1,720,967 research outputs found
Innovative materials for high temperature structural applications: 3rd Generation γ-TiAl fabricated by Electron Beam Melting
Full text linkIn the aeronautics industry, the propulsion systems stand among the most advanced and critical components. Over the last 50 years, gas turbine aeroengines were subjected to intensive research to increase efficiency and reduce weight, noise and harmful emissions. Together with design optimization, breakthrough in materials science for structural applications triggered the development of the most advanced gas turbine engines. For low temperatures, basically ahead of the combustion section, lightweight Ti alloys are preferred for their good mechanical properties. For high temperatures instead, Ni-based superalloys exhibit outstanding properties up to very high temperatures despite a rather high material’s density.
Research have focused on enhancing to the maximum the potential of materials in gas turbine engines. According to the application, the components experience various mechanical and environmental constraints. Special designs, manufacturing process, material compositions and protective coatings have been developed to push the limits of advanced materials. Nowadays, the attention is focused on innovative materials to replace the existing Ti and Ni based alloys leading to substantial benefits. Light weight composite materials in particular were found very attractive to replace some components’ Ti alloys. At higher temperatures, it is of great interest to replace Ni-based superalloys by materials with lower density and/or higher temperatures applications, which in turn would lead to substantial weight reduction and increase efficiency.
At the highest temperatures range, in particular in the combustion chamber and high pressure turbine sections, ceramic based materials offer promising balance of properties. Research are dedicated to overcome the drawbacks of ceramics for such structural applications, and in particular their brittle fracture behavior, by addition of reinforcing fibers. At lower temperatures range, TiAl based intermetallics emerged as very promising materials at half the density of Ni-based superalloys. Significant weight reduction could be achieved by the introduction of TiAl based alloys for rotating components of the compressor and low pressure turbine. 2nd generation γ-TiAl alloys were lately introduced in GE’s GEnx and CFM’s LEAP engines.
The present work concerns the fabrication by the additive manufacturing technique Electron Beam Melting of 3rd generation γ-TiAl alloys for high temperatures application in gas turbine aeroengines. EBM, building parts layer by layer according to CAD, offers many advantages compared to other manufacturing processes like casting and forging. Reported by Avio, 2nd generation γ-TiAl alloys have been successfully fabricated by EBM. To increase the material’s potential, the production of 3rd generation γ-TiAl alloys Ti-(45-46)Al-2Cr-8Nb was therefore studied. The optimization of the EBM parameters led to high homogeneity and very low post-processing residual porosity ≤ 1%. The fine equiaxed microstructure after EBM could be tailored towards the desired mechanical properties by simple heat treatment, from equiaxed to duplex to fully lamellar. In particular, a duplex microstructure composed by about 80 % lamellar grains pinned at grain boundaries by fine equiaxed grains was obtained after heat treatment slightly over the α transus temperature.
The study showed that addition of a higher amount of Nb significantly increased the oxidation resistance of the material, thus increasing the application temperature range of these γ-TiAl alloys
Implementing PHM for Legacy Flight Control Actuators Through Operational Aircraft Data: Approach and Lessons Learned
Full text linkThe prospect of optimizing fleet operations and streamlining maintenance processes has made Prognostic and Health Management (PHM) strategies valued in many engineering applications. However, implementing PHM for legacy equipment presents significant challenges, especially when existing monitoring frameworks were not designed for PHM. This paper presents a case study in which a data-driven PHM framework was developed for an Advanced Jet Trainer's flight control Electro-Hydraulic Actuator (EHA), relying solely on aircraft-level information. Rather than introducing new algorithms, this work documents the process, compromises, and adaptations necessary to extract actionable health and usage insights when ideal data conditions are not available. While PHM typically relies on monitoring equipment status signals to identify precursors of degradation, this approach is often impractical due to the absence or inadequacy of equipment-level data. The architecture described here was specifically designed to operate within these constraints, demonstrating how established PHM concepts can be tailored to real operational environments. The gained experience highlights both the opportunities and limitations of PHM in practice, offering practical guidance for similar efforts in aerospace and other domains where data quality and availability are major concerns. Through this study, we aim to provide a transparent account of the challenges faced, the solutions adopted, and the lessons learned, contributing to the broader understanding of PHM implementation in complex, data-limited settings
Mission profile clustering for usage-based health modeling of flight control actuators applied to a fleet of advanced jet trainers
Full text linkThis work introduces a mission profile clustering pipeline aimed at supporting usage-based health modeling of electro hydraulic flight control actuators employed in a fleet of Advanced Jet Trainer (AJT) aircraft. The study is part of a broader, high-level, modular Prognostics and Health Management (PHM) framework developed to predict Unscheduled Removals (URs) of the AJT horizontal tail flight control actuators. Operating in an industrial setting, this PHM effort specifically addresses the challenge of extracting prognostic information from a legacy fleet already in service, leveraging existing operational data to improve asset availability.
