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

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, (λb)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, (λb)max≅(λ∞)max. For series B vulcanizates, qualitative considerations indicate that (λ∞)max/(λb)max is greater than unity and possibly dependent on crosslink density. Consideration of network models suggests that (λ∞)max should be directly proportional to Mc½ and inversely proportional to (〈r2〉0/M)½. For series A, no correlation between (λb)max and (〈r2〉0/M)½ was found. For series B, it is shown that (λb)max∝Mcβ, where β is a constant in the neighborhood of 0.7. For all vulcanizates, (σb)max≅104(λb)max−1, where (σb)max is the stress in psi (based on the undeformed cross section) at (λb)max.