Fatigue plastique de l'aluminium et d'alliages aluminium-lithium.

Pas de résumé en anglaisLe comportement mécanique et microstructural cyclique à faible déformation plastique del'aluminium et d'alliages binaires aluminium-lithium a été étudié, et comparé à celui du cuivre etd'alliages légers connus tels que l'AI-4 Cu ou l'Al Zn-Mg.L'aluminium monocristallin et polycristallin sollicité en fatigue plastique présente des contraintescycliques très faibles. La structure de fatigue se compose de bandes de glissement associées à descellules, sans structure de bandes en échelle.Les alliages Al-Li, en dehors de la solution solide dont le comportement cyclique est proche decelui de l'aluminium, présentent un comportement en fatigue très sensible au traitement thermique. Lerevenu à 200°C crée une fragilité intergranulaire qui détériore la tenue en fatigu

Assemblages non soudés dans les réacteurs nucléaires

Les réacteurs nucléaires utilisent peu d’assemblages non soudés. Il existe cependant quelques assemblages sans soudure qui concernent le circuit primaire des réacteurs LWR, tels que ceux de nos centrales françaises. Il s’agit essentiellement de trois types d’assemblage : le dudgeonnage, le frettage et le boulonnage. Les deux premières techniques concernent respectivement le générateur de vapeur, les pénétrations dans le couvercle, ou le fond de cuve et la pompe primaire. Elles sont toujours associées à un soudage ultérieur qui garantit l’étanchéité. Il s’agit de composants essentiels au bon fonctionnement du réacteur. Les assemblages boulonnés concernent la pompe primaire, l’assemblage du couvercle de cuve avec la cuve, et les internes de cuve. Certains assemblages boulonnés sont plus sensibles aux phénomènes de corrosion sous tension voire pour les internes de cuve de corrosion sous tension assistée par irradiation

Triple Self-Sorting in Constitutional Dynamic Networks: Parallel Generation of Cu(I), Fe(II) and Zn(II) Imine-Based Metal Complexes

Three imine-based metal complexes, having no overlap in terms of their compositions, have been simultaneously generated from the self-sorting of a constitutional dynamic library (CDL) containing three amines, three aldehydes and three metal salts. The hierarchical ordering of the stability of three metal complexes assembled and the leveraging of the antagonistic and agonistic relationships existing between the constituents within the constitutional dynamic network corresponding to the CDL were pivotal in achieving the desired sorting. The mechanism and the driving forces underlying the self-sorting process have been studied by NMR. The self-sorting of the Fe(II) and Zn(II) complexes was found to depend on an interplay between the thermodynamic driving forces and a kinetic trap involved in their assembling. These results also exemplify the concept of “simplexity” –the fact that the output of a self-assembling system may be simplified by increasing its initial compositional complexity—as the two complexes could self-sort only in the presence of the third pair of organic components, those of the Cu(I) complex.<br /

Mechanistic studies on type 300 stainless steels manufactured by Hot Isostatic Pressing:The impact of oxygen involvement on fracture behaviour

With near-net shape technology becoming an increasingly desirable route toward component manufacture due to its ability to create components with increasingly complex geometries, minimizing the number of potential welded joints, as well as reducing machining time and associated costs, it is important to demonstrate that components fabricated via Hot Isostatic Pressing (HIP) are able to perform to similar standards as those set by equivalent forged materials. Hot Isostatically Pressed (HIP’d) materials are typically accredited with displaying enhanced yield strengths, ultimate tensile strengths, and ductility over their forged counterparts. In this paper we explore the effects of oxygen, which resides in the austenite matrix during the HIP manufacture process, on a material’s fracture toughness properties. We quantify the influence of different concentrations of oxygen on both the microstructural and mechanical properties of HIP’d 304L and 316L stainless steel, highlighting the benefit of reducing the oxygen as much as possible. Various mechanical tests have been performed on materials containing a range of oxygen contents (between 100 ppm and 200 ppm) and over a large temperature range, including J1C fracture toughness testing, instrumented Charpy, and tensile, and the mechanistic involvement of residual oxygen on the results is discussed. The effects of oxygen become more apparent at cryogenic temperatures, whereas the fracture behavior of HIP’d and forged variants of 304L and 316L at elevated temperatures appears to be comparable.</jats:p

1-D hydrogen-bonded organization of hexanuclear {3d-4f-5d} complexes: evidence for slow relaxation of the magnetization for [{L<SUP>Me2</SUP>Ni(H<SUB>2</SUB>O)Ln(H<SUB>2</SUB>O)<SUB>4.5</SUB>}<SUB>2</SUB>{W(CN)<SUB>8</SUB> }<SUB>2</SUB>] with Ln=Tb and Dy

Heterometallic {3d-4f-5d} aggregates with formula [{LMe2Ni(H2O)Ln(H2O)4.5}2{W(CN)8}2 ]&#183;15H2O, (LMe2 stands for N,N'-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato) Schiff-base ligand) with Ln=Gd, Tb, Dy, have been obtained by reacting bimetallic [LMe2Ni(H2O)2Ln(NO3)3] and Cs3{W(CN)8} in H2O. The hexanuclear complexes are organized in 1-D arrays by means of hydrogen bonds established between the solvent molecules coordinated to Ln and the CN ligands of an octacyanometallate moiety. The X-ray structure was solved for the Tb derivative. Magnetic behavior indicates ferromagnetic {W-Ni} and {Ni-Ln} interactions (JNiW=18.5 cm-1, JNiGd=1.85 cm-1) as well as ferromagnetic intermolecular interactions mediated by the H-bonds. Dynamic magnetic susceptibility studies reveal slow magnetic relaxation processes for the Tb and Dy derivatives, suggesting SMM type behavior for these compounds

On the importance of ferromagnetic exchange between transition metals in field-free SMMs: examples of ring-shaped hetero-trimetallic [(LnNi2){W(CN)8}]2 compounds.

Rare cases of genuine (i.e. field-free) SMM have been found for mixed 3d-4f-5d ring-shaped compounds with Tb(iii) (Ueff/kB = 23.0 K) or Dy(iii) (Ueff/kB = 26.4 K). The ferromagnetic interactions between the transition metals are shown to play an essential role in this feature.