Fatigue crack growth of double-networked natural rubber

Tensile stress-strain behaviour, hysteresis and crack propagation resistance were investigated for various double-networked natural rubbers, prepared using a two-step crosslinking technique. Partially cured rubber is strained and then further crosslinked. They were compared with those of a conventional network (single network). The double-networked natural rubbers were found to show a significant improvement in tensile modulus, tensile strength at break, and strain energy density in the direction parallel to the cure stretching direction. The resistance to crack propagation across the residual strain direction was also greatly enhanced. Moreover, no significant deterioration in crack resistance was observed, even in the direction parallel to the residual strain direction. The morphology of the torn surfaces of the double networks generally resembled that of the single networks, except the cross-hatched pattern was somewhat developed and slanted to the residual strain direction.