Letteratura scientifica selezionata sul tema "Microstructure Complexe"
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Articoli di riviste sul tema "Microstructure Complexe":
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Nolan, T. P., R. Sinclair, T. Yamashita e R. Ranjan. "Correlation of micro-structural, micro-chemical and micro-magnetic properties of longitudinal recording media using CM20FEG Lorentz TEM". Proceedings, annual meeting, Electron Microscopy Society of America 52 (1994): 892–93. http://dx.doi.org/10.1017/s042482010017219x.
Abstract (sommario):
Cobalt alloy on chromium thin film magnetic media are used in industry computer hard disk drives because of their large values of coercivity (Hc), remanent magnetization (Mr), squareness (S*), and relatively low noise. The magnetic performance depends strongly on processing conditions and the resulting nanometer scale microstructure.A complete structure-processing-properties analysis requires effective measurement of magnetic and microstructural properties. To date, most structure-properties analyses have involved correlation of bulk magnetic (hysteresis loop) properties and magnetic recording measurements with physical microstructures observed by high-resolution SEM and TEM.The nanoscale microstructural features that dramatically affect magnetic properties are difficult to observe but careful TEM analysis has been used to observe subtle, important differences in the atomic scale physical microstructure. Even these impressive capabilities are becoming insufficient for continued development of improved magnetic recording media. Microstructural design is moving into a regime where appropriate control of magnetic properties requires control of elemental composition and second phase formation as well as crystallography and morphology, at near-atomic levels.
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Müller, Martin, Marie Stiefel, Björn-Ivo Bachmann, Dominik Britz e Frank Mücklich. "Overview: Machine Learning for Segmentation and Classification of Complex Steel Microstructures". Metals 14, n. 5 (7 maggio 2024): 553. http://dx.doi.org/10.3390/met14050553.
Abstract (sommario):
The foundation of materials science and engineering is the establishment of process–microstructure–property links, which in turn form the basis for materials and process development and optimization. At the heart of this is the characterization and quantification of the material’s microstructure. To date, microstructure quantification has traditionally involved a human deciding what to measure and included labor-intensive manual evaluation. Recent advancements in artificial intelligence (AI) and machine learning (ML) offer exciting new approaches to microstructural quantification, especially classification and semantic segmentation. This promises many benefits, most notably objective, reproducible, and automated analysis, but also quantification of complex microstructures that has not been possible with prior approaches. This review provides an overview of ML applications for microstructure analysis, using complex steel microstructures as examples. Special emphasis is placed on the quantity, quality, and variance of training data, as well as where the ground truth needed for ML comes from, which is usually not sufficiently discussed in the literature. In this context, correlative microscopy plays a key role, as it enables a comprehensive and scale-bridging characterization of complex microstructures, which is necessary to provide an objective and well-founded ground truth and ultimately to implement ML-based approaches.
3
Talmon, Yeshayahu. "Cryo-TEM of amphiphilic polymer and amphiphile/polymer solutions". Proceedings, annual meeting, Electron Microscopy Society of America 51 (1 agosto 1993): 876–77. http://dx.doi.org/10.1017/s0424820100150216.
Abstract (sommario):
To achieve complete microstructural characterization of self-aggregating systems, one needs direct images in addition to quantitative information from non-imaging, e.g., scattering or Theological measurements, techniques. Cryo-TEM enables us to image fluid microstructures at better than one nanometer resolution, with minimal specimen preparation artifacts. Direct images are used to determine the “building blocks” of the fluid microstructure; these are used to build reliable physical models with which quantitative information from techniques such as small-angle x-ray or neutron scattering can be analyzed.To prepare vitrified specimens of microstructured fluids, we have developed the Controlled Environment Vitrification System (CEVS), that enables us to prepare samples under controlled temperature and humidity conditions, thus minimizing microstructural rearrangement due to volatile evaporation or temperature changes. The CEVS may be used to trigger on-the-grid processes to induce formation of new phases, or to study intermediate, transient structures during change of phase (“time-resolved cryo-TEM”). Recently we have developed a new CEVS, where temperature and humidity are controlled by continuous flow of a mixture of humidified and dry air streams.
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Yue, Tao, Shenyu Gu, Na Liu, Yuanyuan Liu, Yancong Yu, Xinye Zhang, Weixia Lan, Toshio Fukuda, Long Li e Quan Zhang. "Self-alignment of microstructures based on lateral fluidic force generated by local spatial asymmetry inside a microfluidic channel". AIP Advances 12, n. 3 (1 marzo 2022): 035335. http://dx.doi.org/10.1063/5.0086138.
Abstract (sommario):
Three-dimensional (3D) microstructures have various applications in many fields due to their unique physical properties. Manufacturing 3D microstructures with precise micron-scale features is difficult. Although the assembly of two-dimensional (2D) structures is a smart way to construct complex 3D microstructures, the way to assemble those 2D structures precisely is still immature. One key issue is that alignment errors often occur during the assembly process, affecting the architecture accuracy of the assembled 3D structures. In this paper, we propose a method to eliminate the alignment error during the self-assembly process only by lateral fluid force. Theoretical analysis has been conducted to demonstrate how alignment errors in the assembly channel are automatically corrected, during which a force perpendicular to the flow direction is generated by the channel’s local spatial asymmetry to automatically correct those alignment errors. Besides, the movement of microstructures in the channel has been numerically simulated, whose results were consistent with the theoretical analysis, and there was indeed a lateral force that causes the self-aligning of the microstructure in the channel. The effect of the microstructure’s dimensions and the channel’s size for self-alignment procedure has also been analyzed. It shows that the self-alignment of the microstructure can complete when the ratio of the diameter of microstructures to the width of the channel is greater than 85%. Besides, experiments of the self-alignment between adjacent layers of microstructures were successful, which show the presented idea using lateral fluid force is a promising way to build 3D structures with less assembly errors.
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Rodgers, Theron M., Hojun Lim e Judith A. Brown. "Three-Dimensional Additively Manufactured Microstructures and Their Mechanical Properties". JOM 72, n. 1 (30 ottobre 2019): 75–82. http://dx.doi.org/10.1007/s11837-019-03808-x.
Abstract (sommario):
Abstract Metal additive manufacturing (AM) allows for the freeform creation of complex parts. However, AM microstructures are highly sensitive to the process parameters used. Resulting microstructures vary significantly from typical metal alloys in grain morphology distributions, defect populations and crystallographic texture. AM microstructures are often anisotropic and possess three-dimensional features. These microstructural features determine the mechanical properties of AM parts. Here, we reproduce three “canonical” AM microstructures from the literature and investigate their mechanical responses. Stochastic volume elements are generated with a kinetic Monte Carlo process simulation. A crystal plasticity-finite element model is then used to simulate plastic deformation of the AM microstructures and a reference equiaxed microstructure. Results demonstrate that AM microstructures possess significant variability in strength and plastic anisotropy compared with conventional equiaxed microstructures.
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Beh, Chong You, Ee Meng Cheng, Xiao Jian Tan, Nashrul Fazli Mohd Nasir, Mohd Shukry Abdul Majid, Mohd Ridzuan Mohd Jamir, Shing Fhan Khor, Kim Yee Lee e Che Wan Sharifah Robiah Mohamad. "Complex Impedance and Modulus Analysis on Porous and Non-Porous Scaffold Composites Due to Effect of Hydroxyapatite/Starch Proportion". Polymers 15, n. 2 (8 gennaio 2023): 320. http://dx.doi.org/10.3390/polym15020320.
Abstract (sommario):
This study aims to investigate the electric responses (complex modulus and complex impedance analysis) of hydroxyapatite/starch bone scaffold as a function of hydroxyapatite/starch proportion and the microstructural features. Hence, the non-porous and porous hydroxyapatite/starch composites were fabricated with various hydroxyapatite/starch proportions (70/30, 60/40, 50/50, 40/60, 30/70, 20/80, and 10/90 wt/wt%). Microstructural analysis of the porous hydroxyapatite/starch composites was carried out by using scanning electron microscopy. It shows that the formation of hierarchical porous microstructures with high porosity is more significant at a high starch proportion. The complex modulus and complex impedance analysis were conducted to investigate the electrical conduction mechanism of the hydroxyapatite/starch composites via dielectric spectroscopy within a frequency range from 5 MHz to 12 GHz. The electrical responses of the hydroxyapatite/starch composites are highly dependent on the frequency, material proportion, and microstructures. High starch proportion and highly porous hierarchical microstructures enhance the electrical responses of the hydroxyapatite/starch composite. The material proportion and microstructure features of the hydroxyapatite/starch composites can be indirectly reflected by the simulated electrical parameters of the equivalent electrical circuit models.
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Kim, Young Ho, Jeong-Woo Sohn, Youngjae Woo, Joo-Hyun Hong, Gyu Man Kim, Bong Keun Kang e Juyoung Park. "Preparation of Microstructure Molds of Montmorillonite/Polyethylene Glycol Diacrylate and Multi-Walled Carbon Nanotube/Polyethylene Glycol Diacrylate Nanocomposites for Miniaturized Device Applications". Journal of Nanoscience and Nanotechnology 15, n. 10 (1 ottobre 2015): 7860–65. http://dx.doi.org/10.1166/jnn.2015.11224.
