1,721,021 research outputs found
EVALUATION OF HIGH-TEMPERATURE TENSILE PROPERTIES OF HEAT-TREATED ALSI10MG ALLOY PRODUCED BY LASER-BASED POWDER BED FUSION
Full text linkThe AlSi10Mg alloy is widely used to produce complex-shaped components by Laser-based Powder Bed Fusion (L-PBF); these parts, characterized by light structures and high specific strength, are currently employed in high-performance room temperature applications in the automotive and aerospace industries. However, it is important to increase the data concerning the high-temperature mechanical properties of the L-PBF AlSi10Mg alloy to spread its use. This study aims to fulfill the lack of knowledge by investigating the mechanical behavior at 200 °C, a representative condition of the average temperature of engine heads, of the L-PBF AlSi10Mg alloy subjected to a T5 heat treatment (artificial aging at 160 °C for 4 h) and an innovative T6 heat treatment (solubilization at 510 °C for 10 min and artificial aging at 160 °C for 6 h). The influence of high temperatures on the mechanical behavior of the L-PBF AlSi10Mg alloy was assessed by tensile tests, while microstructural and fractographic analyses were carried out to correlate the mechanical behavior of the alloy to its microstructure, and consequently explain the failure mechanisms. The ultrafine cellular microstructure, characterizing the T5 alloy, led to higher tensile strength than the homogeneous composite-like microstructure of the T6 alloy, which makes it very interesting for future application in the automotive and aerospace industries
Effetto del trattamento termico T6 su microstruttura e comportamento meccanico della lega AlSi10Mg prodotta mediante Selective Laser Melting: stato dell’arte
No full textLa lega AlSi10Mg è sicuramente la più utilizzata tra le leghe di alluminio per la realizzazione di componenti con il processo di Selective Laser Melting (SLM), anche noto come Laser Powder Bed Fusion (LPBF). Negli ultimi anni numerosi studi si sono focalizzati in particolare sull’ottimizzazione del trattamento termico T6 di questa lega, al fine di massimizzarne le proprietà meccaniche, in relazione alle specifiche caratteristiche microstrutturali indotte dal processo. Nella presente memoria sono stati confrontati i risultati delle ricerche più recenti riguardanti l’effetto del trattamento termico T6 sulla lega SLM AlSi10Mg, in termini di evoluzione microstrutturale e di proprietà meccaniche. Sono stati evidenziati gli aspetti microstrutturali che maggiormente influenzano la durezza, la resistenza a trazione, la fatica e la tenacità all’impatto. L’analisi dei dati riportati in letteratura ha confermato la necessità di definire parametri di trattamento termico specifici per la lega AlSi10Mg SLM, rispetto a quelli utilizzati per la stessa lega ottenuta con processi fusori convenzionali, al fine di ridurne la variabilità nella risposta alle sollecitazioni esterne
Linear Friction Welding of a 2024 Al Alloy: Microstructural, Tensile and Fatigue Properties
No full textThe possibility of using linear friction welding (LFW) to produce high quality joints on an aerospace grade aluminium alloy (AA2024) was evaluated. In this solid state joining process the bonding of two flat edged components is achieved through frictional heating, induced by their relative reciprocating motion, under an axial compressive force. The Al joints were subjected to microstructural and mechanical characterization, including hardness and tensile tests. S–N probability curves were also computed after preliminary axial fatigue tests. No post-weld heat treatment was performed. The microstructural analyses showed substantially defect-free joints, with a relevant plastic flow in the thermo-mechanically altered zone. Maximum hardness decrease in the joint zone was approximately only 5% in respect to the base material. The joint efficiency was about 90% with respect to the ultimate tensile strength, with a slight reduction in the elongation to failure. Good fatigue performances were also detected
Friction welding of particle reinforced aluminium based composites
No full textThe widespread use of metal matrix composites (MMC) is often limited due to the difficulties related to their joining by means of traditional fusion welding processes. The aim of this work was to evaluate the effect on microstructure and mechanical properties (hardness and tensile strength) of two different friction welding techniques used for joining two Al-based metal matrix composites. In particular, Friction Stir Welding was applied to a 6061 (Al-Mg-Si) alloy matrix,
reinforced with 20vol.% of Al2O3 particles (W6A20A), while Linear Friction Welding was applied to a 2124 (Al-Cu-Mg) alloy matrix reinforced with 25vol.% of SiC particles (AMC225xe). Both the
welding processes permitted to obtain substantially defect-free joints, whose microstructures was found to be dependent on both the initial microstructure of the composites and the welding processes. Hardness decrease was in the order of 40% for the FSW joint and of 10% for the LFW joint, mainly due to overaging of the matrix induced by the frictional heating, while the joint efficiency in respect to the ultimate tensile strength was 72% and 82%, respectively. Elongation to
failure increased in the FSW joint due to coarsening of precipitates, whereas it decreased in the LFW joints due to the fibrosity in the thermomechanically altered zone. Fracture surface analysis
showed good matrix/reinforcement interface for both composites
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Failure analysis in tribology: two case histories involving contact fatigue of metal components
No full textThis paper deals with two case studies of failure analysis in sliding/rolling contacts between metallic components. The investigated tribosystems belong to two different fields and involve different contact conditions, but in both of them contact fatigue plays a main role. The first case history comes from earth moving equipment, where the non-conformal contact between a rotating pin and its bearing leads to evidence of large surface damage of the cylindrical pin, with spalling, typical of contact fatigue. However, failure analysis highlighted a dominant role of the first crack nucleation by torsion fatigue. The second case history comes from packaging devices, where the non-conformal contact between a rotating compression roll and the punches for powder pressing led to the formation of macro- and micro-pitting on the surface of both the punches and the roll, indicating that the main damage mechanism is surface-origin contact fatigue
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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