relaxation function from dynamic data are within 1% of experimental values.