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Optimizing Spare Parts Management: A Segmentation Approach for Intermittent Demand in Public Transportation Systems
No full textInternational audienceEffective spare parts management is essential for public transportation systems to maintain high service levelswhile minimizing operational costs. This study develops a methodology for optimizing storage strategies by segmentingspare parts based on their consumption patterns. Covering the best practices from the literature and insights from apractical case study, the approach involves redefining the consumption identification process to create a comprehensiveconsumption history using real ERP data. A segmentation method tailored for time-series analysis, defined by demandprofiles, was applied to classify spare parts. The analysis identified nine distinct groups among thousands of active itemsand a group of inactive items still in stock. This group was found to be 60% larger than previously estimated, leading tohigh annual storage costs—double the earlier projection. The findings underscore the critical role of accuratesegmentation in inventory cost optimization, while also addressing implementation challenges such as groupdetermination, subjectivity, and the necessity for dynamic updatesLa gestion efficace des pièces de rechange est essentielle pour les systèmes de transport public afin de maintenirun haut niveau de service tout en minimisant les coûts opérationnels. Cette étude propose ainsi une méthodologie visant àoptimiser les stratégies de stockage en segmentant les pièces de rechange en fonction de leurs profils de consommation.S'appuyant sur les meilleures pratiques issues de la littérature et les enseignements d'une étude de cas pratique,l'approche redéfinit le processus d’identification des consommations pour créer un historique complet à partir de donnéesréelles issues d’un ERP. Une méthode de segmentation adaptée à l’analyse des séries temporelles, basée sur les profils dedemande, a été appliquée pour classer les pièces de rechange. L’analyse a permis d’identifier neuf groupes distincts parmides milliers d’articles actifs, ainsi qu’un groupe d’articles inactifs encore en stock. Ce dernier s’est révélé 60 % plusimportant que les estimations précédentes, entraînant des coûts de stockage élevés , soit le double de la projection initiale.Les résultats montrent l'importance cruciale d'une segmentation précise pour l'optimisation des coûts d'inventaire tout ensoulignant les défis d'implémentation liés à la détermination des groupes, à la subjectivité et à la nécessité d’une mise àjour dynamique
Prediction of crack initiation location and direction in fretting fatigue considering cylindrical contact
No full textInternational audienceFretting phenomenon results in severe contact stresses that develop on the surface near the trailing edge of the contact, which can lead to the formation of microcracks. Combined with fatigue stresses, these cracks may propagate and cause catastrophic specimen failure. Referred to as fretting fatigue, this phenomenon is characterized by both multiaxial and steep stress gradients. Multiaxiality is addressed using various fatigue parameters based on stresses and strains computed along the contact surface. The severity of stress gradients and the contact size are accounted for using process volume averaging methods. Therefore, combining fatigue criteria with averaging methods provides an advantage in better predicting crack nucleation conditions. In this study, salient features of the experimental crack nucleation condition are considered in the finite element analysis. The SWT critical-plane-based multiaxial fatigue criterion, based on the computed stresses and strains at the contact surface, is then employed to predict crack nucleation risk, location, and orientation. Recent analytical expressions derived from the Muskhelishvili potential are used to calculate the stresses. The predicted results are compared with experimental data reported in the literature. Finally, applying an averaging strategy to the localized parameter values within the process volume improved the results and enhanced the accuracy of the predictions
Procédés de thermoconversion et mécanismes de graphitisation de la lignine (Thèse sous embargo)
