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Littérature scientifique sur le sujet « Gradients de microstructure »

Auteur : Grafiati
Publié le 9 novembre 2024

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Articles de revues sur le sujet "Gradients de microstructure"

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McNelley, Terry R., Keiichiro Oh-ishi et Alexandre P. Zhilyaev. « Microstructure Evolution and Microstructure-Property Relationships in Friction Stir Processing of NiAl Bronze ». Materials Science Forum 539-543 (mars 2007) : 3745–50. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.3745.

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Friction stir processing (FSP) has been employed for localized modification and control of microstructures in NiAl bronze materials, which are widely utilized for marine components. The thermomechanical cycle of FSP results in homogenization and refinement and the conversion of microstructures from a cast to a wrought condition within stir zones in the material. However, the direct measurement of stir zone temperatures, strains, strain rates and cooling rates is difficult due to steep gradients and transients in these quantities, and this is an impediment in the assessment of FSP-induced microstructures and properties. Quantitative microstructure analyses following FSP of cast NiAl bronze materials have been used to develop estimates of stir zone thermomechanical cycles. The estimation procedures will be reviewed and the microstructure-based estimates will be compared to results from computational models and embedded thermocouples measurements. Stir zone microstructures comprise a mixture of primary α grains and transformation products of the β that formed during processing. Recrystallization in the primary α occurred due to particle-stimulated nucleation in this low stacking fault energy material. Factors that influence the distribution of strength and ductility in the stir zone appear to include the mixture of microstructure constituents and gradients in microstructure due to gradients in processing conditions.
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Schmidt, Christopher David, Hans-Jürgen Christ et Axel Von Hehl. « Hydrogen as a Temporary Alloying Element for Establishing Specific Microstructural Gradients in Ti-6Al-4V ». Metals 12, no 8 (28 juillet 2022) : 1267. http://dx.doi.org/10.3390/met12081267.

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Parts of vehicles, such as landing gear components of aircrafts, are subject to growing demands in terms of sustainability via lightweight design and durability. To fulfill these requirements, the development of thermochemical processes is auspicious. Titanium alloys allow a heat treatment in hydrogen-containing atmosphere for temporary hydrogen alloying, often called thermohydrogen treatment (THT). The investigation presented intends to realize a local microstructure modification of Ti-6Al-4V by means of THT. The study aims to use hydrogen (H) as a promoter for changing the local distribution and morphology of strengthening precipitates during THT as well as the local grain size (microstructural gradient). Both shall improve the fatigue properties of the material after hydrogen degassing. To derive suitable thermohydrogen treatment process parameters, the resulting fatigue crack propagation resistance and fracture toughness after different solution heat treatments are determined experimentally and compared to each other. Moreover, various graded microstructures are evaluated after hydrogen uptake (hydrogenation) and hydrogen degassing (dehydrogenation) using numerically simulated hydrogen concentration profiles, observed hardness curves, metallographically determined microstructure gradients and the corresponding results of the phase analysis by means of X-ray diffraction. The study shows that hydrogenation at 500 °C and dehydrogenation at 750 °C enables the generation of a promising microstructural gradient.
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Jalme, Margaux Saint, Christophe Desrayaud, Julien Favre, Damien Fabrègue, Sylvain Dancette, Christophe Schuman, Jean Sébastien Lecomte, Etienne Archaud et Christian Dumont. « Microstructure Evolution during Multiaxial Processing of TA6V ». Materials Science Forum 1016 (janvier 2021) : 1211–17. http://dx.doi.org/10.4028/www.scientific.net/msf.1016.1211.

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Subtransus multiaxial hot forging of α+β Ti-6Al-4V (TA6V) titanium alloy with a β-transformed microstructure aims at obtaining an equiaxed microstructure through α phase globularization. The activation of mechanisms involved in microstructural evolution, such as globularization, depends on parameters such as time, temperature, strain and strain rate. It is also sensitive to the crystallographic orientation of α-lamellae. As a result, multiaxial processing of titanium alloys leads to significant microstructural gradients depending on thermomechanical conditions and initial microstructure. In this study, we focused on the effect of complex thermomechanical paths on microstructural evolutions. Thanks to the MaxStrain Gleeble device, we were able to reproduce such thermomechanical treatments to β-transformed TA6V samples. Stress strain fields obtained with finite element modelling of the MaxStrain test were compared to experimental microstructure gradients. This experimental method offers the opportunity to get closer to industrial open die forging conditions.
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Bruder, Enrico, Tilman Bohn et Clemens Müller. « Properties of UFG HSLA Steel Profiles Produced by Linear Flow Splitting ». Materials Science Forum 584-586 (juin 2008) : 661–66. http://dx.doi.org/10.4028/www.scientific.net/msf.584-586.661.

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Linear flow splitting is a new cold forming process for the production of branched sheet metal structures. It induces severe plastic strain in the processing zone which results in the formation of an UFG microstructure and an increase in hardness and strength in the flanges. Inbuilt deformation gradients in the processing zone lead to steep gradients in the microstructure and mechanical properties. In the present paper the gradients in the UFG microstructure and the mechanical properties of a HSLA steel (ZStE 500) processed by linear flow splitting are presented, as well as a calculation of local strength from hardness measurements on the basis of the Ludwikequation. In order to investigate the thermal stability of the UFG microstructure heat treatments below the recrystallization temperature were chosen. The coarsening process and the development of the low angle to high angle grain boundary ratio in the gradient UFG microstructure were monitored by EBSD measurements. It is shown that heat treatment can lead to a grain refinement due to a strong fragmentation of elongated grains while only little coarsening in the transverse direction occurs. A smoothing of the gradients in the UFG microstructure as well as in the mechanical properties is observed.
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Büyük, U., S. Engin et N. Maraşlı. « Directional solidification of Zn-Al-Cu eutectic alloy by the vertical Bridgman method ». Journal of Mining and Metallurgy, Section B : Metallurgy 51, no 1 (2015) : 67–72. http://dx.doi.org/10.2298/jmmb140304007b.

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In the present work, the effect of growth rate and temperature gradient on microstructure and mechanical properties of Zn-7wt.%Al-4wt.%Cu eutectic alloy has been investigated. Alloys prepared under steady-state conditions by vacuumed hot filing furnace. Then, the alloys were directionally solidified upward with different growth rates (V=11.62-230.77 mm/s) at a constant temperature gradient (G=7.17 K/mm) and with different temperature gradients (G=7.17-11.04 K/mm) at a constant growth rate (V=11.62 mm/s) by a Bridgman furnace. The microstructures were observed to be lamellae of Zn, Al and broken lamellae CuZn4 phases from quenched samples. The values of eutectic spacing, microhardness and ultimate tensile strength of alloys were measured. The dependency of the microstructure and mechanical properties on growth rate and temperature gradient were investigated using regression analysis.
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Larivière, Sara, Reinder Vos de Wael, Seok-Jun Hong, Casey Paquola, Shahin Tavakol, Alexander J. Lowe, Dewi V. Schrader et Boris C. Bernhardt. « Multiscale Structure–Function Gradients in the Neonatal Connectome ». Cerebral Cortex 30, no 1 (10 avril 2019) : 47–58. http://dx.doi.org/10.1093/cercor/bhz069.

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Abstract The adult functional connectome is well characterized by a macroscale spatial gradient of connectivity traversing from unimodal toward higher-order transmodal cortices that recapitulates known principles of hierarchical organization and myelination patterns. Despite an emerging literature assessing connectome properties in neonates, the presence of connectome gradients and particularly their correspondence to microstructure remains largely unknown. We derived connectome gradients using unsupervised techniques applied to functional connectivity data from 40 term-born neonates. A series of cortex-wide analysis examined associations to magnetic resonance imaging-derived morphological parameters (cortical thickness, sulcal depth, curvature), measures of tissue microstructure (intracortical T1w/T2w intensity, superficial white matter diffusion parameters), and subcortico-cortical functional connectivity. Our findings indicate that the primary neonatal connectome gradient runs between sensorimotor and visual anchors and captures specific associations to cortical and superficial white matter microstructure as well as thalamo-cortical connectivity. A second gradient indicated an anterior-to-posterior asymmetry in macroscale connectivity alongside an immature differentiation between unimodal and transmodal areas, indicating a connectome-level circuitry en route to an adult-like organization. Our findings reveal an important coordination of structural and functional interactions in the neonatal connectome across spatial scales. Observed associations were replicable across individual neonates, suggesting consistency and generalizability.
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Lomte, Amulya, et Bhisham Sharma. « Modeling the acoustic behavior of stepwise gradient porous structures ». INTER-NOISE and NOISE-CON Congress and Conference Proceedings 264, no 1 (24 juin 2022) : 500–508. http://dx.doi.org/10.3397/nc-2022-764.

