Tesi sul tema "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.
Testo completoBaudoin, Pierre. "Caractérisation et identification de propriétés de matériaux métalliques à gradients de microstructure". Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10015/document.
Testo completoThe 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
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.
Testo completoPh.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr PhD
Largiller, Grégory. "Maîtrise du frittage de matériaux céramique-métal à gradients de composition et de structure". Grenoble INPG, 2010. http://www.theses.fr/2010INPG0160.
Testo completoGraded 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
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.
Testo completoThe 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
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.
Testo completoThe 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
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.
Testo completoFradet, Clémence. "Caractérisation d’élastomères synthétiques par indentation instrumentée (I.I.T.) : protocoles et applications". Thesis, Tours, 2019. http://www.theses.fr/2019TOUR4014.
Testo completoInstrumented 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
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.
Testo completoThe 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
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.
Testo completoErnould, Clément. "Développement et application d’une méthode à haute résolution angulaire pour la mesure des gradients d’orientation et des déformations élastiques par microscopie électronique à balayage". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0225.
Testo completoUnderstanding the deformation mechanisms in crystalline materials requires a fine characterization of microstructures. The precise measurement of lattice rotations and elastic strains in the scanning electron microscope is the aim of the so-called high-angular resolution methods. For this purpose, digital image correlation techniques are used in order to register electron diffraction patterns. In this thesis, an original registration approach is proposed. The displacement field across the whole scintillator is modelled by a linear homography. Such a shape function is often met is the field of computer vision to describe projective transformations. The homography between two patterns is measured from a single and large region of interest using a numerically efficient inverse-compositional Gauss-Newton algorithm. It integrates a correction of optical distortions caused by camera lenses and its convergence is ensured by a pre-alignment step of the patterns. The latter relies on global cross-correlation algorithms based on Fourier-Mellin and Fourier transforms. It fairly accounts for rotations up to approximately ten degrees with an accuracy typically between 0.1 and 0.5°. The homography is measured independently from the projection geometry, which is only considered afterwards to analytically deduce the rotations and elastic strains. The proposed method is validated numerically from simulated and optically distorted patterns showing disorientations up to 14° in the presence of elastic strains up to 5×10⁻². The accurate measurement of elastic strains between 1×10⁻⁴ and 2×10⁻³ requires a correction of radial distortion effects, even when the disorientation angle is small. Finally, the method is applied to patterns acquired by means of electron backscatter diffraction (EBSD) and in transmission using the new on-axis transmission Kikuchi diffraction (TKD) configuration. Plastically deformed polycrystalline metals as well as semiconductors are characterized. The method highlights fine details of the microstructure of a quenched and tempered martensitic steel and of an interstitial free steel deformed by 15% in tension, although plastic deformation deteriorates the diffraction contrast. The deformation structures in a nanostructured aluminium obtained by severe plastic deformation are also analysed by coupling the image registration method to the on-axis TKD configuration. This coupling allows a high spatial resolution (3 to 10 nm) and a high angular resolution (0.01 to 0.05°) to be reached simultaneously. Elastic strain maps are obtained at the nanoscale in a SiGe thin foil. The geometrically necessary dislocation densities in a GaN single crystal are mapped with a resolution of about 2.5×10⁻³ µm⁻¹ (i.e. 8×10¹² m⁻²)
Hasan, Md Nazmul. "Microstructure and mechanical properties of a CrMnFeCoNi high-entropy alloy with gradient structures". Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23036.
Testo completoRhaipu, Soranat. "The effect of microstructural gradients on the superplastic forming of Ti-6Al-4V". Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396242.
Testo completoLu, Peizhen. "Microstructural evolution and macroscopic shrinkage in the presence of density gradients and agglomeration /". The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488194825665703.
Testo completoBenrabah, Imed-Eddine. "Développement d’alliages métalliques à gradient de composition pour l’exploration combinatoire des microstructures". Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALI005.
