1,720,958 research outputs found
The influence of laser pulse shape and separation distance on dissimilar welding of Al and Cu films
No full textPulsed Nd:YAG laser welding of Aluminum-Copper (Al-Cu) electrical connections has been investigated, focusing attention on the definition of optimal process parameters to achieve low thickness joints by varying the laser pulse shape and separation distance. Heterogeneous joints comprising Al and Cu are often required in electrical applications due to the inherent characteristics of these materials. Nevertheless, welding of dissimilar metals such as Al and Cu involves many challenges due to the high reflectivity and poor weldability between the materials, which produce brittle microstructural compounds that lead to a reduction in mechanical and electrical properties. Metallurgical, mechanical, electrical and thermal analyses have been performed on Al-Cu lap joints to evaluate the effect of different pulse separation distances and shapes on the resulting weld seam. Process optimization achieved welded joints with a low penetrating depth and maximum tensile loads of over 110 kgf. Preliminary experiments were carried out to establish a process parameter feasibility window. A first set investigated variations in pulse energy and distance for square pulses, while a second set saw variation of the pulse energy, pulse distance and pulse shape. It was found that an optimal pulse distance for a specific parameter set exists, while a pulse shape that includes material preheating produces better results in terms of mechanical strength and electrical resistance than a pulse with high initial peak power
Hardness Penetration Depth Prediction in the Grind-Hardening Process through a Combined FEM model
Full text linkReal Single Grain Grinding Finite Element Method Simulation for Case-Hardened Steel Based on Equivalent Contact Area Analysis
Full text linkGrinding is an indispensable phase in the gear production chain as it allows very stringent requirements characteristic of the automotive sector to be satisfied. The main goal of this finishing process is to ensure compliance with the surface integrity and dimensional tolerance specifications of the product. A single-grain grinding FEM model has been implemented to predict grinding load values based on real grain geometry using a set of Johnson & Cook coefficients able to represent the flow stress curve of a typical gear case-hardened steel 27MnCr5. Grain geometry acquired through computed tomography was imported into three-dimensional process simulation software DEFORM-3D. As the use of real grain geometry leads to time-consuming simulations, an equivalent defined geometry grain was implemented to compare the cutting behavior and calculate maximum force values through real contact area analysis under the same process parameters. Calculated loads were subsequently compared with experimental results, showing good agreement with a maximum percentage difference less than 13% for two different grain geometries. Grinding force measurements were performed in a single-grain configuration on a CNC surface grinding machine adopting a wheel speed of 384 rad/s, a feed rate of 8.6 mm/s and a depth of cut of 0.1 mm
Prediction of the grinding wheel specification influence on thermal defects in dry grinding through a hierarchical FEM model
Full text linkGrinding represents an indispensable phase in a manufacturing route because it allows to obtain the final required features in terms of dimensions and roughness. Although the grinding technology has always been applied with lubricants, nowadays, oil application becomes more and more limited to reduce the environmental pollution. In dry finishing technologies, heat control represents the main problematic of the process; indeed, grinding usually reaches relevant temperatures causing thermal defects. Therefore, process temperature prediction represents a challenge allowing to prevent thermal defects on the working material. But the final results are influenced by the kinematics parameters and also by the grinding wheel specifications. This paper aims to predict thermal defects in the material also considering the wheel specification. A hierarchical FEM model which considers both the microscopic and macroscopic aspects of the grinding process was developed. Starting from the mechanical action of a single grain on the material, a moving heat source was built to represent the interaction of the grinding wheel with the workpiece. A single grain grinding model is followed by a thermal model which considers the process parameters and the grinding wheel specification. Tangential grinding tests were developed to validate the model by adopting embedded thermocouples and grinding wheels with different structures were used. To further validate the model, metallographic and micro-hardness analyses were developed to verify the microstructural change due to the grinding cycle. A maximum average percentage difference of 10.8% was detected between calculated and measured temperatures and good agreement with the microstructural analysis was found
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
Dry Grinding: A More Sustainable Manufacturing Process for the Production of Automotive Gears
No full textGears represent a fundamental component of automotive transmissions, the performance of which is directly influenced by flank surface integrity. With the exception of grinding, gear production does not require the use of lubricants. The elimination of oils in the final finishing phase represents an important opportunity to greatly improve process sustainability and reduce production costs. However, dry grinding presents several challenges, including dimensional tolerances and roughness requirements, microstructural defects due to excessive heat generation, and maintaining the overall surface integrity of flanks such that wear resistance is not compromised. The present work investigates the geometric accuracy, microstructure, and wear resistance of FIAT 500 4/6 speed gears manufactured by FCA/Stellantis, comparing conventional wet grinding with two alternative processes including superfinishing and dry grinding. The material and manufacturing processes employed prior to grinding were the same in all cases, with grinding then performed by the same manufacturer. The dimensional accuracy, roughness, microstructure, residual stress state, and wear resistance of gear flanks were then analyzed to compare the overall performance of each grinding process. The obtained results show that dry grinding can produce gears with acceptable geometric accuracy, no microstructure defects and greater wear resistance than gears finished with conventional wet grinding or superfinishing. As a result, the complete elimination of lubricant in gear production is possible, leading to a more sustainable process without compromising gear performance
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
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