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ABSTRACTThe goal of the present work is to study and understand the fracture of NR vulcanized with different levels of DCP. The tensile behavior of gum natural rubber (NR) vulcanizates cured with dicumyl peroxide (DCP) was studied. The effect of crosslink density on tensile strength, tear strength, strain, 100% modulus, and the critical cut size was determined. Dumbbell specimens cured with different level of DCP with (normal tensile test) and without (tear test) edge cuts, were strained continuously to rupture. Tensile strengths refer to breaking stress for uncut specimens, while tear strengths are for specimens with precuts.DCP-cured gum natural rubber vulcanizates with different crosslink densities (10 different amounts of curatives were added to the masterbatch) were prepared. Normal tensile and tear tests were determined. As with sulfur cured gums, the tensile strength of DCP cured gum natural rubber passes through a maximum with increased crosslink density. Breaking strain and 100% modulus show a linear relationship with the crosslink density. However, the results obtained from tear tests were quite different from those with the sulfur curing system. Log-log plots of stress at break versus cut size were made for all the vulcanizates. An unstable region is observed for the lightly and moderately crosslinked specimens; results are scattered because some of the specimens undergo bulk crystallization while others with the same cut sizes do not. Values of critical cut sizes as well as the widths of unstable regions also showed a dependence on the crosslink density. No drop in strength could be observed in highly crosslinked specimens due to the lack of crystallization. This is like the results with sulfur curing.