Viscoplasticity and large-scale chain relaxation in glassy-polymeric strain hardening

TL;DR

This paper presents a simple theoretical model for glassy polymer mechanics that explains strain hardening and chain relaxation without entanglements, aligning well with experimental and simulation data.

Contribution

It introduces a novel theory linking chain relaxation and strain hardening in glassy polymers, emphasizing monomer-scale interactions and relaxation dynamics.

Findings

Captures transition from plasticity to strain hardening with increasing polymerization

Predicts the magnitude of strain hardening based on monomer interactions

Aligns with recent experimental and simulation results

Abstract

A simple theory for glassy polymeric mechanical response which accounts for large scale chain relaxation is presented. It captures the crossover from perfect-plastic response to strong 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 $N$ dependence of the characteristic relaxation time by a factor $\sim \dot\epsilon N$ during active deformation at strain rate $\dot\epsilon$. This prediction is consistent with results from recent experiments and simulations, and we suggest how it may be further tested experimentally.