Testo completoThe transformation of austenite into ferrite in steels is of considerable interest in controlling the final properties of steels, in particular Advanced High-Strength Steels (AHSS) such as Dual Phase (DP) steel. Despite tremendous efforts in understanding the mechanisms controlling ferrite formation, the role of substitutional elements during ferrite growth and their interaction with the migrating α/γ interface remain unclear. Several models have been developed to describe ferrite growth kinetics in ternary and higher systems. The solute drag based models have been successfully used to predict kinetics for multiple substitutional solutes, compositions and temperatures in ternary systems. However, the extension of this model to higher order systems highlighted a complex behavior of the interaction between the different interstitial and substitutional elements at the interface. Validation of the developed models requires an experimental study of the effect of both composition and temperature on growth kinetics. The aim of this contribution is to present a complete combinatorial high-throughput methodology to accelerate the investigation of the dependency of ferrite growth kinetics on substitutional composition in alloy steels. It is noteworthy, however, that this new methodology could be used to study any other phase transformation in any other metallic alloy. The essence of the methodology is to fabricate materials with macroscopic composition gradients, and to perform time- and space-resolved in situ high-energy X-ray diffraction experiments to gather the austenite-to-ferrite phase transformation kinetics in many points of the compositional space. Diffusion couples containing millimeter-scale solute gradients and an almost constant carbon content were generated using the present methodology and used to study ferrite growth kinetics at inter-critical temperatures using in-situ high-energy X-ray diffraction experiments. During 4 days of experiments, more than 1500 kinetics were gathered for different compositions and at different temperatures. This dataset of unprecedented size was used validate a modified version of the three-jump solute drag model for both ternary and quaternary systems. The model calculations matched experimental transformation kinetics at all investigated temperatures and over almost all the investigated composition ranges of Si, Cr, Mn, Ni, and Mo, contrary to results from para-equilibrium (PE) and local equilibrium negligible partitioning (LENP) models. Additionally, it was demonstrated that the calibration of thermodynamic parameters in ternary systems held true in quaternary systems, paving the way towards modeling of the transformation in higher-order systems
Lindsay, Marianne Rose. "Development of Lithium Disilicate Microstructure Graded Glass-Ceramic". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/33243.
Testo completoMaster of Science
Luscher, Darby J. "A hierarchical framework for the multiscale modeling of microstructure evolution in heterogeneous materials". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33968.
Testo completoCusick, Michael Christopher. "THE USE OF SELECTIVE ANNEALING FOR SUPERPLASTIC FORMING OF MG AZ31 ALLOY". UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_theses/492.
Testo completoMahajan, Suyog N. "INFLUENCE OF NATURAL CONVECTION DURING DENDRITIC ARRAY GROWTH OF METAL ALLOYS (GRADIENT FREEZE DIRECTIONAL SOLIDIFICATION)". Cleveland State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=csu1537496405142091.
Testo completoD'Agostino, Marco Valerio. "Generalized continua and applications to finite deformations of quasi-inextensible fiber reinforcements". Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0061/document.
Testo completoDered materials in the simplest and more effective way. However, there are some cases in which the considered materials are heterogeneous even at relatively large scales and, as a consequence, the effect of microstructure on the overall mechanical behavior of the medium cannot be neglected. In such situations, Cauchy continuum theory may not be useful to fully describe the mechanical behavior of considered materials. It is in fact well known that such continuum theory is not able to catch significant phenomena related to concentrations of stress and strain and to specific deformation patterns in which high gradients of deformation occur and which are, in turn, connected to particular phenomena which take place at lower scales. Generalized continuum theories may be good candidates to model such micro-structured materials in a more appropriate way since they are able to account for the description of the macroscopic manifestation of the presence of microstructure in a rather simplified way. The present manuscript is organized as follows: In ch.1 a general description of fibrous composite reinforcements is given. In ch.2 some fundamental issues concerning classical continuum mechanical models are recalled. In ch.3 we start analyzing some discrete and continuum models for the description of the mechanical behavior of 2D woven composites. At this stage of the manuscript, we want to show how some discrete numerical simulations allowed us to unveil some very special deformation modes related to the effect of the local bending of fibers on the overall macroscopic deformation of fibrous composite reinforcements. Such discrete simulations showed rather clearly that microscopic bending of the fibers cannot be neglected when considering the deformation of fibrous composite reinforcements. For this reason, we subsequently introduced a continuum model which is able to account for such microstructure-related effects by means of second gradient terms appearing in the strain energy density. In ch.4 we reduce the general continuum mechanical framework introduced in ch.2 to the particular case of 2D continua. In ch.5 we introduce a strong kinematical hypothesis on the admissible deformations, assuming that the yarns composing the woven reinforcements are inextensible
Stephen, Juanita Peche. "3-D Printing, Characterizing and Evaluating the Mechanical Properties of 316L Stainless Steel Materials with Gradient Microstructure". Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/102780.
