Ellipticity loss analysis for tangent moduli deduced from a large strain elastic–plastic self-consistent model

In order to investigate the impact of microstructures and deformation mechanisms on the ductility of materials, the criterion first proposed by Rice is applied to elastic–plastic tangent moduli derived from a large strain micromechanical model combined with a self-consistent scale-transition technique. This approach takes into account several microstructural aspects for polycrystalline aggregates: initial and induced textures, dislocation densities as well as softening mechanisms such that the behavior during complex loading paths can be accurately described. In order to significantly reduce the computing time, a new method drawn from viscoplastic formulations is introduced so that the slip system activity can be efficiently determined. The different aspects of the single crystal hardening (self and latent hardening, dislocation storage and annihilation, mean free path, etc.) are taken into account both by the introduction of dislocation densities per slip system as internal variables and the corresponding evolution equations. Comparisons are made with experimental results for single and dual-phase steels involving linear and complex loading paths. Rice’s criterion is then coupled and applied to this constitutive model in order to determine the ellipticity loss of the polycrystalline tangent modulus. This criterion, which does not need any additional “fitting” parameter, is used to build Ellipticity Limit Diagrams (ELDs).ArcelorMittal Researc

Ellipticity loss analysis for tangent moduli deduced from a large strain elastic–plastic self-consistent model

In order to investigate the impact of microstructures and deformation mechanisms on the ductility of materials, the criterion first proposed by Rice is applied to elastic–plastic tangent moduli derived from a large strain micromechanical model combined with a self-consistent scale-transition technique. This approach takes into account several microstructural aspects for polycrystalline aggregates: initial and induced textures, dislocation densities as well as softening mechanisms such that the behavior during complex loading paths can be accurately described. In order to significantly reduce the computing time, a new method drawn from viscoplastic formulations is introduced so that the slip system activity can be efficiently determined. The different aspects of the single crystal hardening (self and latent hardening, dislocation storage and annihilation, mean free path, etc.) are taken into account both by the introduction of dislocation densities per slip system as internal variables and the corresponding evolution equations. Comparisons are made with experimental results for single and dual-phase steels involving linear and complex loading paths. Rice’s criterion is then coupled and applied to this constitutive model in order to determine the ellipticity loss of the polycrystalline tangent modulus. This criterion, which does not need any additional “fitting” parameter, is used to build Ellipticity Limit Diagrams (ELDs).ArcelorMittal Researc

An English cover-up: masks, murders, and English cruelty in Goncourt, Lorrain, and Schwob

Fin-de-siècle writers from diverse disciplines were drawn to the seductive potential of masks and disguise; mask-wearing characters of indefinite identity, indeterminate gender, and insecure psychology proliferate in their texts. However, when characters are designated as English in such stories, they are also, and with remarkable frequency, associated with cruelty or murder: the mask-wielding murderers of Marcel Schwob’s ‘MM. Burke et Hare, Assassins’ carry out their crimes in Britain upon British victims; Edmond de Goncourt weaves his theatrical narrative around the mask-like demeanour of Lord Annandale in La Faustin; and Jean Lorrain’s malicious Lord Ethal exacerbates the Duc de Fréneuse’s perverse obsessions with masks in Monsieur de Phocas. This article explores this unexpected correlation, and examines the ways that English masks are used as narrative devices – at once to mould and play with national distinctions, and to reflect upon the psychological state of the French subject

Critère de ductilité basé sur la perte d'ellipticité du module tangent élastoplastique déduit d'un modèle autocohérent

