TIME-DEPENDENT MECHANICAL BEHAVIOR OF CARBON BLACK FILLED ELASTOMERS

An extensive set of time-dependent mechanical data was obtained for several filled SBR elastomers, including Mullins experiments, cyclic loading experiments, and stress relaxation. These comprehensive data enable critical evaluation of three classes of constitutive models. Viscoelastic models can naturally describe the hysteresis upon loading/reloading, but are unable to capture the large change in tangent modulus between the initial loading and the modulus just as the specimen is being unloaded. Elastic-damage models can capture the large change in tangent modulus just prior versus subsequent to unloading of a virgin sample, but can only parameterize the hysteresis on cyclic loading and are unable to predict strain rate effects and stress relaxation. A viscoelastic-damage model can predict the large change in tangent modulus upon reversal of the strain, hysteresis, strain rate effects, and stress relaxation; however, viscoelastic-damage models are unable to simultaneously predict the modest amount of hysteresis observed in cyclic experiments and the large amount of stress relaxation observed after loading to large deformations. The analysis indicates that constitutive models that include different deformation mechanics than the traditional elastic, viscoelastic, and damage processes will be needed to describe the full range of mechanical behavior exhibited by carbon black filled elastomers.