Relaxation time of a polymer glass stretched at very large strains

The polymer relaxation dynamic of a sample, stretched up to the stress hardening regime, is measured, at room temperature, as a function of the strain $\lambda$ for a wide range of the strain rate $\dot\gamma$, by an original dielectric spectroscopy set up. The mechanical stress modies the shape of the dielectric spectra mainly because it affects the dominant polymer relaxation time $\tau$, which depends on $\lambda$ and is a decreasing function of $\dot\gamma$. The fastest dynamics is not reached at yield but in the softening regime. The dynamics slows down during the hardening, with a progressive increase of $\tau$. A small inuence of $\dot\gamma$ and $\lambda$ on the dielectric strength cannot be excluded.