Modélisation numérique de l'assise médicale spécifique à la formation d'escarres de pression (S13)

Cet article, propose un modèle éléments finis 3D d'un fessier humain en contact avec un coussin en nid d'abeille à base de thermoplastique polyuréthane (TPU). L'objectif est d'étudier la pression à l'interface fessier/coussin, afin d'améliorer le confort du patient se déplaçant en fauteuil roulant, en particulier dans le cadre de la prévention d'escarres. Pour différents cas de figures de coussins disponibles sur le marché, les résultats numériques démontrent que le coussin à base de TPU est un des coussins les plus approprié et adapté pour réduire la formation d'escarres

Simulation et analyse numérique du procédé de filage de pièces à base d'alliage de cuivre

Au cours du filage à chaud du cupro-aluminium, la forme désirée de la pièce est obtenue par la déformation plastique du lopin initial. La qualité de la pièce finale dépend de différents paramètres mis en jeu au cours du filage, en particulier, la température initiale du lopin et des outils, le coefficient de frottement entre le lopin et la matrice. La nature de l'écoulement de la matière et la formation de la zone morte sont d'une importance particulière pour garantir une bonne qualité des pièces filée. Dans ce travail, une étude paramétrique a été faite afin de déterminer l'effet et l'importance de chaque paramètre à l'aide de simulations 2D sous le logiciel FORGE®

Thermomechanical behavior of C38LTT in the semi-solid state

Semisolid thixoforming is an intermediate process between casting and forging. This process presents several advantages, such as energy efficiency, production rates, smooth die filling, low shrinkage porosity, which together lead to near net shape capability and thus to fewer manufacturing steps than with classical methods. So far, there are only few applications of semisolid processing of higher melting point alloys. Steel is a particularly challenging material to semi-solid process because of the high temperatures involved (about 1410°C). At present, the ability to form steel components in semi-solid state depends on the control of the flow of material during the forming and defects conditions. Semi-solid alloys display thixotropy, which is characterized by time-dependent behavior which drastically changes from a solid like behavior at rest to a liquid like flow when submitted to shear. However, characterizing and modelling such a behaviour for steels is still challenging.   Ascometal has developed the C38LTT (Low Thixoforging Temperature) that is compatible with identified parameters [1] to be suitable for thixoforming: the solidus and liquidus temperatures (TS and TL) have to be as low as possible; the temperature at 50% liquid fraction (T50%) has to be as low as possible; the melting interval (TL-TS) has to be as large as possible; and the slope at 10% and 50% liquid fraction must be as low as possible to ensure a small sensitivity of liquid fraction to temperature.   The aim of the research work was to study the rheological properties of C38LTT. The high temperature range for semi-solid state makes the experiments particularly challenging. An experimental protocol was determined, geometries of specimens, minimize thermal gradients and optical system to improve the precision of measuring temperature (figure1) with a Gleeble simulator to characterize the thermomechanical behaviors.   Uniaxial tensile and compressive tests were carried out on semi-solid specimen having >0.8 solid fraction for different ram speeds and temperatures. The constitutive behavior appears greatly dependent on both fraction solid and strain rate. Furthermore, while the behavior is dominated by the solid phase, the variation in both ductility and stress with temperature has been identified to propose a brittle temperature range and the influence of the temperature on the thermomechanical behavior. Specifically, in tension, a drastic change in ductility with fraction solid/temperature was found in good agreement with some results for aluminum brittle temperature range in literature [2].

