Approche locale de la rupture dans un thermoplastique semi-cristallin : le PolyOxyMéthylène : Application : modélisation thermomécanique d'un procédé de vissage-taraudage

Abstract : The increasing use of polymers in engineering structures is promoted by the need to reduce both cycle/cost production and the weight of these structures. PSA Peugeot Citroën initiated research works to design the assembling process using metallic screwing/threading on polymers. It consists in directly taping the polymeric piece during the mounting operation by using self-threading metallic screw. The final objective of the work deals with the ability to numerically (finite element) model the screwing/threading operation. This numerical tool offers the possibility to perform a large campaign of study highlighting the sensitivity of the assembly procedure to a significant range of parameters. The first investigations showed that this problem consisted of complex thermo-mechanical loading for which all the deformation components of the polymeric material were involved: elastic, viscous, plastic and volumetric. The study was performed within the framework of the local approach to fracture, that required fine examinations of the micro-mechanisms of deformation and damage within the polymer. The experimental database were composed of measurable variables obtained from mechanical tests together with a comprehensive X-ray tomographic inspections. This latter non destructive technique revealing 3D images of the deformed microstructure allowed for characterization of the morphology and the distribution of voids within the polymer in the vicinity of the crest. To account for void volume fraction, a model from the mechanics of porous media was utilized: the Gurson-Tvergaard-Needleman model, modified for polymeric materials studies. The present model allowed for a construction of a failure assessment diagram that would permit to optimize the screwing rotation speed of the screwing-tapping process. An alternative solution consisting of an assembly composed of polymeric screw and polymeric nut was additionally investigated. Thanks to the local approach of fracture criterion based on the critical porosity, the weakest point of the assembly as well as its mechanical residual strength were estimated.
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Jonathan Ricard. Approche locale de la rupture dans un thermoplastique semi-cristallin : le PolyOxyMéthylène : Application : modélisation thermomécanique d'un procédé de vissage-taraudage. Autre. Ecole Nationale Supérieure des Mines de Paris, 2013. Français. ⟨NNT : 2013ENMP0034⟩. ⟨pastel-00945520⟩

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