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Influence of strain rate and temperature on the deformation mechanisms of a fine-grained Ti-6Al-4V alloy
No full textInternational audienceDepending on their initial microstructure, titanium alloys, as the Ti-6Al-4V may have ac-tivation of different deformation mechanisms during hot forming processes. In this work,interrupted tensile tests and heat treatments are used to improve the understanding of themechanical and microstructural behaviour of a fine-grained Ti-6Al-4V alloy at two temper-atures (750◦C and 920◦C) and so for two differentβphase fractions. The microstructuralfeatures like,αgrain size and phase fraction, were determined by Scanning Electron Mi-croscope (SEM) and image analysis. Moreover, evolution of the preferred crystallographicorientation ofαgrains and local misorientations between and inside grains were obtainedby Electron Backscatter Diffraction (EBSD). The strain rate sensitivity parameter as wellas the activation energy were deduced from mechanical tests. It appears, from all these mi-crostructural and mechanical data, that several mechanisms are activated depending on thestrain level and on the temperature range. At 750◦C, for a high strain rate, the deforma-tion is mainly controlled by dislocations activity in theαphase (texture changes, dynamicrecrystallization) and, at very low strain rate, by probably GBS accommodated with dislo-cations activity intoα(recovery) andβ. On the contrary at 920◦C, a clear decrease of theoverall texture intensity associated with a highmvalue suggests that GBS is the dominantmode of deformation. Nevertheless, as theα/βvolume fraction is around 48 %/52 % at thistemperature, not only theαphase but also theβphase as well asα/αandβ/βboundariesmight contribute to the flow behaviour. During long deformation time (low strain rate andhigh temperature), dynamic coarsening behaviour (both intoαandβ), that is controlled bybulk diffusion, can occur and modify the type, the distribution and decrease the number ofα/β,α/αandβ/βboundaries. This can be partly related to the flow hardening observedat 920◦C and 10−4s−1
Towards Model Transformation from a CBM Model to CEP Rules to Support Predictive Maintenance
No full textInternational audienceOver the past decades, the development of predictive maintenance strategies, like Prognostics and Health Management (PHM), have brought new opportunities to the maintenance domain. However, implementing such systems addresses several challenges. First, all information related to the system description and failure definition must be collected and processed. In this regard, using an expert system (ES) seems interesting. The second challenge, when monitoring complex systems, is to deal with the high volume and velocity of the input data. To reduce them, Complex Event Processing (CEP) can be used to identify relevant events, based on predefined rules. These rules can be extracted from the ES knowledge base using model transformation. This process consists in transforming some concepts from a source to a target model using transformation rules. In this paper, we propose to transform a part of the knowledge from a condition-based maintenance (CBM) model into CEP rules. After further explain ing the motivations behind this work and defining the principles behind model-driven architecture and model transformation, the transformation from a CBM model to a “generic rules” model will be proposed. This model will then be transformed into an Event Processing Language (EPL) model. Examples will be given as illustrations for each transformation
Assessing the impact of woody and agricultural biomass variability on its behaviour in torrefaction through Principal Component Analysis
No full textInternational audienceThe influence of biomass macromolecular composition on its behaviour in torrefaction was statistically assessed through Principal Component Analysis (PCA), both in terms of solid conversion kinetics and volatile species released, in function of the operating conditions. The experimental data obtained in the torrefaction of 14 woody and agricultural biomass samples at lab-scale was analysed. Main biomass macromolecular composition on cellulose, hemicelluloses and lignin was shown to acceptably represent biomass diversity, which can be complemented by the extractives and ash content. Similitudes were found in deciduous and coniferous wood families, respectively, while agricultural and herbaceous crops were shown as more heterogeneous, both in terms of characterization and behaviour in torrefaction. Cellulose, hemicelluloses and lignin content strongly influenced solid and volatile species yields in torrefaction, while biomass family exhibited a lower impact. Ash content in potassium, phosphorous and silicon did not show any influence on the extent of solid degradation through torrefaction. A lower variability was found in solid degradation profiles from woods, while agricultural crop behaviour was more heterogeneous. Different volatile species were released from biomass samples from the same family. Furthermore, different production profiles were found for volatile species chemically close, except for deciduous wood. These results indicate that, when modelling biomass torrefaction, solid mass loss can be represented by an exemplar of deciduous and coniferous wood, while several species would be required for the agricultural family. The variability of the volatile species release would require the consideration of several volatile species and several biomass samples per family