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Spatial property gradients can significantly enhance the noise reduction potential of porous structures. However, predicting the acoustic behavior of structures with gradient microstructures continues to remain a challenge. For porous structures with controlled periodic microstructures, researchers have recently demonstrated the use of a multiscale asymptotic method to extract the acoustic transport properties necessary for use in semi-empirical predictive models. Here, we propose the adaptation of this method to enable the modeling of porous absorbers with stepwise property gradients. The unit cell of the chosen microstructure is modeled in COMSOL Multiphysics and the acoustic transport properties are extracted using the multiscale method. The extracted properties are then used to formulate the transfer matrix of each unit cell. The global sound absorption and transmission loss behavior of the stepwise gradient structures are further predicted by combining the appropriate local transfer matrices. Our results show that the integration of the unit cell and transfer matrix methods provides a robust way of predicting the acoustic behavior of stepwise gradient porous structures with various combinations of layer thicknesses and geometries. The method provides a computationally efficient method to model such structures and can further the development of porous structures with application-specific acoustical properties.
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Fischer, K., et H. Oettel. « Microstructure Gradients in PVD-TiN Coatings ». Materials Science Forum 273-275 (février 1998) : 567–72. http://dx.doi.org/10.4028/www.scientific.net/msf.273-275.567.

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Georgiadis, H. G. « The Mode III Crack Problem in Microstructured Solids Governed by Dipolar Gradient Elasticity : Static and Dynamic Analysis ». Journal of Applied Mechanics 70, no 4 (1 juillet 2003) : 517–30. http://dx.doi.org/10.1115/1.1574061.

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This study aims at determining the elastic stress and displacement fields around a crack in a microstructured body under a remotely applied loading of the antiplane shear (mode III) type. The material microstructure is modeled through the Mindlin-Green-Rivlin dipolar gradient theory (or strain-gradient theory of grade two). A simple but yet rigorous version of this generalized continuum theory is taken here by considering an isotropic linear expression of the elastic strain-energy density in antiplane shearing that involves only two material constants (the shear modulus and the so-called gradient coefficient). In particular, the strain-energy density function, besides its dependence upon the standard strain terms, depends also on strain gradients. This expression derives from form II of Mindlin’s theory, a form that is appropriate for a gradient formulation with no couple-stress effects (in this case the strain-energy density function does not contain any rotation gradients). Here, both the formulation of the problem and the solution method are exact and lead to results for the near-tip field showing significant departure from the predictions of the classical fracture mechanics. In view of these results, it seems that the conventional fracture mechanics is inadequate to analyze crack problems in microstructured materials. Indeed, the present results suggest that the stress distribution ahead of the tip exhibits a local maximum that is bounded. Therefore, this maximum value may serve as a measure of the critical stress level at which further advancement of the crack may occur. Also, in the vicinity of the crack tip, the crack-face displacement closes more smoothly as compared to the classical results. The latter can be explained physically since materials with microstructure behave in a more rigid way (having increased stiffness) as compared to materials without microstructure (i.e., materials governed by classical continuum mechanics). The new formulation of the crack problem required also new extended definitions for the J-integral and the energy release rate. It is shown that these quantities can be determined through the use of distribution (generalized function) theory. The boundary value problem was attacked by both the asymptotic Williams technique and the exact Wiener-Hopf technique. Both static and time-harmonic dynamic analyses are provided.
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Schmidt, Christopher David, Vitali Macin, Peter Schmidt et Hans-Jürgen Christ. « Generation of Microstructural Gradients for Improved Mechanical Properties via Thermo-Hydrogen Treatment of the Metastable Beta Titanium Alloys Beta CTM and Ti 10V-2Fe-3Al ». MATEC Web of Conferences 321 (2020) : 12017. http://dx.doi.org/10.1051/matecconf/202032112017.

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Structural components must be lightweight and produced resource-saving while still fulfil the increasing durability and reliability requirements. One approach to fulfil these requests is a temporary hydrogen charging of Ti-alloys, which generates lattice distortion and hydrides. The volume difference between hydride precipitates and the alloy matrix results in localized plastic deformation. This triggers recrystallization and enables a finer microstructure as attainable by a conventional heat treatment. The study aims at an elaboration of a thermo-hydrogen treatment that establishes a change in grain size and/or an alteration in distribution and morphology of strengthening secondary α precipitates as a function of the distance to surface (microstructural gradient). The gradient is based on a gradient of the hydride volume fraction. Generally, THT design requires kinetic (temperature dependency of the hydrogen diffusion coefficient DH) in addition to thermodynamic (H/β-Ti-alloy interaction) data, which has been obtained for Ti 3Al-8V-6Cr-4Mo-4Zr and Ti 10V-2Fe-3Al. Subsequent to a solution treatment the variation of hydrogenation time and temperature is operated to establish comparably slight microstructural gradients on these materials. For further investigations it is concluded that materials with less alloying elements ((α+β)-Ti-alloys (e.g.,Ti 6Al-4V)) than these β-Ti-alloys can satisfy the requirements to generate steeper microstructural gradients even better.
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Thèses sur le sujet "Gradients de microstructure"

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Lin, Ching-Te 1967. « Microstructure, texture, and hardness gradients in aluminum diffusion-bonded to aluminum oxide ». Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50351.

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Baudoin, Pierre. « Caractérisation et identification de propriétés de matériaux métalliques à gradients de microstructure ». Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10015/document.

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L'objectif de ces travaux de thèse est de proposer une démarche de caractérisation et de simulation de matériaux métalliques à gradients de microstructure. Ces résultats doivent permettre de modéliser l'impact du procédé de forgeage sur la tenue en fatigue à grand nombre de cycles d'essieux ferroviaires, produits dans le cadre du projet Innovaxle par la société Valdunes. Des essais de caractérisation réalisés sur un essieu forgé mettent en évidence un gradient de taille de grain entre le cœur et la surface de la pièce. Ce gradient est reproduit à une échelle plus fine sur des éprouvettes recristallisées en fer ARMCO, dont la caractérisation révèle un comportement élasto-plastique fortement hétérogène. Ce comportement est caractérisé à l'aide de la méthode F.E.M.U. (Finite Element Model Updating), qui appuie une hypothèse de modélisation basée sur l'application de la loi Hall-Petch à l'échelle mésoscopique. Cette modélisation sert de base à des simulations en fatigue décrivant la réponse à des sollicitations non-uniformes d'agrégats polycristallins à gradient de microstructure. L'intérêt de microstructures conçues en prévision de chargements spécifiques est mise en avant par ces simulations. Les calculs éléments finis présentés dans ces travaux sont réalisés avec le logiciel Code Aster, et le logiciel libre YADICS est utilisé pour la corrélation d'images numériques
The main objective of this thesis is to design a consistent methodology for the characterization and simulation of functionally graded metals. This approach should allow the assessment of the high cycle fatigue response of forged railway axles produced by Valdunes, in the context of the Innovaxle project. The tests conducted on the forged material reveal a very heterogeneous microstructure, whose grain size varies in the width of the axle. A procedure based on recrystallisation is designed to reproduce this grain size gradient on a smaller scale, on a reference material (ARMCO iron). The characterization of the obtained graded microstructure shows heterogeneities in the local elasto-plastic response of the specimen. This behaviour is tentatively described by a heterogeneously distributed elasto-plastic law over the microstructure, the local yield strength being obtained from the local grain size through a Hall-Petch formulation. This model is used to simulate the response of graded microstructures under heterogeneous loadings in the high cycle fatigue regime. The interests of functionally graded materials are outlined by these simulations. The finite element simulations run in this work make use of the Code Aster software, and the digital image correlation program YADICS is used for image registration purposes
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Mohanty, Rashmi. « Phase-Field Simulation of Microstructural Development Induced by Interdiffusion Fluxes Under Multiple Gradients ». Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4182.

