Analysis of the evolution of space debris through a synthetic population

Space debris are all man-made objects orbiting the Earth which no longer serve a useful function. Space debris have increased substantially in the last decades and can be counted in millions. This paper deals with the idea of the creation of a synthetic population of space debris, which preserves as accurate as possible the characteristics of the real one. All the individuals of the synthetic population will be propagated by powerful numerical integrators, becoming into an excellent tool for global predictions or simulations, useful for the future ADR actions, and for the location of parking orbits

Effect of the over-ageing treatment on the mechanical properties of AA2024 aluminum alloy.

The evolution of the hardness of the over-ageing AA2024 alloy scale was followed by measurements of Vickers hardness. The nanoindentation is adapted to the determination of elastoplastic properties (hardness and Young’s modulus) of the matrix and also of coarse intermetallic precipitates. Influence of the artificial over-ageing time to hardness and to mechanical properties as the local scale was investigated

Regulatory framework of veterinary practice in zoos

Although veterinary practice in zoological institutions accounts for only a small percentage of veterinary services in France, it is subject to complex national, European and international regulations relating to the care, husbandry and exchange of wild animals in captivity. The legislation on zoological veterinary medicine is based mostly on the legal definition of veterinary practice. In addition to the use of devices subject to special regulations (x-rays, remote injection devices), the zoo vet also uses drugs (permanent use of the “cascade”, occasional use of imports) within the limits prescribed by the law on pharmacy. The vet must know the rules and regulations applicable to the kind of institution he is working with, the institution being also subject to regulatory obligations on medical care, identification and registers. The vet’s healthcare duties, recently redefined on a European level, remain complex but essential, particularly when treating (re)-emerging diseases.Même si l'activité vétérinaire en parc zoologique représente un pourcentage assez restreint de la pratique professionnelle en France, elle se place au cœur d'un faisceau complexe de législations nationales, européennes et internationales régissant les soins, la détention et les échanges d'animaux sauvages en captivité. La législation vétérinaire appliquée à l'exercice en parc zoologique relève, pour l'essentiel, de la définition juridique de l'acte vétérinaire. Outre l'utilisation d'outils soumis à réglementation (radiographie, téléinjection), le vétérinaire de parc zoologique fait aussi une utilisation du médicament (recours permanent à la « cascade », recours occasionnel aux importations) dans les limites contraignantes prévues par la loi sur la pharmacie. Il doit connaître les cadres réglementaires qui régissent le type d'établissement où il officie, lequel doit aussi tenir un certain nombre d'engagements envers les autorités (soins, marquage, registre). Ses missions sanitaires, récemment refondues dans un contexte européen, restent complexes mais primordiales, notamment face aux maladies (ré)émergentes

Study of the influence of the artificial ageing temperature on the AA2024 alloy microstructure

For the last 30 years, AA2024 aluminum alloy was very used as structural material in the aerospace industry due to its low density and good mechanical strength. The phenomenon of precipitation hardening in aluminum alloys takes place at relatively low temperature and induces the precipitation of intermetallic particles composed of the main alloying elements i.e., copper and magnesium. The fundamental stage of the age-hardening process consists in the acceleration of the decomposition phenomenon of the supersaturated solid solution, resulting in the coarse intermetallic particle precipitation; stage where the mechanical properties reaches the maximum values, but at the cost of a low corrosion resistance. In this paper, the AA2024 alloy microstructure was studied during the over-ageing process. The over-ageing treatment (T7) is supposed to stabilize the microstructure and the mechanical properties to improve the corrosion resistance. The over-ageing treatment consists in a solution treatment at 495±5°C for 1 hour, quenched into cold water and artificial aged. Three different artificial ageing temperatures were studied: 150°C, 175°C and 190°C. The mechanical properties modifications were followed by Vickers macrohardness measurements. The treatment duration for each temperature (36 days for 150°C, 50 hrs for 175°C and 24 hrs for 190°C) was determined by a given macrohardness reduction. To characterize the over-aged AA2024 alloy microstructure, a statistical analysis of the surface fraction and surface density of intermetallic particles was made. The intermetallic particle dimension distribution, depending on the over-ageing temperature, was also observed. To do so, scanning electron microscope observations were carried out and image analyses were performed from backscattered electron images

Élaboration de céramiques sans ajouts de frittage par Spark Plasma Sintering pour application en électronique de puissance

Des substrats en carbure de silicium et nitrure d’aluminium ont été élaborés par Spark Plasma Sintering en vue de réaliser des refroidisseurs pour l’électronique de puissance. La température et la pression lors de l’élaboration doivent être maximisées pour atteindre des densités relatives proches des densités théoriques de chaque matériau. Les comportements mécanique et électrique des céramiques ont été établis à l’aide d’une approche microstructures/propriétés. Les porosités jouent un rôle très important sur le comportement mécanique et électrique des matériaux. Il apparaît également que les propriétés électriques de l’AlN SPS sont supérieures à celles de l’AlN fritté conventionnellement montrant que le procédé l’élaboration SPS n’induit pas d’impuretés dans le matériau. Les propriétés électriques du SiC SPS sont largement inférieures à celle du SIC fritté conventionnellement avec du bore comme ajout de frittage indiquant le rôle important de la qualité chimique des poudres utilisées pour le frittage

Application of Kelvin probe Force Microscopy (KFM) to evidence localized corrosion of over-aged aeronautical 2024 aluminum alloy

