A Simple Model for the Deformation-Induced Relaxation of Glassy Polymers

TL;DR

This paper presents a minimal model explaining how deformation-induced liquefaction and re-vitrification in glassy polymers lead to strain hardening and relaxation time dips under constant load.

Contribution

It introduces a combined model of flow-induced liquefaction and polymer stress to explain complex deformation behaviors in glassy polymers.

Findings

Explains the dip in segmental relaxation time during deformation.

Shows how flow-induced liquefaction causes strain hardening.

Demonstrates interplay between aging and rejuvenation in polymers.

Abstract

Glassy polymers show strain hardening: at constant extensional load, their flow first accelerates, then arrests. Recent experiments have found this to be accompanied by a striking and unexplained dip in the segmental relaxation time. Here we explain such behavior by combining a minimal model of flow-induced liquefaction of a glass, with a description of the stress carried by strained polymers, creating a non-factorable interplay between aging and strain-induced rejuvenation. Under constant load, liquefaction of segmental motion permits strong flow that creates polymer-borne stress. This slows the deformation enough for the segmental modes to re-vitrify, causing strain hardening.