Article

Rheologica Acta

, Volume 33, Issue 6, pp 506-516

First online:

Assessment of nonlinear strain measures for extensional and shearing flows of polymer melts

  • M. H. WagnerAffiliated withInstitut für Kunststofftechnologie, Universität Stuttgart
  • , J. SchaefferAffiliated withInstitut für Kunststofftechnologie, Universität Stuttgart

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Abstract

From stress-strain experiments in extensional and shearing flows, nonlinear strain measures and effective damping functions are derived for a polyisobutylene melt. The strain measures determined in planar extensional flow and in simple shear flow coincide. Experimental results are compared with predictions of two molecular theories, the Doi-Edwards model and the molecular stress function approach of Wagner and Schaeffer. Discrepancies between theories and experiment lead to a reconsideration of the classification of extensional flows. The symmetry of the flow field is identified and quantified as an important parameter influencing the strain measure, and a unifying strain measure for general extensional and shearing flows of polymer melts is presented.

Key words

Strain measure damping function extensional flow transversely isotropic flow planar flow shear flow Doi-Edwards model molecular stress function classification of extensional flows planarity index