The numerical challenges in multiphysical modeling of laser welding with arbitrary Lagrangian-Eulerian method

International audienceThe interaction of high power laser beam with metallic materials produces a number of interconnected phenomena that represent a serious challenge for numerical modeling, especially for creation of auto-consistent models. Additional difficulty consists in lack of data on materials properties at the temperatures superior to their melting point. The present work summarizes the numerical challenges in creation and validation of free-surface models using ALE moving mesh coupled with heat transfer equation and Navier-Stokes fluid flow

The application of the random balance method in laser machining of metals

International audienceFeatures peculiar to laser technology offer some advantages over more traditional processes, but, like all processes, it has its limitations. This article studies the limitations of laser machining of metals, and quantifies, through an experimental design method, the influence of operating parameters on productivity and on the quality of the machined surface. Three study materials were used: an aluminium alloy, stainless steel and a titanium alloy. An initial reading of the results indicates that productivity depends mainly on the frequency of the laser pulse and that the aluminium alloy behaves differently from the other two. The quality of the machined surface, judged here by roughness, was likewise dependent on pulse frequency and, to a lesser degree, on sweep speed. Surface roughness was minimized by increasing the pulse frequency and reducing the sweep speed. The experimental results were accurately predicted by simple polynomial models

Incorporation d'azote et d'oxygène dans les nanoparticules formées par traitement de surface laser de cibles métalliques dans l'air

International audienceLors de l'irradiation de matériaux métalliques tels que l'aluminium, le fer ou le titane par un faisceau laser de courte durée d'impulsion (de l'ordre de la nanoseconde), il se forme une vapeur très énergétique et fortement ionisée appelée plume-plasma. A la fin de l'interaction, ce plasma se refroidit et se détend à des vitesses supersoniques. Des nanoparticules résultent de la condensation de cette vapeur métallique dans l'air, donc de la réactivité chimique avec les gaz réactifs de l'air tels que l'azote et l'oxygène. L'objectif de cette étude est de quantifier la quantité d'éléments légers afin de comprendre les mécanismes physiques mis en jeu dans le plasma, créé lors de l'interaction laser-cible, qui conduisent à la formation de nanoparticules essentiellement sous la forme d'oxyde voire de nitrure dans le cas de l'aluminium. Dans le but d'analyser les particules au plus près de leur milieu de formation, une analyse « in-situ» par diffusion des rayons X aux petits angles (S.A.X.S.) sous atmosphère contrôlée avait permis d'étudier l'influence de l'oxygène sur la taille et la morphologie des particules formées . Par ailleurs, des caractérisations « ex-situ» ont été également réalisées sur des particules déposées sur des plaques de verre exposées au voisinage de la plume, par spectroscopie micro-Raman, par diffraction aux rayons X (DRX) et par microscopie électronique à transmission (MET). Toutefois, la plupart de ces techniques de caractérisation nécessitent la présence de formes cristallines et en quantité suffisante. Par l'usage des réactions nucléaires induites par les deutérons sur l'oxygène-16 et l'azote-14, la microanalyse nucléaire permet de mesurer les quantités totales d'oxygène et d'azote insérées en fonction des conditions opératoires (nature de la cible, composition des mélanges de gaz de l'atmosphère environnante). On présentera l'état de l'art de la connaissance de ces poudres et on montrera quelques exemples de cartographies quantitatives réalisées sur des amas de nanoparticules

Determination of an empirical law of aluminium and magnesium alloys absorption coefficient during Nd :YAG laser interaction

International audienceWelding laser modelling requires knowledge about relative changes of many thermo-physical parameters involved in the interaction. The absorptivity of the material is one of the most important. In this study, experimental measurements of absorptivity with an integrating sphere on two alloys (aluminium and magnesium) were made. These results were compared with an analytical calculation that takes into account the trapping of the beam by multiple reflections inside the keyhole. Based on a statistical method, an empirical law is proposed connecting absorptivity with the peak power of the laser and the duration of interaction. During the interaction, two distinct phenomenologies are brought to light. A threshold is then defined after which the physical process becomes stable. Below this threshold, the measurement of absorptivity is problematic, and the values are widely dispersed

Preliminary-Analysis of the Pentad of 13CH4 from Raman and Infrared-Spectra

0022-285

Particle Size Determination in Electrical Arcs with Ag and AgSnO2 Electrodes using X-Ray Scattering

International audienceThis article discusses recent synchrotron radiation based measurements of nanoparticle formation between arcing contacts. The studied material is typical in contact applications, Ag and AgSnO

Study of surface layers and ejected powder formed by oxidation of titanium substrates with a pulsed Nd:YAG laser beam.

International audienceLaser treatment of a titaniumsurface at certain conditions initiates the formation of titanium oxide layers as well as micro (nano) scale powder ejected from the surface of the substrate. The resultant morphology of the surface as well as the size and the structure of the particles are all strongly dependent on the treatment parameters (laser fluence, pulse frequency, overlap parameter, etc.). In this study, titanium substrates were treated with an industrial pulsed Nd:YAG laser in air, with varying parameters. Surface layers and ejectedmaterials were compared using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The rutile phase of TiO2 dominates in the surface layers, while the ejected powder is mainly formed of anatase nanoparticles