Modélisation du champ acoustique produit par un traducteur US : application à la focalisation dynamique

We present here a model permitting the calculation of the ultrasonic field emitted by monolithic or phased array transducer and propagated through a liquid-solid interface. The calculations are used for the conception and optimization of phased array transducers for specific applications

A MOLECULAR DYNAMICS STUDY OF THE THERMAL DISPLACIVE PROPERTIES OF THE Σ=13 (θ=22.6°) [001] TWIST BOUNDARY IN NOBLE METALS

Nous avons calculé par simulation, à l'aide de la technique de dynamique moléculaire à température constante, le déplacement quadratique moyen des atomes dans le joint de grains de torsion Σ=13 (θ=22.6°) [001] pour le cuivre, l'argent et l'or. Les interactions interatomiques dérivent d'un pseudopotentiel résonnant adapté aux métaux nobles. A proximité du joint la distance interplanaire suivant l'axe de torsion est modifiée au maximum de +6.5%. La modification des constantes de force locales qui en résulte, induit des amplitudes de vibration plus élevées qu'en volume. Nous avons trouvé que le déplacement quadratique moyen des atomes du joint à cœur est de 1.5 à 2.5 fois plus élevé qu'en volume. Ces résultats sont en accord qualitatif avec les données expérimentales pour l'or.We present the results of a molecular dynamics study at constant temperature of the mean square displacements of atoms in the core of the Σ=13 (θ=22.6°) [001] twist grain boundary in copper, gold and silver. The atomic forces derive from a resonant model pseudopotential adapted to noble metals. The relaxations of atomic planes along the twist axis near the boundary, amount a maximum value +6.5%. Consequently, the local force constants are modified with respect to the bulk and enhanced vibration amplitudes are observed. Depending on the temperature, we found that the atomic mean square displacements in the boundary core are 1.5 to 2.5 times larger than in the bulk. These results are in qualitative agreement with available experimental data for the same boundary in gold

A Molecular dynamics study of the displactive properties of the £ = 13 22,6° [001] Twist boundary in noble metals

info:eu-repo/semantics/publishedIntergranular and Interphase Boundaries in material

Tensile deformation accommodation in microscopic metallic glasses via subnanocluster reconstructions

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The role of Sn doping in the β-type Ti–25at%Nb alloys: Experiment and ab initio calculations

International audiencebeta-Ti-25 at%Nb-xSn alloys with several Sn substitutions (x 12.5 at%) induce instability. These results could be of use in the design of ternary low rigidity biocompatible TiNbSn alloys

Probing the structure of a liquid metal during vitrification

International audienceUsing aerodynamic levitation, vitrification of a ternary Zr-Cu-Al alloy was observed in-situ by high energy synchrotron radiation X-ray diffraction in the temperature range from above the liquidus T-liq to well below the glass transition temperature T-g. The evolution of the atomic structure was studied using pair distribution functions (PDF) and molecular dynamic (MD) simulations. Vitrification was rendered possible due to the enhanced stability of the undercooled Zr-Cu melt after Al addition. Results indicate three regimes in the liquid alloy's structural pathway to vitrification. Short (SRO) and medium range order (MRO) develop significantly during cooling the liquid phase to the glassy state. The rate of structural rearrangements is enhanced in the super-cooled liquid between T-liq-140 K and T-g. The populations of atomic clusters with icosahedral local symmetry become predominant as T-g is approached and facilitate vitrification and suppression of crystal nucleation and growth. The scenario of a possible fragile to strong transition in the super-cooled liquid is discussed

Shear band melting and serrated flow in metallic glasses

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Ab-initio and experimental study of phase stability of Ti-Nb alloys

International audienceA systematic theoretical and experimental study concerning the crystallographic structure and electronic properties of Ti-xNb (x 18.75 at% the beta-phase is favoured against all other crystallographic structures in line with the experimental results. Interestingly, at high Nb content the alpha' and omega hexagonal phases become unstable due to the electronic band filling close to the Fermi level E-F, which is mainly due to Nb-p and Ti-d antibonding hybridizations. On the contrary, in the cubic beta-Ti-25Nb (at%) the depletion of the occupied electronic states at the EF occurs mainly due to Nbd and Ti-d bonding interactions, resulting in a stable beta-TiNb structure. These data could enlighten the electronic origin of the Ti-Nb phase stability, thus, may contribute to the design of beta stabilized low moduli Ti-based alloys suitable for load-bearing biomedical applications. (C) 2016 Elsevier B. V. All rights reserved