Stress-softening effect of SBR/nanocomposites by a phenomenological Gent-Zener viscoelastic model

An experimental study of a tensile loading-unloading procedure, as well as multi-cyclic response in a strain-controlled program of a Styrene-Butadiene (SBR) elastomer reinforced with four different weight fractions of carbon nanotubes (CNTs) has been performed. The Mullins effect features, namely hysteresis, damage and residual strain, exhibited by the SBR/nanocomposites were analyzed by a modified Gent-Zener rheological model, and a damage function. Especially for the multi-cyclic stress-strain curves, phenomenological equation of the model parameters evolution with strain were also introduced. The same loading procedure was applied in pre-stressed materials, revealing a different stress-strain response due to strain prehistory. The model has been proven to accurately capture the loading-unloading behavior, the residual strain, hysteresis loops as well as the multi-cyclic behavior of the SBR/CNT nanocomposites.