On the Laser Powder Bed Fusion based processing route for hard to weld Nickel Superalloys

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Form follows zero energy: technological design for sustainable housing in extreme climate areas

Hot and humid Extreme Climate Areas, like the United Arab Emirates, pose unique challenges for architects and engineers seeking innovative technologies for energy and environmental efficient building designs; at the same time, these regions are characterized by an innovative spirit that pushes to develop and implement projects to test renewable building technologies and solutions. The research team, which includes the Engineering faculty of The British University in Dubai, is working to develop design strategies that contribute to implementing low-energy and off-grid architecture in the UAE. The goal is to design a home balancing human comfort and efficient energy use, and to respond to the site’s climatic and contextual variables. The research aims to design a water-conserving, net-zero energy single-family home that can be used as a prototype for new building developments in this area. The approach developed toward an energy-efficient design process includes both traditional bioclimatic elements and high-performance active technological systems. The experimental design process also aims to reduce the building’s environmental impact while creating a comfortable and responsive living environment. In this way, efficient water use and renewable energy features can be aesthetically, economically and culturally integrated into the home’s architecture to improve its residents' quality of life. The house design responds to the climate challenges and complements active systems reducing energy use and associated carbon emissions. At the same time, it aims to contribute to the development of appropriate architecture, a starting point for simple architectural expression in the UAE

Effect of Cold Rolling on Microstructural and Mechanical Properties of a Dual-Phase Steel for Automotive Field

A new advanced dual-phase (DP) steel characterized by ferrite and bainite presence in equal fractions has been studied within this paper. The anisotropy change of this steel was assessed as a progressively more severe cold rolling process was introduced. Specifically, tensile tests were used to build a strain-hardening curve, which describes the evolution of this DP steel's mechanical properties as the thinning level increases from 20 to 70% with 10% step increments. As expected, the cold rolling process increases mechanical properties, profoundly altering the material's microstructure, which was assessed in depth using Electron Backscatter Diffraction (EBSD) analysis coupled with the Kernel Average Misorientation (KAM) maps. At the same time, the process strongly modifies the material planar anisotropy. Microstructural and mechanical assessment and the Kocks-Mecking model applied to this steel evidenced that a 50% strain hardening makes the DP steel isotropic. The material retains or resumes anisotropic behavior for a lower or higher degree of deformation. Furthermore, the paper evaluated the forming limit of this DP steel and introduced geometric limitations to testing the thin steel plates' mechanical properties

Parameters Optimization and Repeatability Study on Low-Weldable Nickel-Based Superalloy René 80 Processed via Laser Powder–Bed Fusion (L-PBF)

This work aims to investigate the processability of René 80 via laser powder–bed fusion (L-PBF). René 80 is a poorly weldable Ni-superalloy, currently processed via investment casting to fabricate turbine blades working at an operating temperature of about 850 °C. The L-PBF parameters optimization aims to increase part integrity and enhance processing repeatability. This part was tackled by creating a complete design of experiments (DOE) in which laser power, scan speed and hatching distance were varied accordingly. Optimizing the abovementioned parameters minimized the crack density and pore area fraction. Hence, five parameter sets leading to a crack density lower than 100 µm/mm2 and a pore fraction between 0.045% and 0.085% were selected. Furthermore, the intra-print repeatability was studied by producing three specimens’ repetitions for each optimal set of parameters in the same build. The porosity value obtained was constant among repetitions, and the crack density (around 75 µm/mm2) had a slight standard deviation. The third step of the research assessed the inter-prints repeatability by producing a replica of the five selected parameter sets in a different build and by comparing the results with those studied previously. According to this latter study, the porosity fraction (ca. 0.06%) was constant in intra- and inter-print conditions. Conversely, crack density was lower than 100 µm/mm2 only in three sets of parameters, regardless of the intra- or inter-build cross-check. Finally, the best parameter set was chosen, emphasizing the average flaw fraction (least possible value) and repeatability. Once the optimal densification of the samples was achieved, the alloy’s microstructural features were also investigated

Thermal Mass Effect on the Solution Cooling Rate and on HIPped Astroloy Component Properties

Astroloy is a Ni-based superalloy with high-volume fraction of γ′, which gives high temperature properties but reduces its forgeability. Therefore, powder metallurgy manufacturing processes such as Near Net Shape HIPping are the most suitable manufacturing technology for Astroloy. However, NNSHIP has its own drawbacks, such as the formation of prior particle boundaries (PPBs), which usually tend to decrease material mechanical properties. The detrimental effect of PPBs can be reduced by optimizing the entire HIP processing route. Conventional HIP cycles have very low cooling rates, especially in big components from industry, and thus a series of post-heat treatments must be applied in order to achieve desirable microstructures and improve the mechanical properties. Standard heat treatments for Astroloy are long and tedious with several steps of solutioning, stabilization and precipitation. In this work, two main studies have been performed. First, the effect of the cooling rate after the solutioning treatment, which is driven by the materials’ thermal mass, on the Astroloy microstructure and mechanical properties was studied. Experimental analyses and simulation techniques have been used in the present work and it has been found that higher cooling rates after solutioning increase the density of tertiary γ′ precipitates by 85%, and their size decreases by 22%, which leads to an increase in hardness from 356 to 372 HB30. This hardness difference tends to reduce after subsequent standard heat treatment (HT) that homogenizes the microstructure. The second study shows the effect of different heat treatments on the microstructure and hardness of samples with two different thermal masses (can and cube). More than double the density of γ′ precipitates was found in small cubes in comparison with cans with a higher thermal mass. Therefore, the hardness in cubes is between 4 and 20 HB 30 higher than in large cans, depending on the applied HT

