Étude des phénomènes de transport et de performance thermoélectrique dans les alliages à base de Bi-Te-Se élaborés par extrusion

Généralités sur la physique des alliages thermoélectriques -- Effets thermoélectriques -- Critères de performance -- Réfrigération à température ambiante -- Propriétés des matériaux ternaires -- Techniques expérimentales & méthodes d'études -- Extrusion des poudres produites par mécanosynthèse -- Traitement thermique : restauration des propriétés -- Mesures électriques en fonction de la température -- Caractérisation thermoélectrique à température ambiante -- Mesure de la conductivité thermique -- Mesure du coefficient de Seebeck -- Mesure du facteur de mérite A à l'ambiante par la méthode Harman -- Influence de la concentration du dopant -- Corrélation entre les propriétés thermoélectriques -- Influence du recuit sur les propriétés électriques à 300K -- Influence du recuit sur les propriétés thermoélectriques à la température ambiante -- Étude des propriétés électriques en fonction de la température -- Analyse des résultats -- Analyse des paramètres électriques en fonction de la température -- Analyse des paramètres thermoélectriques à 300 K

Coupled rolling and buckling model for friction-sensitive setting of flatness actuators

International audienceFlatness defects in thin strip cold rolling are a consequence of buckling due to roll thermo-elastic deformation and the resulting heterogeneous strip plastic deformation. A coupled rolling - buckling model has been developed [Abdelkhalek et al. 2011]. It has shown that (i) taking buckling into account results in completely different stress fields and fits correctly the measured on-line residual stresses under tension ("stress-meter rolls"); (ii) coupling buckling in the post-bite area and the rolling model, whatever the technique, changes little the in-bite fields. The model is applied here to the effect of friction on optimal setting of a flatness actuator, Work Roll Bending

Flatness Defect in Thin Strip Cold Rolling and the Friction Impact on it

International audienceFlatness defects are one of the major problems in strip rolling. They are manifested by a wavy shape on the edge, in the center or in between. Waves are most of the time transverse, but all directions can be observed. These defects come from the heterogeneity of the stress field and the resulting buckling of the compressive areas out of the roll bite. This paper is based on the approach proposed by [1-3] and [4], and programmed previously [5-7] in the FEM software LAM3/TEC3 [8]. In the present paper, the latter is enhanced and applied to the impact of friction and strip tension on flatness of a rolled thin strip. The study shows how the optimal setting of Work Roll Bending force (WRB) should be changed when friction varies

Manifested flatness predictions in thin strip cold rolling

International audienceThe paper deals with flatness defects prediction in thin plates which appear during rolling. Their origin is the roll stack thermo-elastic deformation. The combination of the elastic deflection, the thermal crown and the roll grinding crown results in a non-parallel bite. If the transverse roll profile is not an affinity of the incoming strip profile, differential elongation results and induces high stresses in the outgoing strip. The latter combine with the imposed strip tension force, resulting in a net post-bite stress field which may be sufficiently compressive locally to promote buckling. A variety of non-developable shapes may result, generally occurring as waviness, and classified as flatness defects (center waves, wavy edges, quarterbuckles...). The purpose of the present paper is to present a coupled approach, following [1]: a simple buckling criterion is introduced in the FEM model of strip and roll deformation, LAM3/TEC3 [2]. The post-bite stress field is in much better agreement with experiments if this treatment is used, as will be demonstrated

Un modèle éléments finis général pour la prédiction des défauts de planéité en laminage des tôles fines

Titre du résumé en anglais joint : Manifested flatness predictions in thin strip cold rolling using a general rolling FEM modelNational audienceL'objectif du présent travail est de développer un modèle de laminage capable de prédire avec précision les défauts de planéité des tôles laminées. Ainsi, on a couplé itérativement un modèle éléments finis 3D de calcul de l'écrasement de la tôle dans l'emprise, un modèle semi-analytique de calcul de la déformation des cylindres de la cage et un modèle éléments finis de flambement de coques donnant les défauts de planéité. Le modèle de laminage obtenu prédit des champs de contraintes en bon accord avec les mesures expérimentales et est capable de simuler les défauts de planéité en laminage des tôles.See http://hal.archives-ouvertes.fr/docs/00/59/26/08/ANNEX/r_690NC59B.pd

Latent and Manifested flatness predictions in thin strip cold rolling using a general rolling FEM model

