1,721,061 research outputs found
Heat transfer in hot stamping of high-strength steel sheets
No full textThis paper focuses on the determination of the heat transfer coefficient (HTC) between blanks and dies in the hot stamping of high-strength steel sheets. Experiments to record the temperature evolution inside the dies were carried out on custom-built test equip- ment, where process conditions typical of hot stamping could be reproduced, but avoiding any deformation of the metal sheet. The HTC was determined by using an inverse analysis procedure, based on the comparison between temperature measured inside the dies and temperatures calculated by means of a numerical model of the test. HTCs between the steel blank and dies made of different materials were identified, showing that the use of ceramic inserts can modify the cooling rate inside the blank in order to avoid a complete martensitic transformation. Moreover, the influence of the contact pressure was investigated, proving that HTC dependence on this factor is not negligible
Laser-Directed Energy Deposition of H13: processing window and improved characterization procedures
No full textAdditive manufacturing has the potential to create, repair, or enhance customized tools, but reliable processing guidelines for tool steels are necessary. This study focuses on printing H13 tool steel on a 316 L substrate using Laser-Directed Energy Deposition technology. A comprehensive study on the most influential process parameters was carried out, i.e. laser power (1400, 1600, 1800, 2000 W), powder feed rate (9, 12, 15 g/min) and scanning speed (1000, 1200 mm/min), for the production of single tracks. Cladding angle, aspect ratio, dilution, shift, microhardness, microstructures were selected as measured output. Manufacturing guidelines were established for a complete characterization of individual tracks, with a new approach for properly calculating the dilution. The tracks exhibited different properties and the influence of process parameters on the measured output was evaluated. The outcomes determine a technological window where it is possible to select the most sensible process parameters depending on the desired applicatio
Positioning error prediction in boring machines
No full textThis paper focuses the attention on the possibility to describe and predict the positioning
error of the end-effector (or tool-holder) of a Cartesian boring machine. The aim of the
work is i) to build a deterministic expression of the positioning error, starting from
independent measurements of linear and angular errors for each independent axis, and
ii) to investigate the precision enhancement, which may eventually be achieved by
implementing such deterministic error-prediction into the numerical control of the boring
machine.
The six components of the end-effector positioning error are expressed on the basis of a
symbolic analysis of the kinematic linkages, which represents the machine layout. Each
component results as a function of the command position, some environmental
parameters (mainly the ambient temperature), and alignment errors for each axis. In
particular, alignment errors may be expressed as six functions of position for each axis:
three position errors and three angular errors [1,2].
An accurate measurement of these errors (which may take place either on-line or at
regular time schedule as a result of an auto-diagnosis procedure) allows expressing the
end-effector positioning error as a deterministic vector field in the whole machine working
space.
Beside these considerations, the paper investigates the applicability of different
techniques allowing the measurement of axes alignment errors
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
Kinematic Synthesis of a D-Drive MEMS Device With Rigid-Body Replacement Method
No full textIn this paper, a microsystem with prescribed functional capabilities is designed and simulated. In particular, the development of a straight line path generator micro electro mechanical system (MEMS) device is presented. A new procedure is suggested for avoiding branch or circuit problems in the kinematic synthesis problem. Then, Ball's point detection is used to validate the obtained pseudo-rigid body model (PRBM). A compliant MEMS device is obtained from the PRBM through the rigid-body replacement method by making use of conjugate surfaces flexure hinges (CSFHs). Finally, the functional capability of the device is investigated by means of finite element analysis (FEA) simulations and experimental testing at the macroscale
A New Direct Deformation Sensor for Active Compensation of Positioning Errors in Large Milling Machines
No full textThe positioning accuracy of large boring and milling machines (with axes travel larger than 5 m) is severely affected by structural deformations. Heat induced deformations, long-period deformation of foundations, and the machining process itself, cause time-dependent structural deformations of the machine body, which are difficult to model and to predict. In order to overcome these difficulties and to enhance the positioning accuracy, a composite sensor has been designed and tested, which allows direct and continuous (up to 250 Hz) measurement of geometrical deformations on machine structural elements. The present paper i) presents the operating principles of the proposed composite sensor, which is based on an array of fiber-optics Bragg gratings (FBG), ii) discusses requisites and performances of the sensor as well as the algorithm used to calculate the deformed shape as a function of the sensor output, iii) illustrates the results of a finite elements virtual model aimed to demonstrate the feasibility and to evaluate the expected performance of the sensor, and iv) validates the model by showing the results obtained by a sensor prototype giving a real-time measurement of the deformed shape of a structural bea
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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