No full textGraphenic biocarbon are composed of carbon atoms organized in structures similar to graphene or graphite. These materials are promising for a wide range of applications thanks to their tunable thermal, electrical and mechanical properties along the production process. Biomass and biowastes can be used to produce these graphenic biocarbons via high-temperature thermal treatment. Such processing is however highly energy-intensive since it requires temperatures higher than 2000 °C, and only partially efficient given the ''non-graphitizable'' nature of the lignocellulosic resource. The challenge of this thesis is to convert a non-graphitizable biomass into a graphenic biocarbon at temperatures below 2000 °C, using more sustainable processes. Lignin (macropolymer of lignocellulosic biomass) was selected as feedstock in this study for its partially aromatic structure. Graphenic biocarbons were produced via four routes: (1) solar carbonization (concentrated solar energy), (2) catalytic solar carbonization of calcium-doped lignin, (3) hydrothermal carbonization (pre-treatment) followed by conventional (electrical) carbonization and (4) hydrothermal carbonization followed by solar carbonization. Conventional and solar carbonizations are carried out between 1000 °C and 1800 °C. The formation of graphenic domains was measured qualitatively and quantitatively using multi-scale analytical and observation techniques. The hydrothermal pre-treatment promotes carbon pre-structuration, facilitating the growth and stacking of graphene layers during high-temperature carbonization. The use of calcium, a non-toxic and hearth-abundant catalyst, lowered the onset of graphenic structures to 1400 °C. Finally, solar carbonization enhances the stacking and growth of graphenic layers thanks to the high energy focused on the sample. Overall, the selected processes allowed the production of graphenic material from lignin at temperatures below 1800 °C, reducing the energy need (electric energy demand reduced by 95 %) and environmental impact (CO2 emissions cut by a factor of 20).Les matériaux carbonés graphéniques sont constitués d'atomes de carbone organisés en structures proches de celles du graphène ou du graphite. Ces matériaux sont prometteurs pour de nombreux domaines, en contrôlant leurs propriétés thermiques, électriques et mécaniques en cours de production. La biomasse et les biodéchets peuvent être utilisés pour produire ces biocarbones graphéniques via un traitement thermique à haute température. Cependant ce traitement est à la fois énergivore, puisqu'il requiert des températures supérieures à 2000 °C, et partiellement efficace, en regard du caractère « non-graphitisable » de la ressource lignocellulosique. L'enjeu de cette thèse est donc de convertir une biomasse non-graphitisable en matériau à taux de graphène élevé à une température inférieure à 2000 °C avec des procédés plus respectueux de l'environnement. La lignine (macropolymère de la biomasse lignocellulosique) a été choisie comme ressource dans cette étude pour sa structure partiellement aromatique favorable à la graphitisation. La production des biocarbones graphéniques a été réalisée selon quatre voies : (1) carbonisation solaire (énergie solaire concentrée), (2) carbonisation solaire catalytique (lignine dopée au calcium), (3) carbonisation hydrothermale (prétraitement) suivie d'une carbonisation conventionnelle (électrique) et (4) carbonisation hydrothermale suivie d'une carbonisation solaire. Les carbonisations conventionnelles et solaires sont effectuées entre 1000 °C et 1800 °C. La formation de domaines graphéniques a été déterminée qualitativement et quantitativement à l'aide de techniques d'analyses et d'observations multi-échelles. Le prétraitement hydrothermal favorise la pré-structuration du carbone, facilitant l'allongement et l'empilement des feuillets de graphène au cours de la carbonisation haute température. L'utilisation du calcium, un catalyseur non toxique et abondant, abaisse la température de formation des structures graphéniques à 1400°C. Enfin, la carbonisation solaire améliore l'empilement et la croissance des feuillets graphéniques grâce à la haute densité d'énergie apportée à l'échantillon. Dans l'ensemble, les procédés sélectionnés ont permis la production de matériaux graphéniques à partir de lignine à des températures inférieures à 1800 °C, réduisant ainsi les coûts énergétiques (demande en énergie électrique réduite de 95 %) et l'impact environnemental (émissions de CO2 divisées par 20)
Préparation et caractérisation d'un analogue de régolithe lunaire avec mise en oeuvre d'un procédé de fabrication additive directe
No full textWith the declared aim of establishing a permanent base on the Moon by the end of the decade, the question of astronaut autonomy is coming to the fore. The development of technologies for In-Situ Resources Utilization (ISRU), in particular lunar soil known as regolith, is becoming a key element in ensuring the viability of these long-duration missions. This thesis investigates one of these solutions, direct additive manufacturing using selective laser melting (SLM), promising in terms of its versatility and its ability to dispense with binders. To achieve this, a comprehensive approach was adopted: firstly, a working material was developed, a lunar mare regolith analog designated as basalt of Pic d'Ysson (BPY). It has a variable composition, allowing it to reproduce the variability inherent in lunar soil, both in terms of the proportion of chemical elements and maturity. This was followed by an in-depth study of the physical phenomena taking