Testo completoMaster of Science
The mechanical performance of Selective Laser Melting (SLM) fabricated materials is an important topic in research. Strengthening the performance of these materials can be achieved through implementing a gradient within the microstructure, referred to as Materials with Graded Microstructure (MGMs). A complicated microstructure can weaken the microstructure, and this can be resolved by optimizing the microstructure during SLM 3D printing, in which the processing parameters are tailored. In this study, the mechanical properties of these MGMs were characterized and evaluated. The gradient in these materials were created by modifying SLM process parameters (scanning speed, hatch spacing, and laser power and scanning speed) during the build. Optical and scanning electron microscopy (SEM) was used to characterize these the microstructure of these MGMs, and image processing was used to examine the distribution of cells and melt pools characteristics throughout the region where the processing parameters changed. This investigation shows that laser power, scanning speed, and hatch spacing have a direct effect on the size and shape of the cells and melt pools, compared to scanning speed, which shows an effect on melt pools. Dog bone structures are 3-D printed with a graded microstructure that has small cells and melt pools at the edges, compared to the center, by changing the laser power and scanning speed. Tensile and fatigue analysis are performed and compared for samples with constant and graded microstructures, which reveal that the mechanical properties of the MGMs perform similar to the parameter at the edges, but differently in fracture mechanics.
Kuhr, Samuel J. "CHARACTERIZATION AND DEFORMATION BEHAVIOR OF MICROSTRUCTURAL GRADIENTS IN THE LOW SOLVUS HIGH REFRACTORY (LSHR) NICKEL BASE SUPERALLOY". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462629676.
Testo completoRaharijaona, Jean-Joël. "Elaboration de matériaux w-Cu à gradient de propriétés fonctionnelles (FGM) par métallurgie des poudres : application en tant que composants face au plasma de machines de fusion thermonucléaire de type Iter". Grenoble INPG, 2009. http://www.theses.fr/2009INPG0123.
Testo completoThe aim of this study was to study and optimize the sintering of W-Cu graded composition materials, for first wall of Iter-like thermonuclear reactor application. The graded composition in the material leads to the functionally graded material (FGM). It was shown the interest to use W-Cu FGM to improve the lifetime of plasma facing components (PCF), by performing simplified thermomechanical calculations. To process W-Cu FGM, powder metallurgy route was analyzed and optimized from W-CuO sintering helped specify mixtures. The interest to reduce the oxides on the sintering of W-Cu powder mixtures was highlightied. An optimal heating treatment under He/H2 atmosphere was defined for W-Cu sintering. The effect of the Cu-content on W-Cu sintering helped specify the sintering mechanisms. The study of W-Cu FGM sintering and differential grain size revealed two liquid migration steps. These two steps were confirmed by using a model of capillary pressure calculation
Hilli, Naima. "Rôle de la localisation (inter ou intragranulaire) des impuretés sur le frittage de l'alumine alpha couplée ou non avec un gradient de température". Saint-Etienne, EMSE, 2009. http://www.theses.fr/2009EMSE0018.
