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Evaluation of the influence of design in the mechanical properties of honeycomb cores used in composite panels
No full textInternational audienceThe aerospace, automotive, and marine industries are heavily reliant on sandwich panels with cellular material cores. Although honeycombs with hexagonal cells are the most commonly used geometries as cores, recently there have been new alternatives in the design of lightweight structures. The present work aims to evaluate the mechanical properties of metallic and polymeric honeycomb structures, with configurations recently proposed and different in-plane orientations, produced by additive and subtractive manufacturing processes. Structures with configurations such as regular hexagonal honeycomb (Hr), lotus (Lt), and hexagonal honeycomb with Plateau borders (Pt), with 0°, 45°, and 90° orientations were analyzed. To evaluate its properties, three-point bending tests were performed, both experimentally and by numerical modeling, by means of the finite element method. Honeycombs of two aluminum alloys and polylactic acid were fabricated. The structures produced in aluminum were obtained either by selective laser melting technology or by machining, while polylactic acid structures were obtained by material extrusion using fused filament fabrication. From the stress distribution analysis and the load–displacement curves, it was possible to evaluate the strength, stiffness, and absorbed energy of the structures. Failure modes were also analyzed for polylactic acid honeycombs. In general, a strong correlation was observed between numerical and experimental results. The results show that the stiffness and absorbed energy increase in the order, Hr, Pt, Lt, and with the orientation through the sequence, 45°, 90°, 0°. Thus, Lt structures with 0° orientation seem to be good alternatives to the traditional honeycombs used in sandwich composite panels for those industrial applications where low weight, high stiffness, and large energy-absorbing capacity are required
Grain size and misorientation evolution in linear friction welding of additively manufactured IN718 to forged superalloy AD730™
No full textInternational audienceSelective Laser Melted (SLM) Inconel718 (IN718) superalloy was linear friction welded (LFWed) to forged AD730™ Nickel-based superalloy. Successful joints free of micro-porosity, micro-cracking, and oxides were obtained. Microstructure variations across the weld line developed during LFW were examined using different techniques, including laser confocal microscopy, scanning electron microscopy, energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The microstructure was also evaluated, particularly in terms of Grain size and misorientation changes were determined and correlated with microhardness evolution in different regions of the weld joint. The characteristics of the microstructure on both sides of the weld joint was analyzed and related to the deformation and temperature paths imposed during the LFW process. Dynamic recrystallization (DRX) occurred on both sides of the dissimilar weld line and it was found that Discontinuous DRX (DDRX) and Continuous DRX (CDRX) took place in the WZ and in the TMAZ, respectively. In order to study the influence of the starting microstructure in the LFW experiments, LFW of a homogenized SLM IN718 sample was analyzed and compared with the non-homogenized sample. A clear change in the size and grain misorientation levels of the heat and thermomechanical affected zones were observed between the two conditions. The differences were related to a greater degree of strain induced in homogenized sample and the increasing effect of the solid solution strengthening mechanism caused by a partial dissolution of the second-phase strengthening particles in the matrix
Influence of different wet milling on the properties of an attapulgite clay, contribution of inverse gas chromatography
No full textInternational audienceAn experimental study, using size measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) and inverse gas chromatography at infinite dilution (IGC-ID) and finite concentration (IGC-FC) conditions, has been carried out to evaluate, respectively, the changes of particles size, crystalline phases, morphology and surface properties evolution of attapulgite powder after grinding in wet media.The particles size decreases significantly after grinding in ball mill in different liquid media. The SEM analysis shows that the fibers are preserved during grinding in aqueous media. With IGC-ID, after grinding using wet ball milling in hydrochloric acid, the values of γsd determined by injection of alkane probes decrease significantly because of the disappearance of the insertion sites able to retain the probes. In the same grinding conditions, with IGC-FC, the specific surface area obtained with octane probe increases significantly from 114 m2/g to 156 m2/g
Chitin and Chitosan Based Composites for Energy and Environmental Applications: A Review
No full textInternational audienceChitin and chitosan are the second most abundant natural biopolymers in the curst of the earth. These polysaccharide biopolymers have a long linear chain-like structure connected with β-d glucosidic linkage with the functionalizable surface groups. Because of the structural features, these biomaterials exhibit unique physical, chemical, mechanical and optical properties, which contributed to the tunable and outstanding properties such as low density, high porosity, renewability, natural biodegradability, and environmental friendliness, etc. Chitin was synthesized via mechanical, chemical, chemo-mechanical, and eco-friendly biological methods and the deacetylation of the synthesized chitin carried for the preparation of chitosan. With the chemical modification used for the preparation of chitosan, there occurs some minor change in characteristics; however, most of the properties were relatable due to major similarities in the microstructures. The inherent antibacterial, non-toxic, and biodegradable properties with the ease of processibility of both polymer has the potential to become a successful alternative to its synthetic counterparts for energy and environmental applications. However, the poor mechanical and thermal properties in comparison to the conventional alternatives have restricted its widespread applications. This review addresses various areas such as extraction techniques of chitin and synthesis of chitosan, discussion of the common characteristics of both polymers together such as crystallinity, thermal properties, mechanical properties, hydrophilicity, and surface charge. Moreover, this review paper also addresses the common functionalization techniques for both polymer and the use of both unmodified chitin and chitosan along with their derivatives in environmental and energy applications such as air pollution, heavy metal adsorption, dye adsorption, biosensors, EMI shielding, fuel cell, solar cell, lithium-ion batteries, and biofuels
