Béryllium

Résumé

Le béryllium est l'élément chimique de numéro atomique 4, de symbole Be. Dans le tableau périodique, c'est le premier représentant des métaux alcalino-terreux. Son nom vient du grec qui désignait l'aigue-marine ou l'émeraude. Dans les conditions normales de température et de pression, le corps simple est un métal d'aspect gris acier, léger et fragile. Le béryllium métallique, ses alliages et ses composés chimiques sont toxiques et peuvent provoquer une inflammation des poumons appelée bérylliose. Caractéristiques notables vignette|gauche|Bloc de béryllium. Le béryllium a le point de fusion le plus élevé de tous les métaux légers. . Sa ductilité est approximativement d'un tiers plus grande que celle de l'acier. Il possède une excellente conductivité thermique, est non magnétique et résiste à l'acide nitrique concentré. Il est fortement perméable aux rayons X, et libère des neutrons quand il est frappé par des particules alpha, comme celles émises par le radium ou le p

Source officielle

https://fr.wikipedia.org/wiki/B%C3%A9ryllium

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This study concerns the evolution of the thermomechanical properties of new high-performance materials. In particular, we focus on the relationship between the microstructure and the mechanical properties of a superalloy based on Co-Ni-Cr. Superalloys are metallic alloys with superior characteristics to conventional alloys, especially in extreme conditions, and find application in all that areas requiring materials with high elastic modulus, yield strength and resistance. The investigated alloy is used with satisfaction since several years, but the origin of its outstanding mechanical properties is still poorly understood, as well as the role of small alloying elements additions on mechanical properties. To understand the influence, on the mechanical properties, of the elements added to the base composition, the study is carried out simultaneously on two variants of the material, differing for the presence of a small amount of beryllium in one them. The variant containing beryllium exhibits superior mechanical properties with respect to the base variant. The microstructural evolution and mechanical properties was monitored by using several complementary techniques. Series of heat treatments were performed on samples from the two variants, and both TEP and hardness were systematically measured. This has allowed us to establish the different stages of microstructural changes with the temperature. The TEP is a parameter very sensitive to the change in matrix's composition. It indicates that exposure of this material to a temperature between 500°C and 600°C produces a precipitation stage (A), involving titanium. Such a precipitation is responsible for a remarkable hardening, as well as an increase in the elastic limit. Mechanical spectroscopy allows us to obtain information about the mobility of structural defects which dissipate energy when undergone to a periodic stress. By developing a phenomenological model based on the ADIF curves, we can affirm that the hardening comes from the pinning of dislocations by A precipitates. A second precipitation stage (B) occurs only on the variant containing beryllium, undergone a complex sequence of heat treatments up to 700°C. The analysis of samples by TEM and APT provided essential support to the interpretation of results, and to characterization of the precipitation B. Precipitates B are nanostructured intermetallic compounds NiBe, analogous to GP zones. Their growth is favored by the segregation of titanium at the precipitate-matrix interface to relieve the coherency strains. The hardening provided by B precipitates, together with the structural hardening due to the cold working and the precipitation hardening due to the heating at 550°C, allows to obtain the maximum hardness values. The peaks on the internal friction spectra, also provide informations about the influence of beryllium on the mobility of grain boundaries. This parameter determines the recrystallization and the relaxation mechanism at high temperature, which can be observed by mechanical spectroscopy. Finally, the work here presented yields an important contribution to the understanding of the performance's origin of a Co-Ni-Cr superalloy. It also points the way for other studies aiming the optimization of production processes, in terms of temperature and time of annealing, to obtain the desired properties. This thesis allowed to discover a new hardening phase (B) previously unknown, which could lead to even higher hardness values.

EPFL2016

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Rotation capacity and stress redistribution ability of R-UHPFRC-RC composite continuous beams: an experimental investigation

Talayeh Noshiravani

The results of tests on two continuous composite beams combining a reinforced concrete (RC) beam with a layer of reinforced ultra-high performance fiber reinforced concrete (R-UHPFRC) are presented. The R-UHPFRC element acts both as a tensile membrane and a flexural element. The tests show the element's contribution to the member capacity by allowing the redistribution of the internal forces. The continuous beams are placed on two intermediate supports; the shear span-depth ratios and stirrup content are chosen to provoke two successive formations of local flexure-shear collapse mechanisms, forming a plastic hinge at each support. With the formation of the first support hinge, the stresses redistribute. As the applied actuator displacement increases, the member continues to resist the increasing force up to the formation of a second support hinge that causes the member to collapse. The member deflection and resistance at collapse were respectively 4.5 and 1.3 times greater than the corresponding values at the formation of the first hinge. The response demonstrates the redundancy in RC beams with additional R-UHPFRC reinforcement, which can be used for designing structures against progressive collapse.

Springer Verlag2013

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Improved ERO modelling of beryllium erosion at ITER upper first wall panel using JET-ILW and PISCES-B experience

Otto Asunta, Patrick Blanchard, Yann Camenen, Stefano Coda, Basil Duval, Ambrogio Fasoli, Jonathan Marc Philippe Faustin, Davide Galassi, Javier García Hernández, Jonathan Graves, Jan Horacek, Samuel Lanthaler, Yves Martin, Mikhail Maslov, Federico Nespoli, Hamish William Patten, Alessandro Pau, Antonio José Pereira de Figueiredo, David Pfefferlé, Richard Pitts, Olivier Sauter, Cristian Sommariva, Duccio Testa, Nicola Vianello, Henri Weisen, Dalziel Joseph Wilson, Marco Wischmeier, Liang Yao, Yao Zhou

ERO is a 3D Monte-Carlo impurity transport and plasma-surface interaction code. In 2011 it was applied for the ITER first wall (FW) life time predictions [1] (critical blanket module BM11). After that the same code was significantly improved during its application to existing fusion-relevant plasma devices: the tokamak JET equipped with an ITER-like wall and linear plasma device PISCES-B. This has allowed testing the sputtering data for beryllium (Be) and showing that the "ERO-min" fit based on the large (50%) deuterium (D) surface content is well suitable for plasma-wetted areas (D plasma). The improved procedure for calculating of the effective sputtering yields for each location along the plasma-facing surface using the recently developed semi-analytical sheath approach was validated. The re-evaluation of the effective yields for BM11 following the similar revisit of the JET data has indicated significant increase of erosion and motivated the current re-visit of ERO simulations.

2019

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EPFL2016