The peculiarities of viscoelastic behavior of high-density polyethylene (HDPE) subjected to the unia.xiat cyclic tensions and retractions below the yield point are studied. This required using three different deformation programs including (i) the successive increase in strain maximum of each cycle, (ii) the controlled upper and lower stress boundaries, and (iii) the fixed strain at the backtracking points. The experimental data are analyzed in a framework of the modified structure-sensitive model (Oshmyan et al., 2006, "Principles of Structural-Mechanical Modeling of Polymers and Composites," Polym. Sei. Ser. A. 48. pp. 1004-1013 of semicrystalline polymers. If is supposed that increase in the interlamellar nanovoid volume fraction results in speeding-up the plastic flow rate while decreasing cavitation rate. Consequenlly, a proper fitting of the stress-strain cyclic diagrams is obtained for the applied deformation programs within the common set of model parameters. This makes it possible to reveal evolution of nanovoid volume fraction in HDPE during cyclic deformations.
Résumé -Modélisation des non-linéarités en vitesse de déformation et du comportement en déchargement des polymères semi-cristallins -Les lois viscoélastiques classiques ne permettent pas de décrire complètement les comportements caractéristiques des polymères semi-cristallins, comme ceux observés lors de sauts de vitesses ou en déchargement. Nous présentons dans cet article certaines particularités du comportement mécanique pour un polyéthylène ou un polypropylène en petites déformations. Un modèle physique incluant une évolution de la microstructure est présenté et comparé aux observations expérimentales. Ce modèle permet une forte amélioration des simulations des comportements mécaniques en chargement et déchargement pour une large classe de polymères semicristallins.
Abstract -Non Linear Strain Rate Dependency and Unloading Behavior of Semi-Crystalline
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