Assessment of the Hardening Behavior and Tensile Properties of a Cold-Rolled Bainitic–Ferritic Steel

The automotive field is continuously researching safer, high-strength, ductile materials. Nowadays, dual-phase (DP) steels are gaining importance, since they meet all these requirements. Dual-phase steel made of ferrite and bainite is the object of a complete microstructural and mechanical characterization, which includes tensile and bending tests. This specific steel contains ferrite and bainite in equal parts; ferrite is the soft phase while bainite acts as a dispersed reinforcing system. This peculiar microstructure, together with fine dispersed carbides, an extremely low carbon content (0.09 wt%), and a minimal degree of strain hardening (less than 10%) allow this steel to compete with traditional medium-carbon single-phase steels. In this work, a full pearlitic C67 steel containing 0.67% carbon was used as a benchmark to build a comparative study between the DP and SP steels. Moreover, the Crussard–Jaoul (C-J) and Voce analysis were adopted to describe the hardening behavior of the two materials. Using the C-J analysis, it is possible to separately analyze the ferriteand bainite strain hardening and understand which alterations occur to DP steel after being cold rolled. On the other hand, the Voce equation was used to evaluate the dislocation density evolution as a function of the material state

Zero Energy. Una sperimentazione per l'housing negli Emirati Arabi Uniti

L’articolo descrive i risultati di una ricerca di carattere sperimentale per l’housing sociale, a zero energia, negli Emirati Arabi Uniti. Un contesto climatico che costituisce una dura sfida in ordine alla definizione delle tecnologie utili a garantire il benessere dell’utenza e il risparmio energetico. Si riassume il frame di lavoro della ricerca finalizzata all’ottimizzazione della progettazione per il risparmio energetico e la sostenibilità. Gli esiti, in termini di prototipazione di un modello, sono quelli di un’architettura fortemente connotata rispetto al contesto, per forma, tipologia, uso di materiali e linguaggio senza che questa pervenga alla espressione di un’architettura tradizionalista o vernacolare. Una sperimentazione progettuale attenta al contenimento dei consumi energetici e al comfort abitativo, capace di sfruttare al meglio le difficili condizioni locali, fondata essenzialmente su un approccio bioclimatico, mirando a controllare contemporaneamente tre livelli: climatico-ambientale, tipologico e tecnico-costruttivo

Nuovi modelli operativi per la gestione del progetto e della costruzione: l’esperienza del solar decathlon me 2018

Il contributo affronta il tema dell’applicazione del BIM al progetto di Architettura, con particolare riferimento alle potenzialità offerte da questa metodologia ai fini della prefigurazione e gestione delle diverse fasi di realizzazione del manufatto edili-zio. Nello specifico il testo riporta l’esperienza condotta dal TEAM dell’Università G. D’Annunzio di Chieti/Pescara al Solar Decathlon Middle East 2018. Esito dello studio, basato sulla realizzazione del modello BIM della casa solare sviluppata per la competizione, è stata l’individuazione concettuale di supporti digitali BIM based, utili a guidare gli operatori (decathleti, maestranze, tecnici) durante le fasi di montaggio e smontaggio, ed a facilitare le verifiche di rispondenza e qualificazione tra quanto progettato e quanto realizzato

Powder spreading and spreadability in the additive manufacturing of metallic materials: a critical review

3noreservedembargoed_20240701Capozzi, Luigi C.; Sivo, Antonio; Bassini, EmilioCapozzi, Luigi C.; Sivo, Antonio; Bassini, Emili

Bioclimatic design and energetic requalification of existing buildings. An integrated approach

The contribution is aimed to address the issue of sustainable energy requalification of public buildings, according to a technological and bioclimatic design approach, aimed to reducing air-conditioning needs even before increasing the efficiency of plants. The main objective was to carry out a deep analysis of the buildings and of their relationship with the surrounding microclimate, in order to determine critical issues, limits and potentiality of individual building elements compared to the maintenance of the wellbeing indoor conditions. The secondary objective was to pay special attention to energetical and economical sustainability of the intervention hypothesis. To this end, we proceeded by adopting an evaluation costs and benefits model, of the specific intervention categories, extended to the whole conditioning cycle (summer and winter) and over the entire life cycle of the buildings. The work has highlighted the benefits achievable through the adoption of bioclimatic solutions aimed at optimizing the use of solar technologies. That under condition that is made a careful and constant evaluation of the design solutions