Abstract (sommario):
Environmentally friendly microstructure molds with montmorillonite (MMT) or multi-walled carbon nanotube (MWCNT) reinforced polyethylene glycol diacrylate (PEGDA) nanocomposites have been prepared for miniaturized device applications. The micropatterning of MMT/PEGDA and MWCNT/PEGDA with 0.5 to 2.0 wt% of MMTs and MWCNTs was achieved through a UV curing process with micro-patterned masks. Hexagonal dot arrays and complex patterns for microstructures of the nanocomposites were produced and characterized with an optical microscope; their thermal properties were studied by thermogravimetric analysis (TGA). The TGA results showed that these nanocomposites were thermally stable up to 350 °C. Polydimethylsiloxane thin replicas with different microstructures were prepared by a casting method using the microstructured nanocomposites as molds. It is considered that these microstructure molds of the nanocomposites can be used as microchip molds to fabricate nanobio-chips and medical diagnostic chip devices.
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Gallardo-Basile, Francisco-José, Yannick Naunheim, Franz Roters e Martin Diehl. "Lath Martensite Microstructure Modeling: A High-Resolution Crystal Plasticity Simulation Study". Materials 14, n. 3 (2 febbraio 2021): 691. http://dx.doi.org/10.3390/ma14030691.
Abstract (sommario):
Lath martensite is a complex hierarchical compound structure that forms during rapid cooling of carbon steels from the austenitic phase. At the smallest, i.e., ‘single crystal’ scale, individual, elongated domains, form the elemental microstructural building blocks: the name-giving laths. Several laths of nearly identical crystallographic orientation are grouped together to blocks, in which–depending on the exact material characteristics–clearly distinguishable subblocks might be observed. Several blocks with the same habit plane together form a packet of which typically three to four together finally make up the former parent austenitic grain. Here, a fully parametrized approach is presented which converts an austenitic polycrystal representation into martensitic microstructures incorporating all these details. Two-dimensional (2D) and three-dimensional (3D) Representative Volume Elements (RVEs) are generated based on prior austenite microstructure reconstructed from a 2D experimental martensitic microstructure. The RVEs are used for high-resolution crystal plasticity simulations with a fast spectral method-based solver and a phenomenological constitutive description. The comparison of the results obtained from the 2D experimental microstructure and the 2D RVEs reveals a high quantitative agreement. The stress and strain distributions and their characteristics change significantly if 3D microstructures are used. Further simulations are conducted to systematically investigate the influence of microstructural parameters, such as lath aspect ratio, lath volume, subblock thickness, orientation scatter, and prior austenitic grain shape on the global and local mechanical behavior. These microstructural features happen to change the local mechanical behavior, whereas the average stress–strain response is not significantly altered. Correlations between the microstructure and the plastic behavior are established.
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Santos, Dagoberto Brandão, Élida G. Neves e Elena V. Pereloma. "Effect of Processing Route on Mechanical Behavior of C-Mn Multiphase High Strength Cold Rolled Steel". Materials Science Forum 539-543 (marzo 2007): 4375–80. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4375.
Abstract (sommario):
The multiphase steels have complex microstructures containing polygonal ferrite, martensite, bainite, carbide and a small amount of retained austenite. This microstructure provides these steels with a high mechanical strength and good ductility. Different thermal cycles were simulated in the laboratory in order to create the microstructures with improved mechanical properties. The samples were heated to various annealing temperatures (740, 760 or 780°C), held for 300 s, and then quickly cooled to 600 or 500°C, where they were soaked for another 300 s and then submitted to the accelerated cooling process, with the rates in the range of 12-30°C/s. The microstructure was examined at the end of each processing route. The mechanical behavior evaluation was made by microhardness testing. The microstructural characterization involved optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) with electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). The use of multiple regression analysis allowed the establishment of quantitative relationship between the microstructural parameters, cooling rates and mechanical properties of the steel.
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Abdalla, Ayad Omran, Astuty Amrin, Roslina Mohammad e M. A. Azmah Hanim. "Microstructural Study of Newly Designed Ti-6Al-1Fe Alloy through Deformation". Solid State Phenomena 264 (settembre 2017): 54–57. http://dx.doi.org/10.4028/www.scientific.net/ssp.264.54.
Abstract (sommario):
Recently, iron (Fe) is introduced to substitute vanadium (V) in Ti-alloy. Therefore, new (α+β) titanium alloy, Ti-6Al-1Fe was designed through a complete replacement of V by Fe with major composition modifications of Ti-6Al-4V. This new alloy is believed could provide similar properties of Ti-6Al-4V through modification of its microstructures. Different heat treatments can lead to a diversity of microstructural permutations and combinations. Thus, it is very crucial to study in-depth understanding about the microstructure of Ti-6Al-1Fe. Results reveal that the microstructure of as-received alloy is a typical fine lamellar microstructure. The bi-modal microstructure can be obtained by hot rolling below beta-transus temperature (Tβ) followed by recrystallization treatment at 925°C. While cold rolling followed by recrystallization treatment at 925°C produce equiaxed microstructure.
Tesi sul tema "Microstructure Complexe":
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Aouak, Taïeb. "Homopolymérisation et copolymérisation des alcynes monosubstitués amorceées par les complexes de Ziegler-Natta : étude de réactions conduites en présence de catalyseurs solubles formés en associant un carboxylate de fer(III) et un alkylaluminium, caractérisation des polyalcynes". Vandoeuvre-les-Nancy, INPL, 1994. http://docnum.univ-lorraine.fr/public/INPL_T_1994_AOUAK_T.pdf.
Abstract (sommario):
L'étude comparative de l'efficacité d'une série de dérivés organoferriques aliphatiques, alicycliques et aromatiques, combinés à AlEt3, sur la polymérisation du hex-1-yne (HX), a revelé que les composés Fe(CH3CH2CO2)3, Fe(naph)3 et Fe(C6H11CO2)3, sont doués d'une haute activité catalytique (Rdt 100%, Mn=6. 10^4). Les essais conduits en présence du couple Fe(CH3CH2CO2)3AlEt3, montrent que cette combinaison est parfaitement appropriée pour polymériser les alcynes terminaux: 3-méthylpent-1-yne, 4-méthylpent-1-yne et phénylacetylène (PA). Les 3-triméthylsiloxyprop-1-yne (TMSOP) et 1-triméthylsilylpenta-1,4-diyne (TMSPD), polymérisent également sous l'action de ces complexes amorceurs (Rdt 70%, mn = 10^5). L'encombrement stérique du groupe Si(CH3)3 est suffisamment important pour protéger efficacement tout site réactif auquel il est directement lié (-O-, -C=C-) envers les agents organométalliques qui composent le système amorceur. Le processus de croissance, évalue en termes de rendement et de microstructure (cis/trans), des produits formes, est influencé par l'encombrement stérique du substituant avoisinant le carbone sp. La copolymérisation des couples PA/HX, PA/TMSPD, HX/TMSOP et PA/TMSOP montre que les alcynes examinés copolymérisent par voie Ziegler-Natta. Les rapports de réactivité indiquent que le régime d'incorporation des deux partenaires est déterminé par le seul effet terminal. Ces rapports révèlent que les trois premiers couples sont dépourvus de composition azéotrope et ont une certaine tendance à l'alternance des deux résidus alors que le quatrième présente un azéotrope à environ 98% de PA dans la charge et une propension à former des séquences homogènes. L’étude du vieillissement à l'air et à la lumière de ces polymères montre que la vitesse d'altération de leurs caractéristiques physicochimiques est une fonction décroissante de l'effet d'encombrement stérique du substituant lié au squelette macromoléculaire
2
Khal, Jeaidi Hana El. "Relations frittage - microstructure - propriétés électriques des céramiques de type LAMOX". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI069/document.
