Viscoplasticity and large-scale chain relaxation in glassy-polymeric strain hardening
RS Hoy and CS O'Hern, PHYSICAL REVIEW E, 82, 041803 (2010).
A simple theory for glassy-polymeric mechanical response that accounts for large-scale chain relaxation is presented. It captures the crossover from perfect-plastic response to Gaussian strain hardening as the degree of polymerization N increases, without invoking entanglements. By relating hardening to interactions on the scale of monomers and chain segments, we correctly predict its magnitude. Strain-activated relaxation arising from the need to maintain constant chain contour length reduces the characteristic relaxation time by a factor similar to epsilon N during active deformation at strain rate epsilon. This prediction is consistent with results from recent experiments and simulations, and we suggest how it may be further tested experimentally.
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