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The diffuse-interface phase-field model is a powerful method to simulate and predict mesoscale microstructure evolution in materials using fundamental properties of thermodynamics and kinetics. The objective of this dissertation is to develop phase-field model for simulation and prediction of interdiffusion behavior and evolution of microstructure in multiphase binary and ternary systems under composition and/or temperature gradients. Simulations were carried out with emphasis on multicomponent diffusional interactions in single-phase system, and microstructure evolution in multiphase systems using thermodynamics and kinetics of real systems such as Ni-Al and Ni-Cr-Al. In addition, selected experimental studies were carried out to examine interdiffusion and microstructure evolution in Ni-Cr-Al and Fe-Ni-Al alloys at 1000°C. Based on Onsager’s formalism, a phase-field model was developed for the first time to simulate the diffusion process under an applied temperature gradient (i.e., thermotransport) in single- and two-phase binary alloys. Development of concentration profiles with uphill diffusion and the occurrence of zeroflux planes were studied in single-phase diffusion couples using a regular solution model for a hypothetical ternary system. Zero-flux plane for a component was observed to develop for diffusion couples at the composition that corresponds to the activity of that component in one of the terminal alloys. Morphological evolution of interphase boundary in solid-to-solid two-phase diffusion couples (fcc-γ vs. B2-β) was examined in Ni-Cr-Al system with actual thermodynamic data and concentration dependent chemical mobility. With the instability introduced as a small initial compositional fluctuation at the interphase boundary, the evolution of the interface morphology was found to vary largely as a function of terminal alloys and related composition dependent chemical mobility. In a binary Ni-Al system, multiphase diffusion couples of fcc-γ vs. L12-γ′, γ vs. γ+γ′ and γ+γ′ vs. γ+γ′ were simulated with alloys of varying compositions and volume fractions of second phase (i.e., γ′). Chemical mobility as a function of composition was employed in the study with constant gradient energy coefficient, and their effects on the final interdiffusion microstructure was examined. Interdiffusion microstructure was characterized by the type of boundaries formed, i.e. Type 0, Type I, and Type II boundaries, following various experimental observations in literature and thermodynamic considerations. Volume fraction profiles of alloy phases present in the diffusion couples were measured to quantitatively analyze the formation or dissolution of phases across the boundaries. Kinetics of dissolution of γ′ phase was found to be a function of interdiffusion coefficients that can vary with composition and temperature. The evolution of interdiffusion microstructures in ternary Ni-Cr-Al solid-to-solid diffusion couples containing fcc-γ and γ+β (fcc+B2) alloys was studied using a 2D phase-field model. Alloys of varying compositions and volume fractions of the second phase (β) were used to simulate the dissolution kinetics of the β phase. Semi-implicit Fourier-spectral method was used to solve the governing equations with chemical mobility as a function of compositions. The simulation results showed that the rate of dissolution of the β phase (i.e., recession of β+γ twophase region) was dependent on the composition of the single-phase γ alloy and the volume fraction of the β phase in the two-phase alloy of the couple. Higher Cr and Al content in the γ alloy and higher volume fraction of β in the γ+β alloy lower the rate of dissolution. Simulated results were found to be in good agreement with the experimental observations in ternary Ni-Cr- Al solid-to-solid diffusion couples containing γ and γ+β alloys. For the first time, a phase-field model was developed to simulate the diffusion process under an applied temperature gradient (i.e., thermotransport) in multiphase binary alloys. Starting from the phenomenological description of Onsager’s formalism, the field kinetic equations are derived and applied to single-phase and two-phase binary system. Simulation results show that a concentration gradient develops due to preferential movement of atoms towards the cold and hot end of an initially homogeneous single-phase binary alloy subjected to a temperature gradient. The temperature gradient causes the redistribution of both constituents and phases in the two-phase binary alloy. The direction of movement of elements depends on their atomic mobility and heat of transport values.
Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr PhD
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Largiller, Grégory. « Maîtrise du frittage de matériaux céramique-métal à gradients de composition et de structure ». Grenoble INPG, 2010. http://www.theses.fr/2010INPG0160.

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Les matériaux à gradient de composition et de structure permettent d'associer des propriétés complémentaires dans une pièce donnée. Les cermets (matériaux composite céramique métal) développés par Rio Tinto Alcan seront potentiellement utilisés en tant qu'anodes inertes pour l'électrolyse de l'aluminium. Pour connecter cette pièce à matrice céramique au réseau électrique, ce matériau doit être associé avec un matériau conducteur électrique en une seule opération de frittage. En associant les connaissances issues de la métallurgie des poudres avec une analyse microstructurale, des calculs thermodynamiques et des considérations mécaniques, une gamme de matériaux appelés metcer (composite métal céramique) a été développée. Selon la proportion et composition de la phase métallique initiale de ces metcers, ils peuvent être cofrittés en une seule opération avec un cermet. Nous avons montré que la proportion de phase métallique influençait fortement la tenue mécanique de l'ensemble pendant le frittage ; que la composition des phases oxydes et métalliques permettait de maîtriser les phénomènes de diffusion entre les parties cofrittées pour construire une interface graduelle. Des lois phénoménologiques basées sur la mécanique des milieux continus ont été développées pour modéliser le frittage d'un cermet et d'un metcer. Ces lois ont été introduites dans un logiciel de calcul par éléments finis pour simuler le frittage d'assemblages bicouches et identifier les éventuels points de fragilité de différentes géométries. En comparant ces résultats de simulation numérique à des observations optiques in situ sur des pièces centimétriques, nous avons montré que l'amorçage de fissures proche de l'interface a lieu lorsque les contraintes sont élevées. A basse température, de faibles écarts de déformations entre les couches suffisent à amorcer des fissures lorsque les viscosités des matériaux sont grandes et qu'ils ont un comportement fragile. A haute température, lorsque les écarts de déformation sont grands et les viscosités faibles, les contraintes entre les couches sont relaxées. En utilisant les connaissances acquises à la fois sur la chimie et la mécanique du système, une pièce centimétrique tricouche à gradient exempt de fissure a été réalisée
Graded materials are used to gather complementary physical and/or chemical properties into a single part. Cermet material (ceramic metal composite) developed by Rio Tinto Alcan may be used as inert anode for aluminium electrolysis. To connect these ceramic matrix materials to the current network, we propose to associate them with a conductive material in a single sintering step. Using our knowledge on powder metallurgy with microstructure analysis, thermodynamical and mechanical calculations, a new range of material called metcer (metal ceramic composite) has been developed. According to their metal phase proportion and composition, the metcer materials can be cosintered with cermets in a single sintering step. By modifying the metal phase proportion, we enabled the parts to keep joined during the whole sintering thermal cycle. The composition of oxides and metal phases change the diffusion phenomena and enable one to build a graded interface between the layers. Based on continuum mechanics, constitutive equations have been used to simulate the sintering of a cermet and a metcer. Constitutive equations have been implemented into a finite element software to identify the weak regions of bilayers parts of complex geometry. We compared numerical simulation results with optical observations made during sintering on large scale bilayers. Cracks near the interface occur at low temperature when the strain mismatch between the layers is low and the viscosities of the layers are high. Thus, the materials have a fragile behaviour. At high temperature, when the viscosities are low and the strain mismatch is high, the stresses in the vicinity of the interface are released. Combining our knowledge on the chemistry and interactions between these materials, we developed a trilayer material. This material showed up a graded interface without any crack
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Beaujoin, Justine. « Post mortem inference of the human brain microstructure using ultra-high field magnetic resonance imaging with strong gradients ». Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS448/document.

