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Comportement, endommagement et fissuration par fluage du Polyamide 6 : étude expérimentale et modélisation

Abstract : PolyAmide 6 (PA6) is a semi-crystalline polymer utilised in many structural components working under steady load. At room temperature, PA6 exhibits complex time dependent (viscoplastic) deformation. The aim of this work is to investigate the PA6 mechanical response as well as the crack initiation and growth under creep conditions at room temperature. The experimental database consists of tests carried out on smooth and notched round bars with various notch root radii. Load versus displacement curves were recorded for tensile monotonic tests at various crosshead speeds. Then, creep tests with constant loads were performed. Creep strain history was plotted for each applied load. Stabilised and stationary creep was observed with two regimes of creep strain rate depending on the level of the applied load. Microscopic observations on cryo-fractured samples highlight the initial spherulitic structure and an initial porosity of about 1.5%. Investigations on samples issued from both interrupted and failure tests allowed evidencing deformation and damage mechanisms. Namely, fracture surfaces clearly showed ductile to brittle failure mechanisms, whereas ductile regime, based on void growth and coalescence, seems to exhibit three various features according the stress triaxiality ratio. Creep strain histories on smooth specimens were used in order to identify material coefficients dealing with both analytical and FE modelling. This latter was provided with multi-mechanisms constitutive relations accounting for crystallinity index. Damage mechanics and fracture mechanics concepts were applied thanks to opening displacement database on notched specimens. To this end, non linear fracture mechanics for creeping solids approach, via C* parameter, was applied to the pre-cracked specimens. A master curve relating C* parameter to the time to failure was obtained. Furthermore, multimechanisms model was associated with mechanics of porous media to simulate void growth in the ductile failure regime. The influence of damage coefficients is discussed. Local parameters such as porosity in the amorphous/ crystalline phases were analysed regarding the damage mechanisms depicted in previous sections.
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Submitted on : Monday, June 21, 2010 - 10:53:07 AM
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  • HAL Id : tel-00493717, version 1

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Cédric Regrain. Comportement, endommagement et fissuration par fluage du Polyamide 6 : étude expérimentale et modélisation. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2009. Français. ⟨tel-00493717⟩

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