A simple process for the production of fuel additives using residual lignocellulosic biomass
No full textInternational audienceIn this work, the direct production of levulinates from cheap residual lignocellulosic biomass was performed using an affordable homogeneous catalyst. A central composite design (CCD) using the response surface methodology (RSM) was applied to analyze the effects of the four selected factors (acid concentration, temperature, α-cellulose content, and reaction time) on the production of levulinates (levulinic acid derivatives). This optimization led to a total production of levulinates of 78 wt%, 72.5 wt%, 83 wt%, and 73 wt% using α-cellulose, poplar, sorghum, and softwood bark, respectively
Construction d'une fonction de transfert par la méthode Monte Carlo Symbolique : application à la thermique couplée en géométries complexes
No full textThe present manuscript addresses the issues of optimization and analysis of thermal systems, specifically, in the case of conducto-convecto-radiative combined heat transfer in 3D complex geometries. The construction of a transfer function with the Monte Carlo Symbolic method will be based on the existing know-how of the Monte Carlo method in thermal transfers as well as on the tools from the computer graphics community. This transfer function will allow a reliable and fast estimation of the probe temperature for a wide range of parameter values. The Symbolic Monte Carlo method developed up to now in radiation for the identification of radiative properties will be extended to combined conducto-convecto-radiative transfers in complex geometries and will demonstrate its use through application examples in thermal imaging. The interaction with different interlocutors from different fields of research in thermal engineering, such as electronic thermal transfer or inversion problems in thermal engineering, will lead to the development of a transfer function that is complementary to their existing optimization methods. In a more theoretical aspect, there will be a classification of the families of parameters resulting essentially in a reflection on the linearity or non-linearity of the transfer functionLes travaux présentés dans ce manuscrit abordent les problématiques d’optimisation et d’analyse de systèmes thermiques, en particulier, dans le cas de transferts de chaleurs couplés conducto-convecto-radiatifs en géométrie 3D complexe. La construction d’une fonction de transfert avec la méthode Monte Carlo Symbolique s’appuiera sur le savoir-faire existant de la méthode de Monte Carlo en transferts thermiques ainsi que sur les outils informatiques issus de la synthèse d’image. Cette fonction de transfert permettra d’estimer de façon fiable et rapide la température sonde pour un intervalle étendu de valeurs de paramètres. La méthode de Monte Carlo Symbolique développée jusqu’ici en rayonnement pour l’identification de propriétés radiatives sera étendue aux transferts couplés conducto-convecto-radiatifs en géométrie complexe et démontrera son utilisation au travers d’exemples applicatifs en thermique. L’interaction avec différents interlocuteurs issus de domaines de recherche en ingénierie thermique, tel que la thermique électronique ou les problèmes d’inversion en thermique, permettra d’aboutir au développement d’une fonction de transfert trouvant une utilité complémentaire à leurs méthodes d’optimisation existantes. Dans un aspect plus théorique, il y aura une classification des familles de paramètres se traduisant essentiellement par une réflexion sur la linéarité ou la non linéarité de la fonction de transfert
Knowledge-based System for Risk Engineering During the Bidding Process
No full textInternational audienceOffer elaboration, when answering to call for tenders, is a complex process, usually characterised by limited information and time restrictions. From the point of view of the bidding companies, this paper explores risk engineering regarding the activities describing the manufacturing of the product from design to delivery. Specifically, the paper proposes a knowledge base system to support the identification and analysis (probability / impact) of key risks that may arise during implementation. This risk identification takes place during the bidding stage so that the identified risks can be taken into account in the proposal. Through the proposed system, risk engineering knowledge can be capitalized and reused to support new bids. Risk engineering knowledge is structured by a unified model. For helping decision-makers in their risk engineering process, a reuse method, based on case based reasoning, is proposed to retrieve relevant knowledge. The proposed system leads to more accurate, less risky and higher confidence bids. This work can be extended to help the decision-makers model risk mitigation strategies
