A microscopy study of the transition from yielding to crazing in polypropylene

Dijkstra, P.T.S. and Dijk van, D.J. and Huetink, J. (2002) A microscopy study of the transition from yielding to crazing in polypropylene. Polymer Engineering and Science, 42 (1). pp. 152-160. ISSN 0032-3888

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Abstract:	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.
Item Type:	Article
Copyright:	© 2002 Wiley InterScience
Faculty:	Engineering Technology (CTW)
Research Chair:	Mechanics of Forming Technology (MFT)
Research Group:	Design, Production and Management (DPM)
Link to this item:	http://purl.utwente.nl/publications/71837
Official URL:	http://dx.doi.org/10.1002/pen.10936
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