Effet de l’épaisseur des échantillons minces sur leur comportement en traction : étude de l’influence de la taille de grain, de la surface libre et de l’état de précipitation pour un superalliage à base de nickel
No full textNational audienceLe comportement mécanique d’éprouvettes minces a été étudié sur différents variants métallurgiques d’un superalliage à base de nickel polycristallin (3 tailles de grains et 2 états de précipitation différents). Une technique d’amincissement d’éprouvettes a été développée afin de tester en traction des échantillons dont l’épaisseur est comprise entre 15 et 500 μm, soit entre 0.1 et 25 fois la taillede grains dans l’épaisseur de l’éprouvette. La transition de comportement polycristal → multicristal, identifiée dans un premier temps par un abattement de la limite d’élasticité, se produit pour des épaisseurs différentes en fonction de la taille de grains: quatre fois la taille de grains pour les microstructures fines et deux fois la taille de grains pour les microstructures grossières
Decision support for supply chain resilience in a risky environment: The DESIIR Project
No full textInternational audienceWe define the Supply Chain Risk Management (SCRM) as a process composed of four steps : Risk identification, Risk assessment, Riskmitigation, Risk control. The first step in SCRM practices concerns the identification of risks through regular screening of potential SCrisks. Risk definition consists in four steps. 1.Categorize the risks: 2.Risk screening[U+FF0C] 3.Risk monitoring[U+FF0C] 4.Risk diagnosis. Risk assessment can be identified as the evaluation of risk’s occurrence including an estimation of its impact. The system needs to make statistics on the impact of risks and the frequency of risks through data analysis. At this time, the risk has occurred, the system will issue an alarm, and the decision support system will intervene in the decision-making of the supply chain at this time. The decision-making suggestions made by the system are divided into four types: 1. Risk avoidance; 2. Loss control; 3. Risk transfer; 4. Risk retention. The decision support system will propose decision-making plans for supply chain managers around four core strategies, and predict the subsequent impact of various suggestions. Risk control is ensured through systematic processes, preparedness, risk awareness of employees, arti-culated procedures and elaborated plans. When the decision maker makes a decision based on DSS’s recommendations, the system will track the data and various indicators of the supply chain to assess whether the impact of risk has been reduced
Mettre à portée d’apprentis la méthode de résolution par éléments finis : "Alignement pédagogique, évaluation par les pairs, classe inversée, analyse d’enseignement"
No full textNational audienceCet ouvrage s’inscrit dans le cadre du colloque international Projectique sur le thème "Entreprendre et innover en formation : partage d’expériences pédagogiques". C’est sous l’impulsion du Collegium Lorraine Management Innovation de l’Université de Lorraine et d’Universiapolis d’Agadir (Maroc) que la communauté de Projectique s’est retrouvée autour d’une réflexion en lien avec l’idée d’entreprendre en formation, réflexion fédérant des questionnements, des rencontres de concepts et de théories, mais aussi des partages de bonnes pratiques, en l’occurrence en milieu universitaire. Etayés par la problématique suivante : "Comment la diversification des méthodes d’apprentissage et l’innovation en milieu pédagogique vont-elles permettre à l’étudiant de développer de nouvelles compétences ?", les chapitres dont cet ouvrage est le recueil mettent en lumières, de manière diversifiée certes et à partir de postures épistémologiques différentes, de nombreux outils permettant "d’entreprendre différemment la formation", notamment au sein de programmes universitaires, ayant pour tremplin l’approche par compétences, la pédagogie par projet, la mise en situation, etc., et aujourd’hui de plus en plus appuyés par le numériqu
Tailoring glass fiber surface for the polymerization and crystallization of anionic polyamide 6
No full textInternational audienceMonomer polymerization after the impregnation of reinforcements is a relevant option for the manufacturing of thermoplastic composites by liquid processes (infusion or RTM). In the case of polyamide 6 synthesized by this process, the system composed of monomers, catalyst and activator reacts within the fibrous environment. Therefore, fiber surface chemistry is a crucial parameter because it does not only influence the polymerization and crystallization processes, but it also controls the fiber-matrix adhesion
The control of hydroxyl density on glass particulates surface: Application to anionic polymerization of polyamide 6
No full textInternational audienceMonomer polymerization after the impregnation of reinforcements is a relevant option for the manufacturing of thermoplastic composites by liquid processes (infusion or RTM). In the case of polyamide 6 (PA6) synthesized by this process, the system is composed of the monomers, the catalyst, and the activator, which react within the fibrous environment. Therefore, controlling the chemistry of the fiber surface is crucial because it influences not only the polymerization and crystallization processes, but it also controls the fiber-matrix adhesion and the resulting mechanical properties. However, the hydroxyl groups typically present on the glass fiber surface inhibit the polymerization process. The objective of this project is to adapt and control the surface chemistry of glass particulate reinforcements in order to promote the polymerization and crystallization processes of PA6. This work was carried out with glass microbeads comparable in size to the diameter of glass fibers. First, the evolution of the hydroxyl groups surface density on the glass beads, as a function of calcination time, was monitored by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The hydroxyl groups surface density was then tuned in order to allow thesynthesis of anionic polyamide 6 (PA6), which was monitored by differential scanning calorimetry (DSC). Next, in order to further promote the polymerization and crystallization of PA6, and to improve interfacial adhesion between the PA6 and glass particulates, the grafting process of an amino-silane coupling agent at the particulates surface was investigated by TGA and FTIR. The results demonstrate that the competition between re-hydroxylation and condensation of the silane on the surface during the grafting process needs to be carefully balanced in order to maintain fast polymerization kinetics, as revealed by DSC analysis. Overall, the systematic methodology presented in this work can be adapted for various combinations of reactive resins and solid fillers, allowing for the preparation of high performance (nano)composite materials