place during additive manufacturing. Starting with radiation-matter interactions, with the determination of the absorptivity of the granular medium, followed by its thermal conductivity and the phase changes occurring in the analog during heating cycles, the experimental characterizations presented are complemented by analytical models to better identify the influence of the various variables involved. Finally, manufacturing trials were carried out, testing a large number of parameters (energy density, application of an annealing aftertreatment,...). The manufactured objects are then used to establish material-process-property relationships through a series of mechanical and microstructural characterizations (identification of the phases and defects using X-ray tomography and electronic imaging methods among others). Finally, the relevance of the choice of SLM in the context of ISRU is argued, and an overall strategy for optimizing part properties with suggestions for possible improvements is given.Alors que la volonté de fonder une base pérenne sur la Lune d'ici à la fin de la décennie apparaît, la question de l'autonomie des astronautes se pose. Le développement des technologies d'utilisation des ressources in-situ (ISRU), en particulier du sol lunaire appelé régolithe, devient un élément clé pour assurer la viabilité de ces missions longue durée. Cette thèse se propose d'étudier l'une de ces solutions, la fabrication additive par fusion sélective laser (SLM), prometteuse de par sa polyvalence et sa capacité à se passer de liants. Pour cela, une approche globale de travail a été conduite : D'abord, un matériau de travail, analogue de régolithe des mers lunaires désigné comme basalte du Pic d'Ysson (BPY), a été élaboré. Sa composition est multiple, et permet de reproduire la variabilité inhérente au sol lunaire, que ce soit en terme de proportion en éléments chimiques ou de maturité. Ensuite, une étude approfondie des phénomènes physiques ayant lieu durant la fabrication additive a été menée. Commençant par les interactions rayonnement-matière avec la détermination de l'absorptivité du milieu granulaire, suivi de sa conductivité thermique et des changements de phases survenant dans l'analogue lors de cycles de chauffe, les caractérisations expérimentales présentées sont complétées de modèles analytiques permettant de mieux identifier l'influence des différentes variables mises en jeu. Enfin, des essais de fabrication ont pu être menés, testant un nombre important de paramètres (densité d'énergie utilisée, application d'un post traitement de recuit,...). Les objets manufacturés permettent alors d'établir les relations matériau-procédé-propriétés par une série de caractérisations mécaniques et microstructurales. Finalement, la pertinence du choix de la SLM dans le contexte de l'ISRU est argumentée, et une stratégie globale d'optimisation des propriétés des pièces avec des suggestions d'améliorations possibles est donnée
Importance of Calibrating Analytical Equipment for Detecting and Quantifying Degradation Byproducts of C4F7N/CO2/O2 Gas Mixtures Insulation Fluid
No full textInternational audienceIn the past few years, the C4F7N/CO2/O2 gaseous blend has been recognized as the best promising alternatives to SF6 gas, allowing to keep the minimum dimensional and environmental footprint of high voltage power transmission equipment’s versus other alternatives. In the event of extreme thermoelectric stress, similar to SF6 the gas mixture undergoes dissociation and produces a diverse range of byproducts in various concentrations. Analytical technologies such as gas chromatography coupled to mass spectrometry (GC-MS) and Fourier Transform Infrared (FTIR) are the key devices that can have the accurate estimation of qualitative and quantitative measurements of byproduct gas samples. Analysis of the arced gas sample reveals a range of byproducts, including CO, CF4, C2F6, C3F8, C2F4, C3F6, COF2, CF3CN, C2F6CN, CF2=CF-CN, (CN)2, CF3-N=CF2, CF(CF3)2-CO-NH2, and (CH3)2SiF2 that can be found as trace-level. However, due to the limited availability of standard gas in the market, only five gases, CF4, C2F6, C3F8, CF3CN, and COF2 were selected as standard for quantification. In our GC-MS method development, achieving complete peak separation was not possible due to the potential matrix effect of the sample. However, the peak area corresponding to the molecular ion of CF4, C2F6, C3F8, CF3CN, and COF2 was carefully determined, and the regression curve was plotted for each molecule individually. In COF2 results, the standard deviation was 69%, which led us to develop the FTIR methodology for COF2 with the classical least squares (CLS) method, in which the standard deviation drops to 4% from 69%
The Heart of Crystalline Materials