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L’ambition des très hauts champs magnétiques (≥ 7T) à forts gradients (≥ 300mT/m) est de dépasser la résolution millimétrique imposée à plus bas champ pour atteindre l’échelle mésoscopique en neuroimagerie. Etudier le cerveau à cette échelle est essentiel pour comprendre le lien entre fonction et substrat anatomique. Malgré les progrès réalisés sur les aimants cliniques à 7T, il n’en est pas de même des gradients. Cette thèse vise à cartographier le cerveau humain à l’échelle mésoscopique via l’étude de pièces anatomiques post mortem. Une approche alternative a été choisie, reposant sur l'utilisation d'imageurs précliniques à très hauts champs (7T et 11.7T) et forts gradients (780mT/m). Après une première étape de préparation (extraction et fixation) opérée au CHU de Tours, une pièce anatomique complète a été scannée à 3T, avant découpe de l’hémisphère gauche en sept blocs. Un protocole d’acquisition IRM ciblant une résolution mésoscopique a ensuite été mis en place à 11.7T. Ce protocole, incluant des séquences anatomiques, relaxométriques, et de diffusion, a été validé à l’aide de deux structures clé: un hippocampe et un tronc cérébral. Les données anatomiques et de diffusion acquises à une résolution mésoscopique sur l’hippocampe ont permis de segmenter ses sous-champs, d’extraire le circuit polysynaptique et d’observer l’existence d’un gradient de connectivité et de densité neuritique positif dans la direction postéro-antérieure de l’hippocampe. L’utilisation de modèles avancés d’étude de la microstructure a également révélé l’apport de ces techniques pour la segmentation de l’hippocampe, les cartes de densité neuritique révélant les trois couches des champs ammoniens. Un tronc cérébral a ensuite été scanné, avec une résolution atteignant la centaine de micromètres. Une segmentation de 53 de ses 71 noyaux a été réalisée au sein du CHU de Tours, permettant d’établir la cartographie IRM du tronc cérébral humain la plus complète à ce jour. Les principaux faisceaux de la substance blanche ont été reconstruits, ainsi que les projections du locus coeruleus, structure connue pour être atteinte dans le maladie de Parkinson. Forts de ces résultats, la campagne d'acquisition de l'hémisphère gauche, d’une durée de 10 mois, a été initiée. Le protocole d’acquisition à 11.7T intègre des séquences anatomiques (100/150µm) ainsi que des séquences d'imagerie 3D pondérées en diffusion (b=1500/4500/8000 s/mm², 25/60/90 directions) à 200µm. Des acquisitions complémentaires réalisées à 7T comprenant des séquence d’écho de spin rapide avec inversion-récupération ont par ailleurs permis d’étudier la myéloarchitecture du cortex cérébral et d’identifier automatiquement sa structure laminaire. Un nouveau modèle de mélange de Gaussiennes a été développé, intégrant les informations myéloarchitecturales issues de la cartographie T1 et les informations cytoarchitecturales issues de l’imagerie de diffusion. Il a ainsi pu être démontré que l’utilisation conjointe de ces deux informations permettait de mettre en évidence des couches du cortex visuel, l’information myéloarchitecturale favorisant l’extraction des couches externes et la densité neuritique celle des couches plus profondes. Enfin, l’exploitation des données IRM acquises à 11.7T sur les différents blocs a nécessité la mise en place d’une chaîne de prétraitements pour corriger les artéfacts d’imagerie et reconstruire l’hémisphère entier à l’aide de stratégies de recalage difféomorphe avancées. L’objectif de ce projet est l’obtention d’un jeu de données IRM de très haute résolution spatio-angulaire de l’hémisphère gauche. Ce jeu de données anatomique et de diffusion unique permettra à terme de constituer un nouvel atlas IRM mésoscopique de la structure, de la connectivité et de la cytoarchitecture du cerveau humain
The aim of ultra-high field strength (≥7T) and ultra-strong gradient systems (≥300mT/m) is to go beyond the millimeter resolution imposed at lower field and to reach the mesoscopic scale in neuroimaging. This scale is essential to understand the link between brain structure and function. However, despite recent technological improvements of clinical UHF-MRI, gradient systems remain too limited to reach this resolution. This thesis aims at answering the need for mapping the human brain at a mesoscopic scale by the study of post mortem samples. An alternative approach has been developed, based on the use of preclinical systems equipped with ultra-high fields (7T/11.7T) and strong gradients (780mT). After its extraction and fixation at Bretonneau University Hospital (Tours), an entire human brain specimen was scanned on a 3T clinical system, before separating its two hemispheres and cutting each hemisphere into seven blocks that could fit into the small bore of an 11.7T preclinical system. An MRI acquisition protocol targeting a mesoscopic resolution was then set up at 11.7T. This protocol, including anatomical, quantitative, and diffusion-weighted sequences, was validated through the study of two key structures: the hippocampus and the brainstem. From the high resolution anatomical and diffusion dataset of the human hippocampus, it was possible to segment the hippocampal subfields, to extract the polysynaptic pathway, and to observe a positive gradient of connectivity and neuritic density in the posterior-anterior direction of the hippocampal formation. The use of advanced microstructural models (NODDI) also highlighted the potential of these techniques to reveal the laminar structure of the Ammon’s horn. A high resolution anatomical and diffusion MRI dataset was obtained from the human brainstem with an enhanced resolution of a hundred micrometers. The segmentation of 53 of its 71 nuclei was performed at the Bretonneau University Hospital, making it the most complete MR-based segmentation of the human brainstem to date. Major white matter bundles were reconstructed, as well as projections of the locus coeruleus, a structure known to be impaired in Parkinson’s disease. Buoyed by these results, a dedicated acquisition campaign targeting the entire left hemisphere was launched for total scan duration of 10 months. The acquisition protocol was performed at 11.7T and included high resolution anatomical sequences (100/150μm) as well as 3D diffusion-weighted sequences (b=1500/4500/8000 s/mm², 25/60/90 directions, 200μm). In addition, T1-weighted inversion recovery turbo spin echo scans were performed at 7T to further investigate the myeloarchitecture of the cortical ribbon at 300µm, revealing its laminar structure. A new method to automatically segment the cortical layers was developed relying on a Gaussian mixture model integrating both T1-based myeloarchitectural information and diffusion-based cytoarchitectural information. The results gave evidence that the combination of these two contrasts highlighted the layers of the visual cortex, the myeloarchitectural information favoring the extraction of the outer layers and the neuritic density favoring the extraction of the deeper layers. Finally, the analysis of the MRI dataset acquired at 11.7T on the seven blocks required the development of a preprocessing pipeline to correct artifacts and to reconstruct the entire hemisphere using advanced registration methods. The aim was to obtain an ultra-high spatio-angular resolution MRI dataset of the left hemisphere, in order to establish a new mesoscopic post mortem MRI atlas of the human brain, including key information about its structure, connectivity and microstructure
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Faham, Mohamed amine. « Influence d’un gradient de microstructure sur la fatigue d’un matériau métallique ». Electronic Thesis or Diss., Centrale Lille Institut, 2024. http://www.theses.fr/2024CLIL0008.

