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Made available in DSpace on 2022-04-28T19:44:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-01-01 AA7050-T7451 aluminum alloy is one of the most used material in aeronautical applications due to its high strength/density ratio and good fatigue resistance. More recently the AA2050-T84 alloy was introduced due to its reduced density and comparable static mechanical properties. However, fatigue crack propagation properties in corrosive environments are yet to be documented. In this paper fatigue crack propagation was evaluated in saline (3.5 wt% NaCl solution) and air environments. The AA2050-T84 alloy presented a better fatigue performance both in air and aqueous saline environments. Its superior performance was ascribed to non-homogeneous deformation and higher corrosion resistance. These results show the AA2050-T84 alloy as a potential candidate to replace AA7050-T7451 alloy in aeronautical components subjected to fatigue in corrosive environments. USP – University of São Paulo, Av. Trabalhador São Carlense 400 Federal University of São Carlos Department of Materials Science and Engineering, Rod. Washington Luis, CEP 13565-905 UNESP – São Paulo State University, Campus of São João da Boa Vista, São João da Boa Vista UNESP – São Paulo State University, Campus of São João da Boa Vista, São João da Boa Vista

The use of aeronautical thermosetting resins in the field of structural materials is still limited because of several drawbacks, such as the absence of electrical and thermal conductivity and the poor impact damage resistance. An important contribution for increasing the composite application in this field can be given by implementing a strategy of autonomous damage-repair and other specific functions integrated into the material structure. This work proposes a successful strategy based on the design of supramolecular self-healing systems. It is aimed at developing self-healing, load-bearing structures with all functionalities integrated into a single material able to fulfill important industrial requirements.

Modern aircraft employ profusely carbon fiber composites (CFC) for their construction. Then, it is mandatory to characterize the behaviour of this kind of materials for its use under harsh electromagnetic environments. In that sense, this paper presents the application of two standards, the ASTM D4935 and the IEC 61000-4-21, to the measurement of the shielding effectiveness (SE) of aeronautical multi-ply CFC laminates frequently used for the construction of aircraft. Each technique is well suited for a specific material or realization and a specific frequency range. So, both techniques are complementary and should be developed in parallel. Taking into account the high SE expected for this kind materials, the set-ups imply the measurement of very low signals, that poses an experimental challenge that has to be faced. Then, in this study, different test samples and realizations of CFC materials have been fabricated and measured. Improvements on the traditional measurement procedures have been applied, obtaining promising results. This work has been funded by the Spanish Ministry of Science (MCIU) under project UAVE3 (TEC2016-79214-C3-1-R). Preprint

International audience; Most of the metals used in aircraft construction are aluminium alloys. These alloys, poorly investigated for conservation purposes, require specific characterisation due to the presence of intermetallic precipitates at various length scales influencing mechanical properties and resistance to corrosion, and because of different surface treatments. This study undertook an investigation into the different aluminium alloy parts of a currently renovated Breguet aircraft and, as a result, revealed the need to research and characterise these materials. An adapted methodological approach was used and the results of the materials characterisation focused on the main materials and on the corroded surfaces. Alongside performing material analysis, archival documents were used to provide additional and complementary historical data. From this, it was concluded that a specific understanding of the alteration processes in aluminium alloys is required in order to develop conservation strategies.

2015 - 2016, In this PhD thesis work, Ruthenium catalysts were covalently and non-covalently linked to carbon-based nanomaterials, in order to give self-repairing ability to the aeronautical materials. These supported catalysts have been characterized and their activity has been evaluated in metathesis reactions. The 1st and 2nd generation Grubbs and Hoveyda-Grubbs catalysts were covalently bonded to graphite oxide and tested in the ring-opening metathesis polymerization reaction of tensed monomers, and subsequently their catalytic activity was verified in the aeronautical composites. To optimize the performance of such supported catalysts, catalytic sites have been protected from the highly reactive environment by a polymeric globular shell. These catalysts have been further supported on multi-walled carbon nanotubes and graphite by an alternative covalent synthetic approach that allows to preserve the chemical and physical properties of the carbon nanotubes employed, avoiding the initial oxidation step. For non-covalent functionalization, the same catalysts were first linked to pyrene molecules and then, by π-stacking, anchored on graphite. Their activity was determined in metathesis reactions and their conductivity was estimated within aeronautical composites. Such complex pyrene-catalyst, highly versatile, have been used to synthesize polymers having a terminal pyrene capable of improving the dispersion of the same carbon nanotubes used in aeronautical materials in order to improve their performance. Lastly, was evaluated the possibility of self-repairing the aeronautical material through radical polymerization of monomers such as styrene, using Copper catalysts.[edited by author]

