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Derivative stress‐strain curves of polyacrylonitrile fibers
Author(s) -
Egbers G.
Publication year - 1969
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760090510
Subject(s) - polyacrylonitrile , materials science , composite material , modulus , viscoelasticity , strain (injury) , derivative (finance) , strain rate , stress (linguistics) , copolymer , stress–strain curve , strain hardening exponent , dynamic mechanical analysis , deformation (meteorology) , polymer , medicine , linguistics , philosophy , financial economics , economics
Derivative stress‐strain curves at constant strain rate for polyacrylonitrile copolymer fibers have been obtained by simple modification of conventional tensile testing apparatus. These derivative curves, considerably more complex and eventful than stress‐strain curves, have been interpreted as direct records of changes undergone by the apparent Young's modulus during experiments which extend from infinitesimal strain to failure. Analysis of the data shows that these changes in the apparent Young's modulus cannot be accounted for to any significant extent by viscoelastic time effects and must therefore be consequences of the deformation process itself. In the light of this analysis, it is concluded that polyacrylonitrile fibers “soften” considerably in the strain range 0.5–3% and that they exhibit moderate “hardening” in the strain range which extends from ca 3% to the breaking strain (10%).