Caractérisation de l'usure et de l'échauffement par frottement de matériaux métalliques et composites à matrice organique, lors des atterrissages d'urgence

International audienceAviation is one of the safest public transport means today. To reach such a performance, aircraft safety mainly relies on experience feedbacks and a set of constantly evolving rules which concern the flying products and operations. This also works for emergency landings or crash situations wherein the aircraft "belly" is directly in contact with the runway (Figure 1). For this purpose, a four years research project (PHYSAFE) funded by the French DGAC started in August 2015. Part of the research aims at experimentally studying and characterizing various phenomena which may have a noticeable influence on aircraft passengers' safety in case of emergency landing or crash. Among these experimental studies, the development of test means and facilities to characterize the dynamic wear behavior of aircraft primary structure materials once in contact with the ground was selected as being of common interest for aircraft and rotorcraft airframes. The part of the PhD work to be presented is notably focusing on the study and characterization of wear and heat phenomena, for metallic and composites aircraft structural materials (reference materials: Au2024, T700/M21) during emergency landing situations. It aims at estimating (through "pin on disc" tests [1]) the main phenomena and principles to be taken into account for an experimental protocol (test bench, specimens, instrumentation, etc.) dedicated to the study of wear and heat of materials in representative conditions, followed by a first comparison of metallic and composite reference materials performances. The methodology set up to partially answer the studied problematic, starts with pin-on-disc tests using a concrete pad and discs made of aluminum or composite material. The preliminary experimental design permits to observe the results of interactions between concrete and the materials like in an aircraft fuselage. A first identification of the tribological systems representing the studied contact, aims at defining the first bodies and the third body produced within the studied contacts. Once the tribological mechanisms identified (by post mortem and in-situ analysis), an estimated dissipated energy may be linked to those mechanisms through the writing of material and energy balances [2,3]. A future step of the work would concern the study of possible similitude rules (through non-dimensional numbers establishment relying on the Vaschy-Buckingham's theorem [4]), for a selection of identified wear and abrasion mechanisms, to check the possible extrapolation of experiments at a laboratory scale at full-scale level.Les transports aériens sont de nos jours assez fiables en matière de sécurité et cela grâce aux avancées constamment faites dans le domaine. Pour continuer l'amélioration de cette sécurité, nombreuses sont les études faites autour différentes thématiques, dont le crash et les atterrissages d'urgence (situations où les aéronefs peuvent se retrouver sur le "ventre").Le projet de recherche (PHYSAFE) de la DGAC a ainsi été lancé à l'ONERA depuis 2015 pour une durée de 4 ans. Il a pour objectif principal d'apporter des éléments de compréhension du contact fuselage/piste via différentes études et notamment la conception d'un banc dédié à l'étude du frottement du fuselage sur la piste.La partie présentée des travaux de thèse, viendra rendre compte de l'étude et la caractérisation de l'usure et de l'échauffement produits dans le contact entre la piste (en béton) et les composants structuraux représentatif du fuselage (alliage d'aluminium Al2024/T3 et composite carbone epoxy T700/M21). Les travaux s'appuient sur des essais de type "pion/disque" qui permettront l'identification d'un système tribologique représentatif afin de pouvoir définir et caractériser le 3ème corps produit dans le contact.Une fois les mécanismes tribologiques identifiés (analyses post-mortem et in-situ), il s'agira d'écrire des équations de bilan de matière et d'énergie pour établir la corrélation entre les mécanismes tribologiques et la dissipation de l'énergie liée à la vitesse.L'étape suivante du travail consistera à étudier l'existence de règles de similitude (nombres adimensionnels définis via le théorème de Vaschy-Buckingham), pour vérifier, dans le cas de certains mécanismes tribologiques, la possibilité d'extrapoler les expériences faîtes en laboratoire à une échelle supérieure

Study of the wear process in an experimental simulation of a fuselage/runway rubbing contact

In this work, the authors tackle the problem of laboratory simulation of frictional contact in wheels-up emergency landing conditions. To design a novel tribometer simulating the contact between an aircraft structure and a runway, one must carry two complementary main tasks: the understanding of the underlying physical mechanisms and the scaling up of the in-lab results to the scale of interest. The authors propose to progress on the first task by conducting exploratory work using existing resources. Their contribution consists of a multi-scale methodology to reconstruct the wear process in a tribological system within wheels-up emergency landing conditions. This could provide guidance for safer aircraft and runway design. The study falls within the framework of three-body tribology. The proposed multi-scale characterisation methodology is made up of four steps. After describing the whole tribological system, its mechanical response is measured and analysed. This measurement is complemented by surface observations and physicochemical analyses. Finally, all the measurements and observations are discussed to come across a phenomenological wear scenario that revealed friction and wear as system responses with the key role of the third body