Comportement d’une matrice alumine-silice au cours de l’élaboration de composites à matrice céramique oxyde/oxyde
No full textOxide/oxide ceramic matrix composites can be used for structural applications operating continuously at temperatures between 500°C and 900°C under oxidizing environments, such as in areas close to aircraft engines. In particular, composites based on a matrix combining alumina and silica are promising. In addition, the processing of these materials comprises several steps. Two of them are essential: the impregnation of the fibrous reinforcement with the suspension and the sintering of the matrix. This PhD thesis focuses on the processing of oxide/oxide ceramic matrix composites using an alumina-silica matrix. It is derived from an aqueous suspension in which the two species are initially present as particles. The aim of this work is to study the behaviour of such a system during the various stages of the manufacturing, i.e. to establish the relationships between processing/microstructure/properties, in order to propose an optimal composition of the matrix regarding the process and the required properties. In particular, the silica proportion will be a crucial parameter. Firstly, since the quality of the impregnation step is based on the ability of the suspension to flow within the fibrous structure, a rheological characterization of the oxide suspensions has been carried out. The rheological behavior has been interpreted on the basis of the domains of predominance of the different interactions within the suspension. Also, the influence of the various suspension characteristics, such as the solid fraction and the alumina-silica ratio, has been examined. Then, the behaviour of this system during the sintering has been studied since this thermal treatment should lead to a microporosity that respects the concept of weak matrix composites. The sintering mechanisms have been identified while the influence of the various parameters on the kinetics has been qualified. Also, relationships with the mechanical properties of the matrix have been established. Finally, composites with Nextel™ 610 reinforcements and a porous alumina-silica matrix have been fabricated and characterized.Les composites à matrice céramique oxyde/oxyde peuvent être considérés pour des applications structurales opérant, en continu, sous environnement oxydant à des températures comprises entre 500°C et 900°C, comme c’est le cas dans les zones proches des moteurs d’avions. En particulier, les composites reposant sur une matrice associant de l’alumine et de la silice présentent un fort potentiel. En outre, la mise en œuvre de ces matériaux comprend plusieurs étapes dont deux sont essentielles : l’imprégnation du renfort fibreux par la suspension et le frittage de la matrice. Cette thèse s’intéresse à l’élaboration de composites à matrice céramique oxyde/oxyde utilisant une matrice alumine-silice. Celle-ci est issue d’une suspension aqueuse dans laquelle les deux espèces sont initialement présentes sous formes de particules. Aussi, l’objectif de ces travaux est d’étudier le comportement d’un tel système au cours des différentes étapes clés de la fabrication, c’est-à-dire d’établir les relations procédé/microstructure/propriétés, afin de proposer une composition optimale de la matrice au regard du procédé et des propriétés visées. En particulier, la proportion de silice sera un paramètre crucial. Tout d’abord, étant donné que la réussite de l’étape d’imprégnation repose sur la capacité de la suspension à s’écouler au sein de la structure fibreuse, une caractérisation rhéologique des suspensions d’oxydes a été menée. Le comportement rhéologique a été interprété sur la base des domaines de prédominance des différentes interactions au sein de la suspension. Aussi, l’influence des différentes caractéristiques des suspensions, comme la concentration volumique en particules et la proportion alumine-silice, a été examinée. Ensuite, le comportement de ce système au cours du frittage a été étudié puisque ce traitement thermique doit permettre, entre autres, d’aboutir à une microporosité respectueuse du concept de composites à matrice faible. Les mécanismes de frittage ont été identifiés tandis que l’influence des différents paramètres sur la cinétique a été qualifiée. Aussi, des liens avec les propriétés mécaniques de la matrice ont été établis. Enfin, des composites à renforts Nextel™ 610 et à matrice poreuse alumine-silice ont été mis en œuvre et caractérisés
A review of current treatments strategies based on paromomycin for leishmaniasis