Testo completoSince the beginning of the 1960’s Years, with the works of Coble, the sintering of alumina was and continues to be the subject of very many research tasks with a special attention on the role of the doping agents on the mechanisms of densification and the microstructural evolution of this model and industrial ceramic material. Their respective effectiveness does not appear in the same stages of densification; it is thus possible to think that their actions could be complementary in the case of a codoping. The objective of the present work is the study of the influence of the presence of impurities in the alumina powders on the densification and the microstructure of the sintered pieces. To be done, three types of impurities were studied: doping agents, codoping agents and residual impurities coming from the elaboration process of the powder or during the processing (crushing). It was shown that the codoping leads to a rate of densification always weaker compared to the monodoped alumina powders. By using the model of “Master Sintering Curve (MSC)”, it was shown that the way of diffusion chosen during the intermediate stage evolves according to the type of doping or codoping agent present in the initial powder. It was also shown that the presence of inter and/or intragranular impurities in alumina is harmful to the densification during a sintering under a heat gradient. Moreover, the combination of a heat gradient and the inter and intragranular impurities lead to a faceting of the grains which will decrease consequently the potentiality of the sintering of the system and will allow obtaining porous materials with fine grains
Guevenoux, Camille. "Réparation de pièces métalliques par Directed Energy Deposition : gradient microstructural, comportement mécanique et tenue en fatigue". Thesis, Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAX006.
Testo completoDirected Energy Deposition (DED) process is a powder-jet additive manufacturing process involving a nozzle composed of coaxial laser beam and powder stream. The laser generates a melt pool in which the powder is projected, it melts and then solidifies creating a deposit as the nozzle moves. However, this process is particularly appealing to repair valuable metallic components. The small spot size and fast motions of the laser causes strong thermal gradient and important cooling rates and this specific thermal evolution is responsible for the formation of microstructures different from traditional processes like forge or foundry. Consequently, the repaired components exhibits an interface between the base material (generally wrought) and the region reconstructed with DED. This microstructural gradient leads to a mechanical gradient and therefore to localization phenomena which can affect the lifetime of repaired components. This thesis proposes a method to characterize the interface region of repaired components. A semi-analytic tool has been developed to model the thermal evolution during the repair process in order to design representative specimens, in terms of geometry but also in terms of thermal history. The microstructural gradient through the interface is first characterized with a SEM and EBSD analyses. Tensile specimen are then taken in the interface region and loaded during SEM in-situ tests. The strain is followed at the micrometric scale with Digital Image Correlation, what provides the information regarding localization phenomena. Those experimental data are then injected into a numerical method to identify the local parameters of the mechanical behavior by minimizing the error between the experimental and numerical fields. Using this mechanical gradient, the stress in fatigue specimens is derived. A fatigue limit is then derived from the experimental results of the fatigue tests and it is compared to the endurance of the original part to estimate the reduction of resistance caused by the repair
Zhang, Chunyang. "Crystallographic study on microstructure and martensitic transformation of NiMnSb meta-magnetic multi-functional alloys". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0030/document.
Testo completoNiMnSb based Heusler type alloys, as a novel multi-functional material has attracted considerable attention due to their multiple properties, such as magnetic shape memory effect, magnetocaloric effect, exchange bias effect, magnetoresistance effect. To date, many aspects of the NiMnSb alloys, such as crystal structure, microstructure, magnetic properties and mechanical properties etc., have been widely investigated. However, many fundamental issues of this family of materials have not been fully revealed, which largely restricts the development of this new kind of multi-functional materials. In the present work, a thorough investigation has been conducted on ternary NiMnSb alloys in terms of crystal structures of austenite and martensite; microstructural and crystallographic features of martensite; martensitic transformation orientation relationship (OR) and its correlation with variant organization; transformation deformation characteristics and self-accommodation of transformation strain. The work confirmed that the austenite of NiMnSb alloys possesses a cubic L21 crystal structure belonging to the space group Fm3m (No. 225). The martensite has a four-layered orthorhombic (4O) structure with space group Pmma (No. 051). The lattice constants of the Ni50Mn37Sb13 and Ni50Mn38Sb12 martensite are aM = 8.5830 Å, bM = 5.6533 Å and cM = 4.3501Å, and aM = 8.5788 Å, bM = 5.6443 Å and cM = 4.3479 Å, respectively. The microstructure of the 4O NiMnSb modulated martensite possesses a hierarchical organization feature. Martensite fine lamellae are first organized into broad plates. Each plate possesses 4 distinct twin related variants A, B, C and D forming type I twins (A and C; B and D), type II twins (A and B; C and D) and compound twins (A and D; B and C). The variant interfaces are defined by the corresponding twinning planes. The complete twinning elements for each twin relation are fully determined. The plates are further organized into sub-colonies and sub-colonies