FATIGUE-CRACK GROWTH OF DOUBLE-NETWORKED NATURAL-RUBBER

Tensile stress-strain behaviour, hysteresis and crack propagation resi stance were investigated for various double-networked natural rubbers, prepared using a two-step crosslinking technique. Partially cured rub ber 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 tensi le modulus, tensile strength at break, and strain energy density in th e direction parallel to the cure stretching direction. The resistance to crack propagation across the residual strain direction was also gre atly enhanced. Moreover, no significant deterioration in crack resista nce was observed, even in the direction parallel to the residual strai n direction. The morphology of the torn surfaces of the double network s generally resembled that of the single networks, except the cross-ha tched pattern was somewhat developed and slanted to the residual strai n direction. (C) 1998 Elsevier Science Ltd. All rights reserved.