The viscoelastic behavior of rubber in extension

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Abstract
Measurements of the (complex) dynamic Young's modulus of natural rubber have been made by a wave propagation technique on filaments held at mean extensions up to 600%. It is shown that the real and imaginary parts vary with strain in the same way as the equilibrium modulus obtained from “static” stress‐strain measurements, the behavior up to about 140% extension being derivable from a Mooney‐type stored‐energy function and at higher strains being dominated increasingly by the effects of finite extensibility in the network. The viscoelastic behavior in the region up to 140% strain may then be characterized by four parameters, of which one vanishes and another is constant for the rubber studied. It is shown how these parameters may be used to derive the strain‐dependence of the damping or loss‐factor (tan δ) in this region. The effect of increasing extension upon the relaxation spectra, over the range 100 to 600% extension, is to displace the whole spectrum progressively to longer times.