Mesure de température par pyrométrie 2D à bande spectrale et pyrométrie spectrale de métaux chauffés par laser dans un environnement fortement oxydant

La calibration et la validation de deux techniques de mesure de température complémentaires basées toutes les deux sur la pyrométrie optique (pyrométrie 2D monobande et pyrométrie spectrale), utilisables dans le cadre de l'étude des métaux chauffés dans des conditions hautement oxydantes et plus généralement au cours des procédés laser sur des métaux dans la gamme de température 2000-4000 K ont été réalisées. Une bonne correspondance des résultats des deux méthodes est obtenue lorsque l'émissivité de l'objet est connue et varie peu, mais seule la pyrométrie spectrale est performante lors de grandes variations d'émissivité, fournissant à la fois une mesure de température et d'émissivité au cours du procédé. Les incertitudes ont été calculées et représentent respectivement 6 et 3% dans une gamme de 1800 à 4500 K pour la pyrométrie 2D et la pyrométrie spectrale

Temperature measurement of laser heated metals in highly oxidizing environment using 2D single-band and spectral pyrometry

Calibration and validation of two temperature measurement techniques both using optical pyrometry, usable in the framework of the study of the heated metals in highly oxidizing environments and more generally during laser processing of materials in the range of 2000-4000 K have been done. The 2D single-band pyrometry technique using a fast camera provides 2D temperature measurement, whereas spectral pyrometry uses a spectrometer analyzing the spectra emitted by a spot on the observed surface, with uncertainties calculated to be, respectively, within ±3 and 6 of the temperature. Both techniques have been used simultaneously for temperature measurement of laser heated V, Nb, Ta, and W rods under argon and to measure the temperature of steel and iron rods during combustion under oxygen. Results obtained with both techniques are very similar and within the error bars of each other when emissivity remains constant. Moreover, spectral pyrometry has proved to be able to provide correct measurement of temperature, even with unexpected variations of the emissivity during the observed process, and to give a relevant value of this emissivity. A validation of a comsol numerical model of the heating cycle of W, Ta, Nb, V rods has been obtained by comparison with the measurement

Temperature measurement of laser heated metals in highly oxidizing environment using 2D single-band and spectral pyrometry

Calibration and validation of two temperature measurement techniques both using optical pyrometry, usable in the framework of the study of the heated metals in highly oxidizing environments and more generally during laser processing of materials in the range of 2000-4000 K have been done. The 2D single-band pyrometry technique using a fast camera provides 2D temperature measurement, whereas spectral pyrometry uses a spectrometer analyzing the spectra emitted by a spot on the observed surface, with uncertainties calculated to be, respectively, within ±3 and 6 of the temperature. Both techniques have been used simultaneously for temperature measurement of laser heated V, Nb, Ta, and W rods under argon and to measure the temperature of steel and iron rods during combustion under oxygen. Results obtained with both techniques are very similar and within the error bars of each other when emissivity remains constant. Moreover, spectral pyrometry has proved to be able to provide correct measurement of temperature, even with unexpected variations of the emissivity during the observed process, and to give a relevant value of this emissivity. A validation of a comsol numerical model of the heating cycle of W, Ta, Nb, V rods has been obtained by comparison with the measurement

Liquid phase combustion of iron in an oxygen atmosphere

In this article, we report an investigation of laser-initiated ignition of pure iron rods, using optical pyrometry, video observations, and analysis of metallographic cross section of quenched burning liquid on copper plates. When ignition occurs, caused by the melting of metal, the combustion takes place in the liquid. Two distinct superposed phases (L1 and L2) are identified in the liquid, according to the known phase diagram of the iron oxide system. Our observations show that the L1 and L2 phases can be either distinct and immiscible or mixing together. The temperature of the transition at which the mixing occurs is around 2350 K. Two mechanisms are proposed to explain the mixing occurring at high temperature: the spontaneous emulsification resulting from a strong decrease of the interfacial tension between L1 and L2 and the reduction of the miscibility gap between them at high temperature. Based on the experimental data of the evolution of the temperature and the video observation of the melt for different ignition conditions, we provide a complete description of the combustion process of iron induced by laser. Eventually, an extrapolation of the iron–oxygen phase diagram, to temperatures higher than 2000 K, is proposed

Laser Ignition of Bulk Iron, Mild Steel, and Stainless Steel in Oxygen Atmospheres

