Optical properties of water under high pressure

International audienc

Surface Damage and Treatment by Impact of a Low Temperature Nitrogen Jet

International audienceNitrogen jets under high pressure and low temperature have been introduced recently. The process consists in projecting onto a surface a low temperature jet obtained from releasing the liquid nitrogen stored in a high pressure tank (e.g. 3000 bars) through a nozzle. It can be used in a range of industrial applications, including surface treatment or material removal through cutting, drilling, striping and cleaning. The process does not generate waste other than the removed matter, and it only releases neutral gas into the atmosphere. This work is aimed at understanding the mechanisms of the interaction between the jet and the material surface. Depending on the impacted material, the thermo-mechanical shock and blast effect induced by the jet can activate a wide range of damage mechanisms, including cleavage, crack nucleation and spalling, as well as void expansion and localized ductile failure. The test parameters (standoff distance, dwell time, operating pressure) play a role in selecting the dominant damage mechanism, but combinations of these various modes are usually present. Surface treatment through phase transformation or grain fragmentation in a layer below the surface can also be obtained by adequate tuning of the process parameters. In the current study, work is undertaken to map the damage mechanisms in metallic materials as well as the influence of the test parameters on damage, along with measurements of the thermo-mechanical conditions (impact force, temperature) in the impacted area

Effects of the impact of a low temperature nitrogen jet on metallic surfaces

Lien vers la version éditeur: http://rspa.royalsocietypublishing.org/content/468/2147/3601.abstractThe technology of nitrogen jets impacting surfaces at low temperature has recently been introduced for surface cleaning/stripping. Under the impact of the jet, the material surface undergoes a thermomechanical shock inducing complex transformation mechanisms. Depending on the material and test parameters such as standoff distance, dwell time, upstream pressure, the latter include cleavage, cracking, spalling, blistering, grain fragmentation, phase transformation and ductile deformation. Quite often, these modes are superimposed in the same test, or even in the same material area. In this study, an overview of these mechanisms is proposed for metallic materials. Measurements of thermomechanical variables in the impacted area are presented and the influence of the test parameters on surface transformation is investigated. Grain fragmentation and ultrafast transport of nitrogen in a deep layer below the surface are explored

Contribution à la modélisation numérique de la détente d’un jet d’azote sous haute pression et basse température

L’impact d’un jet d’azote supercritique sur une surface solide pour son traitement (opérations de décapage ou de découpe) est un procédé nouveau et très peu de travaux concernant cette technologie existent à ce jour. L’objectif de ce travail est d’étudier, par le biais de simulations numériques, l’écoulement axisymétrique, compressible et turbulent, d’azote sous haute pression et basse température, injecté au travers d’une buse et impactant sur une paroi. L’étude est effectuée à l’aide du code de calculs commercial aux volumes finis Fluent®. Une équation d’état spécifique aux fluides réels et basée sur une formulation explicite de l’énergie libre de Helmholtz est utilisée afin de prendre en compte les fortes variations des propriétés thermo-physiques de l’azote lors de la détente. Les résultats numériques obtenus, représentant les contours du nombre de Mach, ainsi que la pression statique et la température sur l’axe du jet, sont présentés afin de caractériser la structure de l’écoulement. Ils sont comparés à ceux obtenus lorsque le fluide est considéré comme parfait

Approche multi-physique des relations Procédés Jets fluides - Propriétés Matériaux. De l’étude des phénomènes à la valorisation et au transfert au monde socioéconomique.

High Pressure (HP) fluid jet processes are used as methods for modifying the properties of materials by cold spraying and high-speed multi-component fluids on the substrate to be treated. Depending on the hydrodynamic and physical characteristics of the impinging jet, such modifications can be obtained by either removing or adding material or without causing any change in the substrate mass. For this, the jet is used as a complex flow carrying physical, chemical, biological, and energy of different natures such as kinetic, thermal. In theory, both these properties and energies are then transferred to the target material via the surface of the substrate according to complex mechanisms as mechanical, thermal, thermomechanical, and inducing metallurgical and microstructural transformations. This work focuses on the relationships of some industrial configurations of complex fluid jets and the surface properties of materials impacted by such impinging fluid jets. The research methods developed in this work provide a framework for several materials issues that are addressed by the considered fluid jet processes. After a brief presentation of each material issue, this work assembles the study of the peculiarities of three types of innovative fluid jets as well as those of four interactions of these jets with materials representative of industrial cases. To determine the behavior as well as the physical and hydrodynamic properties of each type of jet, both qualitative and quantitative approach to modeling the structures of the constitutive phases is presented for namely: low pressure abrasive micro-waterjet, HP waterjet assisted laser, HP supercritical cryogenic nitrogen jet. Knowledge of the scientific and technological fundamentals describing these fluid jets has made it possible to explain the various complex mechanisms of interactions of the studied fluid jets with materials as used in industry: HP waterjet assisted laser - metallic materials, HP supercritical nitrogen jet - metallic and polymer materials, HP supercritical nitrogen jet - porous woody materials, HP supercritical nitrogen jet – polymer based materials.Les procédés jets fluides sous Haute Pression (HP) sont utilisés comme méthodes de modification des propriétés des matériaux par projection à froid et à grande vitesse de fluides multi-composants sur le substrat à traiter. Selon les caractéristiques hydrodynamiques et physiques du jet impactant, ces modifications peuvent être obtenues par enlèvement ou ajout de matière ou encore en conservant la masse du substrat. Pour cela, on utilise le jet comme un flux transportant des propriétés physiques, chimiques, biologiques, et des énergies de natures différentes cinétique, thermique. En théorie, ces propriétés et énergies sont alors transférées au matériau cible via la surface de celui-ci selon des mécanismes complexes, mécaniques, thermiques, thermomécaniques, induisant des transformations métallurgiques et microstructurales. Ce travail s’intéresse aux relations de quelques configurations industrielles de jets fluides complexes et des propriétés superficielles des matériaux impactés par de tels jets. Les méthodes de recherche développées dans ce mémoire proposent un encadrement de plusieurs problématiques matériaux adressées par les procédés jets fluides considérés. Après une brève présentation de chaque problématique, ce mémoire rassemble les travaux d’étude des particularités de trois natures de jets innovants et de quatre interactions de ceux-ci avec des matériaux représentatifs de cas industriels. Pour déterminer le comportement et les propriétés physiques et hydrodynamiques de chaque nature de jet, une approche qualitative et quantitative de modélisation des structures des phases constitutives est présentée : un Microjet d’eau abrasif à basse pression, un Jet d’eau HP assisté Laser, un jet d’azote cryogénique supercritique HP. La connaissance des fondamentaux scientifiques et technologiques qui régissent ces jets fluides complexes, a permis d’expliquer les différents mécanismes complexes d’interactions avec les matériaux marqueurs tels que utilisés en industrie : jet d’eau HP assisté laser - matériaux métalliques, jet d’azote HP supercritique - matériaux métalliques et polymères, jet d’azote HP supercritique - matériaux ligneux poreux, jet d’azote HP supercritique - matériaux à base de polymères

