Ultimate Tensile Properties of Elastomers. IV. Dependence of the Failure Envelope, Maximum Extensibility, and Equilibrium Stress-Strain Curve on Network Characteristics

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Abstract
Uniaxial tensile data from tests at different rates of extension over a wide temperature range are considered for butyl, silicone, Viton B, SBR, and natural rubber vulcanizates (series A) and for six Viton A‐HV vulcanizates (series B) of differing crosslink densities. For series A and for A‐6 in series B, equilibrium stress‐strain data were obtained at large deformations by an indirect method. The ultimate tensile properties of all vulcanizates were previously characterized by a time‐ and temperature‐independent failure envelope. The failure envelope's maximum extension ratio, (λ b )max, is shown to be equal to or less than (λ∞)max, the maximum extension ratio (hypothetical) in the absence of rupture and also the maximum extension ratio of network models. Failure and equilibrium data for series A vulcanizates are represented by a specific function of the equilibrium modulus and the maximum extensibility; except for SBR and possibly Viton B, equilibrium and failure data are sensibly identical; thus, (λ b ) max ≅(λ ∞ ) max . For series B vulcanizates, qualitative considerations indicate that (λ∞)max/(λ b )max is greater than unity and possibly dependent on crosslink density. Consideration of network models suggests that (λ∞)max should be directly proportional to Mc ½ and inversely proportional to (〈r 2〉0/M)½. For series A, no correlation between (λ b )max and (〈r 2〉0/M)½ was found. For series B, it is shown that (λ b ) max ∝M c β , where β is a constant in the neighborhood of 0.7. For all vulcanizates, (σ b ) max ≅10 4 (λ b ) max −1 , where (σ b )max is the stress in psi (based on the undeformed cross section) at (λ b )max.

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