The 2xxx serie aluminum alloys are characterized by good mechanical performances and low density, however they are susceptible to different forms of localized corrosion: pitting corrosion, intergranular corrosion and stress corrosion cracking. The 2024-T351 aluminum alloy is used in the aircraft industry for numerous applications such as fuselage and door skin. Corrosion damage of the material is also very detrimental for the structural integrity of the aircraft. The presence of coarse intermetallic particles, with a heterogeneous size distribution was found to be responsible for the 2024 susceptibility to localized corrosion. These particles are generally the cause of initiation sites. Presence of micro-defects in the oxide film upon coarse intermetallic particles and the galvanic coupling with the matrix contribute to the development of pitting corrosion. The over-ageing treatment (T7) is supposed to stabilize the microstructure and the mechanical properties to improve the corrosion resistance. The 2024 alloy microstructure after the T7 heat treatment remains very complex. The 2024 alloy corrosion behavior was studied in the over-ageing state for three different temperatures (150, 175 and 190 °C). During the corrosion tests in chloride-containing environment, the behavior of coarse intermetallic particles was found to be different. Thus, the 2024 samples suffer a gradual attack upon S-Al2CuMg particles and finally Al(Cu,Mn,Fe,Si) particles. The corrosion damage was studied by Atomic Force Microscopy (AFM) and Kelvin probe Force Microscopy (KFM). This technique allows simultaneous topographical and electric potential mapping to be obtained. This latest potential was shown to be correlated to the corrosion potential of the 2024 alloy. This study focuses on the variation of the KFM potential of the coarse intermetallic particles and the matrix for the over-ageing conditions (T7). Observations using optical microscope and AFM were also performed to obtain the corrosion rate for each condition. The corrosion rate was correlated to the chemical composition variation of the particles obtained by scanning electron microscope observations and EDS analyses

Characterization of refractory titanium alloys welded by TIG and laser processes

The use of refractory titanium alloys for the components of structure subjected to increasing temperatures is in full expansion in the air transport. Within the framework of European project HORTIA, aiming to develop and design a conduit of refractory titanium alloy helicopter by associating innovative processes and the industrial constraints, this work relates to the implementation and characterization of Ti6242 and Beta-21 S welded sheets by TIG and C02 laser processes. The determination of the mechanical characteristics in connection with the metallurgical transformations relating to the Ti6242/Ti6242, Beta 2IS /Beta 2lS and Ti6242/Beta2lS assembly configurations allowed a rigorous comparison of the processes and studied materials. The influence of the heat treatment 600°C/8h on the relations structures/mechanical properties was also studied in order to envisage the behaviour of the assemblies under the real service use conditions

Échantillonnage préférentiel et méta-modèles : méthodes bayésiennes optimale et défensive

National audienceThis paper considers the problem of the choice of an instrumental distribution for the estimation by preferential sampling of an integral $\int h(x) \pi(x)\, {\rm d}x$, where the function $h$ is expensive to evaluate. To build such an instrumental distribution, we adopt a Bayesian approach where we introduce a prior about $h$, which makes it possible to construct a Bayes-optimal instrumental distribution, given evaluation results of $h$. This instrumental distribution minimizes the expectation (with respect to the prior distribution about $h$) of the (frequentist) variance of estimation. However, the variance of estimation obtained using this instrumental distribution can be larger than that of the Monte Carlo estimator in some cases. We present a "defensive" correction of the Bayes-optimal instrumental distribution to address this issue. We illustrate the approach on a problem of estimation of a probability of failure, based on an industrial numerical simulator from the domain of structural reliability.Cet article considère le problème du choix d'une loi instrumentale pour l'estimation par échantillonnage préférentiel d'une intégrale du type $\int h(x) \pi(x)\, {\rm d}x$, la fonction $h$ étant coûteuse à évaluer. Pour construire une telle loi instrumentale, nous adoptons une approche bayésienne consistant à introduire un a priori sur $h$, ce qui permet, étant donnés des résultats d'évaluations de $h$, de construire une loi instrumentale optimale au sens bayésien. Cette loi instrumentale, bien que permettant de réduire l'espérance (par rapport à la loi a priori) de la variance fréquentiste d’estimation, peut conduire dans certains cas à une variance supérieure à celle de l'estimateur de Monte Carlo. Nous proposons une correction, dite "défensive", de la loi optimale bayésienne pour remédier à ce problème. Une application à l'estimation d'une probabilité de défaillance, à partir d'un code industriel issu du domaine de la fiabilité des structures, illustre l'approche proposée

Environmental protection of titanium alloys in centrifugal compressors at 500°C in saline atmosphere

The use of the titanium alloy Ti-6246 (Ti–6Al–2Sn–4Zr–6Mo, wt-%) for gas turbine compressors allows an increase in working temperature and stress level. Under severe service conditions, the material experiences combined high temperature and high mechanical stress and, in saline atmospheres, stress corrosion cracking (SCC) can occur, leading to catastrophic mechanical failure. The present study was performed to evaluate the potential of several surface treatments to protect Ti-6246 alloy, after salt deposit, from hot salt SCC at temperatures ?500°C and 500 MPa static mechanical stress conditions. Shot peening, thermal oxidation and metal–ceramic coatings were investigated. Experimental results confirm the existence of brittle stress corrosion phenomena marked by a low residual elongation of test samples and the presence of oxides on the fracture surfaces. Both shot peening and metal–ceramic coatings increase the hot salt SCC resistance of the alloy. Times to rupture were improved by a factor of 3 for shot peening and by a factor of 10 for metal–ceramic coatings. Inversely, the time to rupture of preoxidised alloys has been halved compared with uncoated alloys. As well as these interesting quantitative results, structural studies of metal–ceramic coatings showed that they are mechanically and chemically compatible with the titanium alloy substructure and should work under severe thermomechanical stresses and aggressive atmospheres