Optical properties of water under high pressure

International audienc

Surface Integrity When Machining Inconel 718 Using Conventional Lubrication and Carbon Dioxide Coolant

Surface integrity induced by machining process affects strongly the performance of functional products, for instance, the fatigue life as well as the resistance to stress corrosion cracking. Consequently, it is relevant to evaluate the induced properties on and beneath the machined surface to ensure the good performance of the mechanical components while operating under either static or cyclic loads. Furthermore, this is even more important when designing critical components that withstand high loads at high temperatures. In this context, many studies have been carried out in order to characterize the surface integrity (residual stresses, surface roughness, micro-hardness of the affected layer) when machining Inconel 718. However, so far, the cryogenic effect on surface integrity of Inconel 718 is not well established although some preliminary works have already been developed. Therefore, this work aimed to point out the performance of cryogenic machining using the carbon dioxide CO2 as a cryogenic cutting fluid, considering as a reference the conventional lubrication. A comparative study has been carried out during turning operations of Inconel 718 using the same cutting parameters and the same tool geometry. Microhardness measurements showed that the CO2 condition induced higher strain hardening near the surface while conventional condition did not generate notable difference compared to the bulk material microhardness. With respect to residual stresses, results showed that conventional lubrication generated higher tensile residual stress near the surface along the cutting direction when using new tools. As for CO2 cryogenic condition, lower tensile residual stresses have been obtained near the surface. In addition, CO2 condition induced the largest compressive peak when using new and semi−worn tools in comparison with conventional lubrication

Endommagement, par érosion de sable, des structures en acier API 5L X52 destinées aux produits pétroliers

Nous traitons l’endommagement des structures métalliques destinées à transporter et stocker du gaz et du pétrole, sous impact de sable. Une étude expérimentale, sur éprouvettes entaillées, évalue la perte de masse et la ténacité en fonction du temps de sablage et du rayon d’entaille. Les résultats montrent que la perte de masse augmente avec le temps de sablage, mais la ténacité diminue. Des essais supplémentaires, en fatigue, ont montré l’effet bénéfique du sablage

A crystal plasticity-based constitutive model for near-β titanium alloys under extreme loading conditions: Application to the Ti17 alloy

A crystal plasticity-based constitutive model is proposed to describe the thermo-mechanical behavior of the Ti17 titanium alloy subjected to extreme loading conditions. The model explicitly incorporates the effect of the crystallographic orientation of the hcp and bcc phases. The constitutive equations are built in the context of continuum thermodynamics with internal variables. The general framework of continuum damage mechanics is used to consider the impact of ductile damage on the mechanical behavior. The proposed model is implemented in a finite element method solver. The material parameters are identified from an extensive experimental dataset with an inverse method. According to the results, the impact of the strain rate and the temperature on the mechanical behavior is correctly depicted. The model is then used to evaluate the impact of temperature on strain localization. The role of the local texture on the development of ductile damage is also discussed for different specimen geometries. Finally, the impact of heat exchanges on the mechanical behavior at low and high temperatures is investigated

Analyse et etude de profils de raies de diffractin des rayons X enregistrees avec un detecteur courbe. Applicatin a l'analyse de proprietes microstructurales de materiaux et notion d'indicatrice

SIGLEINIST T 72076 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Analyse et étude de profils de raies de diffraction des rayons X enregistrées avec un détecteur courbe : application à l'analyse de propriétés microstructurales de matériaux et notion d'indicatrice