Abstract (sommario):
Le matériau La_2 Mo_1,5 W_0,5 O_9 (LMW05) est un conducteur ionique de la famille LAMOX qui a récemment connu un grand potentiel en tant qu’électrolyte solide dans des systèmes électrochimiques haute température. L’objectif de cette thèse est double : d’une part, étudier les effets de certains paramètres microstructuraux, essentiellement la porosité, sur les propriétés électriques des échantillons céramiques de LMW05 et, d’autre part, appliquer le procédé de frittage flash pour la préparation d’échantillons denses.Les échantillons poreux ont été préparés par frittage à des températures comprises entre 750 °C et 1100 °C. La spectroscopie d’impédance complexe a été systématiquement utilisée pour évaluer l’influence de la porosité sur les propriétés électriques de LMW05. La réponse électrique, observée à haute fréquence (HF) sur les diagrammes d’impédance, est très affectée par la porosité. Elle dépend de la morphologie et de la localisation des pores. Les théories du milieu effectif ont été employées pour l’interprétation des résultats obtenus. L’approximation de Bruggeman s’est révélée la plus appropriée pour décrire la réponse électrique haute fréquence pour 0 < P ≤ 22%. En comparaison avec des céramiques de type YSZ, les échantillons poreux de LMW05 présentent une faible valeur du facteur de blocage α_R. Cette dernière est, en fait, liée à la morphologie des pores qui sont de forme sphérique et de grande taille. La mise en contact de deux pastilles denses a permis de simuler le contact entre deux grains de LMW05.Le procédé de frittage flash a été testé avec succès pour la préparation des échantillons de LMW05. Une attention particulière a été portée à l’optimisation des conditions de déclenchement du flash de courant. Nous avons montré que les échantillons frittés de LMW05 présentent le même comportement électrique indépendamment du procédé de frittage employéThe La_2 Mo_1,5 W_0,5 O_9 (LMW05) material is an ionic conductor of the LAMOX family which has recently shown a great potential as a solid electrolyte in high temperature electrochemical systems. The aim of this thesis is double: firstly, to study the effects of certain microstructural parameters, essentially the porosity, on the electrical response of LMW05 ceramic samples and, on the other hand, to apply the flash sintering process for the preparation of dense samples. Porous samples were obtained by varying the sintering temperature in the range of 750 to 1100 °C. Complex impedance spectroscopy was systematically used to evaluate the effect of porosity on the electrical response of LMW05. The electrical response, observed at high frequency (HF) on the impedance diagrams, is greatly affected by the porosity. It depends on the morphology and the location of pores. Effective medium theories were used for the interpretation of obtained results. The Bruggeman approximation proved to be better suited to describe the high frequency electrical response for 0 < P ≤ 22%. Compared with YSZ-type ceramics, the porous LMW05 was found to have a low blocking factor α_R. This low value is related to the morphology of the pores which are spherical in shape and large in size. The contacting of two dense pellets allowed us to simulate the contact between two grains of LMW05.The flash sintering process has been successfully tested for the preparation of LMW05 samples. Particular attention is paid to optimizing the conditions of the flash sintering onset. We have shown that the sintered LMW05 samples exhibit the same electrical behavior independently to the employed sintering process
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Badetti, Michel. "Rhéologie des matériaux granulaires non saturés". Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1020/document.
Abstract (sommario):
Nous reportons dans ce travail le comportement mécanique, dans le régime solide et en écoulement, de matériaux granulaires liés par un liquide non saturant, qui intervient par sa viscosité et par des effets capillaires. De tels matériaux, intermédiaires entre les assemblages granulaires secs et les suspensions très concentrées, sont étudiés expérimentalement et par simulations discrètes depuis la microstructure jusqu'au comportement macroscopique. Ainsi, on adopte une démarche multi-échelle, dont l’objectif est d’établir les fondements de la compréhension des phénomènes capillaires et/ou visqueux, qui interviennent dans la formulation de lois de comportement, et d'y intégrer une caractérisation de la microstructure de ces matériaux. Nous nous intéressons notamment au modèle d'interactions capillaire et visqueuse par ponts simples, dans un cadre où l'on fait varier l'inertie, le degré de confinement, le degré de friction du matériau ainsi que la quantité de liquide introduite. Pour répondre à cet objectif, ce travail de thèse s’articule autour des trois volets suivants :- Un travail de rhéologie expérimentale macroscopique sur matériau modèle (billes de polystyrènes monodisperses, mouillées avec une huile de silicone newtonienne) qui nous permet de délimiter des régimes d'écoulement et de caractériser l'influence de l'effet cohésif. Le format expérimental adopté nous permet de cisailler les échantillons sur des temps très longs et d'atteindre des régimes d'écoulement stationnaires. Ainsi, à l'instar des matériaux secs, on retrouve des régimes quasistatiques puis inertiels à mesure que la vitesse d'écoulement augmente. On met aussi en avant une très forte influence de l'effet cohésif qui tend à augmenter drastiquement la résistance au cisaillement et à diminuer la compacité de nos échantillons.- Des expériences de microtomographie à rayons X qui permettent d'étudier la microstructure à l'état statique. On remarque notamment une bonne homogénéité des échantillons, qu'ils soient faiblement ou fortement saturés. On détecte aussi un nombre non-négligeable de morphologies capillaires complexes, ce qui, par comparaison aux résultats de rhéologie macroscopique, ne semble pas influencer les propriétés d'écoulement. Ce résultat est particulièrement intéressant puisqu’il montre la capacité du modèle d’interactions par pont simple à décrire le comportement de systèmes à priori hors de sa portée descriptive.- Des simulations numériques discrètes qui nous permettent d'élargir fortement la gamme de paramètres étudiés, notamment avec des caractéristiques du matériau comme la friction de Coulomb. L'étude micromécanique, permise par les simulations, autorise aussi l'analyse des questions d'anisotropie, de coordination et de contraintes capillaires. On met en avant l'importance des interactions capillaires à distance lors de l'utilisation d'un modèle de contraintes effectives. Les limites de ce modèle, usuellement adapté à la description du comportement en régime quasi-statique, sont aussi testées et discutées dans le régime inertiel. La bonne concordance entre résultats expérimentaux et numériques nous aura permis de valider et calibrer un modèle numérique qui, en retour, aura donc fourni une analyse viable des effets microstructurels pour la compréhension du comportement et la transition de l'échelle microscopique à l'échelle macroscopiqueWith this doctoral research, we report on the solid and liquid-like mechanical behaviors of wet granular materials, which exhibit viscous and capillary effects. Such systems, standing between dry and immersed granular materials, are studied both in experiments and discrete numerical simulations, from the microstructural aspects to the mechanical behavior. We therefore adopt a multiscale approach whose purposes are to understand the origins and roles of capillary and viscous effects in constitutive laws and to include a microstructural description within these laws. We are interested in the simple bridge model for the illustration of viscous and capillary effects in the case of quasistatic and inertial flows, where the confining forces, the Coulomb friction and the liquid quantity can vary. To answer such questions, this thesis is articulated around the 3 following topics :- A study based on macroscopic rheological experiments with a simple model material (monodisperse polystyrene beads, wetted with a Newtonian silicon oil) which enables us to distinguish the flow regimes and to characterize the influence of cohesive effects. The experimental framework allows for long time shearing experiments, where the materials can reach their steady state behavior. Alike dry systems, wet granular materials still exhibit a quasistatic and an inertial regime with increasing flow velocity. We show the noticeable influence of capillary effects which strongly increases the shear resistance and reduces the materials density.- X-ray microtomographic experiments enabling the microstructural study of static samples. We witness a good homogeneity of our samples whether slightly or strongly saturated. A non-negligible number of very complex capillary bonds were detected, which stresses, when compared with macroscopic rheological results, their lack of influence on the flow properties. This result is very noticeable as it demonstrates the ability of the simple bridge model to illustrate the behavior of materials which would not be included a priori within its reach.- Discrete numerical simulations allowing us to strongly improve the range of the parameters of the study, especially in the case of material characteristics such as Coulomb friction. The micromechanical study emerging from simulations, allows us to analyze anisotropy, coordination and capillary stresses questions. We underline the great importance of long-range capillary interactions when using an effective stress model. The limits of such model, usually adopted to describe the behavior in the quasistatic regime, are also tested and debated in the inertial regime. The good agreement between numerical and experimental results enabled us to validate and calibrate a numerical model which, in return, offered a reliable analysis of microstructural effects for the understanding of the mechanical behavior and for the transition from the microscopic to the macroscopic scale
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Lian, Weidong. "Contribution à l'homogénéisation numérique du comportement élastique de matériaux à microstructure complexe caractérisés par imagerie". Ecole centrale de Nantes, 2011. http://www.theses.fr/2011ECDN0004.
Abstract (sommario):
Les méthodes d'homogénéisation numériques sont maintenant largement utilisées. De plus les techniques d'imagerie permettent une représentation géométrique très précise de la microstructure des matériaux, qui conduit le plus souvant à des modèles éléments finis "voxels". Une autre approche a été recemment proposée pour les modèles à partir d'images, basée sur l'approche X-FEM associée à la méthode level-sets. Ces deux approches sont comparées et il est montré que la méthode X-FEM/levels sets est plus efficace et précise que l'apporche voxels. La prise en compte d'images de la microstructure met en évidence le caractère aléatoire de la microstructure, ce qui soulève la question du choix de la methode d'homogénéisation et de la taille du VER (volume élémentaire représentatif). Il est montré que l'homogénéisation avec conditions aux limites homogènes (en déformation ou contraintes) conduit à des biais sur les propriétés apparentes, liées à des effets de bords. Une approche est proposée pour s'affranchir de ces effets de bords. Une stratégie d'homogénéisation à trois échelles est enfin présentée pour les problèmes ou les échelles microscopique et macroscopique sont très différentes. Une échelle intermédiaire mésoscopique est ainsi coonsidérée, inférieure à la taille du VER. A cette échelle mésoscopique les propriétés apparentes calculées par homogénéisation sont des variables aléatoires, qui sont représentées par un développement sur le chaos polynomial identifié à parir des échantillons extraits de l'image. Des échantillons macroscopiques sont alors générés, avec une échelle de discrétisation mésoscopique, et une distribution spaciale de propriété issue de l'approche précédente. La taille du VER est alors calculéeComputational homogenization approaches are now widely used. Moreover, imaging techniques allow a highly accurate representation of material microstructure, and classically leads to voxel-based finite element models. Another computational approach for image-based modeling has been recently proposed, based on X-FEM and level set method. These two approaches are compared and it is shown that X-FEM/levelset approach is more efficient and accurate than the voxel-based FEM. Using microstructure images highlights its randomness, which raises the problem of the determination of the sizeof the RVE (reprentative volume element). It's shown that homogenization approaches with uniform strins or stresses boundary conditions lead to overcome these edge effects. At last a three scale homogenization approach is presented for problems where the macroscale is much larger than the microscale. An intermediate mescoscale is considered, with a size lower than the RVE size. At this mesoscale computed apparent properies are random variables. These are represented using polynomial chaos expensions identified from samples which are extracted from the image. Macroscopic samples are then generated, with a mesoscopic modeling scale, and a spacial distribution of apparent properties coming form the previous step. Applying again classical homogenization methods at this new scale allows the determination of RVE size
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Dischler, Jean-Michel. "La génération de textures 3D et de textures a microstructure complexe pour la synthese d'images". Université Louis Pasteur (Strasbourg) (1971-2008), 1996. http://www.theses.fr/1996STR13015.
