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Comportement cyclique et tenue en fatigue sous chargement multiaxial d'un polyéthylène : expériences et critère d'endurance

Abstract : The multiaxial fatigue behavior of un-filled semi-crystalline polymers has not been widely investigated. Unlike metals and other polymer materials like rubbers, only a few works about fatigue criteria have been reported in the literature. This study, performed in high-density polyethylene, aims (i) at experimental characterization of the multiaxial fatigue resistance and a multiaxial fatigue criterion proposal, and (ii) at a better understanding of the various strain components leading to failure, among which viscoelasticity, plasticity and damage terms. In the first part, multiaxial tension, torsion and compression fatigue tests have been performed on tubular-shape specimens at constant frequency, amplitude and stress ratio (0, -1 et -\infty), with a triangular wave function. An air circulation device was developed to minimize self-heating and support an isothermal framework for the criterion. As a consequence of the mode of failure, an end-of-life criterion for fatigue tests was proposed first in order to define the number of cycles to failure. It was based on the onset of the softening process observed on the maximal strain evolution with time. Based on stress-controlled fatigue tests under tension, compression and torsion at different stress ratio, a multiaxial fatigue criterion including the stress-ratio effect was proposed for the fatigue design of this polymer. This criterion was based on the maximum and mean values of the second-invariant of the stress tensor. It was also satisfactorily applied to another semi-crystalline polymer i.e. a polypropylene. A few issues, linked to the way of characterizing the fatigue resistance of such materials (constant stress-rate versus frequency, relevance of self-heating methods), were also discussed briefly. The second aim was to analyze the viscoelastic, plastic and damage contribution to the strain evolution enhanced by cycling loading. Temperature, strains and loop evolution was investigated over wide loading conditions (multiaxial loading, frequency, stress ratio, thermal boundary conditions). A major result is that a large part of the strain appears recoverable and that the increasing part of the plastic contribution depends on the strain level regardless the cycling or creep loading history at a given mean stress. Subsequently, two effects linked to viscoelasticity, i.e. the mean stress and the cyclic loading history, have been logically investigated. Cycling was shown to accelerate the strain kinetics, however without noticeably modifying the micro-mechanisms and the plastic component.
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Submitted on : Tuesday, September 14, 2010 - 3:28:17 PM
Last modification on : Wednesday, October 20, 2021 - 3:22:14 AM
Long-term archiving on: : Wednesday, December 15, 2010 - 2:47:30 AM

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  • HAL Id : tel-00517401, version 1

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Abdelmoutalib Berrehili. Comportement cyclique et tenue en fatigue sous chargement multiaxial d'un polyéthylène : expériences et critère d'endurance. Sciences de l'ingénieur [physics]. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2010. Français. ⟨tel-00517401⟩

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