No full textInternational audienceLeishmaniasis is a neglected disease caused by protozoan parasites of the Leishmania genus, which affects many people in several countries. This disease has three major clinical forms: cutaneous, mucocutaneous and visceral. The current treatments consist of an intravenous, intralesional or intramuscular administration of pentavalent antimonials, but other drugs can be used, among them, amphotericin B, pentamidine, paromomycin and miltefosine. However, these therapies have many side effects. Hence, there is an increase of studies searching for new formulations using different technologies and different routes of administration for leishmaniasis treatment. Paromomycin sulfate (PM) is an aminoglycoside antibiotic, belonging to class III of biopharmaceutical classification system, used intravenously and topically with leishmanicidal activity. This review will provide a general overview of PM current leishmaniasis treatments and new PM formulations. Treatments using PM are available in ointments or creams for topical administration and PM solution for intramuscular administration. The topical treatment with PM presents low efficacy, probably related to low drug permeability across the skin. To improve PM permeability and efficacy, researchers are establishing micro and nanotechnologies. However, further studies are still required to investigate more physicochemical properties and in vitro/in vivo parameters
Fast pyrolysis of hemicelluloses into short-chain acids: An investigation on concerted mechanisms
No full textInternational audienceThe nature of main primary mechanisms involved in lignocellulosic fast pyrolysis is often assumed to be radical mecha-nisms. Here we demonstrated that thermal depolymerization of native hemicelluloses can undergo several primary and secondary concerted reactions leading to light oxygenates that can compete with radical mechanisms. To model these reactions at a microscopic level, we used high-level quantum calculations based on functional theory. In parallel, a set of experimental data was collected to confirm the main structural motifs of extracted and purified hemicelluloses and to describe chemical variations within fast pyrolysis products released from various hemicellulosic fractions at 823 K. In general, the barriers computed at 800K for pericyclic reactions were found reasonably low competing with these of homolytic reactions. The critical role of hydrogen bonding and spatial arrangement on product distribution was clearly demonstrated; stabilizing effects depending greatly on temperature. We reported a useful dataset of intrinsic kinetic parameters and a reaction network readily available to complete kinetic models for ‘primary’ and ‘secondary’ fast pyrolysis of hemicelluloses
Integrated approach for risk management in servitization decision-making process
No full textInternational audiencePurposeThe paper proposes an innovative systemic method helping decision-makers to control servitization transition process, through decision process risk diagnosis.Design/methodology/approachThe proposed method is based on the modeling of decision processes and risk identification and analysis. This method was based on an action-research approach, in close relationship with two companies (SMEs). The paper develops the feasibility experiment at Automelec company.FindingsThe method was successfully implemented and delivered concrete diagnosis results.Research limitations/implicationsThe generalization of the applicability of the method needs to be tested on several different cases.Practical implicationsThe first practical implication is related to the efficiency of the method to help decision-makers in a servitization context to limit uncertainty and get a global view of the weaknesses of their decision-making process, it raises their awareness about servitization transition for their companies. Furthermore, the method also helps to explain the strategy of a servitization transition. It enhances the level of maturity of the decision process of the company, and can be used as a training/learning tool for managers.Social implicationsThe results brought by the research contribute to give the decision-making boards for organization living a servitization transition and especially SMEs a better control over the servitization decision process and related risks, which will increase the economic stability of the company and its vision over long, medium and short horizons. This will bring positive impact on the overall economic and social environment and networks of the servitized SME, and enhance the confidence of coworkers, subcontractors and clients.Originality/valueThe first originality of the paper is related to the new way of considering risk, not only as an analysis criterion but as the central driver in steering a strategic transition for the company, such as servitization. The second originality of the study is about assessing risk occurrence over a decision-making process through decision reliability and decision confidence