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Déléris, Jacqueline. "Plutonisme bimodal en contexte décrochant panafricain : étude pétro-structurale du complexe de Toro (Nigeria)". Toulouse 3, 1995. http://www.theses.fr/1995TOU30212.
Abstract (sommario):
Le complexe de toro, situe dans la province nord du nigeria, est un pluton bimodal calco-alcalin faisant partie des older granites panafricains. Il est constitue d'un corps principal de granite porphyroide (75 km2), entourant un corps basique de diorite a hyperstene (25 km2). Le contact entre ces deux magmas est complexe ; roches hybrides tonalitiques temoignant de melanges complets (mixing) ou partiels (mingling), roches provenant de l'encaissant, refusion partielle du granite porphyroide en un granite equigranulaire, bordure microgenus de la diorite. La technique de l'anisotropie de la susceptibilite magnetique, fournissant l'intensite et l'orientation de la fabrique des mineraux magnetiques de la roche, a permis d'acceder a la fabrique interne des plutons, reflet de leur mise en place. Les donnees structurales mettent en evidence deux stades majeurs: (i) mise en place du granite de toro, a l'etat magmatique, le long d'un plan moyennement pente vers l'ouest et selon une direction ouest-est et, (ii) mise en place de la diorite a l'etat magmatique, accompagnee d'hybrides et d'enclaves d'encaissant, lors d'un cisaillement dextre submeridien d'echelle regionale. Enfin, un episode plus tardif de cisaillement dextre n30 echarpe la bordure nord-ouest du complexe de toro. Ainsi, le granite s'est mis en place dans une croute deja fortement structurees et ductile. Il est ensuite poinconne par la diorite qui ramonne l'encaissant et emporte du magma hybride. Les deux signatures structurales, reflet de deux cinematiques differentes mais rapprochees dans le temps, sont reunies dans un meme modele, qui combine decrochement et transpression ou transtension, expression de la tectonique cisaillante nord-sud dextre caracteristique des temps fini-panafricains
7
Karam, Marie-Céleste. "Réhydratation des protéines laitières dans un milieu complexe : influence de l'état d'hydratation sur les propriétés texturales des gels acides". Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0132/document.
Abstract (sommario):
L'objectif de la thèse a été d'élucider le processus de réhydratation des caséines micellaires et des protéines solubles dans un milieu complexe et opaque : le lait. L'influence de l'état d'hydratation de ces ingrédients laitiers en fonction du temps (5, 120, 180, 240, 300, 480, 900 et 1440 min de réhydratation) sur les propriétés rhéologiques, texturales, physiques ainsi que la microstructure des gels laitiers acides a également été étudiée. Il en résulte que le processus de réhydratation des caséines micellaires diffère de celui des protéines solubles, et est extrêmement long avec trois étapes : une étape de mouillage des particules, suivie d'une étape de gonflement caractérisée par une augmentation de la taille des particules et enfin une étape de dispersion marquée par la diminution de la taille des particules. La réhydratation des protéines solubles est caractérisée par une grande rapidité, avec deux phases : le mouillage et la phase de dispersion (superposée). D'autre part, l'allongement de la durée de réhydratation des caséines micellaires est associé à une augmentation du point de gélification ainsi qu'à une nette amélioration des propriétés physiques, texturales et rhéologiques des gels : augmentation de leur fermeté et de leur force, diminution de la synérèse et de la formation de grumeaux. La durée de réhydratation des protéines solubles n'a pas d'influence sur ces paramètres. En revanche, leur dénaturation (par chauffage à sec) est associée à une dégradation des propriétés texturales des gels acides. Finalement, il s'avère que les gels acides formulés à partir des protéines solubles sont de meilleure qualité texturale (à l'exception de la formation de grumeaux) que ceux préparés à partir des caséines micellairesThe main objectives of this work were to elucidate the rehydration mechanism of the two major milk proteins (micellar casein and whey protein) into a complex and opaque medium such as milk and to assess the influence of hydration state (defined as a function of rehydration length after 5,120,180,240,300, 480, 900 and 1440 minutes of rehydration) on the rheological, textural, physical properties and microstructure of the obtained acid milk gels. Whereas, micellar casein presented a long rehydration process into milk characterized by three stages: a wetting, swelling and dispersion phase, whey protein displayed a quick rehydration process characterized by an overlapping of wetting and dispersion phase. Furthermore, an extended rehydration time of micellar casein powder into the milk base was associated with a postponed onset of gelation and enhanced physical, textural as well as rheological properties of the obtained acid milk gels characterized by increases in gel firmness, strength, and decreases in syneresis susceptibility and grains formation. In contrast, acid milk gels prepared with whey protein powder exhibited comparable overall textural properties regardless the different rehydration times. Nevertheless, denaturation of whey protein powder (by dry heating) was associated with a deterioration of the textural properties of the acid milk gels. Finally, acid gels prepared with whey proteins displayed better overall textural quality than those prepared with micellar casein (except for grains formation)
8
Bibalou, Pascal Blaise. "Copolymérisation du 2,5 furannédione 3 méthyle et de l'acétate de vinyle influence d'un complexe entre comonomères sur la microstructure des copolymères". Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37596030f.
9
Du, Kou. "Modélisation micromécanique de géomatériaux en prenant en compte des anisotropies microstructurale et matricielle". Electronic Thesis or Diss., Université de Lorraine, 2021. http://docnum.univ-lorraine.fr/public/DDOC_T_2021_0254_DU.pdf.
