Reference Stress and Temperature for Nonisothermal Creep of Structures

The relationship between the reference stress concept and the nesting surfaces of Calladine and Drucker is examined and the implications for nonisothermal creep are discussed. A method for evaluating a reference stress and temperature is described, which it is argued is more rigorous than methods previously proposed.

Isothermal and Nonisothermal Creep of Lightly Crosslinked cis-1,4-Polybutadiene

A nonisothermal creep experiment has been analyzed to ascertain its suitability for determining the temperature dependence of low-activation-energy viscoelastic processes in elastomers far above Tg. The nonisothermal method was employed to determine the activation energy for creep near 35°C in a lightly crosslinkedcis-1,4-polybutadiene elastomer at small strains within the linear viscoelastic region and at various large deformations up to rupture. The observed activation energy was essentially independent of the level of strain, and the value of ΔHa (∼ 11 kcal/mol) determined via the nonisothermal creep method was in good agreement with the result (∼12 kcal/mol) obtained via time-temperature superposition of isothermal linear viscoelastic creep data. The nonisothermal data allowed for an estimate of the volume of the “flow unit” associated with the controlling viscoelastic creep mechanism, attributed here to slippage of entanglements within lightly crosslinked network.