Etude du processus d'initiation par laser de la combustion d'un alliage métallique sous atmosphère d'oxygène

Abstract : A metallic component placed in an oxygen-enriched atmosphere undergoes a rapid process of ignition when carried beyond a threshold temperature, which may result in severe damage or even in its complete destruction. Problems related to the flammability of metals affect any field of engineering involving metals in contact with oxygen at high concentration and/or high pressure (gas industry, aerospace industry, medical industry etc.). A standard testing of metal for assessing the compatibility with the oxygen of metallic materials exists since the 70's. This standard test consists mainly in the ignition of small cylindrical rods of metal under increasing pressure in order to determine the oxygen pressure threshold leading to the destruction of the sample and the propagation velocity of combustion that follows. Several disadvantages of this test can be identified : the initiation phase is generally poorly studied, either because this study is made impossible by the ignition technique used (promoter), or because it was obtained in a configuration quite far from actual accident conditions (heating in volume). Moreover, little attention has been given so far to the influence of oxygen flowing at the sample surface on the propagated combustion regime. This thesis proposes an original approach for the investigation of iron and steels combustion in an oxygen atmosphere, aiming at understanding the conditions for initiation and propagation of the combustion of metal parts ignited by a focalized laser source. To this end, the successive stages, from initiation to self-sustained combustion regime of the rod ignition were investigated. The work of this thesis can be divided in two parts. In the first part, an experimental investigation the effect of multiple parameters such as laser ignition parameters, oxygen speed, and static pressure on the initiation and propagation was carried out using an original experimental setup (with combustion spreading downward) and various instrumentation and monitoring equipment has been made such as : visualization by high-speed camera, optical pyrometry, thermocouples, metallographic analyzes. Particular attention has been given to the notion of threshold energy (laser) leading to the initiation of combustion, the spread or total destruction of the sample, which were determined under various oxygen speed rate. Based on experimental data obtained previously, the second part of this work has consisted in the development of numerical simulations (with the commercial software COMSOL Multiphysics) of these experiments (only the initiation and localized combustion stages). Unknown parameters associated with the chemical reaction were adjusted to best reproduce the evolution of various phenomena (thermal fields, dynamics of inflammation, behavior of the liquid bath, geometric distortion etc.). This work allowed us describing a phenomenology of initiation and propagation initiated by a laser source and a physical interpretation thereof.
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Maryse Muller. Etude du processus d'initiation par laser de la combustion d'un alliage métallique sous atmosphère d'oxygène. Autre. Ecole Nationale Supérieure de Mécanique et d'Aérotechnique - Poitiers, 2013. Français. ⟨NNT : 2013ESMA0004⟩. ⟨tel-00819759⟩

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