Abstract (sommario):
Les propriétés mécaniques des géomatériaux hétérogènes sont évaluées en prenant simultanément en compte l'anisotropie microstructurale ainsi que celle du matériau matriciel. A cet effet, l'anisotropie de la microstructure est représentée par la complexité de forme poreuse et/ou d'inclusion qui est considérée dans le présent travail comme concave ou convexe en portant nos attentions particulières aux pores supersphériques et supersphéroïdaux axisymétriques. Les tenseurs de concentration et de contribution sont calculés numériquement à l'aide de la méthode des élément finis (FEM), qui est ensuite utilisés au niveau de la modélisation semi-analytique pour l'objectif d'évaluer des propriétés effectives associées, telles que des réponses effectives élastiques et celles de conductivité. Plus précisément, afin de résoudre le 2ème problème d'Eshelby (Eshelby (1961)) dans le cas d'inhomogénéités 3D et non ellipsoïdales, nous utilisons conditions aux limites adaptées récemment développées par Adessina et al. (2017) basé sur une solution en champ lointain (Sevostianov and Kachanov (2011)) pour intégrer l'anisotropie matricielle et la correction du biais induit par le caractère borné du domaine du maillage, ce qui permet d'accélérer la convergence du calcul sans sacrifier sa précision. En adoptant la technique d'homogénéisation numérique, les tenseurs de contribution compliance/résistivité sont calculés pour différentes formes de pores (attention particulière des pores supersphéroïdaux et supersphériques) noyés dans une matrice isotrope transverse. La méthode numérique proposée s'avère efficace et précise après un grand nombre d'estimations et leurs validations. Dans certains cas particuliers, ces validations s'effectuent avec des comparaisons entre les résultats analytiques et numériques disponibles dans littérature. En prenant en compte les résultats numériques obtenus pour des microstructures tridimensionnelles (3D) considérées, les tenseurs de contribution dans les deux cas d'inclusions/pores concaves indiqués ci-dessus, supersphère et supersphéroïde axisymétrique, sont développées dans les contextes des problèmes élastiques et thermiques. Notons ici que la forme d'inclusion/pore sphérique (i.e. paramètre de concavité p=1) ainsi que celle de fissure circulaire (i.e. rapport d'aspect γ → 0), qui peuvent être considérés comme deux cas particuliers, sont également étudiés. Cela permet d'évaluer et de valider la méthode proposée dans le présent travail. De plus, dans le cadre de l'homogénéisation, une application aux géomatériaux poreux à matrice isotrope transverse, tels que les roches argileuses, est présentée pour illustrer l'impact du paramètre de concavité et celui de l'anisotropie de la matrice sur les propriétés globales à travers plusieurs schémas d'homogénéisation micromécanique, tels que l'approche basée sur l'approximation de non-interaction (i.e. NIA: Non-Interaction Approximation), schéma de Mori-Tanaka-Benveniste et celui de Maxwell. Les propriétés effectives des composites à pores réguliers sont également estimées à l'aide de l'approche dite champ complet par simulations numériques, puis comparées à la modélisation micromécanique. L'effet de microstructure complexes est étudié en considérant des Volumes Elémentaires Représentatifs (VERs) périodiques contenant des arrangements aléatoires des pores noyés dans des matrices isotropes transversesThe mechanical properties of heterogeneous geomaterials are evaluated by simultaneously taking into account the microstructural anisotropy as well as the one of matrix. To this end, the microstructural anisotropy is represented by the complexity of porous shape which is considered in the present work as concave or convex by particular attention to the superspherical and the axisymmetrical superspheroidal pores. The concentration and contribution tensors are numerically computed using Finite Element Method (FEM), which are next approximated by analytical expressions for the case of the concavity parameter being p<1, to evaluate the associated effective properties, such as effective elastic and thermal responses. Specifically, to solve the 2nd Eshelby problem (Eshelby (1961)) in the case of 3D non-ellipsoidal inhomogeneities, we make use of a recently developed adapted boundary condition (Adessina et al. (2017)) based on far-field solution (Sevostianov and Kachanov (2011)) to incorporate the matrix anisotropy and to correct the bias induced by the bounded character of the mesh domain, which allows to accelerate the computation convergence without sacrificing its accuracy. Simultaneously by complying with the numerical homogenization technique, the compliance/resistivity contribution tensors are computed for different forms of pores (particular attention of superspheroidal and superspherical ones) embedded in a transversely isotropic matrix. The proposed numerical method is shown to be efficient and accurate after several appropriate assessments and validation by comparing its predictions, in some particular cases, with analytical results and some available numerical ones. On the basis of these "3D" Finite Element Modeling, approximate relations of the property contribution tensors in the two aforementioned reference concave cases, supersphere and axisymmetric superspheroid, are developed for both elastic and thermal problems. Note here that the spherical pore (i.e. concavity parameter p=1) and circular crack (i.e. aspect ratio γ → 0), which can be considered as two particular cases, are also numerically studied. This allows to assess and validate the proposed method in the present work. Moreover, in the frame of homogenization, application to the typical porous geomaterials with transversely isotropic matrix such as clay rocks is presented to illustrate the impact of the concavity parameter and the matrix anisotropy on overall properties through several micromechanical homogenization schemes such as non-interaction approximation, Mori-Tanaka-Benveniste scheme and Maxwell scheme. The methodology of evaluation of the elastic and thermal properties of heterogeneous material aforementioned is proposed based on micromechanical homogenization via multiscale modeling. The overall properties of composites with regular pores are also predicted using direct finite element approaches and then compared against micromechanical modeling. The effect of microstructure is analyzed by considering periodic RVEs containing random arrangements of pores formed by transversely isotropic phases
10
Lucas, Iris. "Dynamique et contrôle d'un marché financier avec une approche système multi-agents". Thesis, Normandie, 2018. http://www.theses.fr/2018NORMLH39/document.
Abstract (sommario):
Cette thèse propose une réflexion autour de l'étude des marchés financiers sous le prisme des systèmes complexes.Tout d'abord une description mathématique est proposée pour représenter le processus de prises de décision des agents dès lors où celui-ci bien que représentant les intérêts individuels d'un agent, est également influencé par l'émergence d'un comportement collectif. La méthode est particulièrement applicable lorsque le système étudié est caractérisé par une dynamique non-linéaire. Une application du modèle est proposée au travers de l'implémentation d'un marché artificiel boursier avec une approche système multi-agents. Dans cette application la dynamique du marché est décrite à la fois aux niveaux microscopiques (comportement des agents) et macroscopique (formation du prix). Le processus de décision des agents est défini à partir d'un ensemble de règles comportementales reposant sur des principes de logique floue. La dynamique de la formation du prix repose sur une description déterministe à partir des règles d'appariement d'un carnet d'ordres central tel que sur NYSE-Euronext-Paris. Il est montré que le marché artificiel boursier tel qu'implémenté est capable de répliquer plusieurs faits stylisés des marchés financiers : queue de distribution des rendements plus épaisse que celle d'une loi normale et existence de grappes de volatilité (ou volatility clustering).Par la suite, à partir de simulations numériques il est proposé d'étudier trois grandes propriétés du système : sa capacité d'auto-organisation, de résilience et sa robustesse. Dans un premier temps une méthode est introduite pour qualifier le niveau d'auto-organisation du marché. Nous verrons que la capacité d'auto-organisation du système est maximisée quand les comportements des agents sont diversifiés. Ensuite, il est proposé d'étudier la réponse du système quand celui-ci est stressé via la simulation de chocs de marché. Dans les deux analyses, afin de mettre en évidence comment la dynamique globale du système émerge à partir des interactions et des comportements des agents des résultats numériques sont systématiquement apportés puis discutés.Nos résultats montrent notamment qu'un comportement collectif grégaire apparait à la suite d'un choc, et, entraîne une incapacité temporaire du système à s'auto-organiser. Finalement, au travers des simulations numériques il peut être également remarqué que le marché artificiel boursier implémenté est plus sensible à de faibles répétitions répétées qu'à un choc plus important mais uniqueThis thesis suggests reflection in studying financial markets through complex systems prism.First, an original mathematic description for describing agents' decision-making process in case of problems affecting by both individual and collective behavior is introduced. The proposed method is particularly applicable when studied system is characterized by non-linear, path dependent and self-organizing interactions. An application to financial markets is proposed by designing a multi¬agent system based on the proposed formalization.In this application, we propose to implement a computational agent-based financial market in which the system is described in both a microscopie and macroscopic levels are proposed. The agents' decision-making process is based on fuzzy logic rules and the price dynamic is purely deten-ninistic according to the basis matching rules of a central order book as in NYSE-Euronext-Paris. We show that, while putting most parameters under evolutionary control, the computational agent- based system is able to replicate several stylized facts of financial time series (distributions of stocks returns showing a heavy tau l with positive excess kurtosis and volatility clustering phenomenon).Thereafter, with numerical simulations we propose to study three system's properties: self-organization, resilience and robustness. First a method is introduced to quantify the degree of selforganization which ernerges in the system and shows that the capacity of self-organization is maximized when the agents' behaviors are heterogeneous. Secondly, we propose to study the system's response when market shock is simulated. in both cases, numerical results are presentedI and analyzed, showing how the global market behavior emerges from specific individual behavior interactions.Our results notably show that the emergence of collective herding behavior when market shock occurs leads to a temporary disruption on the system self-organization. Finaily, numerical simulations highlight that our artificial financial market can be able to absorb strong mono-shock but be lead to the rupture by low but repeated perturbations
Libri sul tema "Microstructure Complexe":
1
R, Stevens, e Taylor Derek 1939-, a cura di. Complex microstructures. Stoke-on-Trent: Institute of Ceramics, 1989.
2
R, Stevens, Taylor D e British Ceramic Society, a cura di. Complex microstructures. Shelton, U.K: Institute of Ceramics, 1989.
3
Botterill, Sarah Lindsay. The electroforming of complex structures and microstructures. Birmingham: University of Birmingham, 1997.
4
A, Bednarcyk Brett, e United States. National Aeronautics and Space Administration., a cura di. An efficient implementation of the GMC micromechanics model for multi-phased materials with complex microstructures. [Washington, DC: National Aeronautics and Space Administration, 1997.
5
A, Bednarcyk Brett, e United States. National Aeronautics and Space Administration., a cura di. An efficient implementation of the GMC micromechanics model for multi-phased materials with complex microstructures. [Washington, DC: National Aeronautics and Space Administration, 1997.
6
Gordeeva, N. D. Microstructural analysis of the execution complex motor actions: Methods and results. New Delhi: Oxonian Press, 1989.
7
G, Capriz, e Mariano Paolo Maria 1966-, a cura di. Material substructures in complex bodies: From atomic level to continuum. Amsterdam: Elsevier, 2007.
8
Gordeeva, N. D. Microstructural analysis of the execution of complex motor actions: Methods and results. New Delhi: Published for the National Library of Medicine by Amerind Pub. Co. ; Springfield, Va. : Available from the U.S. Dept. of Commerce, National Technical Information Service, 1989.
9
Evans, Robert. Art, science and informatics: Visualisation of large, complex data sets in high-speed measurement of the microstructure of wood. Vancouver, B.C: University of British Columbia, 2002.
10
Evans, Robert. Art, science and informatics: Visualisation of large, complex data sets in high-speed measurement of the microstructure of wood. Vancouver, B.C: University of British Columbia, 2002.
