Caractérisation du comportement anisotrope de tôles d'aluminium

National audienceDeux méthodes de caractérisation du comportement anisotrope de tôles sont comparées. Les coefficients de Lankford de tumé : ôles en alliage d'aluminium-magnésium sont tout d'abord déterminés via des essais de traction à température ambiante. Un système de reconnaissance automatique de motifs aléatoires est utilisé pour analyser ces essais en termes de comportement mécanique et pour identifier les coefficients d'anisotropie. En parallèle, des essais d'emboutissage de type Nakazima ont été réalisés, puis analysés à l'aide d'un module d'analyse inverse. Ce modèle s'appuie sur une méthode d'optimisation automatique couplée à un logiciel éléments finis tridimensionnel. Le comportement anisotrope des tôles d'aluminium est modélisé en utilisant un critère de Hill. Les mesures de champs de déformation obtenues avec le système de corrélation d'images sont utilisées pour identifier les paramètres du critère de Hill. Les coefficients de Lankford ainsi déterminés sont comparés à ceux issus des essais de traction

Finite element thermomechanical simulation of steel continuous casting

International audienceIn continuous casting (CC), thermomechanical simulation is essential to analyze important issues: gap formation; stress and deformation of the solidified shell; bulging of product between supporting rolls in the case of steel CC; size of final product, butt-curl defect in direct chill casting of aluminium. The numerical simulation package THERCAST has been developed with the objective of supplying an accurate analysis of those phenomena, permitting to define relevant process actuators. In this paper, some characteristic features especially developed for steel continuous casting are presented and illustrated by examples of industrial application

Perfusion Imaging to select patients with large ischemic core for mechanical thrombectomy

International audienceBackground and purpose: Patients with acute ischemic stroke, proximal vessel occlusion and a large ischemic core at presentation are commonly not considered for mechanical thrombectomy (MT). We tested the hypothesis that in patients with baseline large infarct cores, identification of remaining penumbral tissue using perfusion imaging would translate to better outcomes after MT.Methods: This was a multicenter, retrospective, core lab adjudicated, cohort study of adult patients with proximal vessel occlusion, a large ischemic core volume (diffusion weighted imaging volume ≥70 mL), with pre-treatment magnetic resonance imaging perfusion, treated with MT (2015 to 2018) or medical care alone (controls; before 2015). Primary outcome measure was 3-month favorable outcome (defined as a modified Rankin Scale of 0-3). Core perfusion mismatch ratio (CPMR) was defined as the volume of critically hypo-perfused tissue (Tmax >6 seconds) divided by the core volume. Multivariable logistic regression models were used to determine factors that were independently associated with clinical outcomes. Outputs are displayed as adjusted odds ratio (aOR) and 95% confidence interval (CI).Results: A total of 172 patients were included (MT n=130; Control n=42; mean age 69.0±15.4 years; 36% females). Mean core-volume and CPMR were 102.3±36.7 and 1.8±0.7 mL, respectively. As hypothesized, receiving MT was associated with increased probability of favorable outcome and functional independence, as CPMR increased, a difference becoming statistically significant above a mismatch-ratio of 1.72. Similarly, receiving MT was also associated with favorable outcome in the subgroup of 74 patients with CPMR >1.7 (aOR, 8.12; 95% CI, 1.24 to 53.11; P=0.028). Overall (prior to stratification by CPMR) 73 (42.4%) patients had a favorable outcome at 3 months, with no difference amongst groups.Conclusion: s In patients currently deemed ineligible for MT due to large infarct ischemic cores at baseline, CPMR identifies a subgroup strongly benefiting from MT. Prospective studies are warranted

Alexandrie (actions du Centre d’études alexandrines, 2022)

Données scientifiques produites :https://www.cealex.org/ Introduction En 2022, le Centre d’études alexandrines (CNRS/Ifao, UAR 3134 CEAlex) a été à même de poursuivre ses fouilles sur le site de Kôm Bahig, de même que ses prospections en Maréotide dans la région au sud du lac Mariout. En revanche, en raison des retards dans l’accord de l’autorisation de travail par la sécurité nationale égyptienne, ni les fouilles sous-marines sur le site du Phare, ni la campagne d’étude sur la tombe 2 de la..

