A theory of necking in semi-crystalline polymers

Abstract

Necking or cold drawing is a smoothed jump in cross-sectional area of long and thin bars (filaments orfilms) propagating with a constant speed. The necks in polymers, first observed about seventy years ago, arenow commonly used in modern processing of polymer films and fibers. Yet till recently there was a lack infundamental understanding of necking mechanism(s). For semi-crystalline polymers with co-existingamorphous and crystalline phases, recent experiments revealed that such a mechanism is related tounfolding crystalline blocks. Using this idea, this paper develops a theoretical model and includes it in ageneral continuum framework. Additionally, the paper explains the forced (reversible) elasticity observedin slowly propagating polymeric necks, and also briefly analyses the viscoelastic effects and dissipative heatgeneration when polymer necks propagate fast enough.