into plate colonies. The neighboring plates in one sub-colony and plate colony share one common plate interface orientation. Plate colonies with different oriented plate interfaces finally take the whole original austenite grain. The Pitsch OR, specified as {011}A // {221}M and <011>A // <122>M, is the effective OR between the cubic austenite and the 4O modulated martensite. Under this OR, a maximum of 24 distinct variants can be produced. The 24 variants are organized into 6 distinct variant colonies, 12 distinct sub-colonies and finally 6 distinct plate colonies. The twinning plane of type I twin and the intra-plate plate interfaces all correspond to the same family of {011}A planes of austenite. The formation of martensite variant colonies can be both form intragranular and intergranular during the phase transformation. The sandwich structured variant colony is the basic microstructural unit of the martensite. This structure is composed of twin related variants and possesses the full compatible inner variants interfaces and invariant habit planes. The deformation manner of the twin related variants result in the high occurrence frequency of the type II twins and affects the morphology of the sandwich colonies. The wedge-shaped structure is composed of two compatible sandwiches and conjoined by a midrib plane with a small atomic misfit. All these results indicate that the martensitic transformation is self-accommodated and the microstructure is determined by the self-accommodation of the microstructural constituents. The aim of this work is to provide fundamental crystallographic and microstructural information of NiMnSb alloys for interpreting their magnetic and mechanical characteristics associated with the martensitic transformation and further investigations on property optimization
Chen, Zhe. "Relation microstructure et propriété mécanique des films de ZrO2 obtenus par MOCVD". Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00637177.
Testo completoLe, Duc Trung. "Modèle d'endommagement à gradient : approche par homogénéisation". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066662/document.
Testo completoThe aim of this work is to propose a general framework to obtain a gradient damage model from the micro-structural level. It is based, firstly, on the homogenization method to derive an effective medium from the microstructure, and secondly, on the variational formulation of a damage evolution law from the homogenized medium. We propose, as a first step, an approach based on asymptotic expansion and the variational method for homogenizing a periodic elastic medium. To model the localization of damage, this approach has been extended to a quasi-periodic heterogeneous medium. From an example of quasi periodically micro-cracked solid, we obtain an elastic energy that not only depends on the gradient of the damage but also the strain gradients. Based on the principle of energy minimization, we propose the construction of a gradient damage model from the elastic energy homogenized in the second part. By adding some hypothesis to simplify the model, we can construct localized damage and strain solutions in closed form. Finally, a numerical resolution scheme, which is based on an alternate minimization algorithm, is proposed for the one-dimensional traction bar test. From the numerical results, the advantages and disadvantages of the model are discussed
Maurel, Pierre. "Déformation plastique sévère des surfaces d’alliages à faible densité par grenaillage ultrasonique : gradients de microstructures, comportements en fatigue et en tribologie". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0182.
Testo completoThe impact of ultrasonic shot peening on titanium and aluminium alloys is studied at room temperature and at cryogenic temperature. This process may also be called surface mechanical attrition treatment (SMAT). Fatigue strength and tribological behaviour are investigated in order to better understand the pros and cons of this process. Two titanium alloys were chosen: pure titanium in its fully α form and β-metastable titanium in its fully β form. This choice makes it possible to correlate the influence of the initial microstructure on the treatment of severe plastic deformation and on the final properties. The β-metastable titanium is sensitive to strain-induced martensitic transformation, which allows exploring the possibility of introducing martensite to the shot-peened surface to delay, for example, short crack propagation in fatigue testing. Shot peening at cryogenic temperature in this case improves the initiation of the martensitic transformation. In addition to facilitating martensitic transformation, cryogenic temperature shot peening increases the yield strength of alloys during processing, which has the effect of reducing the flow of material at the shot-peened surface. Thereby, it improves surface integrity and changes tribological and fatigue properties. Two precipitation hardenable aluminum alloys were also studied: 2024 and 7075. The purpose of this aluminium study is to compare the impact of ultrasonic shot blasting when used before or after precipitation aging. As the dislocations produced during ultrasonic shot-peening serve as preferential nucleation sites, the objective is to explore the possibility of improving (e.g. in terms of hardness) the precipitation aging by refining the size of the precipitates and increasing their density. The use of two series of aluminium should make it possible to compare the effect of the treatment on the two different alloying compositions. In addition, these two alloys show significant differences in terms of defect sensitivity, permitting to study the impact of surface integrity after ultrasonic shot-peening on mechanical properties. The study of tribological and fatigue behaviour allows to conclude about the effectiveness of these treatments under common conditions of use
Hanke, Hauke. "Rigorous derivation of two-scale and effective damage models based on microstructure evolution". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2014. http://dx.doi.org/10.18452/17031.
