In tensile tests the flax/polypropylene composites clearly show nonlinear behavior in loading and hysteresis loops in unloading. In creep tests performed at different load levels the response was nonlinear viscoelastic, and after recovery, viscoplastic strains were detected. No degradation in stiffness could be seen and thus nonlinear viscoelasticity and viscoplasticity were assumed to be the main cause for the observed behavior. The fracture surface of a specimen that experienced creep rupture at 24 MPa was investigated using a scanning electron microscope. The viscoplastic response was studied experimentally and described by a power law with respect to time and stress level in the creep test. The nonlinear viscoelasticity was described using Schapery’s model. The application of Prony series and a power law to approximate the viscoelastic compliance was investigated. Both descriptions have accuracy sufficient for practical applications. However, at high stresses the attempts to describe the viscoelastic compliance by a power law with a stress-independent exponent failed and therefore stress dependence of this exponent was included in the data analysis. The accuracy within the considered stress range is good, but the thermodynamic consistency of this procedure has to be proven.
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e-mail: erik.marklund@ltu.se
e-mail: janis.varna@ltu.se
e-mail: lennart.wallstrom@ltu.se
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October 2006
Research Papers
Nonlinear Viscoelasticity and Viscoplasticity of Flax/Polypropylene Composites
Erik Marklund,
Erik Marklund
Division of Polymer Engineering,
e-mail: erik.marklund@ltu.se
LuleåUniversity of Technology
, SE-97187, Luleå, Sweden
Search for other works by this author on:
Janis Varna,
Janis Varna
Division of Polymer Engineering,
e-mail: janis.varna@ltu.se
LuleåUniversity of Technology
, SE-97187, Luleå, Sweden
Search for other works by this author on:
Lennart Wallström
Lennart Wallström
Division of Polymer Engineering,
e-mail: lennart.wallstrom@ltu.se
LuleåUniversity of Technology
, SE-97187, Luleå, Sweden
Search for other works by this author on:
Erik Marklund
Division of Polymer Engineering,
LuleåUniversity of Technology
, SE-97187, Luleå, Swedene-mail: erik.marklund@ltu.se
Janis Varna
Division of Polymer Engineering,
LuleåUniversity of Technology
, SE-97187, Luleå, Swedene-mail: janis.varna@ltu.se
Lennart Wallström
Division of Polymer Engineering,
LuleåUniversity of Technology
, SE-97187, Luleå, Swedene-mail: lennart.wallstrom@ltu.se
J. Eng. Mater. Technol. Oct 2006, 128(4): 527-536 (10 pages)
Published Online: June 30, 2006
Article history
Received:
January 12, 2006
Revised:
June 30, 2006
Citation
Marklund, E., Varna, J., and Wallström, L. (June 30, 2006). "Nonlinear Viscoelasticity and Viscoplasticity of Flax/Polypropylene Composites." ASME. J. Eng. Mater. Technol. October 2006; 128(4): 527–536. https://doi.org/10.1115/1.2345444
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