Effect of terminal accuracy requirements on temporal gaze-hand coordination during fast discrete and reciprocal pointings

Background\ud \ud Rapid discrete goal-directed movements are characterized by a well known coordination pattern between the gaze and the hand displacements. The gaze always starts prior to the hand movement and reaches the target before hand velocity peak. Surprisingly, the effect of the target size on the temporal gaze-hand coordination has not been directly investigated. Moreover, goal-directed movements are often produced in a reciprocal rather than in a discrete manner. The objectives of this work were to assess the effect of the target size on temporal gaze-hand coordination during fast 1) discrete and 2) reciprocal pointings.\ud \ud Methods\ud \ud Subjects performed fast discrete (experiment 1) and reciprocal (experiment 2) pointings with an amplitude of 50 cm and four target diameters (7.6, 3.8, 1.9 and 0.95 cm) leading to indexes of difficulty (ID = log2[2A/D]) of 3.7, 4.7, 5.7 and 6.7 bits. Gaze and hand displacements were synchronously recorded. Temporal gaze-hand coordination parameters were compared between experiments (discrete and reciprocal pointings) and IDs using analyses of variance (ANOVAs).\ud \ud Results\ud \ud Data showed that the magnitude of the gaze-hand lead pattern was much higher for discrete than for reciprocal pointings. Moreover, while it was constant for discrete pointings, it decreased systematically with an increasing ID for reciprocal pointings because of the longer duration of gaze anchoring on target.\ud \ud Conclusion \ud \ud Overall, the temporal gaze-hand coordination analysis revealed that even for high IDs, fast reciprocal pointings could not be considered as a concatenation of discrete units. Moreover, our data clearly illustrate the smooth adaptation of temporal gaze-hand coordination to terminal accuracy requirements during fast reciprocal pointings. It will be interesting for further researches to investigate if the methodology used in the experiment 2 allows assessing the effect of sensori-motor deficits on gaze-hand coordination

Développement d'une méthode d'identification de paramètres par analyse inverse couplée avec un modèle éléments finis 3d

The aim of this work is the developement of an automatic parameter identification method coupled with the finite element software FORGE3. Mechanical tests analysis involving refined material flows and complex rheological behaviour requires the use of inverse methods coupled with finite element solvers. The method developed in this study is coupled with the 3D direct model FORGE3 in order to take into account 3D material flows encountered in some tests. The inverse problem is formulated as a least square optimisation problem. In order to minimise the computational time associated with the resolution of the inverse problem, a descent direction method (Gauss-Newton method) is chosen. This algorithm is a good compromise between accuracy and computational time. Since descent direction method can show some instabilities, the Gauss-Newton method is stabilised in order to allow the identification of relatively complex rheological model parameters. The proposed approach is validated for several numerical problems which cover a wide range of mechanical tests. In order to compute the Gauss-Newton algorithm and to study its accuracy, a sensitivity analysis module is developed. This module is based on a semi-analytical scheme, which is flexible, accurate and not too time consuming. The global parameter identification scheme is tested on practical problems: compression, torsion and plane strain compression tests. The proposed approach also allows the study of formability tests to obtain rheological behaviours. SICO tests, bulge tests and Nakazima on metallic sheets tests are analysed. The proposed parameter identification module allows to identify various rheological models (viscoplastic, elastic-viscoplastic, Hill's anisotropic criterion) from various simple or complex mechanical tests. Finally, the sensitivity analysis has been used as a tool to design the experiments themselves, for instance for the Nakazima tests and for the plane strain compression tests.Le but de ce travail est le développement d'une méthode automatique d'identification de paramètres couplée au logiciel éléments finis FORGE3. L'analyse d'essais mécaniques faisant intervenir des écoulements de matière complexes ainsi que la prise en compte de modèles rhéologiques de plus en plus raffinées rendent nécessaire l'utilisation de méthodes inverses couplée avec des solveurs éléments finis. La méthode développée est couplée avec le modèle direct tridimensionnel FORGE3, afin de prendre en compte l'écoulement de matière tridimensionnel intervenant dans certains essais. Le problème inverse est formulé comme un problème d'optimisation au sens des moindres carrés. Afin de minimiser les temps de calcul associé à la résolution de ce problème inverse, une méthode à direction de descente (méthode de Gauss-Newton) est choisie. Cet algorithme permet un bon compromis entre précision et temps de calcul. Les méthodes à direction de descente pouvant présenter des instabilités numériques, l'algorithme de Gauss-Newton est stabilisé afin d'être en mesure d'identifier les paramètres de modèles rhéologiques relativement complexes. L'approche proposée est validée sur quelques problèmes numériques représentatifs des problèmes concret que l'on veut étudier. Afin de programmer l'algorithme de Gauss-Newton et d'étudier sa stabilité, un module d'analyse de sensibilité est développé. Celui-ci est basé sur un schéma semi-analytique, alliant flexibilité, précision et faible coût en terme de temps de calcul. L'approche globale d'identification de paramètres est testée sur un certain nombre de cas concrets: des essais de compression simple, de torsion, de bipoinçonnement. L'approche proposée permet aussi d'utiliser des essais de formabilité comme des essais rhéologiques. Dans ce contexte, l'essai SICO, l'essai de gonflage hydraulique de tôle ainsi que l'essai Nakazima sont analysés. Le module d'identification de paramètres proposé permet d'identifier divers modèles rhéologiques (e.g. viscoplastiques, élasto-viscoplastiques, critère de Hill anisotrope), à partir de divers essais mécaniques plus ou moins complexes. Enfin, l'analyse de sensibilité s'est révélée être un outil d'aide à la conception des expériences elles-mêmes pour l'essai Nakazima et pour l'essai de bipoinçonnement

