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Endommagement par cavitation du Polypropylène renforcé au choc par des particules d'élastomère

Abstract : Because of its high impact strength, PP toughened by inclusion of micrometric rubber particles (PP-EPR blends) is often used as a structural material. The study of the mechanisms involved in material damage is an important field of investigation to understand and improve the efficiency of the rubber toughening. The main process controlling the material behaviour is the cavitation of the rubber particles. The strong mechanical contrast between rubber and matrix mechanical properties produces a high level of internal positive hydrostatic stress in the particles. Above a certain pressure threshold, particles are destroyed. Experimentally cavitation can be detected by the increase of the non elastic volume and by the optical whitening of the material. Uniaxial tension experiments and microscopic analysis show the density and the size of the voids in the destroyed particles. The competition between several types of micro deformation mechanisms and the influence of the particle's neighbourhood have also been explored by a finite elements analysis. In the case of a crack tip multiaxial stress state, cavitation can lead to an increase of the impact properties: the material is able to accommodate the volume increase imposed by plain strain stress state, and the stress state changes from plane strain to plane stress. As the size of the plastic zone increases, the energy spent for the matrix flow is increased too. The critical depression level is roughly the same for uniaxial and triaxial stress states. It only depends on the type of rubber or the particle. In front of a sharp crack, mechanical interactions between particles seem to have a second order influence : the particles suddenly cavitate altogether when the state stress reaches the cavitation threshold. Further work should try to predict more precisely the material behaviour at the crack tip according to the knowledge of the individual properties or each phase (matrix and rubber particles), taking also into account the ability to accommodate the plain strain volume increase.
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https://tel.archives-ouvertes.fr/tel-00007229
Contributor : Laurence Scodellaro <>
Submitted on : Wednesday, October 27, 2004 - 3:29:45 PM
Last modification on : Friday, October 23, 2020 - 4:38:39 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:48:44 PM

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Laurence Scodellaro. Endommagement par cavitation du Polypropylène renforcé au choc par des particules d'élastomère. Matériaux. Université Louis Pasteur - Strasbourg I, 2001. Français. ⟨tel-00007229⟩

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