Cyclic behaviour of short glass fibre reinforced polyamide: Experimental study and constitutive equations |
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Authors: | A. Launay M.H. MaitournamY. Marco I. RaoultF. Szmytka |
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Affiliation: | a Laboratoire de Mécanique des Solides (CNRS UMR 7649), École polytechnique, 91128 Palaiseau, France b Laboratoire Brestois de Mécanique et des Systèmes (EA 4325 ENSIETA/UBO/ENIB), 2 rue François Verny, 29806 Brest Cedex 9, France c PSA Peugeot Citroën (Direction Scientifique et des Technologies Futures), Route de Gisy, 78943 Vélizy-Villacoublay Cedex, France |
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Abstract: | Polymer matrix composites are widely used in the automotive industry and undergo fatigue loadings. The investigation of the nonlinear cyclic behaviour of such materials is a required preliminary work for a confident fatigue design, but has not involved many publications in the literature. This paper presents an extensive experimental study conducted on a polyamide 66 reinforced with 35 wt% of short glass fibres (PA66 GF35), at room temperature. The material was tested in two conditions: dry-as-moulded (DAM) and at the equilibrium with air containing 50% of relative humidity (RH50).An exhaustive experimental campaign in tensile mode has been carried out, including various strain or stress rates, complex mechanical histories and local thermo-mechanical recordings. Such an extended database allowed us to highlight several complex physical phenomena: viscoelastic effects at different time scales, irrecoverable mechanisms, non-linear kinematic hardening, non-linear viscous flow rule, cyclic softening.Taking into account this advanced analysis, a constitutive model describing the cyclic behaviour is proposed. As the experimental database only includes uniaxial tensile tests, the general 3D anisotropic frame is reduced to an uniaxial model valid for a specific orientation distribution. The robust identification process is based on tests which enable the uncoupling between the underlined mechanical features. This strategy leads to a model which accurately predicts the cyclic behaviour of conditioned as well as dry materials under complex tensile loadings. |
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Keywords: | Cyclic loading Constitutive behaviour Elasto-viscoplastic material Polymeric material Mechanical testing |
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