1,721,086 research outputs found
Effect of the tool geometry on composite forming and the contribution of additive manufacturing
No full textLes matériaux composites ont un intérêt majeur dans différents domaines car ils présentent une alternative intéressante en raison de leurs propriétés bénéfiques. Cette demande croissante a créé un besoin de comprendre et de maîtriser leurs procédés de fabrication afin de les rendre plus efficient. C'est dans ce cadre que ces travaux de thèse, s'inscrivant dans le cadre de la chaire industrielle "Matur", ambitionnent à contribuer à comprendre l'effet de la géométrie de la préforme sur le comportement et les défauts lors du préformage de renforts secs et proposer une géométrie modèle pour des études de formabilité. Afin de proposer une géométrie du modèle. Dans un premier temps, une étude détaillée des différents défauts répertoriés dans la littérature a été établie et une classification avec des dénominations ont été proposées selon différentes échelles et modes de déformation. Après un état de l’art sur les géométries étudiées dans la littérature, un essai expérimental a été mené sur une sélection de cinq géométries et comparées. Les résultats ont montré que la géométrie a un effet important sur le comportement induit des renforts et le profil des défauts. Chacune des géométries a généré un comportement différent selon ses caractéristiques et ses détails géométriques. L’analyse des résultats a permis de sélectionner certaines facettes géométriques qui ont été utilisées pour construire plusieurs géométries qui ont été testées. La sélection finale a convergé vers le choix d’une géométrie qui est capable de générer une gamme importante du comportement en cisaillement et les différents mécanismes de défauts, offrant ainsi la possibilité d'étudier la mise en forme des renforts et de les discriminer sur la base de leur formabilité.Composite materials have been a major interest in different fields because they constitute an interesting alternative due to on demand beneficial properties. This increasing demand generated a requirement for a better understanding and mastering of their manufacturing process to make them more efficient. It is in this context that this PhD work, falling within the framework of industrial chair” Matur", aims to contribute to understanding the effect of the preform geometry on the behavior and defects during the dry reinforcements preforming and propose a model geometry for the formability study. So, as a first step, a detailed investigation of the various defects listed in the literature has been established and a classification with denominations was proposed following different scales and deformation modes. After a literature review of the studied geometries, an experimental test has been conducted on five selected geometries and compared. The results have shown that geometry has an essential effect of the induced fabric behavior and the defect’s profile. Each geometry has triggered different behavior depending on its characteristics and details. The results analysis allowed us to select certain geometric facets which were used to build several geometries that were tested. The final selection resulted in choosing a geometry that had offered a wide range of the shearing behavior and different defect mechanisms, thus offering a possibility to study the shaping of the reinforcements and to discriminate between the reinforcements based on their formability
Characterization by Digital Volume Correlation of structures obtained by additive manufacturing and link properties / processes
No full textCes travaux de thèse s’inscrivent dans de la chaire industrielle "MATUR" (matériaux architecturés) et visent à contribuer à l’identification et la caractérisation des interactions du triptyque matériau/procédé/propriétés pour des structures architecturées obtenues par fabrication additive et destinées pour des applications de santé. Pour ce faire, deux objectifs ont été définis. Le premier concerne la mise en place d’une chaine expérimentale de caractérisation in-situ sous tomographe et le second à l’utilisation de cette chaine pour caractériser les propriétés induites par les procédés. Ainsi, une chaine expérimentale a été définie puis mise en place afin de mener des essais in-situ de compression sous tomographie aux rayons X suivis de calculs de corrélation d’images volumiques (DVC) utilisant les volumes issus de la tomographie. Le triptyque matériau / procédé / propriétés a été abordé en étudiant deux types de structures : une structure pleine qui a servi pour faire la validation et la calibration de la chaine expérimentale et une structure architecturée. La corrélation d’images volumiques a permis d’évaluer l’effet du procédé de fabrication additive de stéréolithographie (SLA) sur les propriétés géométriques et structurelles des structures architecturées.This thesis work is part of the "MATUR" industrial chair (architectural materials) and aims to contribute to the identification and characterization of the interactions of the material / process / properties triptych for architected structures obtained by additive manufacturing and intended for health applications. To this end, two objectives have been defined. The first concerns the implementation