Testo completoThis dissertation at hand deals with the rigorous derivation of such effective models used to describe damage processes. For different rate-independent damage processes in linear elastic material these effective models are derived as the asymptotic limit of microscopic models. The starting point is represented by a unidirectional microstructure evolution model which is based on a family of ordered admissible microstructures. Each microstructure of that family possesses the same intrinsic length scale. To derive an effective model, the asymptotic behavior of this intrinsic length scale is investigated with the help of techniques of the two-scale convergence. For this purpose, a microstructure-regularizing term, which can be understood as a discrete gradient for piecewise constant functions, is needed to identify the limit model. The microstructure of the effective model is given pointwisely by a so-called unit cell problem which separates the microscopic scale from the macroscopic scale. Based on these homogenization results for unidirectional microstructure evolution models, effective models for brutal damage processes are provided. There, the microstructure consists of only two phases, namely undamaged material which comprises defects of damaged material with various sizes and shapes. In this way damage progression can be modeled by the growth of inclusions of weak material, the growth of voids, or the growth of microscopic cracks. The size of the defects is scaled by the intrinsic length scale and the unidirectional microstructure evolution prevents that, for a fixed length scale, the defects shrink for progressing time. According to the unit cell problem, the material of the limit model is then given as a mixture of damaged and undamaged material. In a specific material point of the limit model, that unit cell problem does not only define the mixture ratio but also the exact geometrical mixture distribution.
Wang, Huan. "Viscous and second gradient regularization techniques for the description of the behavior of geomaterials". Thesis, Ecole centrale de Nantes, 2019. http://www.theses.fr/2019ECDN0063.
Testo completoGeomaterials may exhibit timedependent behaviors as their microstructures evolve. This process may vary from a few minutes (sand) to several days or even years (soft soils). To describe this time-dependent behavior, viscoplastic models are commonly used. Other than providing an intrinsic description of the viscous behavior, rate-dependent constitutive laws are sometimes presented in the literature as a regularization technique. In this thesis, we study the possibility to use viscoplastic constitutive laws in transient problems to describe the time-dependent response of soft soils and strain localization. Analytical and numerical studies are presented and several conclusions are found based on the Hill’s criterion, the Rice’s criterion, a numerical perturbation algorithm and classical linear perturbation theory. It turns out that the use of viscoplastic models in transient problems is not able to regularize the problem. Viscoplastic models are then integrated in a higher order continuum, the second gradient model. Problems concerning the uniqueness, bifurcation and mesh dependency are examined and a classical linear perturbation analysis is presented. The combination of a second gradient model with viscoplastic laws makes possible both to regularize the problem and to take into account rate effects. Finally, the bearing capacity and progressive failure of a shallow foundation are analyzed in order to demonstrate the performance of the approach on a real case study
Gozdecki, Nicolas. "Nouveaux alliages de titane à gradient de propriétés pour l'implantologie dentaire : approches expérimentale et numérique". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066710.
