Microscopic Dynamics in the Strain Hardening Regime of Glassy Polymers

We study by dielectric spectroscopy the molecular dynamics of relaxation processes during plastic flow glassy polymers up to strain hardening regime for three different protocols deformation. The measured spectra cover 4 decades in frequencies and allow us measure evolution as a function applied dominant time τα width wτ distribution times. first protocol is performed at constant rate λ̇. confirm that increasing both decrease, reaching minimum stress softening before regime. In second we stop deformation some point λw regime, let sample age waiting tw, which remains high. Upon resuming λ̇, stress–strain displays yield comparable magnitude reference rejoining curve. contrast, spectrum recovers one curve much later than strain–stress. third canceled tw. this case, after recovering λ̇ rejoin almost immediately interpret these behaviors consequence changes free energy barriers α-relaxation induced sample. These are sum two contributions: (a) one, allows flow, due σ and, according recently published theory, scales −σ2. (b) contribution κ(λ), chain orientation monomer level, positive responsible evolves upon varying stress, whereas relaxes very slowly cessation stress. Our interpretation results aging frozen when removed, it known polycarbonate room temperature. experiments set precise conditions theory hardening.