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Fatigue properties of as-built and heat-treated Inconel 625 obtained by the hybridization of two laser-powder based additive processes
No full textInternational audienceLaser Powder Bed Fusion and Direct Energy Deposition processes have complementary characteristics. Their hybridization can increase the variety of applications for additive manufacturing. This paper investigates the static and fatigue behaviors of hybrid Inconel 625 parts using monotonic and high cycle fatigue tests, local strain measurements and self-heating method. Fatigue properties of as-built and recrystallized LPBF, DED and hybrid Inconel 625 were evaluated and compared. The effect of heat treatment on hybrid microstructure homogeneity was investigated. Their consequences on mechanical compatibility and fatigue strength were proved. The fatigue strength was attributed to the competition between defects and the strain compatibilities
Nano-engineered prepreg manufacturing: control of capillary rise of resin into VACNTs’ forests
No full textInternational audienceThe incorporation of vertically aligned carbon nanotubes (VACNTs) between composites plies has been said to enhance the through-thickness strength, and it can also decrease the risk of interply delamination and reduce crack initiation. Thanks to these high mechanical performances, nano-engineered hybrid composites are seen as promising for highly demanding structural reinforcement applications. This paper is part of a study that focuses specifically on the methodology for transferring VACNTs onto a prepreg surface while maintaining their initial vertically aligned morphology. The chosen method involved bonding the VACNTs’ forest through capillary impregnation of the forest by the prepreg’s resin. Key parameters for an effective transfer and to achieve a partial capillary rise of the resin into the VACNTs will be discussed here
Steam gasification of cellulose pulp char: Insights on experimental and kinetic study with a focus on the role of Silicon
No full textInternational audienceThis paper deals with steam gasification kinetics of cellulose pulp extracted from biomass with on the focus silicon effect. Isothermal TGA tests were performed under various operating conditions. The gasification reactivity increased with increasing temperature and steam pressures. The reactivity of cellulose pulp biochar was 3 times lower than that of the biomass char. This is attributed to the difference in the inorganic content, namely AAEM and Si. The gasification of pulp biochar revealed the negative effect of Si, which was the main inorganic element present in the cellulose pulp. Biochar reactivity decreased with increasing Si concentration. The reactivity could be correlated to Si content. The morphological structure had an impact at a low conversion rate, although it was less influential than Si. Thus, a kinetic model for describing the gasification kinetics was developed using %Si as a key-parameter. The comparison to the experimental data showed that the proposed model can reasonably predict the gasification behavior of different biochars with satisfactory accuracy (10%) as far as industrial processes are concerned. Further analysis of alkaline-washed cellulose confirmed the inhibiting effect of Si on the gasification process. The reaction time was 2.5 times lower after the partial elimination of Si
A Monte Carlo-Based Strategy to Assess Complex Kinetics: Application of the Null-Reaction Method to DAEM
No full textInternational audienceThe distributed activation energy model (DAEM) is widely used in chemical kinetics to statistically describe the occurrence of numerous independent parallel reactions. In this article, we suggest a rethink in the context of a Monte Carlo integral formulation to compute the conversion rate at any time without approximation. After the basics of the DAEM are introduced, the considered equations (under isothermal and dynamic conditions) are respectively expressed into expected values, which in turn are transcribed into Monte Carlo algorithms. To describe the temperature dependence of reactions under dynamic conditions, a new concept of null reaction, inspired from null-event Monte Carlo algorithms, has been introduced. However, only the first-order case is addressed for the dynamic mode due to strong nonlinearities. This strategy is then applied to both analytical and experimental density distribution functions of the activation energy. We show that the Monte Carlo integral formulation is efficient in solving the DAEM without approximation and that it is well-adapted due to the possibility of using any experimental distribution function and any temperature profile. Furthermore, this work is motivated by the need for coupling chemical kinetics and heat transfer in a single Monte Carlo algorithm
Absorption de gaz par des solutions réactives : adaptation de l’instrumentation d’une cellule agitée d’étude cinétique et application à des systèmes CO2/amines
No full textInternational audienceThe elimination of impurities from natural gas (water, CO2, H2S, mercaptans) is an obligation: in Europe, a max. of 20 mg/Sm3 in total sulfur (at 15°C and 1 atm) is allowed, as well as 2.5 vol% in CO2. It maximizes the calorific value of delivered gas and limits chemical risks (corrosion, toxicity) associated with this transition fuel to cleaner energy sources. Acid gas separation is commonly performed by reactive gas-liquid absorption. Raw gas and absorptive solution are brought into counter current contact in an absorber at 40-80°C and 30-80 bar. Then the acid-gas loaded solvent is sent to a stripper where acid gas desorption from the solvent takes place at T between 105 and 140°C and P ≤ 2.5 bar. The solvent is an aqueous base (e.g., amine) solution. A good solvent has a high reactivity with the dissolved gas during absorption and a low regeneration energy, hence the advantage of mixtures of two amines. Here we study an aqueous solution of a small amount of piperazine (PZ) added to methyldiethanolamine (MDEA). PZ reacts faster with CO2 than MDEA, and the major reaction product with CO2 is the hydrogen carbonate ion HCO3-, which lowers the solvent regeneration duty. This work aims at characterising the kinetics of the absorption of CO2 in an aqueous solution of MDEA-PZ. Indeed, no consensus has been found on the reaction mechanism of CO2 in this amine mixture; the synergies between MDEA and PZ observed in the literature remain poorly explained. However, its knowledge is essential to optimize solvent formulation and industrial unit design.L’élimination des impuretés du gaz naturel (eau, CO 2 , H2S, mercaptans) est une obligation : en Europe, les teneurs max. autorisées sont de 20 mg/Sm 3 en soufre total (à 15°C et 1 atm) et 2,5 vol% en CO 2 . Elle permet de maximiser le pouvoir calorifique du gaz délivré et de limiter les risques chimiques (corrosion, toxicité) liés à ce combustible de transition vers des sources d’énergies plus propres. La séparation des gaz acides se fait communément par absorption gaz-liquide avec réactions chimiques. Le gaz à traiter et la solution sont alors mis en contact à contre-courant dans un absorbeur à 40-80°C et 30-80 bar. Puis le solvant chargé en gaz acides se dirige vers une colonne de régénération où la désorption des gaz acides du solvant a lieu à T comprises entre 105 et 140°C et P ≤ 2,5 bar. Le solvant est une solution aqueuse de base (e.g., d’amine). Un bon solvant a une grande réactivité avec le gaz dissous lors de l’absorption et une faible énergie de régénération, d’où l’avantage des mélanges de deux amines. Ici, nous étudions une solution aqueuse avec une faible concentration de pipérazine (PZ) ajoutée à la méthyldiéthanolamine (MDEA). La PZ réagit plus rapidement avec le CO 2 que la MDEA, et le produit majoritaire de réaction avec le CO 2 est l’ion hydrogénocarbonate HCO - , ce qui abaisse l’énergie requise pour régénérer le solvant. L’objectif de ce travail est la caractérisation cinétique de l’absorption de CO 2 par une solution aqueuse de MDEA-PZ. En effet, le mécanisme réactionnel du CO 2 dans ce mélange d’amines ne fait pas consensus ; les synergies entre MDEA et PZ observées dans la littérature demeurent mal expliquées. Or, sa connaissance est primordiale pour optimiser la formulation du solvant et le dimensionnement des unités industrielles
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Comparison study of physicochemical and biopharmaceutics properties of hydrophobic drugs ground by two dry milling processes.
No full textInternational audienceThis study focuses on the dry milling of BCS (Biopharmaceutical Classification System) class II molecules. These molecules have a limited bioavailability because of their low aqueous solubility, poor water wettability and low dissolution rate. In order to improve these properties, indomethacin (IND) and niflumic acid (NIF) were milled using two different types of equipment: Pulverisette 0® and CryoMill®. Milled samples were characterized and compared to commercial molecules. IND shows a modified solid state, like surface crystallinity reduction and an increase in water vapor adsorption from to 2 up to 5-fold due to milling processes. The obtained solubility data resulted in an improvement in solubility up to 1.2-fold and an increase in initial dissolution kinetics: 2% of dissolved drug for original crystals against 25% for milled samples. For NIF no crystallinity reduction, no change of surface properties and no solubility improvement after milling were noticed. In addition, milled particles seemed more agglomerated resulting in no changes in dissolution rate compared to the original drug. IND solubility and dissolution enhancement can be attributed to the modification of surface area, drug crystallinity reduction and water sorption increase due to specific behaviour related to the drug crystal disorder induced by milling process
Advection, diffusion and linear transport in a single path-sampling Monte-Carlo algorithm : getting insensitive to geometrical refinement
No full textWe address the question of numerically simulating the coupling of diffusion, advection and one-speed linear transport with the specific objective of handling increases of the amount, the geometrical refinement and the accuracy level of input data. The computer graphics research community has succeeded in designing Monte Carlo algorithms simulating linear radiation transport in physically realistic scenes with numerical costs that are insensitive to geometrical refinement: adding more details to the scene description does not affect the computation time. The corresponding benefits in terms of engineering flexibility are already fully integrated in the cinema industry and are gradually inherited by the video game industry. We show here that the same insensitivity to the complexity of the geometrical description can also be achieved when considering one-speed linear transport not only alone but coupled with diffusion and advection. Pure linear-transport paths are replaced with advection-diffusion/linear-transport paths constituted of subpaths, each representing one of the three physical phenomena in a recursive manner. Illustration is made with a porous medium involving up to 10000 pores, the computation time being strictly independent of the number of pores
Influence of Interlayer Time on the Microstructural State of CoCrMo Coatings Applied by Selective Laser Melting on an Iron-based Substrate for Different Numbers of Layers
No full textInternational audienceThe Selective Laser Melting process was used to perform cobalt-based alloy coatings on a C35 steel substrate. The relationships between interlayer times, iron dilution, crystalline structures, and micro-hardness were studied for different numbers of layers with an initial lased powder layer of 50μm thickness. Reducing the interlayer time increased the temperature reached in the melting bed and promoted matter transport from the substrate. The coating thickness consisted of a Co-Cr-Fe mixture, divided into two zones: a transition zone near the interface and a stabilized zone towards the substrate. The real coating thickness was found to be always greater when the interlayer time was reduced. For an interlayer time equal to 11 s (series 2), the iron dilution was always higher than for an interlayer time ranging between 42 s and 16 s (series 1), leading to a higher coating thickness. The microstructural state was also dependent on the interval time between successive layers. The coating microstructure was always cellular because of the high cooling rate. XRD analysis of the surface showed that this microstructure is essentially composed of two non-equilibrium phases: FCC and α’ BCC. The high hardness is due to the high content of iron which induces a martensite phase (series 2). Starting from 5 layers for series 1 and from 6 layers for series 2, the α’ BCC phase disappeared if the iron content on the coating surface was reduced by more than 45% content in weight. The mean coating hardness decreased with an increasing number of layers because of the decrease in the iron content. Finally, the micro-hardness of the FCC phase, for its part, was found to be dependent on the iron content in solution in the Co matrix