The ignition of pure iron, mild steel S355J, and stainless steel 316L has been investigated. The whole ignition and combustion processes have been monitored using a high-speed video camera and adapted pyrometry. Our results show that the absorptivity of the iron and mild steel to laser radiation increases rapidly at 850 K, from 0.45 to 0.7, and that of stainless steel increases more gradually during the heating process from 0.45 to 0.7. The ignition of iron, mild steel, and stainless steel is controlled by a transition temperature, at which the diffusivity of the metal increases sharply. The transition temperature of pure iron and mild steel is around 1750 K, when molten material appears, and that of stainless steel is around 1900 K, when the solid oxide layer loses its protective properties. These temperatures are independent of the oxygen pressure (from 2 to 20 bar) and of the laser intensity (from 1.6 to 34 kW•cm ). During ignition, the temperature increases very strongly at first, and after that a change in the heating rate of the surface is observed. A diffusive-reactive model, provided with equations describing the diffusion of oxygen in the metal and the transfer of heat released by the oxidation reactions has been solved. The model correctly reproduces the sharp rise of temperature as well as the decrease in the heating rate that follows. Comparison between calculated and experimental data shows that, without liquid convection flow in the melt, combustion would extinguish as soon as the metal surface is fully oxidized and that the combustion front moves into the metal

Experimental and theoretical study of iron and mild steel combustion in oxygen flows

The effects of oxygen flow speed and pressure on the iron and mild steel combustion are investigated experimentally and theoretically. The studied specimens are vertical cylindrical rods subjected to an axial oxygen flow and ignited at the upper end by laser irradiation. Three main stages of the combustion process have been identified experimentally: (1) induction period, during which the rod is heated until an intensive metal oxidation begins at its upper end; (2) static combustion, during which a laminar liquid “cap’’ slowly grows on the upper rod end, and, after the liquid cap detachment from the sample; (3) dynamic combustion, which is characterized by a rapid metal consumption and turbulent liquid motions. An analytical description of these stages is given. In particular, a model of the dynamic combustion is constructed based on the turbulent oxygen transport through the liquid metal-oxide flow. This model yields a simple expression for the fraction of metal burned in the process and allows one to calculate the normal propagation speed of the solid metal–liquid interface as a function of the oxygen flow speed and pressure. A comparison of the theory with the experimental results is made, and its potential application is mentioned

Analyse Transactionnelle Suisse romande – Recueil d'articles 2020

Articles diffusés par l'Association Suisse d’Analyse Transactionnelle – Suisse romande durant l'année 2020. Articles - Qu’est ce que l’AT apporte au monde ? - Enseignement spécialisé et AT – Entrevue - Conseil pédagogique et AT – Entrevue - L’accouchement-marathon - Les enjeux relationnels de la coopération - Les étapes de la coopération - La fosse de rösti – une mine d’or pour des expériences sur la diversité -La complexité par la diversité – Quelle signification pour la gestion des organisations ? - L’économie de l’autonomie – Les martiens ont-ils disparu ? - La coopération dans les institutions et hôpitaux – Entrevue Résumés - Le sens des valeurs que l’on porte - Interventions dans l’accompagnement professionnel de couples - Brunch entre amis - Lors des moments difficiles, l’AT nous porte - Counselling de couple avec AT et sexualité : un couple inégal ? - On devait toujours parler de tout... discussion père fille Divers - Éditorial - Prendre soin de nous durant la pandémie - Célébrons Fanita English, joyeux 104e anniversaire - Pleine conscience – regards croisés : retour sur la journée de l’ASAT-SR - Hommages à Jenni Hine - Entrevue avec Sally Cuénin - Anciens numéro

A fast method for morphological analysis of laser drilling holes

Version éditeur : http://jla.aip.org/resource/1/jlapen/v22/i4/p127_s1?isAuthorized=noThis paper presents an original method for analyzing laser drilled holes. The so-called Direct Observation of Drilled hOle (DODO) method is introduced and its applications. The hole characterization that’s been made is compared with x-ray radiography and cross-section analysis. Direct Observation of Drilled hole provides instantaneously surface state, geometric shape, as well as recast layer structure, without additional operation. Since no mounting resin is used to embed the sample, the preparation for analysis is simplified and, gives access to a 3D analysis of hole morphology. The principle of this technique consists in positioning the drilling axis on the joint plane of a butt configuration. Surfaces of the two parts of the sample to be joined are polished beforehand, to increase the contact surface, and then holes are drilled in the joint plane. Once the sample is drilled, the two parts are split so that one half of the hole is in each part of the sample. The preparation time of DODO method samples is shorter than the polishing time of the classical method. Moreover the implementation of the DODO method is much easier, for quality control as well as process development in laser drilling.This work has been supported by Commissariat à l’Energie Atomique CEA-France and Trumpf Laser for HL201P Laser facility and Agence Nationale pour la Recherch

