1,720,957 research outputs found
Residual stresses and distortion in additively-manufactured SS316L-IN718 multi-material by laser-directed energy deposition: A validated numerical-statistical approach
No full textIn the present work, a numerical-statistical approach was used to study the distortion and residual stress in the additive manufacturing (AM) of SS316L-IN718 multi-material structure. Also, the structure was fabricated by laser-directed energy deposition (L-DED), and experimental measurements via thermocouple and micro X-ray diffraction were performed to validate the numerical results. In a good agreement with the experiments, the thermomechanical modeling of the process showed that through-thickness residual stresses (build direction) are distributed as a large accumulation of compressive residual stress in the mid-length of the structure-substrate interface and the maximum tensile residual stress at its two free ends. The critical development of longitudinal residual stresses (scanning direction) at the interface of the structure due to the sudden change in properties has caused the formation of the maximum tensile residual stress (up to 475 MPa) in this area and immediately changed its nature to compressive that can easily lead to localized cracking. Besides, Von Mises stress distribution indicated the concentration of stress at the interfaces of structure-substrate and base alloys, in such a way that it causes yielding in the SS316L section. On the contrary, less (plastic) strain occurred in the IN718 section due to higher yield strength. The results of the statistical modeling using multiple response analysis in the response surface method (RSM) also determined the desirable minimum level of longitudinal strain and stress of the structure (about 0.013 and 320 MPa, respectively) in the laser power range of 300–380 W and the powder per unit length of 5–25 g/m. In addition to minimization, it was demonstrated that sharp changes in longitudinal strain and stress at the interface of multi-material structure can be effectively reformed to mild changes by designing compositional gradients through thermodynamic calculations, owing to the approximation of the properties of adjacent layers
Design optimization for defect-free AISI 316 L/IN718 functionally graded materials produced by laser additive manufacturing
Full text linkAdditive manufacturing (AM) of functionally graded materials (FGM) has become an important growing trend in the research and development of various sectors. The main challenging issue is alloy design for the transition zone between terminal alloys so that the expected performance is achieved with minimal risk of defects. In this study, the transition zone design in AISI 316 L-IN718 FGM via laser-directed energy deposition (L-DED) is investigated concerning susceptibility to cracking defect, its formation mechanisms, as well as the design effect on mechanical properties. Consequently, the compatible design of the AISI 316 L-IN718 graded materials is established for laser-based AM. The evaluation of the gradient structures showed that the 75 % AISI 316 L-25 % IN718 region, with the continuous evolution of low-melting eutectic compounds caused by the formation of crystallographic texture in the build direction, is highly sensitive to liquation cracking, which occurs in the presence of thermal stresses arising from the deposition of subsequent layers. In addition, defects of porosity and oxide micro-inclusions intensify the discontinuity and cracking in the remarked composition region. Finally, it was demonstrated that the improvement of the dissimilar structure of AISI 316 L and IN718 alloys can be purposefully fulfilled by designing a compositional gradient in the form of a 50 wt% mixed region between the base alloys (FGM-50 %) resulted in the maximum mechanical properties (tensile strength 540 ± 10 MPa, elongation 52 ± 2 %, and toughness 24 ± 1.4 kJ/mm3)
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
Additive manufacturing of thin-walled SS316L-IN718 functionally graded materials by direct laser metal deposition
Full text linkFunctionally graded materials (FGMs) are a good response to those advanced applications that service requirements are diverse and require high performance. Additive manufacturing (AM) technology, with its many advantages, including high flexibility for complex geometries and near-net-shape integration, has attracted special attention in the development of FGMs. In this research, the solidification behavior and microstructure evolution in the laser additive manufacturing of thin-walled stainless steel 316L-Inconel 718 graded materials have been studied with the help of solidification concepts in the welding metallurgy, according to the common principles of welding and additive manufacturing processes. For this purpose, optical and electron microscopy techniques, X-ray energy dispersive spectroscopy, and microhardness measurement were used along the build direction of FGMs with different transition designs. Microstructure evaluation showed that due to re-melting of layers, despite the increased undercooling in the build direction, morphological evolution occasionally occurred periodically between solidification modes, and due to thermal accumulation, a coarser microstructure is formed in the final layers. In addition, in the chemical analysis, it was observed that the mixing of adjacent layers caused by dilution led to a deviation of the composition distribution from the desired design. Also, the microsegregation of some elements during the non-equilibrium solidification of the process caused secondary phases such as carbides and intermetallic compound of Laves, which can have an adverse effect on the mechanical properties of the structure. However, microhardness variations along the cross-section of the samples showed that the gradation of the dissimilar thin-walled structure can effectively bring the properties and behavior of adjacent layers closer together and therefore be very useful in improving the service life
Printability and microstructure of directed energy deposited SS316l-IN718 multi-material: numerical modeling and experimental analysis
Full text linkIn the present paper, the interrelated aspects of additive manufacturing-microstructure-property in directed energy deposition of SS316L-IN718 multi-material were studied through numerical modeling and experimental evaluation. The printability concept and solidification principles were used for this purpose. The printability analysis showed that the SS316L section is more susceptible to composition change and lack of fusion, respectively due to the high equilibrium vapor pressure of manganese and the more efficient heat loss in the initial layers. However, the IN718 section is more prone to distortion due to the formation of a larger melt pool, with a maximum thermal strain of 3.95 × 10-3 in the last layer. As the process continues, due to heat accumulation and extension of the melt pool, the cooling rate decreases and the undercooling level increases, which respectively result in coarser microstructure and more instability of solidification front in the build direction, as also observed in the experimental results. The difference is that the dendritic microstructure of the IN718 section, due to the eutectic reaction L → γ + Laves, is formed on a smaller scale compared to the cellular microstructure of the SS316L section. Also, the decrease in cooling rate caused the secondary phase fraction in each section (delta ferrite in SS316L and Laves in IN718) to increase almost linearly. However, the hardness calculation and measurement showed similarly, even though with the transition from SS316L to IN718 the hardness is significantly increased due to higher yield strength of the matrix and the presence of Laves intermetallic phase (~ 260 HV0.3), the hardness in each section decreases slightly due to the coarsening of the microstructure from the initial layer to the final
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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