1,721,091 research outputs found
Development of a stress compensating substrate and associated processes to produce large infrared detectors in the context of spatial imaging
No full textAfin de réaliser des détecteurs infrarouges de très grands formats, deux grandeurs thermomécaniques préalablement identifiées comme critiques ont été étudiées à la température de fonctionnement de 100 K : le niveau de contraintes résiduelles dans le semi-conducteur HgCdTe et la planéité du plan focal.Dans un premier temps les deux structures de détecteurs actuellement produites par la société Lynred ont été caractérisés à la fois par des méthodes expérimentales (mesures de contraintes résiduelles par diffraction des rayons X et de planéité, à température ambiante et à 100 K) et numériques (modélisations analytiques et éléments finis), afin de bien comprendre leur comportement thermomécanique. Deux nouvelles structures apportant des voies d’amélioration ont pu être ensuite définies, prototypées, puis étudiées avec le même protocole, afin de pouvoir conclure sur leur pertinence et permettre une extrapolation pour le cas des très grands formats (applications spatiales).Two critical thermomechanical parameters have been studied at the operating temperature of 100 K in order to manufacture very large format of infrared detectors: the level of residual stress in the semiconductor material HgCdTe and the planarity of the focal plane array.First, the two types of detector currently produced at Lynred have been characterized, both through experimental measurements (X-ray diffraction residual stress analysis and planarity measurements, both at room temperature and at 100 K) and numerical simulations (analytical and finite element modelling), so as to clearly understand their thermomechanical behavior. Then two improved structures have been defined, prototyped, and studied with the same approach, in order to finally conclude on the most relevant for very large formats (spatial applications)
Prediction of DP steel fracture by FEM simulations using an advanced Gurson model
Full text linkThis numerical investigation of an advanced Gurson–Tvergaard–Needleman (GTN) model is an extension of the original work of Ben Bettaieb et al. (2011). The model has been implemented as a user-defined material model subroutine (VUMAT) in the Abaqus/explicit FE code. The current damage model extends the previous version by integrating the three damage mechanisms: nucleation, growth and coalescence of voids. Physically based void nucleation and growth laws are considered, including an effect of the kinematic hardening. These new contributions are based and validated on experimental results provided by high-resolution X-ray absorption tomography measurements. Also, the numerical implementation of the kinematic hardening in this damage extension has obliged to readapt the classical triaxiality definition. Besides, a secondary fracture initiation criterion based on the ultimate average inter-cavities distance has been integrated to localize and quantify with good accuracy the strain distribution just before the material fails apart. The current damage model is applied in industrial conditions to predict the damage evolution, the stress state and the fracture initiation in various tensile thin flat sheet geometries and the cross-die drawing tests
Parameter identification of thermomechanical behavior in hot foring with industrial means
No full textL’objectif principale de cette thèse est de procéder à une identification paramétrique d’un modèle rhéologique de matériau métallique à chaud en utilisant des données expérimentales issues d’une presse industrielle. Dans le premier chapitre, le principe de l’identification paramétrique est exposé. Des essais de compressions uniaxiale faites sur machine d’essais spécialisés y servent alors comme cas d’étude. Les notions de choix de la fonction-coût, du plan d’expérience et du modèle y sont alors abordées ainsi qu’une analyse de sensibilité. Le chapitre suivant présente l’outillage utilisé pour faire les expériences sur presse. Enfin, une évaluation des échanges thermiques et des frottements que subis la pièce lors de l’essai est faite. Le troisième chapitre se concentre sur l’identification paramétrique proprement dite. Ainsi, des simulations par élément fini de la compression sont faites et comparées aux essais expérimentaux. Les résultats de l’identification sont discutés et comparés à ce que proposait initialement la base de données du logiciel FORGE® ainsi que les paramètres identifiés pour le même matériau au chapitre 1. Une simulation d’une pièce complexe avec ces différents jeux de paramètres est ensuite comparée avec le forgeage réel de cette pièce. Le quatrième chapitre reprend les acquis du troisième en faisant une identification paramétrique pour la rhéologie d’Inconel 625. Une tentative d’identification d’un modèle de microstructure pour l’Inconel à partir d’essais industriel termine ce manuscrit.The main objective of this thesis is to identify the parameters of a hot metal rheology model by using experimental data from an industrial press. In the first chapter, the principle of parameter identification is exposed. Uniaxial compression testing done on specialized devices serves as a case study. The notions of cost function, experimental design and rheological model are examined. A sensitivity analysis is also performed. The next chapter present the experimental tools used on the industrial press. Finally, the friction and thermal exchange that will happen during the tests are evaluated. The third chapter is about the inverse analysis on industrial press. Finite elements modelling of the compression is made and compared with the experiments. The identification results are then compared with the FORGE® software database and the material parameters found in chapter 1. A complex part is then simulated with these different parameters and compared with a real forging of this part. The fourth chapter uses the same methods as in chapter 3 to perform an identification on the rheological parameters of an Inconel 625. A microstructural model for the Inconel is then identified with industrial testing as reference
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
A Material Model Optimization Approach for the Sheet Metal Forming Process Using the Hole Expansion Test
No full textPublisher Copyright: © 2024, The Author(s), under exclusive license to Springer Nature Switzerland AG.Sheet metal forming is an important manufacturing process widely used to produce complex stamped parts from flat sheet stock in industries such as automotive and packaging. Due to the global economic climate, these industries need to be highly competitive by reducing production costs and increasing process efficiency. Numerical simulation combined with sheet metal forming expertise is one of the technological innovations adopted to meet these requirements by reducing the traditional time-consuming and costly testing steps. With the progress of finite element simulation, questions about the accuracy or limitations of the type of material description adopted have become particularly important. The influence of the plasticity model is examined in this work by a numerical study using the hole expansion test. This work first presents the yield locus criterion adopted and developed by Tata Steel, which is hereafter referred to as the Tata Steel material model. Hole expansion tests are performed at different hole diameters and the results are compared with FE simulation. The simulations are performed with the finite element software Autoform R11 in which the yield criterion proposed by Abspoel & Scholting [1] has been implemented. The discussion therefore focuses on the influence of the material model on the numerical predictions and its accuracy based on the optimization of the different material parameters measured.The authors would like to acknowledge experimental work carried out at Tata Steel R&D by Frank Schouten and Tushar Khandeparkar.Peer reviewe
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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