Capitoli di libri sul tema "Microstructure Complexe":
1
Lewis, Jennifer A. "Colloidal Stability in Complex Fluids". In Ceramic Microstructures, 495–501. Boston, MA: Springer US, 1998. http://dx.doi.org/10.1007/978-1-4615-5393-9_48.
2
Tsimpli, Ianthi Maria, Lina Mukhopadhyay, Anusha Balasubramanian e Jeanine Treffers-Daller. "Chapter 4. Microstructural properties in the narrative retellings of young English learners in EMI schools in India". In Studies in Bilingualism, 68–122. Amsterdam: John Benjamins Publishing Company, 2024. http://dx.doi.org/10.1075/sibil.66.04tsi.
Abstract (sommario):
The present study investigates narrative microstructure in the English oral retellings of primary school children from disadvantaged backgrounds in India. For these children, the combination of rich linguistic diversity and English as the medium of instruction is a challenge since exposure to English is almost exclusively in the school context. Measures of microstructure include syntactic complexity and finiteness marking as well-known indices of English language ability. Microstructural properties are examined in relation to literacy performance in order to identify possible links between the two modalities. Participants’ language background was included to investigate a possible (dis)advantage associated with minority language speakers exposed to English as the medium of instruction. Our findings suggest that finiteness errors and number of function words are associated with performance on reading comprehension. English input in the classroom selectively predicts performance on complex syntax but not other aspects of microstructure measures. Children speaking minority languages at home are not disadvantaged in their English performance compared to children speaking the majority language (Telugu). Finally, error analysis suggests similarities between types of errors found in other studies of child L2 English. This study sheds light on English L2 narrative skills in a multilingual and underprivileged context with learners exposed to low levels of English language input.
3
Wu, Meng-jen John. "Complete Waveguide Structures". In Integrated Optics, Microstructures, and Sensors, 117–41. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-2273-7_5.
4
Vega, Clara, e Christian S. Miller. "Market MicrostructureMarket microstructure". In Complex Systems in Finance and Econometrics, 567–79. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-7701-4_32.
5
Osler, Carol. "Market Microstructure, Foreign Exchange". In Complex Systems in Finance and Econometrics, 580–614. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-7701-4_33.
6
White, Lee F., James R. Darling, Desmond E. Moser, David A. Reinhard, Joseph Dunlop, David J. Larson, Daniel Lawrence e Isabelle Martin. "Complex Nanostructures in Shocked, Annealed, and Metamorphosed Baddeleyite Defined by Atom Probe Tomography". In Microstructural Geochronology, 351–67. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2017. http://dx.doi.org/10.1002/9781119227250.ch17.
7
Holzer, Lorenz, Philip Marmet, Mathias Fingerle, Andreas Wiegmann, Matthias Neumann e Volker Schmidt. "Towards a Quantitative Understanding of Microstructure-Property Relationships". In Tortuosity and Microstructure Effects in Porous Media, 161–84. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-30477-4_5.
Abstract (sommario):
Abstract100 years ago, the concept of tortuosity was introduced by Kozeny in order to express the limiting influence of the microstructure on porous media flow. It was also recognized that transport is hindered by other microstructure features such as pore volume fraction, narrow bottlenecks, and viscous drag at the pore surface. The ground-breaking work of Kozeny and Carman makes it possible to predict the macroscopic flow properties (i.e., permeability) based on the knowledge of the relevant microstructure characteristics. However, Kozeny and Carman did not have access to tomography and 3D image analysis techniques, as it is the case nowadays. So, their descriptions were developed by considering simplified models of porous media such as parallel tubes and sphere packings. This simplified setting clearly limits the prediction power of the Carman-Kozeny equations, especially for materials with complex microstructures. Since the ground-breaking work of Kozeny and Carman many attempts were undertaken to improve the prediction power of quantitative expressions that describe the relationship between microstructure characteristics (i.e., tortuosity τ, constrictivity β, porosity ε, hydraulic radius rh) and effective transport properties (i.e., conductivity σeff, diffusivity Deff, permeability к,). Due to the ongoing progress in tomography, 3D image-processing, stochastic geometry and numerical simulation, new possibilities arise for better descriptions of the relevant microstructure characteristics, which also leads to mathematical expressions with higher prediction power. In this chapter, the 100-years evolution of quantitative expressions describing the micro–macro relationships in porous media is carefully reviewed,—first, for the case of conduction and diffusion,—and second, for flow and permeability.The following expressions are the once with the highest prediction power:$$\sigma_{eff} \left( {or D_{eff} } \right) = \varepsilon^{1.15} \beta^{0.37} /\tau_{{dir_{geodesic} }}^{4.39} ,$$ σ eff o r D eff = ε 1.15 β 0.37 / τ d i r geodesic 4.39 , for conduction and diffusion, and$$\kappa_{I} = 0.54\left( {\frac{\varepsilon }{{S_{V} }}} \right)^{2} \frac{{\varepsilon^{3.56} \beta^{0.78} }}{{\tau_{dir\_geodesic}^{1.67} }},$$ κ I = 0.54 ε S V 2 ε 3.56 β 0.78 τ d i r _ g e o d e s i c 1.67 , $$\kappa_{II} = \frac{{\left( {0.94r_{min} + 0.06r_{max} } \right)^{2} }}{8} \frac{{\varepsilon^{2.14} }}{{\tau_{dir\_geodesic}^{2.44} }},$$ κ II = 0.94 r min + 0.06 r max 2 8 ε 2.14 τ d i r _ g e o d e s i c 2.44 , both, for permeability in porous media.
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Porubov, Alexey V. "Essentially Nonlinear Strain Waves in Solids with Complex Internal Structure". In Mechanics of Microstructured Solids, 119–26. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00911-2_13.
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Schmauder, Siegfried, e Leon Mishnaevsky. "Complex, Graded and Interpenetrating Microstructures". In Micromechanics and Nanosimulation of Metals and Composites, 213–310. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-540-78678-8_4.
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Faran, Eilon, e Doron Shilo. "Microstructural Effects During Crackling Noise Phenomena". In Understanding Complex Systems, 167–98. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-45612-6_9.
Atti di convegni sul tema "Microstructure Complexe":
1
Rangarajan, Aswath, e Veera Sundararaghavan. "Design of Microstructure Response Using a Complex Step Plasticity Approach". In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-39011.
Abstract (sommario):
Microstructure-sensitive design is performed using a newly developed Multiscale Complex Step Method. Algorithmic implementation of the complex-step method is based on conventional multiscale Taylor or FE2 direct model, with the difference being that the microstructural deformation gradient is modeled as a complex number with a small imaginary component. We introduce methods to calculate derivatives of microstructural fields with respect to loading parameters. The sensitivities are used to identify optimal microstructures with desired elastic and plastic properties.
2
Xu, Hongyi, Ruoqian Liu, Alok Choudhary e Wei Chen. "A Machine Learning-Based Design Representation Method for Designing Heterogeneous Microstructures". In ASME 2014 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/detc2014-34570.
Abstract (sommario):
In designing microstructural materials systems, one of the key research questions is how to represent the microstructural design space quantitatively using a descriptor set that is sufficient yet small enough to be tractable. Existing approaches describe complex microstructures either using a small set of descriptors that lack sufficient level of details, or using generic high order microstructure functions of infinite dimensionality without explicit physical meanings. We propose a new machine learning-based method for identifying the key microstructure descriptors from vast candidates as potential microstructural design variables. With a large number of candidate microstructure descriptors collected from literature covering a wide range of microstructural material systems, a 4-step machine learning-based method is developed to eliminate redundant microstructure descriptors via image analyses, to identify key microstructure descriptors based on structure-property data, and to determine the microstructure design variables. The training criteria of the supervised learning process include both microstructure correlation functions and material properties. The proposed methodology effectively reduces the infinite dimension of the microstructure design space to a small set of descriptors without a significant information loss. The benefits are demonstrated by an example of polymer nanocomposites optimization. We compare designs using key microstructure descriptors versus using empirically-chosen microstructure descriptors to validate the proposed method.
3
Li, Xiaolin, Zijiang Yang, L. Catherine Brinson, Alok Choudhary, Ankit Agrawal e Wei Chen. "A Deep Adversarial Learning Methodology for Designing Microstructural Material Systems". In ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/detc2018-85633.
Abstract (sommario):
In Computational Materials Design (CMD), it is well recognized that identifying key microstructure characteristics is crucial for determining material design variables. However, existing microstructure characterization and reconstruction (MCR) techniques have limitations to be applied for materials design. Some MCR approaches are not applicable for material microstructural design because no parameters are available to serve as design variables, while others introduce significant information loss in either microstructure representation and/or dimensionality reduction. In this work, we present a deep adversarial learning methodology that overcomes the limitations of existing MCR techniques. In the proposed methodology, generative adversarial networks (GAN) are trained to learn the mapping between latent variables and microstructures. Thereafter, the low-dimensional latent variables serve as design variables, and a Bayesian optimization framework is applied to obtain microstructures with desired material property. Due to the special design of the network architecture, the proposed methodology is able to identify the latent (design) variables with desired dimensionality, as well as capturing complex material microstructural characteristics. The validity of the proposed methodology is tested numerically on a synthetic microstructure dataset and its effectiveness for materials design is evaluated through a case study of optimizing optical performance for energy absorption. Additional features, such as scalability and transferability, are also demonstrated in this work. In essence, the proposed methodology provides an end-to-end solution for microstructural design, in which GAN reduces information loss and preserves more microstructural characteristics, and the GP-Hedge optimization improves the efficiency of design exploration.