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L’étude de la propagation de fissure dans les composants ferroviaires, notamment les essieux, revêt une grande importance. Les aciers ferrito-perlitiques utilisés pour la fabrication de ces composants ferroviaires peuvent avoir une microstructure différente de la surface du composant à cœur, ce qui nous amène à étudier l'influence d'un gradient de microstructure sur la propagation des fissures. Particulièrement, comprendre l'influence d'un gradient de microstructure (taille des constituants, fraction de constituants) sur le régime de fissuration proche du seuil de non propagation, et dans le régime de propagation de Paris et aussi comprendre l’interaction locale d’une fissure avec la microstructure ferrito-perlitique en couplant les essais avec des mesures de champs reposant sur la corrélation d’images numériques. Globalement, il s’agit d’identifier le gradient le plus bénéfique vis-à-vis du ralentissement de la propagation de fissure en fatigue. Plusieurs protocoles expérimentaux et méthodologies expérimentales ont été développés pour atteindre les objectifs fixés, notamment le développement de microstructure grâce à des traitements thermiques, la réalisation de courbe de résistance (Cyclic R-curve) reposant sur la pré-fissuration en compression, la réalisation d'essai de fissuration à amplitude constante de facteur d'intensité de contrainte
The study of crack propagation in railway components, especially axles, is of great importance. The ferrite-perlite steels used for the fabrication of these railway components may have a different microstructure from the surface to the bulk of the component, which leads us to investigate the influence of a microstructure gradient on crack propagation. Specifically, understanding the influence of a microstructure gradient (constituent size, constituent fraction) on crack propagation near the threshold of non-propagation, as well as in the Paris regime, and also understanding the local interaction of a crack with the ferrite-perlite microstructure by coupling tests with field measurements relying on digital image correlation. Overall, the aim is to identify the most beneficial gradient regarding the slowing down of fatigue crack propagation. Several experimental protocols and methodologies have been developed to achieve the set objectives, including the development of microstructure through heat treatments, the realization of cyclic R-curve based on compression pre-cracking, and the conduct of crack growth test at constant stress intensity factor amplitude
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Kuchi, Satish C. « Effect of Finite Geometry on Solidification Microstructure in Beam-Based Fabrication of Thin Wall Structures ». Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1253252782.

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Fradet, Clémence. « Caractérisation d’élastomères synthétiques par indentation instrumentée (I.I.T.) : protocoles et applications ». Thesis, Tours, 2019. http://www.theses.fr/2019TOUR4014.

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L’essai d’indentation instrumentée est une technique de caractérisation locale très largement développée qui a mis en lumière son potentiel considérable pour sonder le comportement des matériaux. Elle est néanmoins circonscrite aux métaux, aux céramiques voire aux polymères. De ce fait, elle est peu présente dans la littérature relatant de la mécanique des élastomères, notamment en raison de leur hétérogénéité locale et de leur viscoélasticité, qui sont responsables de biais expérimentaux non négligeables. Cette thèse a donc pour objectif premier de mettre en place un protocole expérimental robuste de manière à apporter des éléments de réponse pertinents à des problématiques industrielles concrètes. Pléthore de phénomènes locaux dans les élastomères sont de très bons candidats à l’emploi de cette technique. Ces travaux s’intéressent spécifiquement à l’influence de la micro-morphologie et de la cinématique de chargement-déchargement sur les essais d’indentation d’un élastomère synthétique. Le protocole ainsi ajusté s’est vu appliqué à des matériaux de l’industrie aéronautique et automobile pour capturer les effets locaux d’un vieillissement thermique, d’une fatigue mécanique, de différents taux de vulcanisation et des gradients interfaciaux d’un composite polymère-élastomère
Instrumented indentation testing (IIT) is a local method of caracterization which has highlighted a significant potential to probe materials’ behaviors. Nevertheless, for now, its use has been limited to metals, ceramics or more polymers. Thus IIT is rare in literature about mechanics of elastomers, mainly due to their local heterogeneity and viscoelasticity which are responsible for non-negligible experimental bias. The first aim of this thesis is to set up a robust protocol so as to bring relevant responses to practical industrial issues. Plethora of local phenomena in elastomers are serious candidates for the application of this technique. These works deal specifically with the influence of the micro-morphology and the loading-unloading kinematics when indenting a synthetic elastomer. The established protocol has then been used on industrial materials, for aeronautic and automotive uses, so as to probe the effects of a thermal ageing, a mechanical fatigue, different vulcanization rates and interfacial gradients of a polymer-elastomer composite
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Pecora, Marina. « Development of a Cyclic Indentation Method for the Characterisation of Material Gradients in Polymers and Polymer Composites Due to Thermal Aging ». Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2018. http://www.theses.fr/2018ESMA0011/document.

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Le marché des matériaux composites à matrice organique (CMO) pour la réalisation de pièces structurales "froides" (-55°C < T < Tamb) arrive à saturation et l’industrie aéronautique vise à utiliser les CMO tissés 3D dans les pièces structurales dites "chaudes" (50°C < T < 300°C) des avions (nacelles,turbomoteurs). Ces conditions environnementales peuvent entrainer des phénomènes de dégradation à long terme. L'action de l'environnement et la complexité de la microstructure peuvent conduire au développement de gradients de propriétés dans les matériaux. À haute température, la matrice polymère peut présenter un comportement complexe dépendant du temps. Il est donc nécessaire de mettre au point une technique expérimentale capable de caractériser le comportement du matériau en fonction du temps à l'échelle locale, pour saisir les gradients des propriétés. Ce travail propose la mise en place d'un essai cyclique d'indentation instrumentée pour répondre à ces questions.L'indentation instrumentée est une technique expérimentale qui a rencontrée un grand succès au cours des dernières années. Dans sa forme classique, développée pour les matériaux à comportement élasto-plastique, elle consiste à réaliser un seul cycle de charge/décharge pour en déduire la dureté du matériau et le module élastique d’indentation. Cette analyse n'est pas appropriée pour les matériaux présentant un comportement dépendant du temps, ce qui nécessite de développer une nouvelle méthode optimisée pour les matériaux polymères. Les méthodes d'indentation pour les matériaux polymères proposées dans la littérature (fluage, dynamique), sont limitées à certaines charges. L'essai cyclique d'indentation proposé dans ce travail vise à mettre en évidence la complexité du comportement du polymère. Il est dérivé des essais cycliques macroscopiques et emploi une méthode d’analyse similaire. La technique est développée sur un polymère thermoplastique, le PEHD, pour lequel la réponse cyclique macroscopique en traction et cisaillement est connue. En suivant l’évolution au cours du temps des principaux indicateurs du comportement cyclique (le module d'indentation,l’aire de la boucle d'hystérésis et l'accumulation du déplacement) pour différentes fréquences, il est possible de mettre en évidence la réponse du matériau et d'effectuer une comparaison qualitative avec le comportement macroscopique. Le protocole d'indentation cyclique est ensuite utilisé pour étudier les gradients de propriétés dans la résine époxy thermodurcissable PR520 soumise à un vieillissement thermique à 150°C sous air à pression atmosphérique (jusqu'à 1000h), sous 2 bar d’O2et de N2 (pour 400h). Il est montré que la cinétique d’évolution du module d'indentation et du déplacement n'est pas affectée par le vieillissement. Cependant, leurs valeurs absolues varient de la surface au cœur du polymère, ce qui indique la présence de gradients. L'hystérésis du premier cycle est différente à travers le gradient, mais à partir du deuxième cycle, l'hystérésis est similaire pour toutes les conditions de vieillissement et les distances de la surface exposée. Les résultats obtenus sur des échantillons vieillis sous 2 bar d’O2 et de N2 permettent de conclure que la cinétique de vieillissement n'est pas de la pure thermo-oxydation. La méthode d'indentation cyclique est ensuite appliquée pour caractériser le comportement de la matrice époxy PR520 dans un composite tissé 3D,à l'état vierge et vieilli à 150°C sous air à pression atmosphérique. L'étude du composite à l'état vierge révèle que le comportement de la matrice polymère à proximité de la surface externe est différent de celui situé dans les zones internes du composite et du polymère pur. La comparaison entre le polymère pur et la matrice à l’état vieilli montre que les gradients de propriétés induits par l'environnement sont similaires
The market of organic matrix composite (OMC) materials for the realisation of “cold” (-55°C < T < RT) structural parts is going towards saturation and aircraft manufacturers foresee the employment of 3D reinforced OMC in “warm” (50°C < T < 300°C) aircraft structural parts (nacelles, turbo-engines). These environmental conditions may lead to degradation phenomena over long time. The action of environment and the complexity of the material microstructure may lead to the development of material property gradients. At high temperature, the organic polymer matrix may exhibit complex time-dependent behaviour. Therefore, there is a need to develop an experimental technique able to characterise the material behaviour at local scale and to capture material gradients and time-dependent behaviour. The present work proposes the development of a cyclic instrumented indentation test to tackle all these issues. Instrumented indentation is a popular testing technique: its basic version, appropriate for elasto-plastic materials, includes the realisation of a single loading/unloading test, the measurement of the material hardness through the analysis of the indentation print, and the analysis of the unloading curve based on the assumption of elastic unloading behaviour to obtain the indentation modulus. This analysis is inappropriate for materials exhibiting time-dependent behaviour, which leads to the need of a new method optimized for polymer materials.Several indentation methods are available for polymer materials (indentation creep, nanoDMA), but are limited to some specific loadings. The instrumented indentation cyclic test proposed in this work tries to emphasize the whole complexity of the polymer behaviour, is inspired by macroscopic cyclic tests and is analysed similarly. The technique is first set up and developed by testing a HDPE thermoplastic polymer, for which the response to macroscopic cyclic tension and shear loading isknown. By following, at different frequencies, the evolution with time (with cycles) of the principal indicators of the cyclic behaviour – that is, the indentation modulus, the hysteresis loop area and the indentation depth accumulation - it is possible to highlight the time-dependent response of the material and to perform a proper – though qualitative - comparison with the macroscopic behaviour. The cyclic indentation protocol is then employed to study the material gradients in a thermoset PR520epoxy resin subjected to thermal aging at 150°C under air at atmospheric pressure (up to 1000h), 2 barO2 (for 400h) and N2. It is shown that the evolution with cycles of the indentation modulus and the cyclic creep is not affected by thermal aging. However, their absolute values vary from the surface to the core of polymer indicating the presence of gradients. The hysteresis of the first cycle is different through the gradient: from the second cycle, however, the hysteresis is similar for all aging conditions and distances from the exposed surface. Moreover, the time-dependent behaviour stays unchanged. Results from samples aged under 2 bar O2 and 2 bar N2 allow to conclude that the aging kinetics is not related to pure thermo-oxidation phenomena. The cyclic indentation method is finally applied to characterise the behaviour of PR520 epoxy matrix within a 3D interlock textile composite, in its virgin state and thermally aged at 150°C under air at atmospheric pressure (up to 1000h). The polymer inlarge matrix pockets between the fibrous reinforcements is studied in this work, so the constrainingeffect coming from the reinforcement is negligible. The study of the composite in virgin state revealsthat the behaviour of polymer matrix close to the external surface is different from that located ininternal zones of the composite and from the neat polymer. The comparison between the thermallyaged neat polymer and matrix in internal zones of the composite shows that the environment-inducedproperty gradients are similar
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Tran, Thu Huong. « Comportement homogénéisé des matériaux composites : prise en compte de la taille des éléments microstructuraux et des gradients de la déformation ». Phd thesis, Université Paris-Est, 2013. http://tel.archives-ouvertes.fr/tel-01038058.

