Caractérisation de la variation volumique du polyethylène au cours de la deformation plastique en traction et en fluage :

Abstract : The mechanical behavior of polyethylene with a rubbery amorphous phase is determined by the means of the VidéoTraction system under uniaxial tension and creep. This technique gives access to the constitutive behavior but also to the volume strain of a representative volume element situated at the center of the neck. It is found that the stress - strain curves depend on experimental conditions and on the microstructure of the polyethylene. The most unexpected result is the evolution of volume strain: one notes a competition between a compaction phenomenon and a dilatation process after the initial elastic expansion. Other densitometric techniques (microtomography, radiography, hydrostatic weighing) have been used to measure volume variation of the materials, and a critical evaluation of experimental errors arising from our video extensometer has been carried out. From theses studies, it is concluded that volume dilatation is the leading phenomenon while compaction effect are of second order. Scanning electron microscopy and X-ray diffraction investigations have been performed on diferent déformation states in order to identify the microscopic origin of recorded volume changes. The overall behavior is controlled both by the evolution of the solid polymer matrix and by the development of cavitation. The polymer matrix is affected by two opposite processes that compensate nearly exactly one another: dilatation due to crystalline order destruction and compaction due to orientation of amorphous chains. As such, cavitation is the most active mechanism that controls macroscopic volume strain. A theoretical damage factor predicting the experimental dilatation amplitude has been developed from the microstructural parameters of the polyethylene. The overall mechanical equations have been decomposed into an intrinsic component (the matrix behavior) and a volume component (the cavitation behavior)
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Frédéric Addiego. Caractérisation de la variation volumique du polyethylène au cours de la deformation plastique en traction et en fluage :. Autre. Institut National Polytechnique de Lorraine, 2006. Français. ⟨NNT : 2006INPL013N⟩. ⟨tel-01752491⟩

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