Cognitive cost of motor reorganizations associated with muscular fatigue during a repetitive pointing task

International audienc

Estimation of constitutive parameters using an inverse method coupled to a 3D finite element software

International audienceForming process simulations require a precise knowledge of the input material parameters. These parameters are usually estimated from mechanical tests. The classical analysis of these tests are usually based on a few assumptions: material flow homogeneity, isothermal conditions, etc. But in some cases with strain localisation or self-heating, these assumptions overestimate material strength. Analysis techniques using inverse methods are then good alternatives. This paper deals with the estimation of mechanical parameters using an inverse method. The direct model is a 3D forming process simulation software (FORGE3®). The numerical formulation is based on a mixed finite element method using two unknowns, the velocity and the pressure. The tetrahedron element is linear in velocity and pressure and the thermal problem is solved using a linear element. The inverse problem associated with the estimation of mechanical parameters is expressed as a least square problem. The aim is to obtain output of the direct model which fits experimental data measured during the mechanical test. The optimisation problem is solved using a Gauss-Newton algorithm. At the end of the optimisation, an estimation of confidence intervals is done. A Gauss-Newton algorithm requires the computation of the derivatives of the output with respect to the parameters to be identified. In this work, a semi-analytical differentiation is performed. The proposed method is first validated on artificial experimental data obtained from direct simulations of hot uniaxial compressions for a viscoplastic cylinder. The confidence interval is provided by the algorithm for different configurations with additional random noise. Finally a real steel compression test is analysed to provide parameters for the Norton-Hoff viscoplastic la

Inverse analysis of thermomechanical upsetting tests using gradient method with semi-analytical derivatives

International audienceThe starting point of this work is the need of precise and correct input data for material forming codes. The use of these codes as a direct model for inverse analysis of the processes permits to extend the validity range of the thermomechanical parameters in terms of temperature, strain and strain rate. The identification software was developed on the basis of the 2D and of a 3D finite element code (FORGE2((R)) and FORGE3((R))) simulating forming processes and using a thermo-elasto-viscoplastic behaviour. The optimisation problem is based on a Gauss Newton algorithm and necessitates the evaluation of the derivatives of the cost function and of the sensitivity matrix to solve the system. Different methods are proposed to evaluate these derivatives. We have studied deeply analytical evaluation, finite difference techniques and recently semi-analytical derivatives. In this paper we present the main feature of the semi-analytical derivatives and the comparison with numerical ones on the parameter identification during upsetting tests. The semi-analytical method of sensitivity analysis for inverse problems is very attractive thanks to the compromise between computational time and ease of derivatives evaluation. Especially for parameter identification in material forming domain, this technique seems to be promising