The overall project leverages an extensive real-world dataset that spans over ten years and more than 25000 flight hours accumulated by a fleet of as many as 20 aircraft. This paper specifically focuses on the Flight Clustering Module within the Data Processing layer of the PHM framework, which serves as a critical enabler for future feature projections. Through an in-depth analysis of the underlying principles and a detailed overview of the main system interfaces, this work proposes a practical solution for categorizing and classifying mission profiles while highlighting the challenges of working with real operational data. After a pre-processing pipeline, developed to standardize and align time-series flight data, the clean trends are then clustered via a Self-Organizing Map (SOM). In this work, a systematic SOM hyperparameter tuning pipeline is also introduced. The tuning routine employs a grid search strategy to optimize the SOM hyperparameters by jointly evaluating the topographic error, the quantization error, and the percentage of grid utilization. The result of the application of the trained SOM on the dataset is a set of Clustered Mission Types (CMTs), each linked to specific statistical distributions of actuator usage increments. These clusters are integrated into the broader PHM framework to simulate future aircraft behavior and estimate component degradation. Placed in an operational industrial environment, this methodology effectively connects mission-specific usage patterns with predictive health modeling, improving the modeling ability of PHM systems, and laying the foundation for smarter usage-based maintenance planning in aviation operations
Titanium aluminides for automotive applications processed by Electron Beam Melting
No full textI materiali del tipo γ-TiAl rappresentano una classe importante di materiali strutturali che, grazie alle loro ottime proprietà fisiche e meccaniche, giocano un ruolo importante nell'industria aerospaziale e automobilistica. In modo particolare, sono considerati una valida alternativa alle superleghe a base nichel grazie ad una densità minore (circa 4 g/cm3 per γ-TiAl e circa 8 g/cm3 per superleghe). In questo lavoro, realizzato nell'ambito del progetto europeo TIALCHARGER, polveri di Ti-48Al-2Cr-2Nb (48-2-2) e Ti-48Al-2Nb-0.7Cr-0.3Si (RNT650) sono state utilizzate per fabbricare mediante Electron Beam Melting (EBM) alcuni provini e prototipi di turbine per turbocharger. Questa tecnologia di fabbricazione del tipo additive manufacturing che utilizza un fascio di elettroni per generare dei componenti mediante la fusione selettiva di polveri procedendo strato per strato basandosi su un progetto CAD. I manufatti prodotti con le diverse polveri sono stati caratterizzati in termini di difettosità residue e sono risultati adeguati sia in termini di porosità media complessiva che di taglia massima del difetto residuo individuato. Inoltre è stata valutata la microstruttura del materiale cosi come prodotto e sono stati messi a punto i trattamenti termici per ottenere la microstruttura finale. Questo è un punto essenziale per questi materiali poichè le loro proprietà meccaniche sono estremamente influenzate dalla microstruttura finale. È stata inoltre analizzata la composizione chimica di polveri e massivo sia di 48-2-2 che RNT650 da cui si è osservata una perdita di Al mentre i livelli di impurità erano confrontabili con quelli della polver
Initial Oxidation Behavior in Air of TiAl-2Nb and TiAl-8Nb Alloys Produced by Electron Beam Melting
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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