No full textInternational audienceMaterials punctuate our daily lives. Directly related to their use but also their production, transformation and extraction of raw materials, they set the pace for rational industrial growth. Among them, metals and ceramics are of considerable economic importance. Crystalline materials and their structural and functional applications are the focus of particular attention, growing interest and advanced research, and contribute to meeting the major societal challenges of today and tomorrow, in a context of technological excellence and sustainable development. The sole ambition of this book is to provide the scientific background that today's engineers, who are necessarily generalists, need in this field. It is the fruit of over twenty-five years of experience in teaching, sharing and transmitting knowledge, mainly acquired at IMT Mines Albi but also in numerous foreign universities around the world. It forms the basis of teaching in materials science and engineering for undergraduates intending to study materials and their applications in greater depth
Simulation par la méthode de Monte Carlo en espace de chemins du couplage conducto-radiatif : Application à la Gyroïde
No full textInternational audienceGlobal population growth is driving an increase in energy demand, encouraging theuse of renewable energy sources such as biomass, which is essential for cooking. However, its scarcity,inefficient use, and health impacts necessitate optimizing the thermal performance of ovens and stoves.This work presents a numerical study of the thermal properties of a gyroid-type porous medium,generated numerically and representative of clay, an aperiodic porous material. The analysis is based onthe Monte Carlo method to study coupled heat transfer (conduction and radiation). The study examinesthe effective thermal conductivity in both pure conduction and conduction-radiation coupling, whileevaluating the influence of anisotropy, geometry size, and temperature on thermal properties.La croissance démographique mondiale entraîne une augmentation de la demande énergé-tique, incitant à l’utilisation d’énergies renouvelables telles que la biomasse, essentielle pour la cuisson.Cependant, sa raréfaction, son utilisation inefficace et ses impacts sur la santé rendent nécessairel’optimisation du rendement thermique des fours et foyers. Ce travail propose une étude numérique despropriétés thermiques d’un milieu poreux de type gyroïde, généré numériquement et représentatif del’argile, un matériau poreux apériodique. L’analyse repose sur la méthode de Monte Carlo pour étudierle transfert de chaleur couplé (conduction et rayonnement). L’étude examine la conductivité thermiqueeffective en conduction pure et en couplage conduction-rayonnement, tout en évaluant l’influence del’anisotropie, de la taille de la géométrie et de la température sur les propriétés thermiques
Vehicle routing optimisation with time windows for home healthcare
No full textInternational audienceThe vehicle routing problem with time windows (VRPTW) is crucial for improving the efficiency of transport services, especially in the home healthcare sector, where meeting clients' time constraints is essential. To solve this problem, we have developed an approach based on meta-heuristic optimisation algorithms hybridised with artificial intelligence (AI) models, which allows for optimal resource utilisation and improved solution quality. The results show that this combination of techniques leads to significant gains in cost reduction and time window compliance, providing an effective solution to the challenges of VRPTW
Preface to the special issue on “Decision Support Systems in an uncertain world”
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Activated Carbon from Birch Wood as an Electrode Material for Aluminum Batteries and Supercapacitors
No full textInternational audienceDue to its sustainable approach, biomass is the subject of much research focused on the synthesis of multifunctional materials including electrodes for batteries and supercapacitors. In this work, sawdust from the processing of birch logs was used to produce a highly porous carbon material (CBW) that is employed for the construction of electrodes for aluminum batteries (ABs) and supercapacitors (SCs). A multitude of characterizations indicated that CBW is built in with highly disordered amorphous carbons and an extremely high specific surface area of 3029 m 2 g −1 which is predominant with microporous features. The chemical analysis of CBW indicated the presence of a significant amount of oxygen functionalities. As a cathode of AB, CBW achieved discharge capacities 115, 74, 54, 50, 47, 43, and 29 mAh g −1 at current rates 0.1, 1.0, 2.0, 3.0, 4.0, 5.0, and 10.0 A g −1 , respectively. Similarly, SC with CBW symmetric electrodes exhibited capacitances 143, 94, 87, 79, 74, 69, 65, and 51 F g −1 at current rates 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 10.0 A g −1 , respectively. The electrochemical characterization revealed that CBW is promising for ABs and SCs, and controlling the porosity type could further enhance the performance