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Étude expérimentale du thermoformage assisté par poinçon d'un mélange de polystyrènes

Abstract : The plug-assisted thermoforming of a polystyrenes blend is experimentally studied to better understand the physical phenomena involved and to better control the process. This is done on the basis of an experimental approach, including thermoforming tests, rheological studies over a wide range of temperatures, strain rates and loading histories and plug-sheet contact characterisation, including friction and thermal contact resistance measurements. The analysis of the kinematics of the thermoforming process (using a rapid video-camera) leads to the characterisation of the actual loading features, which are rapid (strain-rates up to 100 s-1), sequenced, inhomogeneous and non-isothermal. The influence of the processing parameters is investigated, in particular the importance of the tool-sheet contact where thermal exchanges, friction and rheology interact. The behaviour of the blend within the thermoforming range drastically depends on temperature and strain-rate, due to the proximity of the glass transition. It is mainly reversible and poorly dissipative. The polymer exhibits a progressive change from a hyper-viscoelastic behaviour to an elastic-viscoplastic behaviour, where the a transition temperature deviation, as defined by the couple temperature/strain-rate, appears to be the main driving parameter. The time-temperature principle is extended to large strains. The thermal conditions of the contact, which defines the local temperature close to the plug-sheet interface, qi, are of prime importance. They depend on the plug and sheet temperatures and on the thermal properties of the two materials. Additionally some thermal contact resistance, which remains nevertheless difficult to estimate, can exist. The thermal contact also influences friction, whose effects is significant only when the local cooling of the sheet remains reasonable (qi >Ta). Finally, the friction coefficient between the plug and the sheet appears to depend on the local temperature and on the relative velocity. Phenomenological models are proposed and experimental identification protocols are proposed for each parameter. Their asset are demonstrated within the frame of a numerical simulation.
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Submitted on : Monday, July 4, 2005 - 8:00:00 AM
Last modification on : Wednesday, November 17, 2021 - 12:27:20 PM
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  • HAL Id : pastel-00001313, version 1


Aliza Erner. Étude expérimentale du thermoformage assisté par poinçon d'un mélange de polystyrènes. Chimie. École Nationale Supérieure des Mines de Paris, 2005. Français. ⟨NNT : 2005ENMP1255⟩. ⟨pastel-00001313⟩



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