A microscopy Study of the Transition From Yielding to Crazing in Polypropylene

P.T.S. Dijkstra, D.J. van Dijk, Han Huetink

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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 ε = 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 ε = 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.
Original languageUndefined
Pages (from-to)152-160
JournalPolymer engineering and science
Issue number1
Publication statusPublished - 2002


  • METIS-210547
  • IR-71837

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