The Behavior of Rubberlike Materials in Moderately Large Deformations

Abstract

Introduction of the nonlinear n‐measure of strain into the Boltzmann superposition integral allows accurate prediction of the viscoelastic behavior of soft (rubberlike) materials if the relaxation spectrum remains unchanged during the deformation. This condition is generally satisfied in moderately large deformations (typically about 150% strain in simple tension). Apart from the strain parameter n, only the small deformation relaxation modulus is required by the theory. Both pieces of information are obtained from the response to a step of strain in simple tension. Data obtained in the temperature range −40 to 23°C on a dicumyl‐peroxide‐cured styrene‐butadiene rubber (SBR), lightly plasticized with silicone oil (1.5%), gave excellent agreement with the theory in various strain histories including sensitive tests in which small deformations were superposed on a finite stretch. Published data were used to corroborate the theory further. The temperature dependence of n was obtained from the authors' data on SBR and from published data on Viton A‐HV. The dependence of n on crosslink density and swelling ratio was also examined.