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A microscopy study of the transition from yielding to crazing in polypropylene
Author(s) -
Dijkstra P. T. S.,
Van Dijk D. J.,
Huétink J.
Publication year - 2002
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.10936
Subject(s) - necking , materials science , strain rate , crazing , homogeneous , deformation (meteorology) , strain (injury) , polypropylene , scanning electron microscope , composite material , crystallography , thermodynamics , chemistry , physics , anatomy , polymer , medicine
The deformation mechanisms in polypropylene as a function of strain rate have been studied by scanning electron microscopy. Injection molded, dogbone specimens were tested in tension at a temperature of 50°C and strain rates from 10 −4 to 90 s −1 . With increasing strain rate a gradual transition from cold drawing and necking to nearly homogeneous deformation was observed. The transition is characterized by a strong elastic recoil after fracture. At \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \varepsilon } $\end{document} = 90 s −1 , the elastic recovery has its maximum value of 70% of the strain at break (ε = 0.3). The morphology was studied post mortem at small strains outside the neck using permanganically etched samples. The transition in the macroscopic behavior was found to coincide with a change in the deformation mechanism. Whereas yielding is the dominant mechanism at low strain rates, homogeneous voiding is found at \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \varepsilon } $\end{document} = 90 s −1 . A correlation is suggested between the failure of chain slip within the lamellae and the occurrence of voiding, leading to distinct voiding patterns in the spherulites.

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