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L'objectif principal du travail réalisé au cours de la thèse consistera à proposer une démarche théorique rigoureuse visant à intégrer les éléments microstructuraux et les gradients de déformation dans une approche micromécanique. La thèse comportera deux volets : - Dans une première partie, on s'attachera à établir un cadre théorique rigoureux permettant d'intégrer les effets du gradient de la déformation et les longueurs caractéristiques de la microstructure sur le comportement effectif des matériaux composites - L'approche par développement asymptotique conduit à la résolution d'une succession problèmes d'élasticité tridimensionnelle posée sur une cellule élémentaire du milieu périodique. La résolution de ces problèmes d'élasticité, et par conséquent la détermination des propriétés effectives du composite, nécessite la mise en œuvre d'une méthode de résolution numérique. Dans cette seconde partie du travail, il s'agira de proposer une méthode de résolution basée sur la transformée de Fourier rapide (Méthode FFT)
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Livres sur le sujet "Gradients de microstructure"

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Zhou, Liucheng, et Weifeng He. Gradient Microstructure in Laser Shock Peened Materials. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-1747-8.

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P, Gangloff R., Kelly R. G et United States. National Aeronautics and Space Administration., dir. NASA-UVa light aerospace alloy and structures technology program, LA²ST. : Research on materials for the high speed civil transport. [Washington, DC : National Aeronautics and Space Administration, 1997.

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P, Gangloff R., Kelly Robert G et United States. National Aeronautics and Space Administration., dir. NASA-UVa light aerospace alloy and structures technology program, LA²ST. : Research on materials for the high speed civil transport. [Washington, DC : National Aeronautics and Space Administration, 1997.

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P, Gangloff R., Kelly Robert G et United States. National Aeronautics and Space Administration., dir. NASA-UVa light aerospace alloy and structures technology program, LA²ST. : Research on materials for the high speed civil transport. [Washington, DC : National Aeronautics and Space Administration, 1997.

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P, Gangloff R., et United States. National Aeronautics and Space Administration., dir. NASA-UVa light aerospace alloy and structures technology program (LA²ST) : A progress report July 1, 1994 to December 31, 1994. Charlottesville, VA : School of Engineering & Applied Center, 1995.

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P, Gangloff R., et United States. National Aeronautics and Space Administration., dir. NASA-UVa light aerospace alloy and structures technology program (LA²ST) : A progress report July 1, 1994 to December 31, 1994. Charlottesville, VA : School of Engineering & Applied Center, 1995.

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P, Gangloff R., et United States. National Aeronautics and Space Administration., dir. NASA-UVa light aerospace alloy and structures technology program (LA²ST) : A progress report July 1, 1994 to December 31, 1994. Charlottesville, VA : School of Engineering & Applied Center, 1995.

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Rhaipu, Soranat. The effect of microstructural gradients on the superplastic forming of TI-6AL-4V. Birmingham : University of Birmingham, 2000.

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Patrick, Dunn, et United States. National Aeronautics and Space Administration., dir. An evaluation of a coupled microstructural approach for the analysis of functionally graded composites via the finite-element method. [Washington, DC : National Aeronautics and Space Administration, 1995.

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J, Roth Don, et Lewis Research Center, dir. Scaling up the single transducer thickness-independent ultrasonic imaging method for accurate characterization of microstructural gradients in monolithic and composite tubular structures. [Cleveland, Ohio] : National Aeronautics and Space Administration, Lewis Research Center, 1998.

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Chapitres de livres sur le sujet "Gradients de microstructure"

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Graja, Paul, et Norbert Meyendorf. « Characterization of Materials Microstructure and Surface Gradients using Advanced Techniques ». Dans Handbook of Nondestructive Evaluation 4.0, 799–818. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-73206-6_28.

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Graja, Paul, et Norbert Meyendorf. « Characterization of Materials Microstructure and Surface Gradients using Advanced Techniques ». Dans Handbook of Nondestructive Evaluation 4.0, 1–20. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-48200-8_28-2.

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Genzel, C. « Problems Related to X-Ray Stress Analysis in Thin Films in the Presence of Gradients and Texture ». Dans Diffraction Analysis of the Microstructure of Materials, 473–503. Berlin, Heidelberg : Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-662-06723-9_18.

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Chen, J. Z., Liang Zhen, Bao You Zhang, Y. X. Cui et Sheng Long Dai. « Through-Thickness Microstructure, Texture and Strength Gradients in AA 7055 Rolled Plate ». Dans Materials Science Forum, 957–60. Stafa : Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-432-4.957.

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Zhou, Liucheng, et Weifeng He. « Gradient Microstructure Characteristics and the Formation Mechanism in Titanium Alloy Subjected to LSP ». Dans Gradient Microstructure in Laser Shock Peened Materials, 41–76. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-1747-8_3.

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Zhou, Liucheng, et Weifeng He. « Improvement of High Temperature Fatigue Performance in Ni-Based Alloys by LSP-Induced Gradient Microstructures ». Dans Gradient Microstructure in Laser Shock Peened Materials, 103–38. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-1747-8_5.

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Zhou, Liucheng, et Weifeng He. « Study on the Compound Process of LSP and the Strengthening Mechanism on Aero-Engine Blades ». Dans Gradient Microstructure in Laser Shock Peened Materials, 179–227. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-1747-8_7.

