1,720,965 research outputs found
Hybrid laser welding of stainless and high strength steels
Full text linkIn manufactory industry, welding is a joining technology with noticeable properties. Among fusion welding technologies, laser welding employs high power laser beam with high density. Laser beam welding debuted several decades later, after the invention of the laser in 1960, and has demonstrated to be especially useful in high-speed, automated welding. The laser beam produces a reduced melting zone, which has always been seen positive for the industrial products. Low thermal distortion, high speed and little heat input per unit of volume can be reached by fiber laser with some limitations like crack susceptibility, porosity, strict tolerances for edges preparation, and high reflectivity. Hybrid laser arc welding can overcome some of those limitations since its tendency to flexibility, low crack formation and porosity, high precision, narrow melting zones, high cooling and heating speeds, deep penetration. Mixing and diffusion phenomena can be controlled and that reduces the formation of intermetallic compounds in the case of dissimilar joints. In fact, dissimilar metal welding implicates joining two different metals or alloys by melting, which the addition of filler metal as an option. Among dissimilar metal weld, aluminum/steel (Al/Fe), advanced high strength steel (AHSSs) /austenitic stainless steel have increased the attention from aeronautical and automotive industry because of the properties such as reduced weight, good formability, high mechanical strength, and more. Dissimilar joining of hybrid Al-Fe structures is often challenging because of the inevitable formation of brittle intermetallic compounds (IMCs), which can compromise the mechanical properties of the weld due to their poor ductility. Therefore, it is necessary to limit their formation to obtain good quality welds. The major goal of this thesis is to analyze the microstructural and mechanical aspects of dissimilar joints used in the automotive industry, which were welded by different laser techniques. Particularly, great importance was given to the microstructure of the fuse (FZ) and heat affect zones (HAZ), being those zones mainly associated to the mechanical behavior of the weld. The mechanical and microstructural aspect of the joint were related with the process parameters to study the defects and to obtain the better mechanical properties. After the state-of-art on fusion welding processes, the research activity concerned the study of the fiber laser/TIG weldability of AISI 304 and AISI 410 stainless steel (SS), weldability of Twinning-induced plasticity steels (TWIP) and Dual Phase (DP) steel dissimilar joint by laser arc hybrid welding with austenitic filler and finally the assessment of weldability of TWIP and DP steels with AISI 316 stainless steel. Since the automotive industry has been reducing the vehicle weight and fuel consumption, advanced high strength steels and stainless steel can be help to this achievement. Research activity concerned also the study of the laser welding of the annealed alloy AA5754 with austenitic stainless steel AISI 316. Particularly, the laser off-set welding (LOW) was used to limit the formation of brittle intermetallic compounds during the welding process. The laser beam was directed onto the stainless steel side of the butt weld at a small distance from the edge of the aluminum sheet. The keyhole formed and the full penetration was reached in the SS side of the weld. Thin layer of intermetallic compounds of different stoichiometry was found at the interfaces between SS and Al fusion zone (FZ). Finite Element (FE) analysis was employed to evaluate both the temperature distribution, residual stress and distortions in the joints. Using Simufact commercial software, the numerical model of the joint was created and validated through the available experimental data. The target of this part of the research was to build a methodology to build a numerical model for laser and hybrid welding process, with a particular attention to the set-up of the heat source model
Microstruttura e difettosità in giunti laser AA5754/Ti-6Al-4V
No full textIn questo lavoro sono stati caratterizzati giunti di testa tra la lega AA5754 e la lega Ti-6Al-4V ottenuti mediante saldatura a fascio laser. La microstruttura e le difettosità dei giunti sono state analizzate al variare dei parametri di processo. I campioni sono stati processati focalizzando il fascio laser sulla lega di Titanio sia a 0.75mm che a 1mm di distanza dall’interfaccia con la lega di Alluminio (distanza di offset). L’energia di linea (rapporto tra la potenza laser e la velocità di avanzamento) è stata variata su tre livelli (30.0 J/mm, 36 J/mm e 72 J/mm).
Tutti i giunti analizzati hanno esibito completa penetrazione del keyhole. Per ciascuna distanza di offset, la zona di fusione (ZF) della lega di Titanio si estende fino all’interfaccia con la lega di Alluminio determinandone a sua volta la fusione. Le ZF delle due leghe sono chiaramente distinguibili come pure le rispettive zone termicamente alterate (ZTA). La microstruttura della ZF della lega di Ti è prevalentemente martensitica mentre quella della ZTA è solo parzialmente martensitica. Come conseguenza la durezza del giunto è massima nella ZF della lega di Ti e decresce gradualmente dalla linea di fusione verso il materiale base. L’interfaccia tra le ZF è caratterizzata da un sottile strato di composti intermetallici (IMC) di differente stechiometria
Caratterizzazione microstrutturale e meccanica di rivestimenti in lega AA 2024 ottenuti mediante Electrospark Deposition
No full textIn questo studio sono stati caratterizzati rivestimenti in lega d’alluminio AA2024 realizzati su substrato omologo mediante ElectroSpark Deposition (ESD). L’ESD è un processo di microsaldatura ad arco pulsato che utilizza impulsi elettrici di breve durata, generati dalla scarica di un condensatore, per trasferire il materiale di un elettrodo mobile ad un substrato metallico.
I rivestimenti prodotti, analizzati con indagini in microscopia ottica ed elettronica a scansione, sono di tipo strato su strato, componendosi di diversi strati sovrapposti. All’interno di ciascuno strato deposto la microstruttura è risultata abbastanza fine a causa delle elevate velocità di raffreddamento coinvolte nel processo.
La durezza media dei rivestimenti non cambia in maniera significativa al variare dei parametri di processo considerati. I rivestimenti presentano difettosità quali vuoti e micro-cricche perpendicolari o parallele all’interfaccia con il substrato. Anche il substrato è caratterizzato dalla presenza di micro-cricche all’interfaccia. All’aumentare dell’energia di scarica si è osservata una riduzione delle difettosità all’interno del coating e un aumento della lunghezza media delle micro-cricche nel substrato
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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