THE AIM OF THIS PHD THESIS IS TO MODEL A DUCITLITY LOSS CRITERION. TO DO THAT, THIS WORK HAS BEEN DONE IN THREE STEPS. IN A FIRST TIME, THE BEHAVIOR AT THE LOCAL SCALE (WHICH IS THE ONE OF A GRAIN OR A SINGLE CRYSTAL) HAS BEEN MODELED BY A MICROMECHANICAL LAW WRITTEN IN THE LARGE STRAIN FRAMEWORK. HARDENING IS, AS FOR IT, TAKEN INTO ACOUNT BY A MATRIX WHICH INTERNAL VARIABLE IS THE MEAN DISLOCATION DENSITY ON A SLIP SYSTEM. THIS MODELISATION IS ABLE TIO REPRODUCE THE BEHAVIOR OF FERRITE AND IRON-SILICIUM SINGLE CRYSTALS FOR SIMPLE AND COMPLEX LOADING PATHS. IN A SECOND TIME, THE SCALE TRANSITION BETWEEN THE LOCAL BEHAVIOR AND THE ONE OF A POLYCRYSTALLINE AGGREGATE IS REALIZED THANKS TO THE SELF-CONSISTENT SCHEME AT THE SENSE OF HILL. IT IS SHOWN THAT, AT THIS STEP, THE ADOPTED MODEL IS ABLE TO PREDICT THE BEHAVIOR FOR SINGLE-PHASE, DUAL-PHASE FERRITE AND MARTENSITE AND SINGLE-PHASE WITH PRECIPITATES STEELS FOR SIMPLE AND COMPLEX LOADING PATHS. IN PLUS, THIS MODEL GIVES ALSO GOOD RESULTS FOR CALCULUS OF LANKFORD COEFFICIENT AND YIELD SURFACE AND ALSO FOR PREDICTING TEXTURE EVOLUTION. THE THIRD STEP CONISTS IN THE INTRODUCTION OF A DUCTILITY LOSS CRITERION BASED ON THE ELLIPTICITY LOSS OF THE ELASTIC-PLASTIC TANGENT MODULUS, THIS IS RICE'S CRITERION. THIS CRITERION IS USED TO PLOT FORMING LIMIT DIAGRAMS AND IT IS SHOWN THAT GOOD RESULTS CAN BE GIVEN.Cette thèse a pour but de modéliser un critère de perte de ductilité. Pour cela, ce travail a été fait en trois étapes. Dans un premier temps, le comportement à l'échelle locale (qui est celle d'un grain ou d'un monocristal) est modélisé par une loi micromécanique écrite dans le cadre des grandes déformations. L'écrouissage étant quant à lui pris en compte par une matrice dont la variable interne est la densité de dislocations moyenne par système de glissement. Cette modélisation est apte à reproduire le comportement de monocristaux de ferrite ou d'alliage fer-silicium pour des trajets simples et complexes. Dans un deuxième temps la transition d'échelles entre le comportement local et celui d'un agrégat polycristallin est réalisée grâce au schéma autochérent au sens de Hill. A cette étape il es montré que la modélisation adoptée est capable de prédire le comportement pour des aciers monophasés, biphasés et monphasés contenant des précipités pour des trajets simples et complexes. De plus, le modèle donne aussi de bons résultats dans le calcul de coefficient de Lankford et des surfaces de charge ainsi que pour la prédiction de l'évolution des textures. La troisème étape consiste à introduire un critère de perte de ductilité basé sur la perte d'ellipticité du module tangent élastoplasique, c'est le critère de Rice. Ce critère est ensuite utilisé pour tracer des courbes limite de formage et il est montré que de bons résultats sont obtenus

Critère de ductilité basé sur la perte d'ellipticité du module tangent élastoplastique déduit d'un modèle autocohérent

PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

Stable isotope variations in benthic filter feeders across a large depth gradient on the continental shelf

International audienceSpatial variations in carbon and nitrogen stable isotopes (δ13C and δ15N) of benthic filter feeders were investigated on an inshore-offshore gradient (0-250 km) along the continental shelf of the northern Bay of Biscay (NE Atlantic Ocean). δ13C and δ15N values were measured in muscle tissues of four filter-feeding mollusc species (epifaunal: Pecten maximus, Aequipecten opercularis; infaunal: Glycymeris glycymeris, Venus casina) and in benthic particulate organic matter along a corresponding water-depth gradient from 6 to 220 m. All four species showed a decreasing pattern of muscle δ13C and δ15N values with increasing depth. At the Ushant front (∼130 m water depth), where there is a decrease in both bottom water chlorophyll a and suspended particulate matter, muscle δ13C and δ15N values decreased in all species. Although δ13C values of infaunal clams initially decreased at 30 m depth, δ13C values of epifaunal scallops decreased around 120 m depth, far below the expected depth reduction in microphytobenthic production suggesting that carbon isotopes might not simply track microphytobenthic utilization. The difference between infaunal and epifaunal bivalve stable isotope values may reflect differences in feeding strategies. Muscle δ15N values at the deepest stations (∼2‰) were lower than expected considering the typical trophic enrichment value of 3-4‰ between prey and consumers. These low δ15N values may result from low metabolic rates and suggest the classic trophic enrichment may not hold true in species inhabiting deep waters. Stable isotopes in benthic filter feeders can reveal much information regarding their ecology and environment, but are not straightforward recorders of stable isotope baseline variations as is often assumed

Palaeoclimatology: The record for marine isotopic stage 11

International audienceThe marine isotopic stage 11 (MIS 11) is an extraordinarily long interglacial period in the Earth's history that occurred some 400,000 years ago and lasted for about 30,000 years. During this period there were weak, astronomically induced changes in the distribution of solar energy reaching the Earth. The conditions of this orbital climate forcing are similar to those of today's interglacial period and they rendered the climate susceptible to other forcing — for example, to changes in the level of atmospheric carbon dioxide. Here we use ice-core data from the Antarctic Vostok core to reconstruct a complete atmospheric carbon dioxide record for MIS 11. The record indicates that values for carbon dioxide throughout the interglacial period were close to the Earth's pre-industrial levels and that both solar energy and carbon dioxide may have helped to make MIS 11 exceptionally long. Anomalies in the oceanic carbonate system recorded in marine sediments at the time, for example while coral reefs were forming, apparently left no signature on atmospheric carbon dioxide concentrations

La mise en œuvre de l'unification allemande (1989-1990)

L'unification de l'Allemagne en 1990 a suscité durant son déroulement espoirs, craintes et projets contradictoires, actions et réactions nombreuses. Au fur et à mesure de leur ouverture, les archives permettent aujourd'hui de confirmer certaines interprétations ou de les éclairer sous un jour nouveau.The 1990 unification of Germany aroused during its unfolding many contradictory hopes, fears, projects and numerous actions and reactions. Today, as they become more and more available, archives allow to confirm certain interpretations or to enlighten them with new perspectives