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Zhou, Liucheng, et Weifeng He. « Characteristics of Laser-Induced Plasma Shock Wave in Metal Materials ». Dans Gradient Microstructure in Laser Shock Peened Materials, 15–40. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-1747-8_2.

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Zhou, Liucheng, et Weifeng He. « Mechanical Behavior and the Strengthening Mechanism of LSP-Induced Gradient Microstructure in Metal Materials ». Dans Gradient Microstructure in Laser Shock Peened Materials, 139–77. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-1747-8_6.

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Zhou, Liucheng, et Weifeng He. « General Introduction ». Dans Gradient Microstructure in Laser Shock Peened Materials, 1–14. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-1747-8_1.

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Actes de conférences sur le sujet "Gradients de microstructure"

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Dollhofer, Benjamin, Christian Krämer, Niki Nouri1, Stefan Dietrich et Volker Schulze1. « Characterization of Martensitic-Bainitic Mixed Microstructures Created by Inductive Short Time Austempering of AISI 4140 ». Dans IFHTSE 2024, 41–49. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.ifhtse2024p0041.

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Abstract Induction surface hardening is a process often used in industrial applications to efficiently increase the lifetime of components. Recently, this process has been enhanced with the inductive short time austempering process, creating a martensitic-bainitic microstructure. It is well-known that in homogeneous mixed microstructures, an optimally adjusted volume fraction of bainite can significantly increase the lifetime of the components even further. Regarding inductive short time austempering, there is a lack of knowledge in characterizing and differentiating graded microstructures, which occur due to the temperature gradients within the process. Therefore, three methods were investigated: the analysis of the grayscale profile of metallographic sections, the hardness profile and the full width at half maximum (FWHM) profile from the intensity curve (rocking curve) of the X-ray diffraction pattern. These methods were initially applied to homogeneous structures and evaluated. The findings were then transferred to graded microstructures. Finally, the graded microstructures could be differentiated both via the hardness profile and the FWHM value, while the grayscale analysis only allowed qualitative statements to be made. It became evident that both the volume fractions and their structure are crucial for subsequent mechanical characterization. Since the martensitic microstructure is easier to identify, it serves as a reliable reference for evaluating the mixed microstructure. In summary, these findings offer the foundation for further characterization of graded martensitic-bainitic mixed microstructures.
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Teixeira, J., K. Jeyabalan, G. Geandier, J. Dulcy, B. Denand, S. Denis, M.-R. Chini, S. D. Catteau et M. Courteaux. « In Situ High-Energy XRD Determination and Modeling of Internal Stresses during Heat Treatment of Carburized and Carbonitrided Low-Alloyed Steels ». Dans IFHTSE 2024, 316–20. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.ifhtse2024p0316.

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Abstract Thermochemical treatments like carburizing and carbonitriding allow to improve the properties in low-alloyed steels, which depend mainly on the distributions of residual stresses and microstructures. As the fatigue properties depend mainly on the latter, a fundamental understanding must be established regarding their formation during the cooling after the enrichment treatment. This study introduces an experimental and simulation analysis of microstructure and internal stresses evolutions and their couplings. Influence of the carbon and nitrogen enrichments is highlighted. An original experimental technique is introduced to follow in situ by High-Energy XRD the phase transformation kinetics and the evolutions of the internal stresses during cooling, inside laboratory scale samples with C/N composition gradients. The usual trends are confirmed regarding the carburizing: the carbon-enriched case is the last to undergo phase transformations. Due to the phase transformation strains, the surface ends up with compression residual stresses, whereas the center is put in tension. Conversely, for carbonitriding, unusual profiles of microstructures and residual stresses are observed. The presence of nitrogen induces a drastic loss of hardenability in the enriched case. This modifies the chronology of the phase transformations and this leads to tensile residual stresses at the surface for the studied cooling conditions. In the nitrogen-enriched case, a fine microstructure is formed during cooling and retained austenite remains, leading to a lower hardness than in the martensite layer beneath. A coupled thermal, mechanical and metallurgical model predicting the phase transformation kinetics and the evolutions of internal stresses is set up. It takes account of the local carbon and nitrogen concentrations in the case. For carburizing, predictions are in good agreement with experiment. Simulations for carbonitriding achieve to predict the tensile stresses in the nitrogen-enriched case, which are due to the loss of hardenability. In both cases, residual stresses come mostly from phase transformation plasticity strains.
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Koko, Abdalrhaman, Wesley Bond, Rob Simpson, Maria Lodeiro, Aldo Mendieta et Gavin Sutton. « Investigating the Microstructural Evolution of Inconel 718 under a Controlled Thermal Gradient ». Dans AM-EPRI 2024, 449–60. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.am-epri-2024p0449.

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Abstract This study demonstrates the Electro-Thermal Mechanical Testing (ETMT) system's capability to analyze the thermo-mechanical behavior of Inconel 718 (IN718) at a heating rate of 5 °C/s, achieving temperatures up to 950 °C. The temperature profile peaks at the sample's center and is approximately 25 °C at the extremes. Upon reaching 950 °C, the sample was aged for 30 hours before being rapidly quenched. This process froze the microstructure, preserving the phase transformations that occurred at various temperatures across the temperature parabolic gradient, which resulted in a complex gradient microstructure, providing a comprehensive map of phase transformations in IN718. The integration of thermal measurement, COMSOL modeling, scanning electron microscopy enabled a thorough characterization of the microstructural evolution in IN718, linking observed phases to the specific temperatures which provided a rapid screening of the effect of using different heating treatment routes.
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Nouri, Niki, Stefan Dietrich et Volker Schulze. « Transformation Induced Plasticity during Precipitation Strengthening of Maraging Steels ». Dans IFHTSE 2024, 50–56. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.ifhtse2024p0050.

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Abstract Effective heat treatment is essential for optimizing the properties of steels in various applications. Understanding the evolution of steel microstructure during intrinsic or post-heat treatment, along with managing distortions and residual stresses, is crucial for ensuring component usability. In laser-based additive manufacturing, high temperature gradients and cooling rates induce residual stresses, impacting the heat-affected zones. However, there remains a gap in understanding how stress influences precipitation during heat treatment, particularly regarding transformation-induced plasticity (TRIP), where a stress triggers deformation during phase transformation. This study aims to investigate TRIP effects during the aging of maraging steels, commonly employed in laser-based powder bed fusion. During the experiments, the steels were continuously aged under varying compression stresses. By isolating TRIP strain from total strain, the study establishes a relationship between maximum TRIP strain after phase transformation and applied stress, defining specific TRIP constants for each steel. The presence of TRIP strain has been confirmed during short time continuous aging treatments, indicating its significance even in the initial stages of the heat treatment process. While the applied stress level does not affect hardness, significant differences in maximum hardness values after aging were observed among the investigated materials. Furthermore, a comparative analysis of different maraging steels revealed a positive correlation between the TRIP constant and the amount of precipitation, and consequently, hardness. These findings confirm the role of TRIP in precipitate formation in maraging steels and provide a foundation for further understanding and predicting post-heat treatment material states.
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Wang, Anning, Hui Zhang, Feng Qi, Yelong Wang et Runsheng Liu. « Phase Gradient Metasurface RCS Reduction Technique Based on Metal Mesh Microstructure ». Dans 2024 2nd International Conference on Signal Processing and Intelligent Computing (SPIC), 1028–33. IEEE, 2024. http://dx.doi.org/10.1109/spic62469.2024.10691553.

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Samanta, Avik, Ninggang Shen, Haipeng Ji, Weiming Wang, Hongtao Ding et Jingjing Li. « Simulations of Microstructure Evolution During Friction Stir Blind Riveting Using a Cellular Automaton Method ». Dans ASME 2017 12th International Manufacturing Science and Engineering Conference collocated with the JSME/ASME 2017 6th International Conference on Materials and Processing. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/msec2017-3034.

