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    A material model for multiaxial stretching and stress relaxation of polypropylene under process conditions

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    Publication date
    2012-11
    Author
    Sweeney, John
    O'Connor, C.P.J.
    Spencer, Paul E.
    Pua, H.
    Caton-Rose, Philip D.
    Martin, P.J.
    Keyword
    Constitute equation
    Large deformations
    Polypropylene
    Peer-Reviewed
    Yes
    
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    Abstract
    Polypropylene sheets have been stretched at 160 °C to a state of large biaxial strain of extension ratio 3, and the stresses then allowed to relax at constant strain. The state of strain is reached via a path consisting of two sequential planar extensions, the second perpendicular to the first, under plane stress conditions with zero stress acting normal to the sheet. This strain path is highly relevant to solid phase deformation processes such as stretch blow moulding and thermoforming, and also reveals fundamental aspects of the flow rule required in the constitutive behaviour of the material. The rate of decay of stress is rapid, and such as to be highly significant in the modelling of processes that include stages of constant strain. A constitutive equation is developed that includes Eyring processes to model both the stress relaxation and strain rate dependence of the stress. The axial and transverse stresses observed during loading show that the use of a conventional Levy-Mises flow rule is ineffective, and instead a flow rule is used that takes account of the anisotropic state of the material via a power law function of the principal extension ratios. Finally the constitutive model is demonstrated to give quantitatively useful representation of the stresses both in loading and in stress relaxation.
    URI
    http://hdl.handle.net/10454/18228
    Version
    No full-text in the repository
    Citation
    Sweeney J, O'Connor CPJ, Spencer PE et al (2012) A material model for multiaxial stretching and stress relaxation of polypropylene under process conditions. Mechanics of Materials. 54: 55-69.
    Type
    Article
    Collections
    Engineering and Informatics Publications

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