4
Wu, Yulun, e Yumeng Li. "How to Encode Microstructure in Machine Learning: A Comparison Study". In ASME 2023 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/detc2023-116704.
Abstract (sommario):
Abstract Accurately predicting the response of materials under different loading conditions is crucial for designing and developing new materials with desired properties. However, this process can be computationally expensive and challenging, especially for heterogeneous materials with complex microstructures. Recently, machine learning has been widely used to address the challenge for developing predictive models for various material systems with reduced reliance on extensive experimental testings and repetitive expensive physics simulations. The microstructure of a material plays a critical role in determining its properties, making it a key factor that needs to be accounted for in predictive modeling. Heterogeneous materials, specifically, often have complex microstructures with numerous features like pores, inclusions, and grain boundaries, which need to be accurately captured but is hard to be quantified for developing machine learning based predictive models. Therefore, accurate encoding of microstructural features is essential for making reliable predictions. Nevertheless, how to effectively and efficiently capture the complex microstructural features in developing machine learning based predictive models largely remains an open question for researchers in the field of materials science. In this paper, we present a comparison study of different encoding methods for microstructures in machine learning models. Specifically, we investigate pre-defined encoding methods and automatic encoding methods for a synthetic heterogeneous material system. the performance of each machine learning model is evaluated by predicting material responses such as strain energy. Our results show that convolutional neural networks (CNNs) have the ability to auto-encode the microstructure information of material and make promising prediction, especially when good pre-defined descriptors are not available. Overall, this study provides valuable insights into the performance of different encoding methods for microstructures in machine learning models, and can inform the development of more accurate and efficient models for materials science applications.
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Henrich, Manuel, Michael Dölz e Sebastian Münstermann. "Development of a Numerical Framework for Microstructure Sensitive Fatigue Life Investigations". In ASME 2023 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/pvp2023-106419.
Abstract (sommario):
Abstract Modern steel grades with increasingly complex microstructure morphologies demand advanced modeling methods. Especially in terms of geometrical microstructure modeling these steels tend to be very challenging. In this study a framework is presented that tackles the modelling of modern microstructures using a new generator for representative volume elements called DRAGen (Discrete Rve Automation and Generation), and a strategy for the numerical investigation of the influence of the surface roughness and residual stresses on the fatigue life and endurance is proposed. The proposed framework consists mainly of three parts: microstructural characterization, generation of statistical representative volume elements and the investigation of micromechanical behavior under extrinsic loading conditions. The microstructural characterization is supported by neural networks while the generation algorithms of the representative volume elements uses the information generated by those neural networks. The mechanical behavior of these representative volume elements is simulated with Abaqus. Due to the usage of a neural network DRAGen can produce very realistic microstructure models following the statistical behavior of the real world material with a high level of detail. It is also possible to introduce features such as surface roughness and residual stresses into the simulations of DRAGen’s representative volume elements. Therefore, the fatigue life estimations performed with these representative volume elements enable a better understanding of the influences that single microstructural features have on fatigue life. This understanding will help to generate a good basis for numerical optimization of the structural integrity of safety-related components.
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Li, Jizhan, Zhichao Fan, Tao Chen e Yu Zhou. "Mechanism of High Temperature Stability on Microstructures of 25Cr35NiNb Alloy Prepared by Laser Additive Manufacturing". In ASME 2022 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/pvp2022-84663.
Abstract (sommario):
Abstract The performance of static casting 25Cr35NiNb alloy pipe fittings with complex shapes for ethylene cracking furnace is insufficient, which affects the safe operation of equipment, and becomes an urgent problem to be solved in this field. Laser additive manufacturing (LAM) technique is suitable for the fabrication of complex components with high performance. 25Cr35NiNb alloy prepared by LAM is different from that prepared by static casting or centrifugal casting due to the solidification with the cooling rate of 102∼105 K/s in a tiny molten pool. In order to fabricate complex pipe fittings by LAM, the performance of 25Cr35NiNb alloy prepared by LAM needs to be clarified and the mechanism also needs to be revealed. This paper focuses on the mechanism of high temperature stability on microstructures of 25Cr35NiNb alloy prepared by LAM. Firstly, two kinds of 25Cr35NiNb alloy deposits were prepared by LAM with different processing parameters. Secondly, heat treatments were executed in the temperature range from 850°C to 1275°C for 25Cr35NiNb alloy deposits. Then, the microstructures of 25Cr35NiNb alloy were observed by optical microscope (OM) and scanning electron microscopy (SEM). It is found that the finer the microstructures of the original deposits was, the better the high temperature stability of microstructures was. The results of electron probe microanalysis (EPMA) show that the distribution of Nb and Ti elements in the original deposits affects the high temperature stability of microstructures. The finer microstructure has the more uniform distribution of Nb and Ti elements, which improves the high temperature microstructural stability.
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Bonacuse, Peter J., Subodh Mital e Robert Goldberg. "Characterization of the As Manufactured Variability in a CVI SiC/SiC Woven Composite". In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45890.
Abstract (sommario):
The microstructure of a 2D woven ceramic matrix composite displays significant variability and irregularity. For example, a chemical vapor infiltrated (CVI) SiC/SiC composite exhibits significant amount of porosity arranged in irregular patterns. Furthermore, the fiber tows within a ply frequently have irregular shape and spacing, and the stacked plies are often misaligned and nested within each other. The goal of an ongoing project at NASA Glenn is to investigate the effects of the complex microstructure and its variability on the properties and the durability of the material. One key requirement for this effort is the development of methods to characterize the distribution in as-fabricated ceramic matrix composite (CMC) microstructures with the objective of correlating microstructural distribution parameters with mechanical performance. An initial task in this effort was to perform quantitative image analysis of polished cross sections of CVI SiC/SiC composite specimens. This analysis provided sample distributions of various microstructural composite features, including: inter-tow pore sizes and shapes, transverse sectioned tow sizes and shapes, and within ply tow spacing. This information can then be used to quantify the effect of extreme values of these features on the local stress state with the goal of determining the likelihood of matrix cracking at a given external load.
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Jiang, Quanxin, V. M. Bertolo, V. A. Popovich e Carey L. Walters. "Recent Developments and Challenges of Cleavage Fracture Modelling in Steels: Aspects on Microstructural Mechanics and Local Approach Methods". In ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-95464.
Abstract (sommario):
Abstract Offshore activity in low-temperature areas requires the use of analysis methods that are capable of reliably predicting cleavage (brittle) fracture of ferritic steels in order to guarantee the structural integrity during service. Cleavage fracture is controlled by physical events at different size scales and is influenced by the multiple microstructural parameters of the material. The prediction of fracture toughness of steels based on the microstructure has received great attention, and relevant techniques have been continuously developed. This paper is aimed at reviewing the recent development of cleavage fracture modelling in steels and identifying the existing challenges to inspire further research. The paper contains three parts aimed at explaining how methods are developed and utilized to predict fracture toughness of steel from its microstructures. (1) The complex multiparametric nature of the microstructures of ferritic steels and its influence on cleavage fracture is introduced. (2) A review is given on the main perspectives and models in micromechanisms of cleavage fracture in steels. (3) Discussion is contributed to the link between micromechanisms and the local approach in cleavage fracture modelling. As a result, the paper gives a state of the art on microstructural mechanics and local approach methods of cleavage fracture modelling in structural steels.
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Stalheim, Douglas, Andrew Slifka, Pello Uranga, Dong-Hoon Kang e Enrico Lucon. "Cross-Sectional Grain Size Homogeneity Effect on Structural Steel Fatigue Performance in Air and Hydrogen Environments". In 2020 13th International Pipeline Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ipc2020-9404.
Abstract (sommario):
Abstract Structural steel mechanical properties of strength and ductility for a given microstructure are predominately driven by the average ferrite grain/packet size and by the through-thickness homogeneity of the ferrite grain/packet size in the final product. Fatigue performance, a ductility property, in air for applications of wind towers, bridges or high-rise buildings along within environments of high-pressure gaseous hydrogen for various pipeline systems is critical to the end-use design. Fracture and fatigue testing of a commercially produced low carbon 20 mm thick API X60 Sour Service steel had been completed which showed good and stable performance when compared to other commercially produced pipeline and structural steel microstructures. This commercially produced API steel was reported as “Alloy D” in prior published work. The microstructure was predominately polygonal ferrite with industrial quality of steel cleanliness, minimum of microstructural banding and a small but relatively homogenous through-thickness grain size required for a successful API X60 Sour Service specification/application. Based on the initial fatigue performance reported for the “Alloy D” through-thickness microstructure a more comprehensive study on the effect of the through-thickness grain size/homogeneity on fatigue was initiated. To isolate and study this effect of the, laboratory developed samples of a low carbon API X60 Sour Service steel with the same alloy design as “Alloy D”, which is characterized by a predominately single-phase polygonal ferrite microstructure with excellent cleanliness and no microstructural banding. Two sets of steels were made with the only difference being variations in average through-thickness and homogeneity of the final ferrite grain size.
