Impact of strain-induced softening on the fracture of a carbon-black filled styrene butadiene rubber

The effect of strain-softening due to Mullins effect on the propagation of a crack is experimentally investigated by applying various pre-stretches to a non-crystallizing carbon-black filled elastomer, followed by crack propagation tests. Pure shear tests carried at constant crosshead speed on notched samples, are chosen to characterize crack growth properties. The stretches at which critical propagation is observed are measured, allowing calculation of the critical energy release rate. For a given geometry, the values of critical stretches are found to be always identical to the virgin material`s within experimental accuracy, independantly from the pre-stretch. However the calculated energy release rates are found to decrease with increasing strainsoftening.