Mechanical characterization of carbon black filled NR/BR compounds from small strains up to fracture

In this research filled natural rubber (NR), butadiene rubber (BR) and a 50/50 NR/BR blend, having different carbon black (CB) contents, were studied. Dynamic-mechanical characterization, tensile tests were carried out. Fracture tests using notched pure shear test specimens were also performed. The fracture mechanics approach was applied so as to determine J-integral at crack onset. Fracture phenomenology was analysed from video-recordings of the tests. It was observed that ‘sideways’ cracks propagating at the crack tip in the loading direction before the onset of a ‘forward’ crack propagating along the notch plane and which are responsible for high toughness values develop for rubber contents above 35 phr of rubber for NR and the NR/BR blend, while for BR a larger carbon black content is required.