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Sahoo, Seshadev, e Kevin Chou. "Review on Phase-Field Modeling of Microstructure Evolutions: Application to Electron Beam Additive Manufacturing". In ASME 2014 International Manufacturing Science and Engineering Conference collocated with the JSME 2014 International Conference on Materials and Processing and the 42nd North American Manufacturing Research Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/msec2014-3901.
Abstract (sommario):
Powder-bed electron beam additive manufacturing (EBAM) is a relatively new technology to produce metallic parts in a layer by layer fashion by melting and fusing metallic powders. EBAM is a rapid solidification process and the properties of the parts depend on the solidification behavior as well as the microstructure of the build material. Thus, the prediction of part microstructures during the process may be an important factor for process optimization. Nowadays, the increase in computational power allows for direct simulations of microstructures during materials processing for specific manufacturing conditions. Among different methods, phase-field modeling (PFM) has recently emerged as a powerful computational technique for simulating microstructure evolutions at the mesoscale during a rapid solidification process. PFM describes microstructures using a set of conserved and non-conserved field variables and the evolution of the field variables are governed by Cahn-Hilliard and Allen-Cahn equations. By using the thermodynamics and kinetic parameters as input parameters in the model, PFM is able to simulate the evolution of complex microstructures during materials processing. The objective of this study is to achieve a thorough review of PFM techniques used in various processes, attempted for an application to microstructure evolutions during EBAM. The concept of diffuse interfaces, phase field variables, thermodynamic driving forces for microstructure evolutions and the kinetic phase-field equations are described in this paper.
Rapporti di organizzazioni sul tema "Microstructure Complexe":
1
Daniel. L52353 Materials Selection, Welding and Weld Monitoring - Optimized Welding Solutions for X100 Line Pipe. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), aprile 2012. http://dx.doi.org/10.55274/r0010650.
Abstract (sommario):
Two rounds of pipe welding were completed to understand the influence of the welding parameters on the weld metal and HAZ properties and microstructure. Thermal data was also obtained from these welds. This information was used to refine the thermal microstructural model with predictive capabilities. Essential welding variables were validated on flat plate experiments and recommendations for welding process control established. Ultimately, these recommendations were evaluated by pipeline welding contractors to assess its viability for field application.
2
Miller, Gregory H., e Gregory Forest. Modeling and Algorithmic Approaches to Constitutively-Complex, Microstructured Fluids. Office of Scientific and Technical Information (OSTI), maggio 2014. http://dx.doi.org/10.2172/1150221.
3
Diaz de la Rubia, T, M. J. Caturla e M. J. Fluss. Dimensional Stability and Microstructure Evolution in Irradiated Systems with Complex Kinetics. Office of Scientific and Technical Information (OSTI), aprile 2003. http://dx.doi.org/10.2172/15007305.
4
Diaz de la Rubia, T., M. Caturla e M. J. Fluss. Dimensional Stability and Microstructure Evolution in Irradiated Systems with Complex Kinetics. Office of Scientific and Technical Information (OSTI), ottobre 1999. http://dx.doi.org/10.2172/793932.
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Dinovitzer, Aaron. PR-214-144500-R01 Weld Hydrogen Cracking Susceptibility Characterization. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), marzo 2016. http://dx.doi.org/10.55274/r0010924.
Abstract (sommario):
Hydrogen cracking has been and continues to be observed in both heat-affected zones and weld metals. High carbon equivalent weldment heat-affected zones (HAZ) combined with rapid cooling have been related to the development of hydrogen cracking susceptible microstructures. Weld metal cracking is observed in both high and low strength weldments and is a particular concern for root passes due to the use of cellulosic electrodes, parent metal dilution, applied load, and weld fault stress riser effects promoting cracking. The risk of HAZ and weld cracking are increased for repair and in-service welds and/or welds deposited on older generation materials (e.g., pipe or fittings) and this can pose a significant risk to the integrity of welded connections. This report presents the result of the first year of research toward the application and extension of the �Slow Bend� testing technique used to quantify the hydrogen cracking susceptibility of a weldment. This testing is being used to quantify the susceptibility of a microstructure to hydro-gen cracking by defining the critical combinations of strain and hydrogen concentration that result in cracking in a given material. The testing and modelling results complete in this first year of work are planned to support the definition of a Hydrogen Embrittlement characterization technique considering the effects of strain and hydrogen concentration for a material.
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Dinovitzer, Aaron, Morvarid Ghovanlou e Nick Pussegoda (Archived). PR-214-123734-R01 In The Ditch Non-Destructive Mechanical Property Measurement. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), aprile 2016. http://dx.doi.org/10.55274/r0011019.
Abstract (sommario):
This report describes a new approach using existing non-destructive examination (NDE) techniques to determine pipe properties when existing data and information are absent or incomplete. The research work developed a neural network-based tool making use of linepipe hardness, chemistry and microstructure information to determine pipe characteristics, including strength and toughness. This research was completed to develop a tool to fill gaps in pipeline operators' knowledge and records and provide the basis to meet the requirements of "traceable, verifiable, and complete" (TVC) records requirements and regulatory Integrity Verification Processes (IVP), where applicable, and to establish and maintain operating pressure thresholds that provide for safe operation of liquids and gas pipeline systems. This download includes a copy of the report and a copy of the Excel based Check Mate software (aka Checkmate). This report has a related webinar.
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Patchett, B. M., e A. C. Bicknell. L51706 Higher-Strength SMAW Filler Metals. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), dicembre 1993. http://dx.doi.org/10.55274/r0010418.
Abstract (sommario):
The welding of high strength steels in general, and for pipeline fabrication in particular, has shown that cracking due to hydrogen absorption during welding is more complex in these steels than in older, lower strength steels. In older steels, primary strengthening was accomplished with carbon, which caused hydrogen cracking in the base metal HAZ under reasonably predictable conditions involving microstructure, residual stress and hydrogen level. Pipeline steels were and are in the vanguard of change in strengthening philosophy. The change involves two areas of steel making, chemical composition and deformation processing. Pipeline steels now contain low carbon levels, in many cases less than 0.10%, and the resulting lack of strength is reclaimed by adding higher alloy levels to promote solution hardening (e.g. Mn), precipitation hardening (e.g. Cb, Cu) or transformation hardening (e.g. MO). In addition, alloy elements are added to improve toughness at high strength levels (e.g. Ni). At the same time, improvements have been made in reducing impurity and residual element levels, notably for S, P and O and N. Limitations on the effects of alloying additions on strength and toughness encouraged the use of deformation processing, primarily during rolling, to promote fine-grained microstructures to increase strength andtoughness simultaneously. Electrodes for the SMAW process have been developed for welding high-strength pipeline steels by using core wires made from high-strength microalloyed skelp extruded with cellulosic (Exx10) and low hydrogen (Exx16) flux coatings. The required alloy elements for high-strength deposits were therefore obtained from the core wire and not ferroalloy powders added to the flux, as is standard industrial practice. The idea behind this change was two fold: to avoid the possibility of introducing impurities from the varying sources of ferro alloy powders, including oxygen from the oxidized powder surfaces, and also to provide a closer match of the microalloy level to modern pipeline steel chemistries. The unknowns in this work were the effects of lower impurities/similar alloy content on the mechanical properties in the cast microstructure of a weld, compared to a pipe, and of the effect on electrode welding behaviour of a flux containing no ferro powders other than FeSi.
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Jung. L52232 Weld Metal Cooling Rate Prediction of Narrow Groove Pipeline Girth Welds FEA Modeling. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), gennaio 2008. http://dx.doi.org/10.55274/r0011321.
Abstract (sommario):
As part of a larger, DoT-sponsored program to develop optimized weld metal chemistries for X80 and X100, a finite-element approach was used to predict weld metal cooling rates and to provide a better understanding of the factors which influence them. The models can then be used to predict how changes in the welding procedure will affect the cooling rates of the weld joints. The changes in the welding procedure can include the joint details, the heat input of the weld as well as the preheating temperature. The predicted cooling rate from the model will be used as input, along with the weld metal chemistries, to predict the weld metal microstructure and mechanical properties of a completed weld. The cooling rate model and microstructure prediction subroutine will aid in the development of optimized welding consumables that will improve the weldability of X80 and X100 pipelines.
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Hoelzer, David T., Rachel Seibert e Caleb Massey. Complete Status Report Documenting the Processing, Microstructure and High-Temperature Mechanical Properties of the Nanostructured Ferritic Alloy OFRAC. Office of Scientific and Technical Information (OSTI), giugno 2019. http://dx.doi.org/10.2172/1550736.
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Weertman, J. R. Use of anomalous small angle x-ray scattering to investigate microstructural features in complex alloys. Office of Scientific and Technical Information (OSTI), agosto 1988. http://dx.doi.org/10.2172/5934503.