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Friction stir blind riveting (FSBR) is a novel and highly efficient joining technique for lightweight metal materials, such as aluminum alloys. The FSBR process induced large gradients of plastic deformation near the rivet hole surface and resulted in a distinctive gradient microstructure in this domain. In this study, microstructural analysis is conducted to analyze the final microstructure after the FSBR process. Dynamic recrystallization (DRX) is determined as the dominant microstructure evolution mechanism due to the significant heat generation during the process. To better understand the FSBR process, a two-dimensional Cellular Automaton (CA) model is developed to simulate the microstructure evolution near the rivet hole surface by considering the FSBR process loading condition. To model the significant microstructure change near the rivet hole surface, spatial distributed temporal thermal and mechanical loading conditions are applied to simulate the effect of the large gradient plastic deformation near the hole surface. The distribution grain topography and recrystallization fraction are obtained through the simulations, which agree well with the experimental data. This study presents a reliable numerical approach to model and simulate microstructure evolution governed by DRX under the large plastic deformation gradient in FSBR.
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KROMER, Robin. « Multiscale Analysis of 316L stainless steel microstructures for WAAM manufacturing tool prediction ». Dans Material Forming. Materials Research Forum LLC, 2024. http://dx.doi.org/10.21741/9781644903131-38.

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Abstract. This study proposes a new approach on a multiscale analysis of 316L stainless steel microstructures to enhance the predictability and homogeneity of microstructure for the Wire Arc Additive Manufacturing (WAAM) process. Despite the promise in the fabrication of large-scale metallic components, achieving consistent microstructure and mechanical properties remains a challenge with WAAM. This research investigates the solidification behaviors, grain morphology, and mechanical characteristics of 316L stainless steel, aiming to develop a predictive framework for WAAM process optimization. By employing a systematic approach to the fabrication and subsequent analysis of 316L stainless steel walls, the study reveals critical insights into thermal gradients, solidification rates, and their impacts on microstructural features. The findings are anticipated to inform improved fabrication strategies, leading to enhanced mechanical properties and reliability in WAAM-manufactured components based on mereotopology philosophical framework. A spatio-temporal of the different tracks could be defined based on trajectory analysis.
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Voyiadjis, George Z., Robert J. Dorgan et J. R. Dorroh. « Bridging Length Scales Between Macroscopic Response and Microstructure Through Gradient Anisotropic Damage for MMC ». Dans ASME 2001 Engineering Technology Conference on Energy. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/etce2001-17034.

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Abstract This work provides a consistent and systematic framework for the gradient approach in coupled damage-plasticity that enables one to better understand the effects of material inhomogeneity on the macroscopic behavior and the material instabilities. The idea of multiple scale effects is made more general and complete by introducing damage and plasticity internal state variables and the corresponding gradients at both the macro and mesoscale levels. The development of evolution equations for plasticity and damage is treated in a similar mathematical approach and formulation since both address defects such as dislocations for the former and cracks/voids for the later.
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Collins, R. W., et Sangbo Kim. « Spectroscopic Ellipsometry with Multichannel Detection : Applications in Real Time Monitoring of Optical Coatings ». Dans Optical Interference Coatings. Washington, D.C. : Optica Publishing Group, 1995. http://dx.doi.org/10.1364/oic.1995.wa15.

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Inhomogeneities in the composition and microstructure as a function of depth in thin film coatings, whether intentional or unintentional, strongly influence their performance in a variety of applications including optical coatings, electrochromics, and photovoltaics. Spectroscopic ellipsometry has proven to be a very useful technique for characterizing such property gradients.1 With ex situ measurements, however, the available data are insufficient to handle continuous gradients with high resolution. In our work, we have solved this problem by collecting ellipsometric data continuously versus wavelength and time during film growth. By applying this real time spectroscopic ellipsometry (RTSE), we have extracted continuous microstructural gradients having complex profiles with ~10 Å depth resolution, at the same time determining the instantaneous deposition rate and the evolution of the surface roughness layer thickness. Although the approach has been first demonstrated for characterizing intentional void volume fraction gradients in the window layers used for thin film photovoltaic devices, it has wider generality in a variety of other thin film coatings applications.
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Van Nguyen, V., A. Brunet-Bruneau, S. Fisson, J. M. Frigerio, G. Vuye, Y. Wang, F. Abelès, J. Rivory, M. Berger et P. Chaton. « Determination of Refractive Index Profiles by Combining Visible and IR Ellipsometry Measurements ». Dans Optical Interference Coatings. Washington, D.C. : Optica Publishing Group, 1995. http://dx.doi.org/10.1364/oic.1995.wb14.

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The determination of refractive index profiles in transparent layers, like every inverse problem remains a difficult task. The chance to get a realistic solution depends of course on the magnitude and shape of the profile and on the distance over which it is spread out. Two classes of problems can be identified: non intentional gradient resulting for example from the microstructure of the evaporated films (columnar growth in dielectric films) DI, or the adsorption of a polymer solution onto a solid wall[2], and intentional gradients designed for specific applications. In the second case, the profile deduced from optical measurements can be compared with the target after taking into account the errors introduced during the deposition process. The results that we present in this paper concern compositional gradients in silicon oxynitride films.
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Rapports d'organisations sur le sujet "Gradients de microstructure"

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Castelluccio, Gustavo, Hojun Lim, John Emery et Corbett Battaile. Fracture Toughness of Microstructural Gradients. Office of Scientific and Technical Information (OSTI), octobre 2016. http://dx.doi.org/10.2172/1761823.

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McNeil, Anne J. New Microstructures for Old Monomers : Syntheses of Gradient pi-Conjugated Copolymers. Fort Belvoir, VA : Defense Technical Information Center, juin 2010. http://dx.doi.org/10.21236/ada534918.

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Burton R. Patterson. Effect of Casting Conditions and Composition on Microstructural Gradients in Roll Cast Aluminum Alloys. Office of Scientific and Technical Information (OSTI), mai 2008. http://dx.doi.org/10.2172/927781.

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Wootton, K. P., Z. Wu, B. M. Cowan, A. Hanuka, I. V. Makasyuk, E. A. Peralta, K. Soong, R. L. Byer et R. J. England. Observation of 690 MV m-1 Electron Accelerating Gradient with a Laser-Driven Dielectric Microstructure. Office of Scientific and Technical Information (OSTI), janvier 2016. http://dx.doi.org/10.2172/1234198.

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Oliynyk, Kateryna, et Matteo Ciantia. Application of a finite deformation multiplicative plasticity model with non-local hardening to the simulation of CPTu tests in a structured soil. University of Dundee, décembre 2021. http://dx.doi.org/10.20933/100001230.

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In this paper an isotropic hardening elastoplastic constitutive model for structured soils is applied to the simulation of a standard CPTu test in a saturated soft structured clay. To allow for the extreme deformations experienced by the soil during the penetration process, the model is formulated in a fully geometric non-linear setting, based on: i) the multiplicative decomposition of the deformation gradient into an elastic and a plastic part; and, ii) on the existence of a free energy function to define the elastic behaviour of the soil. The model is equipped with two bonding-related internal variables which provide a macroscopic description of the effects of clay structure. Suitable hardening laws are employed to describe the structure degradation associated to plastic deformations. The strain-softening associated to bond degradation usually leads to strain localization and consequent formation of shear bands, whose thickness is dependent on the characteristics of the microstructure (e.g, the average grain size). Standard local constitutive models are incapable of correctly capturing this phenomenon due to the lack of an internal length scale. To overcome this limitation, the model is framed using a non-local approach by adopting volume averaged values for the internal state variables. The size of the neighbourhood over which the averaging is performed (characteristic length) is a material constant related to the microstructure which controls the shear band thickness. This extension of the model has proven effective in regularizing the pathological mesh dependence of classical finite element solutions in the post-localization regime. The results of numerical simulations, conducted for different soil permeabilities and bond strengths, show that the model captures the development of plastic deformations induced by the advancement of the cone tip; the destructuration of the clay associated with such plastic deformations; the space and time evolution of pore water pressure as the cone tip advances. The possibility of modelling the CPTu tests in a rational and computationally efficient way opens a promising new perspective for their interpretation in geotechnical site investigations.
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