of an experimental chain for in-situ characterization under X-ray tomography and the second concerns the use of this chain to characterize the properties induced by the processes. Thus, an experimental chain was defined and set up to perform in-situ compression tests under X-ray tomography followed by Digital Volume Correlation (DVC) using the volumes obtained from the tomography. The material / process / properties triptych was addressed by studying two types of structures: a full filled structure which was used to validate and calibrate the experimental chain and an architected structure. Digital Volume Correlation was used to evaluate the effect of a parameter of the stereolithography additive manufacturing process (SLA) on the geometric and structural properties of architected structures
prediction of proximal femur fracture : finite element modeling based on mechanical damage and experimental validation
No full textLes fractures causées par l'ostéoporose de l’extrémité supérieure du fémur sont devenues un problème majeur de santé publique. Par conséquent, ce sujet devient un axe de recherche de plus en plus important pour les cliniciens et les chercheurs biomédicaux. Le but de cette étude est de développer une nouvelle approche pour prédire la fracture du col du fémur. Cette étude propose de développer et valider des modèles par éléments finis (EF) en 2D et 3D, basés sur le concept de l’endommagement mécanique des milieux continus, permettant de simuler la fracture de la partie proximale du fémur en tenant compte de l’initiation progressive de fissures et leur progression. Deux configurations ont été utilisées: appui monopodal et chute. L’ensemble des lois de comportements quasi fragile couplées à une loi d’endommagement sont implémentées en langage FORTRAN dans ABAQUS/Standard (sous-programme de type UMAT). La densité minérale osseuse (BMD) a été mesurée par l’absorptiométrie à rayon X en double énergie DXA pour la région d'intérêt. Les modèles ont été développés dans deux variantes (l’une isotrope et l’autre orthotrope) puis validés avec des résultats expérimentaux obtenus sur des essais en appui monopodale réalisés sur des fémurs humain. Durant ces essais, des mesures optiques basées sur la méthode de corrélation d'images numériques (DIC) ont été réalisées afin d’acquérir les différents champs de déplacement et de déformation. Le modèle numérique 3D a réussi à prédire l’ensemble de la courbe force-déplacement ainsi que l'emplacement et l'amorce de la rupture des fémurs. Par ailleurs, Malgré sa robustesse, la variante 3D du modèle numérique reste difficilement exploitable dans l’état pour réaliser un diagnostic préventif dans des délais acceptables pour des cliniciens, car très consommatrice en temps de calcul. Pour pallier à cela, le modèle simplifié en 2D a été préliminairement validé sous les mêmes conditions aux limites et les résultats ont montré une bonne corrélation avec l’expérience. Ces travaux ont souligné le potentiel de la modélisation par éléments finis basée sur l’endommagement quasi-fragile à devenir un outil complémentaire de prédiction du risque de la fracture osseuse.Femoral fractures caused by the osteoporosis become major problem of public health, and therefore, this subject becomes an increasingly important goal for both clinicians and biomedical researchers. The purpose of this study is to develop a new coupled approach to predict the fracture of neck femoral. The current study proposes a validated 2D and 3D finite element (FE) models based on continuum damage mechanics in order to simulate human proximal femur fracture considering the progressive cracks initiation and propagation. These models are applied and validated under single limb stance and sideways fall configuration. Quasi brittle behavior laws coupled to damage are implemented in FORTRAN and fed into ABAQUS/Standard codes to describe the constitutive behavior (subroutine UMAT). Bone mineral density (BMD) is measured using dual energy X-ray absorptiometry (DXA) for the region of interest. The models have been developed within two variants (one isotropic, the other anisotropic) and validated with experimental results of tests performed on human femur samples under single limb stance configuration. During these tests, optical measurements based on the method of digital image correlation (DIC) were conducted to acquire the various fields of displacement and deformation. To calculate the fracture risk of the femoral head, it is necessary to assign correctly the bone material properties. The 3D FE models were able to predict the overall force-displacement curve, location and initiation of femur fractures. Moreover, despite its robustness, this 3D FE model is still limited to be used, within clinically acceptable time, for diagnostic purposes. To overcome this, the model was simplified into 2D model which has been preliminarily validated under identical boundary conditions and the results showed a good correlation with experiments. These studies have highlighted the potential of the finite element model based on quasi-brittle damage to become a complementary tool for predicting the risk of bone fracture
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
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
- …
