FE modelling of cellular materials under compressive load

Structures made of tubes, stacked in square or hexagonal patterns, have been considered here as model cellular materials. Compression tests have shown large deformations, transformations and also many contact points. Two Finite Element codes have been used to investigate the influence of the elements type (quadrangular or triangular, linear or quadratic) and the numerical scheme (implicit or explicit) on the structural numerical responses. A contact algorithm based on the Pinball method has been implemented in the explicit code. A very good agreement has been found between the predictions of both codes. The numerical responses are close for a given meshes order, whatever the elements type. Whereas the linear meshes cannot be considered as converged, the quadratic meshes predict very well the experimental responses of the structures, especially for the square stacking. The overestimation of the numerical response of the hexagonal stacking might be explained because, experimentally, this stacking exhibits a more scattered and irregular behaviour due to defects (missing brazes, tube misalignment) which were not modelled.JRC.E.4-Safety and Security of Building

Modélisation par élément finis de la compression de matériaux cellulaires

International audienceStructures made of tubes, stacked in square or hexagonal patterns, have been considered here as model cellular materials. Compression tests have shown large deformations, transformations and also many contact points. Two Finite Element codes have been used to investigate the influence of the elements type (quadrangular or triangular, linear or quadratic) and the numerical scheme (implicit or explicit) on the structural numerical responses. A contact algorithm based on the Pinball method has been implemented in the explicit code. A very good agreement has been found between the predictions of both codes. The numerical responses are close for a given meshes order, whatever the elements type. Whereas the linear meshes cannot be considered as converged, the quadratic meshes predict very well the experimental responses of the structures, especially for the square stacking. The overestimation of the numerical response of the hexagonal stacking might be explained because, experimentally, this stacking exhibits a more scattered and irregular behaviour due to defects (missing brazes, tube misalignment) which were not modelled

Essais de caractérisation dynamique des matériaux aux vitesses moyennes de déformation

International audienceL’exposé s’intéresse au moyen le plus conventionnel de caractérisation dynamique des matériaux, à savoir la machine d’essai hydraulique. On pourrait penser que ces essais sont aujourd’hui parfaitement maîtrisés, ce qui est vrai dans le domaine des sollicitations quasi-statiques où ils sont même normalisés. Ce n’est toujours pas le cas dans le domaine des sollicitations moyennes vitesses (avant le domaine d’application des barres de Hopkinson), alors que ces essais s’avèrent indispensables pour plusieurs raisons qui sont mise en évidence dans le papier. L’exposé rappelle dans un premier temps et dans les grandes lignes quelles sont les capacités et les limitations actuelles de ces vérins hydrauliques rapides. Il adresse ensuite, au-delà des limitations des moyens, plusieurs sources de difficultés qui peuvent – si l’on n’y prend pas garde – rendre caduque tout espoir d’atteindre une caractérisation dynamique intrinsèque du comportement des matériaux testés. Sont évoquées plusieurs questions qui semblent majeures, les pièges et les précautions à prendre pour les éviter : définition des éprouvettes de caractérisation, introduction des efforts dynamiques, instrumentation, acquisition et mesure, et enfin traitement et exploitation de ces essais. En conclusion, après que les principaux acquis du laboratoire CRD de l’ONERA/DADS sur ces questions depuis 30 ans aient été rappelés, sont présentées quelques perspectives et voies d’amélioration aujourd’hui explorées pour adresser les nouveaux défis et les enjeux pour le secteur aéronautique dans ce domaine

Experimental and Finite Element Analysis of cellular materials under large compaction levels

This work aims at investigating the experimental characterisation and the modelling of the mechanical behaviour of cellular sandwich structures for large compaction levels, especially focusing on the collapse mechanisms of their constitutive cells and the role of the contacts created between neighbour cells. For that purpose, brazed cellular sandwich structures made of tube stackings have been considered as model architectures. The experimental characterisation of stackings consisting of either a square pattern or a hexagonal one has highlighted that the collapse mechanism was very reproducible in the case of the square stacking. On the contrary, the one observed for the hexagonal stacking showed an important sensitivity to the architectural defects such as missing braze joints or tube misalignment. Internal self-contacts created plaid also an important role regarding the densification plateau. In parallel, these compression tests have been simulated through the finite-element method; two different codes have been considered, one implicit (Z-set) and one explicit (Europlexus). The predictions of both codes have been compared to investigate their differences depending on finite strain and contact formulations. The comparison of their predictions with the experimental results has highlighted that quadratic meshes were necessary, involving the implementation of a second-order pinball method for the modelling of contacts in Europlexus. Both codes have also shown very close predictions whatever the mesh order and the finite strain formulation.JRC.E.4-Safety and Security of Building

Adverse effects of licorice consumed as food: An update; [Toxicités de l'exposition alimentaire à la réglisse: mise au point]

International audienceThe word “licorice” refers to the plant, its root, and its aromatic extract. From a commercial point of view, Glycyrrhiza glabra is the most important species with a wide range of uses (herbal medicine, tobacco industry, cosmetics, food and pharmaceutical). Glycyrrhizin is one of the main constituents of licorice. Glycyrrhizin is hydrolyzed in the intestinal lumen by bacterial β-glucuronidases to 3β-monoglucuronyl-18β-glycyrrhetinic acid (3MGA) and 18β-glycyrrhetinic acid (GA), which are metabolized in the liver. Plasma clearance is slow due to enterohepatic cycling. 3MGA and GA can bind to mineralocorticoid receptors with very low affinity, and 3MGA induces apparent mineralocorticoid excess syndrome through dose-dependent inhibition of 11β-hydroxysteroid dehydrogenase type 2 in renal tissue. The cases of apparent mineralocorticoid excess syndrome reported in the literature are numerous and sometimes severe, even fatal, most often in cases of chronic high dose consumption. Glycyrrhizin poisonings are characterized by hypertension, fluid retention, and hypokalemia with metabolic alkalosis and increased kaliuresis. Toxicity depends on the dose, the type of product consumed, the mode of consumption (acute or chronic) and a very large inter-individual variability. The diagnosis of glycyrrhizin-induced apparent mineralocorticoid excess syndrome is based on the history, clinical examination, and biochemical analysis. Management is primarily based on symptomatic care and stopping licorice consumption. © 2023 Société Nationale Française de Médecine Interne (SNFMI