1,721,044 research outputs found
Probeless friction stir welding of dissimilar metal welds
Full text linkIn recent years, the number of lightweight parts made of high-strength aluminium alloys and advanced high strength steels (AHHS) has increased fivefold to further enhance engine efficiency and reduce CO2 emissions in automotive sector. Furthermore, lightweight assemblies increasingly utilize dissimilar structures combining both AHSS and high-strength aluminium alloys.
Widespread in automotive industry fusion method of resistance spot welding (RSW) triggers notable alterations in resolidified seam microstructure from its original state. Moreover, high thermal conductivity of aluminum alloys lead to rapid electrode wear, thereby enhance the formation of pores, voids, solidification and liquation cracking. Joining of dissimilar materials suffers even more challenges due to additional disparities in their electrical and thermal properties. At last, the formation of brittle intermetallic compounds (IMCs) detrimentally effects on the final mechanical properties. Temperature and holding time are two critical parameters that influence the formation of above-mentioned defects and formation of IMCs. Thus, reducing the amount of heat input and time of the welding process become an inevitable demand for both similar and dissimilar materials.
Being a solid-state welding method, Friction Stir Spot Welding (FSSW) involves joining between materials by plunging a non-consumable rotating tool involving a shoulder and a probe into the workpiece with further material heating and stirring. However, the crucial drawback of FSSW is the formation of a permanent central keyhole due to presence of probe, which significantly reduces the effective cross-sectional area.
Among all variations being invented to eliminate the keyhole, Probeless Friction Stir Spot Welding (P-FSSW) gains significant attention due to its process simplicity, high efficiently, and negligible tool wear. The weld formation is primarily influenced by the combined effects of vertical compression and horizontal material, which are exclusively driven by the shoulder. Thus, the contact between shoulder and workpiece surface plays a vital role in the heating and following material plasticization.
The featureless flat shoulder of P-FSSW has been primarily served as a reference point, while it demonstrated promising results in forming strong joints among different featured shoulders. Notably, it possesses minimal tool wear and contamination from plasticized material compared to other shoulder designs. Its main drawback is solely the requirement for a longer dwell time to attain the same level of strength as those achieved with featured shoulders.
The objective of this study is to investigate the feasibility of creating robust spot joints between dissimilar aluminum-aluminum and aluminum-steel materials using Probeless Friction Stir Spot Welding (P-FSSW) assisted by flat featureless shoulder. The study systematically evaluates heat generation, material flow, microstructural evolution and mechanical properties, aiming to optimize parameters and expand the scope of this technology.
Four sets of experiments on P-FSSW with different combination of dissimilar aluminum-aluminum and aluminum-steel material couples were performed at Hybrid Welding Laboratory at DMMM Polytechnic University of Bari. Optical microscopy, microhardness tests, tensile test, and scanning electron microscopy (SEM) equipped with the electron backscatter diffraction (EBSD) technique were employed to provide fundamental insight into the microstructural development. In regard to provide a better understanding of P-FSSW, the experimental findings were coupled with numerical results of thermal fields and material flow. Finite element model was developed in assist with Simufact Forming® 2021 software
Development of in-situ optical sensor-based monitoring methodologies for Additive Manufacturing processes
Full text linkProcess monitoring has proven to be essential in manufacturing fields, where quality and precision are paramount. The introduction of AM techniques has enabled the production of complex parts but has also increased the complexity of manufacturing systems. This has led to the demand for monitoring systems able to provide significant information about the process while it is running as well as give real-time insights to detect and prevent, when possible, process anomalies. Reliable monitoring systems provide a window into the process dynamics, allowing for process parameters adjustment that could maintain product quality and reduce waste of materials and energy. Despite the numerous advantages introduced by monitoring systems, widespread traditional solutions remain limited, prompting significant effort from researchers and industries in this direction. This thesis addresses the current critical gaps in terms of monitoring purposes by proposing innovative and cost-effective in-situ optical-based monitoring methodologies for three key AM processes: Material Extrusion Additive Manufacturing, Laser Powder Bed Fusion and Direct Energy Deposition. Material Extrusion showed to be lacking adequate metrics able to describe the process, together with the absence of solutions exploiting profilometers as monitoring sensors. The monitoring activities on L-PBF were driven by the lack of robust monitoring systems able to characterize lattice structures. Finally, the monitoring activities on L-DED were led by the current absence of real-time monitoring system capable of monitoring more than one direction, since the majority of the system focused on single direction thin wall monitoring. First, two layerwise monitoring approaches for MEX, based on a high-resolution blue laser line profilometer embedded within a consumer grade MEX printer, were presented to characterize the surface quality, to detect defect occurrence layer-by-layer and to expand the metrology field related to the MEX process, which is currently lacking, by proposing new metrics. The three proposed quality indexes (ADLH, RAD and slope s) proven to be representative of the layer height accuracy, the occurrence and distribution of surface defects, such as over/under-fill, and, also, the process stability respectively. In the second approach, functional analysis tools were successfully used to detect, localize, and characterize the topology of common surface defects caused by over-extrusion and under-extrusion conditions. An optical-based monitoring procedure was also developed and applied for layerwise in-situ monitoring of complex geometries produced by L-PBF through a tailor-made image processing algorithm. Based on High-Resolution Optical Tomography (HR-OT), this procedure effectively detected geometric distortions and, at the end of the process, provided a 3D reconstruction of the lightweight structure suitable for post-process quality assessment. Finally, a preliminary study on a cost-effective off-axis dual-camera real-time 3D monitoring method for L-DED process was conducted. The aim was to enable a reliable measure of the melt pool height regardless of the laser head scanning direction. Results showed that the proposed methodology was able to provide acceptable melt pool height measures for all the scanning direction tests. By introducing robust process signatures and defect metrics, this work significantly advances the metrology of AM processes. The comprehensive monitoring methodologies developed during the research activities not only improve in-process quality evaluation and process stability but also pave the way for real-time, closed-loop corrective actions
The Conference on the Future of Europe and its democratic potential
No full textSince some 15 years, the European Union is challenged by an accumulation of significant
crises. One of such crises involves the state of democratic institutions. As also witnessed by
the recent European elections, political forces with questionable democratic credentials are
increasingly successful in mobilizing the European electorate (even if numbers of electoral
abstention remain very high). European democracy, as liberal, representative democracy in
general, appears to be in a dire state. It suffers from augmenting citizen distrust in politicians,
political parties, and institutions, a structurally low levels of citizen engagement and participation in elections, increasing voter volatility, a weakening of traditional political parties, and
increased polarization and radicalization of the political landscape.
According to many observers, (European) democracy needs to be reinvented or at least prominently renovated. One core problem is the lack of meaningful and effective input by ordinary citizens in the democratic decision-making process. A core instrument to counter democratic malaise lies in the area of participatory democracy and enhanced citizens engagement. The most debated democratic innovation in recent years is the citizens’ assembly (or related forms such as mini-publics or citizens’ juries).
This chapter discusses one unique experiment with a citizens’ assembly on the transnational level, the Conference on the Future of Europe (CoFE), a one-year event organized by the European institutions and held between 2021-22. I will first briefly discuss the origins of the Conference. Second, I will discuss the CoFE’s operation in particular in terms of actual citizens engagement and participation.37 Third, I will briefly conclude that the CoFE process,
if to lead to significant effects on citizens engagement with the EU, would need a proper institutionalization of a permanent European Citizens’ Assembly
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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