1,720,966 research outputs found
Very high cycle fatigue characteristics of laser beam powder bed fused AlSi10Mg: A systematic evaluation of part geometry
Get PDFThis study explores the influence of geometry and part size on defect distribution, melt pool size, and mechanical characteristics in laser beam powder bed fused (LB-PBF) AlSi10Mg. Five distinct geometries—hourglass, small rod, small block, large block, and large rod—were fabricated under identical process parameters. Fully reversed ultrasonic fatigue testing, operating at a frequency of 20 kHz, was conducted to assess the very high cycle fatigue properties. The findings indicated that part geometry had a major impact on the fatigue properties of the material in the very high cycle fatigue regime. Specimens machined from large rods and large blocks had the lowest porosity and highest fatigue resistance. Microstructural analysis indicated that hourglass, small rod, and small block specimens had shallower melt pools and overlap depths compared to other geometries. This observation suggests a higher cooling rate in specimens with smaller cross-sectional areas, leading to the increased presence of entrapped gas pores and a lack of fusion defects. Understanding the relationship between part geometry and fatigue properties in LB-PBF components offers insights for optimizing design and manufacturing processes in additive manufacturing applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Small-Scale Characterization Of Additive Manufactured Ti-6al-4v Alloy Through Instrumented Indentation
Get PDFTi-6Al-4V alloy has been favored by the transportation applications in the automotive and aerospace industries due to its good combination of excellent physical and mechanical properties. Ti alloys are naturally suited to additive manufacturing (AM) method, a layer wise manufacturing technique, since conventional manufacturing method of Ti alloys are quiet challenging. However, cooling rate and thermal processing history of AM Ti-6Al-4V alloy are quite different in comparison to conventionally fabricated Ti-6Al-4V alloy which leads to undesirable microstructures in the AM Ti-6Al-4V alloy with respect to large columnar prior β grains being found to grow potentially across the entire height from bottom layer to top layer. Therefore, it is required to assess the microstructure-process-structure-property-performance relationship of the additive manufactured Ti-6Al-4V alloy to assess whether it could meet the demands of engineering design considerations.
The samples studied in this research were prepared using laser powder bed fusion (L-PBF) method, a well-developed AM process to print Ti-6Al-4V alloy in different scan direction and scan size. Instrumented indentation testing technique, a robust, reliable, convenient, and non-destructive characterization method to study small-scale mechanical properties in metals and alloys at ambient and elevated temperatures, was used to assess ambient-temperature indentation creep of AM Ti-6Al-4V alloy. To examine depth-sensing indentation creep behavior of Ti-6Al-4V alloy at ambient temperature, a dual-stage scheme (loading followed by a constant load-holding and unloading) at different peak loads of 250 mN, 350 mN, and 450 mN with holding time of 400 s was performed. Creep parameters i.e. creep rate, creep stress exponent, and indentation size effect were analyzed and compared with conventional findings, according to the Oliver and Pharr method, at different additive manufacturing scan directions and scan sizes.
The effect of post heat treatment (i.e. aging and solutionizing with different cooling rates) on the microstructure and micromechanical properties of a Ti-6Al-4V alloy processed by laser powder bed fusion (L-PBF) technique is studied. Heat treatment cycles employed in this study include solutionizing at 950 °C (for 1 h) followed by three different cooling rates (water quench, air cooling, and furnace cooling). A separate set of samples were also used toward artificial aging (solutionizing followed by water quenching and artificial aging). To assess small-scale properties of as-printed/ heat treated materials, instrumented nanoindentation testing technique as a robust, convenient, and non-destructive approach is employed. The martensitic α and ά in as -printed Ti-6Al-4V alloy grows in lamellar structure in epitaxial way upon various heat treatments below β- transus temperature. With the relatively steep cooling rate, the β phase recrystallization transforms into a compact secondary basket-weave α phase since the primary α-phase develops and connects each other with different orientations.
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Microstructural quantitative analyses (i.e. optical microscopy and scanning electron microscopy) were performed as well to assess processing parameter-microstructure-property correlations in the additively manufacture Ti-6Al-4V alloy. These studies were done in parallel to the two main tasks of this project to be able to elaborate the mechanical measurements with microstructural evidences. Also, the obtained results were compared against traditionally processed Ti-6Al-4V
Understanding the effects of volumetric defects on the uniaxial fatigue behavior of additively manufactured metallic materials
No full textVolumetric defects in additively manufactured parts cause significant fatigue scatter due to the variations in their size, shape, and location. This dissertation aimed to identify the morphological features of process-induced volumetric defects that most influence the fatigue behavior of laser powder bed fused (L-PBF) Ti-6Al-4V. Firstly, fatigue test specimens were machined from round bars fabricated using eight distinct process parameter sets and three build orientations to ensure a wide range of defect morphologies and populations. Uniaxial, constant amplitude, fully-reversed fatigue tests were conducted on these specimens. Fractography was performed to identify the defect responsible for the fatigue crack initiation and extract its morphological features. The influence of these features on fatigue behavior was examined by analyzing experimental data and finite element analysis results. While size was the most critical defect feature influencing fatigue behavior, it could not fully explain the variation in fatigue life by itself. For defects of similar size located at the same location, circular defects appeared to be more detrimental than irregularly shaped ones. A new defect size parameter, √area of the maximum inscribed circle, was introduced to account for both the size and shape of the volumetric defects, which exhibited an improved correlation with life compared to existing parameters. Fatigue cracks initiated from the surface and internal defects exhibited distinct crack growth behavior. Using the distinct material constants for surface and internal defects obtained from the Shiozawa plots, a novel fatigue life prediction model was proposed, which accounted for the distinct crack growth rates for surface and internal defects. Additionally, a probabilistic approach was utilized to determine the size of the largest possible defect for a given probability of failure. The fatigue design curve estimated with this defect size, using the proposed crack growth model, has been shown to be a more accurate estimate compared to the design curves developed using conventional approaches for fatigue qualification. Furthermore, the cross-platform transferability of the structure-property relationships, specifically defect-fatigue, was assessed for L-PBF Ti-6Al-4V. The transferability of defect-fatigue relationships established for the specimens fabricated on the EOS M290 platform was tested and validated with those fabricated on the Renishaw RenAM 500Q platform. Fatigue crack growth parameters derived from the EOS M290 specimens could be successfully applied to the fatigue life prediction of the RenAM 500Q specimens. The validity of fatigue design curves constructed using the short crack growth model with parameters from the EOS M290 platform was verified with data from the RenAM 500Q
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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