Surface and microstructure modifications of Ti-6Al-4V titanium alloy cutting by a water jet/high power laser converging coupling

International audienceThe metallurgical evolution of the Ti-6Al-4V samples is analyzed after an appropriate cutting using a converging water jet/high power laser system. New surface microstructures are obtained on the cutting edge as a result of thermo-mechanical effects of such hybrid fluid-jet-laser tool on the targeted material. The laser beam allows to melt and the water-jet to cool down and to evacuate the material upstream according to a controlled cutting process. The experimental results have shown that a rutile layer can be generated on the surface near the cutting zone. The recorded metallurgical effect is attributed to the chemical reaction between water molecules and titanium, where the laser thermal energy brought onto the surface plays the role of reaction activator. The width of the oxidized zone was found proportional to the cutting speed. During the reaction, hydrogen gas H2 is formed and is absorbed by the metal. The hydrogen atoms trapped into the alloy change the metastable phase formation developing pure β circular grains as a skin at the kerf surface. This result is original so it would lead to innovative converging laser water jet process that could be used to increase the material properties especially for surface treatment, a key value of surface engineering and manufacturing chains

Surface oxidation and phase transformation of the stainless steel by hybrid laser-waterjet impact

International audienc

Wear under brittle removal regime of an under-expanded cryogenic nitrogen jet machining of bio-composites

Machining of biocomposites using traditional techniques has shown some limitations due to the multiscale complex cellulosic structure of natural fibrous reinforcement. This paper aims to demonstrate the feasibility of the cryogenic nitrogen jet, which is a novel cutting process that combines sustainable resources and cryogenic temperatures from −175 °C to 150 °C, as a machining process for biocomposites made of unidirectional flax fibers and polylactic-acid polymer (PLA). A high-velocity stream of liquid nitrogen with and without abrasives (400–700 m/s) is hence directed onto the workpiece surface. For the abrasive jet, both conventional garnet abrasives and bio-based abrasives made from walnut shells were used for the nitrogen jet process. The kerf depth, which is representative of the erosion wear mechanisms, was calculated to assess the erosion rate of the biocomposite structure after the nitrogen jet cutting operation. Then, scanning electron microscope observations are performed to characterize the induced damages on the machined biocomposite surfaces. Results show that the pressure and the traverse speed of the nitrogen jet are the relevant process parameters that control the mechanical and thermal stresses viewed by the biocomposite during the machining operation. Each impinging abrasive particle removes a small amount of biocomposite material during the jet cutting process, which depends on the brittleness of the anisotropic work structure and the abrasiveness of the incorporated particles into the jet stream

Water density and polarizability deduced from the refractive index determined by interferometric measurements up to 250 MPa

International audienceThe refractive index of water is precisely determined in the visible light range as a function of the pressure until 250 MPa by means of a new measurement device that uses a special pipe tee included in an interferometer set. This technique allows revisiting the Bradley-Tait and Sellmeier equations to make them dependent on the wavelength and the pressure, respectively. The Bradley-Tait equation for the pressure dependence of the water refractive index is completed by a wavelength-dependent factor. Also, in the considered pressure and wavelength ranges, it is shown that the Sellmeier coefficients can be straightforwardly linked to the pressure, allowing the determination of the refractive index of water for either any wavelength or pressure. A new simple model allows the determination of the density of water as a function of the measured refractive index. Finally, the polarizability of water as function of pressure and wavelength is calculated by means of the Lorentz-Lorenz equation

Mécanismes d’endommagement de surfaces par un jet d’azote diphasique sous haute pression et basse température

Un jet d’azote sous haute pression (3000bar) et à basse température (150K), se présente comme une technologie propre et innovante de préparation et de traitement de surface. Nous cherchons donc à identifier, caractériser et modéliser les mécanismes d’endommagement de surface obtenus par l’impact de ce jet, puis à optimiser sa conception et son exploitation, pour une meilleure adaptation à différentes applications industrielles dans les domaines du décapage et du traitement de surfaces