The nature of the nonlinear anelasticity of glassy polymers

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Abstract
Nonlinearity in stress‐strain behavior under conditions where the strain is completely recoverable is often observed in glassy amorphous polymers. In the present work a suggestion is made that the nonlinearity is often associated with a secondary (β) relaxation process. By means of a model calculation it is shown that the onset of stress saturation of the relaxed or equilibrium compliance associated with localized group motion is a reasonable explanation for the phenomenon. The effect of stress on relaxation times is predicted to have some contribution but to be less important than the effect on the relaxed compliance.