The tearing test as a means for estimating the ultimate properties of rubber

SBR, unfilled and filled with glass beads, MT, and HAF carbon blacks, was tested for tearing energy, rupture values in simple tension, tear diameter, and strain distribution at four rates and seven temperatures. The energy density to failure at the tear zone Wt was obtained from the tearing energy τ and the natural tear diameter d using a modified Rivlin and Thomas relationship Wt ≈ τ/d. This was then compared with the nominal energy density at rupture in simple tension W. It is shown that always Wt > W (sometimes Wt/W = 10), that Wt is subject to a smaller statistical scatter than W, and that Wt is more amenable to the WLF type of superposition than W. It is concluded that Wt and not W is the strength-determining property. Where W data permitted superposition, it is followed the WLF equation. It is presumed that so would Wt. τ, although more superposable than W, showed a bigger shift factor than that dictated by WLF, the difference being the result of the temperature dependence of the diameter. The reinforcing effects of the various fillers are also discussed. It is shown that the carbon black fillers increase both Wt and d. Glass beads have only a small effect on d and none on Wt.