Comportement mécanique en grandes déformations du polyéthylène haute densité : approche thermodynamique de l'état relaxé

Abstract : The semicrystalline polymers are the subject of many scientific researchs aiming to understanding their microscopic mechanisms of deformation. Nevertheless, the modelling which we currently find in the literature do not approach the mechanical tests with unloading or the cyclic tests at large strains. Among the reasons of these insufficiencies appears themultiplicity of the internal reorganization processes which is seldom described finely in the physical modelling. Moreover, a main aspect of the semicrystalline polymer behaviour is often ignored, it acts of the relaxed state. Within the framework of formalism Distribution of Non Linear Relaxation (D.N.L.R.), we are interested more closely in these two aspects of the mechanical behaviour: multiplicity of the mechanisms, relaxed state. To clarify these two concepts, the objective was to characterize the relaxed state at large strains and to propose a physical modelling based on the thermodynamics of irreversible processes and on the microscopic aspects of the deformation. The distribution of the weights of the various modes has been described following observations given by a clip tests. The material used is the High Density Polyethylene HOPE. The tests were carried out with VideoTraction technology. The relaxed state modulus measured during tension loading is definitely more important than that of the unloading, which translates a damage phenomenon. The irreversibility of the relaxed state imposes that the modelling must use a functional formulation which integrates the memory effect and damage. In addition, the dip test has shawn the presence of mechanical cross over. A bibliographical study showed that this phenomenon is closely related to the processes multiplicity. Thus, we have shawn that the modal partition adopted in practice has to be re-examined. We have shawn that the modelling set up is able to reproduce complex loadings, in particular the cyclic tests with relaxation, and to predict behavior very depending on the .loading history and the irreversible relaxed state.
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Theses
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http://docnum.univ-lorraine.fr/prive/INPL_T_2003_MRABET_K.pdf
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Submitted on : Thursday, March 29, 2018 - 12:39:59 PM
Last modification on : Friday, March 30, 2018 - 1:28:26 AM

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Kaïs Mrabet. Comportement mécanique en grandes déformations du polyéthylène haute densité : approche thermodynamique de l'état relaxé. Autre [cond-mat.other]. Institut National Polytechnique de Lorraine, 2003. Français. ⟨NNT : 2003INPL036N⟩. ⟨tel-01750174⟩

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