Experimental Investigation and Constitutive Modeling of the Large Deformation Mechanical Behavior of Filled Elastomers

The stress-strain response of vulcanized carbon black filled rubber during loading/unloading has been studied as a function of temperature, filler content and filler properties such as structure and particle size. At low temperature, R, which is the ratio of the instantaneous modulus on unloading to that during loading at the beginning of unloading, increases significantly. Lowering temperature also lead to an increase in the hysterisis observed during the first loading/unloading cycle. Cyclic loading/unloading and Mullins experiments have been performed on materials containing 5 phr to 50 phr of carbon black. The filler structures range from DBPA numbers of 40 ml/100g to 620 ml/100g and their particle sizes from 25 nm to 250 nm. At a given filler content, structure is found to have a very small effect on R. A dramatic effect on R is observed for fillers having the same structure but varying particle sizes, where R increases with decrease in particle size. The amount of filler affects the hysterisis as well as R, and a distinct increase in R is observed at filler content in the range of percolation threshold. Stress relaxation experiments were used to characterize the mobility of the material at various points in the deformation history. The dependence of relaxation times on stress-strain, temperature are filler properties are presented.