International audienceFlatness defects in thin strip cold rolling are a consequence of roll thermo-elastic deformation and the resulting heterogeneous strip plastic deformation. But in the case of on-line, manifested flatness defects, buckling reorganizes the stress field in the pre- and post-bite areas, which might impact strain and stress fields in the bite or at its ends. Such effects have always been neglected in the past. The purpose of the present paper is to present two coupled approaches to examine to what extent such potential in-bite / out-of-bite feedback determines the in-bite fields and the flatness of the strip. Using both methods and comparing with the standard case where buckling is not accounted for, it has been shown that (i) taking buckling into account results in completely different stress fields and fits correctly the measured on-line residual stresses under tension ("stress-meter rolls"); (ii) coupling buckling in the post-bite area and the rolling model, whatever the technique, changes little the in-bite fields; differences, if any, concentrate in the immediate vicinity of the bite exit; (iii) but in the case where manifested flatness defects occur, these tiny interactions (namely, through the exit velocity transverse profile) are essential for the precise description of the residual stresses and for accurate flatness prediction

Electrical Resistivity Behavior and VRH Transport Mechanism in Semiconducting La0.6Sr0.4Mn1−2x Fe x Cr x O3 (0.10≤x≤0.25) Manganites

International audienceThe transport properties and conduction mechanism in La0.6Sr0.4Mn1−2x Fe x Cr x O3 (0≤x≤0.3) have been investigated. The undoped samples show metal-semiconductor transition with a peak of resistivity at a temperature T P , whereas for all doped compounds the semiconducting behavior persists in the whole temperature range. The insertion of Cr3+ and Fe3+ ions leads to the increase of resistivity because the simultaneous substitution of Fe3+ and Cr3+ for Mn3+ reduces the number of available hopping sites for the Mn e g↑ electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states in a model where the various parameters estimated from Mott's relation obey the variable range hopping (VRH) mechanism

Modélisation du flambage des tôles laminées sous contraintes résiduelles

978-2-11-098374-9National audienceLa modélisation des défauts de planéité occupe une position prioritaire parmi les axes de recherche pour les producteurs des tôles métalliques. Par ailleurs, on dispose d'un logiciel Lam3/Tec3 dédié pour la simulation de laminage des tôles qui présente certaines limitations dans sa version standard, surtout quand il s'agit des cas de laminage des tôles pour les quels le flambage, d'où des défauts de planéité, peut se produire. De ce fait, il a été complété durant les présents travaux par un modèle de flambage des plaques afin de combler ses insuffisances

Applications of advanced models to prediction of flatness defects in cold rolling of thin strips

International audienceFlatness defects in thin strip cold rolling are a consequence of roll thermo-elastic deformation, from which heterogeneous strip plastic deformation results. When flatness defects manifest on line, buckling reorganizes the stress field in the pre- and post-bite areas. This might impact strain and stress fields in the bite, an effect which had been neglected. Two coupled Finite Element Method (FEM) approaches are presented here to examine to what extent such potential in-bite / out-of-bite feedback determines the in-bite fields and the flatness of the strip. Using both methods and comparing with the standard case where buckling is not accounted for, it has been shown5 that (i) taking buckling into account results in a completely different stress field and fits correctly the measured on-line residual stress profile under tension (by "stress-meter rolls"); (ii) coupling buckling in the post-bite area and the rolling model, whatever the technique, changes little the in-bite fields. The models are applied here to several questions, namely the impact on flatness of heterogeneous temperature fields and of thinner edges, and the effect of friction on optimal setting of a flatness actuator, Work Roll Bending (WRB)

Coupled and uncoupled approaches for thin cold rolled strip buckling prediction

International audienceSevere thin strip cold rolling conditions usually induce heterogeneity of in-bite plastic deformation always translated to irregular stress field. This stress field may dwell sufficiently compressive in several out-of-bite areas to cause buckling (flatness defects) which generates stress reorganisation in rolled strip and probably affects the bite zone. Hence, out-of-bite buckling, in-bite elastic-(visco)plastic deformation and thermo-mechanical roll-stack/strip interaction may be strongly coupled. However, a completely coupled model providing realistic rolled strip shape specially when flatness defects occur is not easy to establish. This call for two ways of flatness defect modelling in thin strip rolling: with a completely coupled approach but using a simple buckling criterion, or using an uncoupled approach by chaining strip rolling model calculation with shell element models presenting good buckling computing capabilities. Our objective is the improvement of the flat product rolling - specialized FEM software Lam3/Tec3 [1] using Counhaye simple buckling criterion [3] and Asymptotic Numerical Method (ANM) for shell element model [9, 10] respectively with coupled and uncouple approaches detailed in the present paper. These two approaches bring computed stress profiles to very good agreement with experiments and the most important result at this stage is the weak influence of buckling on in-bite stress and strain fields providing a more rigorous justification of the traditional decoupled methods [2,5-8]