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Contribution à l'étude du couplage thermique-mécanique-électrique dans les contacts électriques : application à l'élaboration d'un modèle de durée de vie d'un contacteur

Abstract : A contactor is an electromechanical device designed to establish or disconnect anelectrical current in a circuit by closing or opening contacts. During each operation, anelectric arc is created, due to the enormous power density involved to reach and locallyexceed the melting temperature of the material. As a result, the repeated action of thearcs during the life of the device (up to several hundred thousand closing/opening cycles)gradually leads to the ruin of the contact pads and the malfunction of the contactor. Thethesis work aims to propose tools for modelling the damage of contact pads under the effectof repeated impacts, with the longer-term objective of predicting the life of the contactoraccording to its operating conditions. The material considered is a pseudo-alloy made ofsilver and tin oxide SnO 2 . As a first step, several experimental campaigns were carried outto collect all the input data required for modelling : determination of the thermomechanicalproperties of the material, characterization of damage – surface and bulk – produced by asingle arc and by an accumulation of arcs, estimation of the power density provided by anarc to the contact material. Many experimental techniques have been used : monotonoustensile tests and cyclic loading, indentation (microhardness), 3D profilometry, opticalmicroscopy and scanning electron microscopy, EDS and EBSD analysis, thermal imagingcamera, high speed camera. Then two types of models were successively developed. Thefirst one uses the Zset finite element code. Developped in an axisymmetric geometry, itaims to describe within the material the evolution of temperatures, stresses and strainsresulting from an arc (assumed fixed), then the initiation of cracks after a few hundredof impacts at the same point. A 3D variant was then discussed to approach the case ofmoving arcs. The second model, of a phenomenological nature, is based on simplifieddescriptions of topography and tensile strength in silver in the vicinity of the surface, aswell as on rules of occurrence and spatial distribution, taken as much as possible fromexperimental observations. It is intended to simulate in a manageable calculation time thedamage resulting from the accumulation of a very large number of arcs over the entiresurface of the pellets.
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Aurélien Fouque. Contribution à l'étude du couplage thermique-mécanique-électrique dans les contacts électriques : application à l'élaboration d'un modèle de durée de vie d'un contacteur. Electronique. Université Paris-Saclay, 2020. Français. ⟨NNT : 2020UPASC001⟩. ⟨tel-02880580⟩

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