Study the Hyper-Viscoelastic and Stress Softening Behaviors of Various SBR/CB Filled Compounds Using a Triple Model

Hypothesis:

 A three-component material model based on the combination of three hyper-viscoelastic equations,eight-chain constitutive equation, Bergstrom-Boyce relation and Ogden-Roxburgh stress softening model (Mullins effect)  was selected to study the mechanical behavior of various SBR/CB (carbon black) filled rubber compounds.

Three rubber compounds based on E-SBR were prepared using different carbon black contents (20, 40 and 60 phr) and cured into rubber sheets. The rubber test specimens (ASTM D412 C) were then cut and underwent cyclic tensile tests at two extension rates of 500 and 100 mm/min. In order to show the stress softening behavior, three cycles were selected in a way that the maximum stretch at each cycle was increased consecutively. The volumetric tests were also carried out to determine the bulk modulus of the samples. The stress-strain data were calibrated using MCalibration software in which three different optimization algorithms were utilized to compute the parameters of the models.  

Very good agreements were found between experimentally measured and predicted stress-strain data for low and medium CB filled compounds. However, for highly filled compounds there were some discrepancies at higher extensions, which may be due to the formation of a strong filler network and percolation threshold. This indicates that we may need another modeling component to be incorporated into main model for the description of the mechanical behavior of the filler-filler network itself. Moreover, it is found that there is good correlation between variation of the model parameters and filler content.