Identification du comportement mécanique dynamique de tubes d'aluminium par un essai d'expansion électromagnétique

National audienceLes vitesses de déformation mises en jeu au cours du magnétoformage sont de l'ordre de 102 à 104 s-1. La maîtrise du procédé exige donc la caractérisation des métaux dans ces conditions de déformation. Cet article présente la mise en place d'une démarche d'identification du comportement dynamique basée sur un essai d'expansion de tube instrumenté à l'aide d'un système de mesure de vitesse par interférométrie doppler-laser. Les simulations numériques sont réalisées à l'aide du code LS-Dyna®, et l'analyse inverse est menée grâce à l'interface d'optimisation LS-Opt®. Après une analyse numérique, des résultats d'identification sur tubes d'aluminium 1050-O sont présentés

A coupled experimental/numerical approach for the characterization of material behavior at high strain-rate using electromagnetic tube expansion testing

International audienceHigh speed forming processes such as magnetic pulse forming are gaining interest in the sheet metal industry. Their design and development require specific effort on numerical modelling as well as on the characterization of the high strain-rate mechanical behaviour of metals. Standard dynamic tests (SHPB, plate impact, simple tension…) are limited in their representativeness of the deformation modes encountered in high speed processes. The present study describes how the electromagnetic tube expansion test can be used as a high strain-rate test for the identification of material constitutive parameters. Through numerical analysis, the deformation mode and the sensitivity of radial expansion to material constitutive behaviour are depicted. Then, the material parameter identification methodology is applied to annealed 1050 aluminium tubes. It is shown that the test is capable of highlighting the strain-rate sensitivity of behaviour, in spite of relatively high sensitivity to measurement uncertainties

Determination of high strain-rate behavior of metals: applications to magnetic pulse forming and electrohydraulic forming

International audienceThe design of processes like magnetic pulse forming and electrohydraulic forming involves multiphysical couplings that require numerical simulation, and knowledge on dynamic behaviour of metals. The forming process is completed in about 100 μs, so that the workpiece material deforms at strain-rates between 100 and 10 000 s-1. In this range, the mechanical behaviour can be significantly different than that in quasi-static conditions. It is often noticed that the strength and the formability are higher. The main goal of this study is to use an electromagnetically driven test on tubes or sheets to identify the constitutive behaviour of the workpiece material. In the case of tube, an industrial helix coil is used as inductor. Simulations with the code LS-Dyna® permit to find a configuration where the tube deforms homogeneously enough to allow axisymmetric modelling of the setup. The coil current is measured and used as an input for the simulations. The radial expansion velocity is measured with a Photon Doppler Velocimeter. The parameter identification is lead with the optimization software LS-Opt®. LS-Dyna axisymmetric simulations are launched which different set of parameters for the constitutive behaviour, until the computed expansion velocity fits the experimental velocity. The optimization algorithm couples a gradient method and a global method to avoid local minima. Numerical studies show that for the Johnson-Cook constitutive model, two or three experiments at different energies are required to identify the expected parameters. The method is applied to Al1050 tubes, as received and annealed. The parameters for the Johnson-Cook and Zerilli-Armstrong models are identified. The dynamic constitutive behaviour is compared to that measured on quasi-static tensile tests, and exhibits a strong sensitivity to strain-rate. The final strains are also significantly higher at high velocity, which is one of the major advantages of this kind of processes

Comptabilités et Société. Entre représentation et construction du monde

Cet ouvrage de recherche est une réflexion sur les liens entre Comptabilités et Société. Il envisage la comptabilité, au sens large, comme mode de représentation et construction du Monde. La comptabilité est tout d'abord présentée comme étant le reflet du monde. Le monde et ses visions évoluant en permanence, la comptabilité a dû se mettre à jour mais certaines images qu'elle fournit demeurent incomplètes. Sont ensuite soulignées les capacités de la comptabilité à influencer le monde qui nous entoure ; le monde résulterait alors du pouvoir de la comptabilité. La comptabilité a en effet des capacités structurantes pour les organisations et pourrait même, sous certaines conditions, permettre de « changer le monde ». Cet ouvrage offre une réflexion sur la double relation qui unit la comptabilité et le monde aux enseignants-chercheurs, aux étudiants, aux professionnels comptables, aux directions d'entreprise mais également aux consultants en management qui sont confrontés aux mutations de la comptabilité face aux enjeux sociaux, environnementaux et technologiques de la société

Identification du comportement mécanique dynamique de métaux par un essai d'expansion électromagnétique de tube

International audienc

Imaging long distance propagating calcium signals in intact plant leaves with the BRET-based GFP-aequorin reporter

Calcium (Ca2+) is a second messenger involved in many plant signaling processes. Biotic and abiotic stimuli induce Ca2+ signals within plant cells, which, when decoded, enable these cells to adapt in response to environmental stresses. Multiple examples of Ca2+ signals from plants containing the fluorescent yellow cameleon sensor (YC) have contributed to the definition of the Ca2+ signature in some cell types such as root hairs, pollen tubes and guard cells. YC is, however, of limited use in highly autofluorescent plant tissues, in particular mesophyll cells. Alternatively, the bioluminescent reporter aequorin enables Ca2+ imaging in the whole plant, including mesophyll cells, but this requires specific devices capable of detecting the low amounts of emitted light. Another type of Ca2+ sensor, referred to as GFP-aequorin (G5A), has been engineered as a chimeric protein, which combines the two photoactive proteins from the jellyfish Aequorea victoria, the green fluorescent protein (GFP) and the bioluminescent protein aequorin. The Ca2+-dependent light-emitting property of G5A is based on a bioluminescence resonance energy transfer (BRET) between aequorin and G FP. G5A has been used for over 10 years for enhanced in vivo detection of Ca2+ signals in animal tissues. Here, we apply G5A in Arabidopsis and show that G5A greatly improves the imaging of Ca2+ dynamics in intact plants. We describe a simple method to image Ca2+ signals in autofluorescent leaves of plants with a cooled charge-coupled device (cooled CCD) camera. We present data demonstrating how plants expressing the G5A probe can be powerful tools for imaging of Ca2+ signals. It is shown that Ca2+ signals propagating over long distances can be visualized in intact plant leaves and are visible mainly in the veins

Identification of material constitutive parameters for dynamic applications: Magnetic Pulse Forming and electrohydraulic forming.

International audienc

Determination of High Strain-Rate Behavior of Metals: Applications to Magnetic Pulse Forming and Electrohydraulic Forming

International audienc

How to strengthen the presence of patients in health technology assessments conducted by the health authorities

International audienc