This study presents works done by using a curved position sensitive detector in the field of X-ray diffraction analysis. The introduction of exeprimental technics allow us to use this detector with a very high accuracy. We propose a simplified expression of asymetric Pearson VII distribution for the fitting and dessomation of mixed X-ray line profiles. We introduce usefull technics for the measurement of residual stresses analysis for large grain materials (discontinuous integration and diffraction lines smoothing). We developpe and extended the pole figure concept to the other X-ray line characteristics (named indicatrix). Using them formal relation between size of the coherently diffracting domains and micro-strain are obtained. The distribution of integrated intensity versus form factor of X-ray line profile show us in cunjunction with X-ray line breadth, that it is one of the best descriptive parameter for polycristalline materials analysis. Using well-known relationships, the relation between size and micro-stress present some analogy with the Hall-Petch relationship. The study of oscillation in graph giving the deformation versus the measurement direction present predominent effect of microstructural parameter such as domain size or micro-strain. This work allow us to say that the indicatricies which reflect structural anisotropy are usefull tools for polycristalline materials analysisCette étude présente les travaux réalisés grâce à un détecteur courbe dans le cadre d'analyses classiques de diffraction des rayons X. L'introduction de critères expérimentaux permet une utilisation rationnelle de ce détecteur. Nous proposons une expression simplifiée des fonctions de Pearson VII asymétriques pour le lissage et la séparation de profils de raies de diffraction X. Nous introduisons des techniques d'analyse adaptées aux matériaux à gros grains lors de la mesure des contraintes résiduelles (intégration discontinue et filtrage numérique des raies de diffraction). Nous développons et étendons le principe des figures de pôles aux caractéristiques des raies de diffraction (notion d'indicatrice). Grâce à celles-ci nous obtenons des relations formelles entre la taille des domaines de diffraction cohérente et la micro-déformation. Les distributions de l'intensité diffractée en fonction du facteur de forme du profil de raie de diffraction X montre qu'il représente, combiné avec les variations de la largeur à mi-hauteur, une variable adéquate pour la description des matériaux polycristallins déformés. Dans le cadre d'hypothèses généralement admises, les relations micro-contrainte/taille des domaines de diffraction cohérente rappellent les diverses formes de la relation de Hall-Petch. L'étude des oscillations des graphes relatant les variations de la déformation en fonction de la direction de mesure précise le caractère prédominant des caractéristiques microstructurales. Ce travail montre d'une façon générale que l'analyse des matériaux polycristallins peut être significativement améliorée par l'utilisation et la construction d'indicatrices qui reflètent l'anisotropie du milieu polycristalli

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

International audienc

Mesure de déformation par CBED (développement et application d'une approche multi-clichés)

La connaissance des déformations et des contraintes est importante pour une meilleure compréhension des propriétés des matériaux. Plusieurs techniques expérimentales sont disponibles (XRD, Raman ), mais une seule est capable de déterminer les déformations à une échelle microscopique: la diffraction électronique en faisceau convergent (CBED: Convergent Beam Electron Diffraction). Cette technique est connue pour sa haute résolution spatiale (de l'ordre de quelques nanomètres) qui provient de son utilisation dans un Microscope Électronique en Transmission (MET). Les clichés de diffraction en faisceau convergent sont constitués de lignes de HOLZ dont la localisation dépend de la valeur des paramètres cristallins ou de la déformation du matériau. La comparaison de la position des lignes entre un cliché expérimental et un cliché simulé permet la détermination des paramètres cristallins. Dans ce travail, nous avons appliqué une nouvelle approche pour la détermination des paramètres cristallins. Elle utilise l'équation algébrique des "K-lines" et offre la possibilité de travailler simultanément avec plusieurs clichés de diffraction. Nous avons quantifié l'incertitude associée à l'approche KLEBS. Les causes de l'incertitude ont été présentées et nous avons proposé une approche statistique (multi-clichés) pour réduire sa valeur. Ensuite, l'approche multi-clichés a été appliquée à l'étude des superalliages monocristallins à base nickel, et une nouvelle méthode a été proposée pour la détermination du désaccord paramétrique. La dernière partie de ce travail traite de l'étude des hétérogénéités de déformation dans un matériau déformé plastiquementThe knowledge of strains and stresses is important for a better understanding of the materials properties. Several experimental techniques are available (XRD, Raman ...), but only one allows the determination of the strain at a microscopic scale: the Convergent Beam Electron Diffraction (CBED). This technique is known for its high spatial resolution (of a few nanometers), which comes from its use in a Transmission Electronic Microscope (TEM). The diffraction patterns acquired with a convergent beam are constituted of HOLZ lines whose localization depends on the values of the lattice parameters or strain of the material. The comparison of the lines position between an experimental and a simulated pattern allows the determination of the lattice parameters. In this work, we have applied a new approach for the lattice parameters determination. It is based on the algebraic equation of "K-lines" and enables to work simultaneously on several diffraction patterns. We have quantified the uncertainty linked to the KLEBS approach. The causes of the uncertainty have been presented and we have proposed a statistical approach (multiple patterns) to reduce its value. Then, the multiple patterns approach has been applied to the study of the single crystal nickel based superalloys, and a new method for the misfit determination has been proposed. The last part of this work deals with the study of the strain heterogeneities in a material plastically strainedMETZ-SCD (574632105) / SudocSudocFranceF

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

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