Gas investigation for laser drilling

Version éditeur : http://jla.aip.org/resource/1/jlapen/v19/i3/p165_s1?isAuthorized=noThis article deals with the gas effect on percussion laser drilling in ms pulse duration range. On the one hand, the flow of assistance gas jet is investigated with and without a target using a strioscopy setup and Pitot’s tube. By this way, the position of shock waves in the supersonic jet and near the target surface is revealed. From this characterization, the distance between exit nozzle and target can be optimized to induce higher pressure on surface and protect optics from liquid ejection. On the other hand, metal liquid and vapor jets from irradiated target are observed with a high-speed camera (100 000 Img/sec). Without assistance gas, a surprising result on the video is a shock wave inside the metal vapor jet like a supersonic flow. The assistance gas limits the propagation of the vapor and facilitates the deposition of metallic liquid around the front surface holes

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

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.En présence d'une atmosphère riche en oxygène, à haute pression, un composant métallique porté au-delà d'une certaine température seuil, subit dans certaines conditions un processus de combustion ou d'inflammation rapide, qui peut endommager plus ou moins sérieusement, voire détruire complètement, le composant en question. Les problèmes liés à l'inflammabilité des métaux concernent tout domaine d'ingénierie mettant en jeu des métaux en contact avec de l'oxygène à forte concentration et/ou sous pression (industrie aéronautique et spatiale, secteur médical, industrie gazière etc.) Il existe depuis les années 70 un test standard pour l'évaluation de la compatibilité à l'oxygène des matériaux métalliques. Ce test standard consiste à allumer un barreau cylindrique de métal sous oxygène afin de déterminer la pression ou concentration seuil d'oxygène menant à la destruction totale de l'échantillon et la vitesse de propagation de la combustion qui s'ensuit. Ce test présente plusieurs inconvénients : la phase d'initiation est généralement mal étudiée, soit parce que son étude est rendue impossible par la technique d'allumage utilisée (amorce pyrotechnique), soit parce qu'il a été obtenu dans une configuration correspondant assez peu aux conditions réelles des accidents (chauffage en volume). Par ailleurs, très peu d'attention a été donnée jusqu'à présent à l'influence d'écoulements d'oxygène à la surface de l'échantillon sur la propagation de la combustion. Cette thèse propose une approche originale d'étude de la combustion du fer et des aciers au carbone et inoxydable sous atmosphère d'oxygène, afin de comprendre et de définir les conditions d'initiation et de propagation de la combustion de pièces métalliques en utilisant un laser focalisé comme source d'initiation. À cette fin, les mécanismes successifs de l'initiation par laser de la combustion puis sa propagation ont été étudiés. Le travail de cette thèse s'articule en deux parties. Dans la première partie, une étude expérimentale de l'influence des paramètres d'initiation de la combustion par laser, des conditions de soufflage d'oxygène, et de pression statique sur l'initiation et la propagation a été réalisée dans une configuration expérimentale originale (propagation de haut en bas), grâce à la mise en oeuvre de divers outils d'instrumentation : visualisation par caméra rapide, pyrométrie optique, thermocouples, analyses métallographiques. Une attention particulière a été donnée à la notion de seuil en énergie (laser) menant à l'initiation de la combustion, à la propagation ou à la destruction totale de l'échantillon, qui ont été déterminés dans différentes conditions de soufflage. Sur la base des données expérimentales précédemment obtenues, la deuxième partie de ce travail de thèse a consisté en la mise au point de simulations numériques (sous le logiciel commercial COMSOL Multiphysics) de ces expériences (limitée au démarrage de la combustion). Des paramètres inconnus liés à la réaction ont été ajustés afin de reproduire au mieux l'évolution des divers phénomènes observés (les champs thermiques, la dynamique d'inflammation, le comportement du bain liquide, la déformation géométrique etc.). L'ensemble de ce travail a permis de formuler une phénoménologie de l'initiation et de la propagation de la combustion par laser ainsi qu'une interprétation physique de celle-ci