Nowadays, the study of the direct effects of lightning on aeronautical structures could be based, at least in part, on simulation tools. Nevertheless, the lack of experimental data on the transient phase of the lightning arc does not allow us to justify the predictive nature of the simulation tools. The objective of this thesis is to produce an experimental database based on the characterization of lightning arcs in standardized situations. These data can be used both for the understanding of the phenomena observed during the tests, but especially as a reference comparable to the simulation tools.First, we are interested in the free arc column in air, without interaction with the electrodes. Furthermore, time- and space-resolved profilesof temperature and pressure are evaluated by emission spectroscopy. For a 100 kA arc, it is shown that the temperature reaches 37400 K in the arc axis at 2 μs after arc ignition, with a corresponding pressure of 45 bar.Second, we are interested in the interaction of the lightning arc with aeronautical materials. The dynamics of the arc roots and the characteristics of the shock wave are analyzed for different aeronautical materials such as aluminum or carbon fiber composites. The thermo-mechanical constraints applied on the material are studied by infrared thermography and by rapid deflection measurements at the center of panel, leading to an evaluation of the pressure exercised by the arc at the attachment point., Aujourd’hui, l’étude des effets directs de la foudre sur les structures aéronautiques pourrait s’appuyer, au moins en partie, sur des outils de simulation. Néanmoins, le manque de données expérimentales sur la phase d’arc impulsionnelle ne permet pas de justifier le caractère prédictif des outils de simulation.L’objectif de cette thèse est de réaliser une base de données expérimentale en s’appuyant sur la caractérisation des arcs de foudre dans des situations standardisées. Ces données peuvent être utilisées à la fois pour la compréhension des phénomènes observés lors des essais, mais surtout comme référence comparable aux outils de simulation.Dans un premier temps, on s’intéresse à la colonne d'arc libre dans l’air, hors interaction avec les électrodes. Par ailleurs, les profils spatio-temporels de température et de pression sont évalués par spectroscopie d'émission. On montre ainsi que, pour un arc de 100 kA, la température maximale atteint 37400 K sur l'axe de la colonne à 2 μs après l’amorçage, avec une pression de l’ordre de 45 bars.Dans un second temps, on s’intéresse à l'interaction de l'arc foudre avec des matériaux aéronautiques. La dynamique du pied d'arc ainsi que les caractéristiques de l’onde de choc sont analysées sur différents matériaux aéronautiques tels que l’aluminium ou des composites à fibres de carbone. Les contraintes thermomécaniques subies par le matériau sont étudiées par thermographie infrarouge, et par des mesures de déflexion rapide au centre du matériau, conduisant à une évaluation de la pression exercée par l’arc au point d’impact.

The use of different materials as metals, wood and other modern materials like composites, require a previous evaluation of its performance under corrosion, creep, tension, compression, bending and fatigue. In general, these requirements lead to a few number of materials to choose during the project of one component, but in some cases, there’s a lot of options that can be selected. In this work, a mechanical approach is considered for some classes of materials. Of course, a complete analysis involves a management science, also called, operational research, with an application of linear programming or, in some cases, heuristics models like ants colony, but this isn’t our target at this moment. It’s possible to see, with the mechanical approach, the advantage of composites materials application. O uso de diferentes materiais tais como metais, madeira e outros materiais modernos tais como os compósitos, requer uma avaliação prévia do seu desempenho e resistência à corrosão, fluência, tensão, compressão, dobragem e fadiga. Em geral, estes requisitos levam à escolha de uns tantos materiais durante o projecto de um componente, mas nalguns casos as opções possíveis são numerosas. Neste trabalho, é feita uma abordagem mecânica para algumas classes de materiais. Claro que uma análise completa envolve uma investigação operacional, com aplicação de uma programação linear e, nalguns casos modelos heurísticos como colónia de formigas, mas este não é o nosso objectivo neste momento. Com a abordagem mecânica, é possível ver a vantagem da aplicação dos materiais compósitos.

International audience; Sandwich structures represent a very interesting approach for the development of new multifunctional and lightweight materials for aerospace and space applications. Nomex® or aluminum honeycomb is at this date the most widely used core materials for sandwich structures, given their extraordinary strength-to-weight-ratio. However, these materials exhibit some important drawbacks as a poor vibrational and acoustic damping, along with a limited impact energy absorption capability. Several studies are in progress in order to develop new composite materials with enhanced acoustic and vibrational damping properties. A very promising solution to overcome these issues is represented by thermoplastic foams, having several advantages as ease of processing, good impact energy absorption, recyclability and enhanced properties in terms of thermal and acoustic isolation, along with the possibility to modify their intrinsic properties through micro and nano-particles addition.A relatively new and promising technique to develop thermoplastic foams is represented by supercritical CO2 (sc-CO2) assisted foam extrusion, with sc-CO2 acting as Physical Blowing Agent (PBA). Sc-CO2 has limited environmental impact, given its low toxicity and energetic requirements to attain its supercritical conditions (31 C, 74 bars), making this process economic, sustainable and totally green. In the frame of this work, a continuous process has been used to produce PLA foams with different microstructures depending on the operating conditions. Typical densities range from 20 to 60 kg/m3, crystallinity from 10 to 30 % and cell size from 90 to 500 µm.