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Mécanismes et modélisation mécanique de la déformation, de l'endommagement et de la rupture du PolyAmide 11 pur et renforcé choc

Abstract : Arkema is interested in the manufacturing of toughened thermoplastic materials by incorporating rubber particles in the matrix during the processing. The addition of a second phase of elastomeric particles is a common technique used to improve the toughness of a polymer. The presence of rubber particles induces a modification of the damage mechanisms by voids nucleation, growth and coalescence either within the rubber particles or at the interface rubber-matrix. The studied toughened polymers have a PolyAmide 11 (PA11) matrix which is a semi-crystalline thermoplastic. This material which has an initial amount of porosity of 1% whitens when loaded. Whitening is related to cavitation occuring within the material by voids growth which generates a volume change. Thus we investigate the damage by cavitation which may be transformed into craze which, in turn, may provoke the failure. The understanding of the damage mechanisms are analysed for the neat PA11, a plasticized and aged PA11 as well as two rubber toughened PA11. The materials named "aged P40", "aged P20 EPR" and "aged P20 XNBR" have been aged in similar conditions for the context of the study.
This PhD work highlights the fact that once again, the GTN model, initially developed to study the ductile failure of metallic materials, can be used in the case of semi-cristalline polymer. The model turns out to be relevant to describe the mechanical behaviour of the PA11 as well as its damage. As the PVDF, craze initiation may occur through two criteria : at high stress triaxiality ratio, the coaslescence of voids may induce the initiation of a crack whereas at low stress triaxiality ratio, it should be explained by the reach of a critical maximum principal plastic strain. Results from the numerical simulations taking into account the self heating of the polymer seem promising and agree well with the experimental results. Regarding the rubber-toughened PA11, this work also shows that rubber toughening may preserve the ductility of the materials despite the ageing and the range of accounted temperature below the glass transition. Therefore, we highlight that depending on the second phase characteristics, damage mechanisms may change and thus the crack initiation criterion may also change as well.
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Submitted on : Tuesday, October 6, 2009 - 11:54:58 AM
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  • HAL Id : tel-00422223, version 1

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Guillaume Boisot. Mécanismes et modélisation mécanique de la déformation, de l'endommagement et de la rupture du PolyAmide 11 pur et renforcé choc. Sciences de l'ingénieur [physics]. École Nationale Supérieure des Mines de Paris, 2009. Français. ⟨NNT : 2009ENMP1635⟩. ⟨tel-00422223⟩

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