Etude de fonctions passives à base de nanostructures photoniques

Thèse de doctorat en Instrumentation et Analyses Avancées, Université de Lille 1, 4 décembr

Étude de fonctions passives à base de nanostructures photoniques

Ce travail présente une étude de guides d'onde de taille submicrométrique (GOTS) réalisés en filière InP, filière particulièrement adaptée aux composants actifs des télécommunications à 1,3æm et 1,55æm. L'intérêt de tels dispositifs à fort confinement optique se manifeste dans la miniaturisation des systèmes optoélectroniques. Plusieurs méthodes de gravure des GOTS ont été envisagées : humide, RIE et ICP ; ce qui, parallèlement à des simulations par BPM (beam propagation method) de la propagation dans des GOTS idéaux permettant de déterminer l'influence des différents paramètres technologiques sur les pertes de propagation, nous a permis de dégager une structure épitaxiale et une technologie préférentielles. L'analyse de ces différentes informations nous a permis de réaliser par gravure ICP des GOTS de 0,3æm de large au minimum, présentant des pertes du même ordre de grandeur que celles relevées dans la littérature pour des structures similaires réalisées en filière GaAs.LILLE1-BU (590092102) / SudocSudocFranceF

Influence of processing gases on the properties of cold atmospheric plasma SiOxCy coatings

International audienceThin layers of SiOxCy (y = 4−x and 3 ≤ x ≤ 4) were applied using a cold atmospheric plasma torch on glass substrates. The aim was to investigate using Atomic Force Microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (Tof-Sims) the influence of the gases used on the morphology and composition of the deposits. A hexamethyldisilane (HMDS) precursor was injected in post-discharge in an air or nitrogen plasma using a carrier gas (air or nitrogen) and was applied on the substrate previously pre-treated by an air or nitrogen plasma. The carrier gas and plasma gas flows and the distance between the substrate and the plasma torch, the scanning speed, and the precursor flows were kept constant during the study. The gas used during activation pre-treatment showed no particular influence on the characteristics of the deposit. When air is used both as plasma and carrier gas, the coating layer is thicker (96 nm) than when nitrogen is used (64 nm). It was also evidenced that the gas carrying the precursor has little influence on the hydrophobicity of the coating, contrary to the plasma gas. The latter significantly influences the surface characteristics of the coatings. When air is used as plasma gas, a compact coating layer is obtained and the surface has a water contact angle (WCA) of 82°. When nitrogen is used, the deposit is more hydrophobic (WCA of 100°) and the deposit morphology is different. This increase in hydrophobicity could be correlated to the increase of Sisingle bondOsingle bondC bonds in the upper surface layers evidenced by XPS analyzes. This observation was then confirmed by Tof-Sims analyzes carried out on these thin layers. A uniform distribution of Carbons in the siloxane coating could also be observed using Tof-Sims 2D reconstruction images of cross sections of the deposited layers

Etude par spectroscopie Raman de la décomplexation photoinduite du matériau GaAs hydrogéné

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Effects of annealing temperature and heat-treatment duration on electrical properties of sol–gel derived indium-tin-oxide thin films

International audienceTransparent indium tin oxide (ITO) thin films have been deposited by the dip-coating process on silica substrates using solutions of 2,4-pentanedione, ethanol, indium and tin salts. The films have been first dried in air at 260 °C for 10 min and then annealed in a reducing atmosphere at different temperatures for various durations. The resistivity of ITO layers was found to decrease with increasing the metal concentration of the starting solution or the annealing temperature. Hence, by adjusting both metal concentration in the coating solution and heat-treatment, resistivities lower than 5 × 10− 3 Ω cm for an annealing temperature of 550 °C and lower than 2 × 10− 2 Ω cm for an annealing temperature of 300 °C, were obtained. These results are correlated with the density and the size of ITO grains in the films

Three-Dimensional MOF-Type Architectures with Tetravalent Uranium Hexanuclear Motifs (U 6 O 8 )

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