Plastics response to extreme stretching

By coupling a tensile machine and an in situ dielectric measurement, physicists from Lyon (ENS de Lyon Physicis Laboratory and MATEIS) have made a breakthrough in understanding the molecular reorganizations that allow a polymer film to stretch. The results of this study are published in the journal Macromolecules . We study by dielectric spectroscopy the molecular dynamics of relaxation processes during plastic flow of glassy polymers up to the strain hardening regime for three different protocols of deformation. The measured dielectric spectra cover 4 decades in frequencies and allow us to measure the evolution as a function of the applied strain of the dominant relaxation time -_α and of the width w_? of the distribution of relaxation times. The first protocol is performed at constant strain rate '. We confirm that for increasing strain both -α and w? first decrease, reaching a minimum in the stress softening regime before increasing in the strain hardening regime. In the second protocol we stop the deformation at some point -_w in the strain hardening regime, and we let the sample age for a waiting time t_w, during which the applied stress remains high.