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Conception automatique et optimisation des surfaces additionnelles pour le procédé d'emboutissage

International audienceL’emboutissage de pièces en tôles minces nécessite l'ajout de surfaces additionnelles autour de la pièce désirée afin d'améliorer la formabilité et la qualité. Ces surfaces additionnelles sont principalement constituées de murs de protection et de surfaces sous serre-flan. La conception automatique des surfaces additionnelles s'appuie sur la création des courbes de profile et des surfaces de COONS. Des outils paramétriques de conception-simulation-optimisation permettent d’aboutir rapidement à des surfaces additionnelles optimales

Conception automatique et optimisation des surfaces additionnelles pour le procédé d’emboutissage

Lors de la fabrication, à l’aide d’un procédé d’emboutissage, de pièces en tôles minces telles que les carrosseries automobiles ou les composants d’électroménager, certaines surfaces doivent être ajoutées à la pièce désirée afin d’éviter des défauts comme la rupture, le plissement et la rayure. Ces surfaces additionnelles sont constituées de murs de protection et de surfaces sous serre-flan. L’objectif principal de cette étude est de proposer une méthodologie d’aide à la conception des surfaces additionnelles s’appuyant sur le développement d’une procédure numérique automatique de conception et d’optimisation de ces surfaces additionnelles dans le cadre d’un procédé d’emboutissage de tôles minces. La conception automatique des surfaces additionnelles s’appuie sur la création des courbes de profil et de surfaces de COONS. Ces surfaces sont ensuite maillées automatiquement et la simulation du problème d’emboutissage est résolue avec l’Approche Inverse. Enfin, les paramètres géométriques nécessaires à la création des surfaces sont optimisés afin de satisfaire des critères mécaniques propres au procédé d’emboutissage. Ces outils paramétriques de conception-simulation-optimisation permettent d’aboutir rapidement à des surfaces additionnelles optimales

Conception et optimisation de surfaces additionnelles dans le procédé d emboutissage par l approche inverse

Cette thèse traite la conception et l optimisation des surfaces additionnelles dans le procédé d emboutissage en présence de fortes non linéarités, en utilisant la méthode des éléments finis couplée à un procédé de conception de ces surfaces et à un algorithme d optimisation aux méthodes de programmation mathématique. L objectif principal concerne la mise en œuvre d un emboutis utilisé en carrosserie. Pour atteindre notre objectif, nous avons combiné les trois codes suivants : (i) Un code de simulation du procédé d emboutissage dénommé Approche Inverse , qui a été développé par les Professeurs Batoz, Guo et leurs collaborateurs, au sein de l Université de Technologie de Compiègne depuis 1987. (ii) Un code de conception des surfaces additionnelles dénommé Addendum Surface Design , basé sur la CAO de la pièce finale. (iii) Un algorithme d optimisation basé sur la méthode SQP (Sequential Quadratic Programming)REIMS-BU Sciences (514542101) / SudocSudocFranceF

FE optimization of the ejection force of a spring-maintained connector

The connector studied herein is a self-ejecting microconnector that features a circular compression spring. This type of circular connector ensures reliable connections for systems requiring reduced weight and miniaturization. Being implemented in various military and aerospace applications, the connector is liable to undergo extreme vibratory loadings and shocks; but even in more common applications (medical sensors, power control systems, communications, etc.) the manufacturer has to guarantee that the two ends will remain properly assembled to ensure electrical continuity. The main purpose of this work is to simulate the whole insertion-extraction process using the finite element method (FEM) and to optimize the ejection force required to unplug the connector. The shape of the groove machined on the male part of the connector is investigated, allowing determination of the geometric parameters of interest. Results will provide manufacturers with useful data, which may also help their customers choose their interconnection solution

Fatigue behaviour FEM modeling of deep groove ball bearing mounted in automotive alternator submitted to variable loading

Ball bearings subsurface materials are subjected to rolling contact fatigue with multiaxial stress state during loading cycle. The complex operating conditions of automotive bearings are different from classic operating conditions their fatigue crack initiation predicted by standards can be seen underestimated. This work presents a numerical approach of ball bearings to evaluate its fatigue behaviour in order to predict the life. A preliminary study has been done to evaluate the load distribution in the bearings. The results are integrated in a numerical dynamic model to study the bearing material rolling fatigue behaviour in constant and variable loading cases. By using fatigue criteria and damage laws, the analysis of stress state in bearing material leads to life prediction or the number of cycles before crack initiations. These results are compared to current standard methods used for ball bearing life prediction