Strain Hardening in Polymer Glasses: Limitations of Network Models

TL;DR

This study uses simulations to explore the microscopic mechanisms of strain hardening in polymer glasses, revealing limitations of traditional network models and highlighting the roles of energetic and thermal stress components.

Contribution

It demonstrates that traditional entropic network models are inconsistent with simulation results and emphasizes the importance of energetic and thermal contributions to stress.

Findings

Energetic stress rises rapidly as segments are pulled taut.

Thermal stress is less sensitive to entanglements and related to local plasticity.

Strain hardening is similar in entangled and unentangled chains when considering microscopic orientation.

Abstract

Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While traditional entropic network models can be fit to the total stress, their underlying assumptions are inconsistent with simulation results. There is a substantial energetic contribution to the stress that rises rapidly as segments between entanglements are pulled taut. The thermal component of stress is less sensitive to entanglements, mostly irreversible, and directly related to the rate of local plastic arrangements. Entangled and unentangled chains show the same strain hardening when plotted against the microscopic chain orientation rather than the macroscopic strain.