Fracture behavior of filled elastomers: How do strain induced softening and its thermally induced recovery affect the fracture toughness?

In this work, two peroxide-crosslinked hydrogenated nitrile butadiene rubbers for hydrogen system applications have been studied. Both elastomers are carbon black filled and one of these also contains a small quantity of polyamide. At the beginning, a preliminary analysis of the strain rate effect on the mechanical response and of the strain-induced softening is reported. Moreover, the dissipated and stored energies involved in the deformation of both the virgin and softened materials are evaluated. The thermally induced recovery of the strain-softening is analyzed by performing two treatments. In the second part of the work, the fracture behaviour of the two materials is compared and the effects of softening and its thermally induced recovery on fracture behavior are evaluated on one of the two compounds. The main finding is that softened material has a lower fracture toughness compared to the virgin material, while toughness of the thermally treated softened material is comparable to that of the virgin one.