Testo completoIn the field of biomaterials, titanium alloys are among the most attractive materials for osseointegrated implants due to their high biocorrosion resistance, increased general biocompatibility and specific mechanical properties. Among these properties, low elastic modulus of titanium alloys has attracted much attention regarding the transmission of functional loads from the implant to the surrounding bone. The aim of this work consists in developing functionally graded materials, with careful attention to the thermomechanical treatments. In one hand, this allows us to obtain a gradient of elasticity in bulk materials and in the other hand, a gradient of grain sizes. This is possible thanks to the reversible martensitic transformation β ↔ α’’ and also to the α phase dissolution during flash treatments. The microstructural scale is also controlled in order to develop homogeneous materials at the nanoscale, thermally stables, and exhibiting superplasticity at low temperatures. These results are thought to be good strategy to avoid the use of SPD processes. A complete characterization of these new materials is performed with the combination of SEM, TEM and XRD analyses to appreciate the modifications of the microstructures and grain sizes. Values of elastic modulus are obtained by tensile tests, and locally determined with the use of instrumented microindentation measurements
Avila, de oliveira silva Lais. "Investigation de l’effet du gradient microstructural généré pendant le patentage sur les propriétés mécaniques finales des fils d’acier perlitiques". Electronic Thesis or Diss., Centrale Lille Institut, 2022. http://www.theses.fr/2022CLIL0007.
Testo completo: Pearlitic steels could appear to be a simple and classic microstructure, with a rather simple eutectoid composition containing twophases (cementite and ferrite) in a lamellar distribution. However, they feature a hierarchical microstructure, which is composed of nodulesthat present the same crystallography and are grain-equivalent, then the nodules comprise the colonies that contain the parallel ferrite andcementite lamellas at a nanometric scale. As a result, pearlitic steels offer high strength and ductility at a reasonable cost, which fits verywell for various structural and reinforcement applications, e.g., steel core, bridge cables, wire ropes, springs…Although pearlitic steels areknown and vastly studied for over 150 years, it could appear outrageous to still propose manners of improving their mechanical properties.However, some options have not yet been considered such as the microstructural gradient or the control of the pearlite morphologies. Themicrostructural gradient concept has been widely explored in simple microstructure in steels, such as ferrite or austenite, but it is morecomplicated to export it in the pearlitic steel. The present Ph.D. aims to investigate the feasibility of producing a microstructural gradient infully pearlitic steels and of controlling the pearlite morphology. It is sought the understanding of the involved metallurgical mechanisms andthe impact on the mechanical properties, especially fatigue, considering the final application of this material. The control of themicrostructure and the gradient is based on the transformation of austenite into pearlite and, therefore, all the parameters that couldinfluence this transformation must be studied. It includes heat treatment parameters (heating rates, cooling rates, cooling modes,temperature of transformation…) and materials ones (initial interlamellar spacing, deformation state of pearlite…). The spacing between theferrite and cementite lamella, known to govern the mechanical properties of pearlitic steels, varies with the transformation temperature,which results in coarse and fine pearlite when transformed at high or low temperatures, respectively. It is found that a microstructuralgradient of interlamellar spacing is possible to be formed but is limited by the rod diameter. Using the dilatometer, it was successfullyprocessed in a 6 and 12 mm diameter rod. The gradient-containing wires were then drawn and the mechanical properties before and afterdrawing are compared to assure that the gradients formed during the heat treatment of the 6 mm diameter wires are still present on the2.25 mm final diameter wires. The morphology of pearlite has also been modified by control of heat treatments using continuous andisotherm cooling. Divorced, connected and well-aligned perfect pearlites with the same interlamellar distance have been processed. It turnsout that the morphology of the monolithic pearlite specimen has a higher impact on cyclic plasticity than the presence of a gradient. Theresults obtained in this Ph.D. gave rise to discussions on the pearlitic transformation under continuous and isotherm cooling, on themechanisms controlling the morphology of pearlite (mostly divorced or lamellar), on the phenomena happening during heating,(recrystallization, recovery, and spheroidization), and also on the mechanisms of plasticity of pearlite. Finally, the feasibility of the productionof the gradients by real cooling technologies is assessed by transforming the wires in a pilot line. It is of most interest that the gradients areproduced by alternative cooling technologies since the lead patenting technique is not the most environmentally friendly, although the mostwidely used
Biotteau, Katia. "Elaboration et caractérisation de composites Alumine/Zircone à vocation orthopédique". Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00995100.
Testo completoAyad, Mohammad. "Homogenization-based, higher-gradient dynamical response of micro-structured media". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0062.
Testo completoA discrete dynamic approach (DDM) is developed in the context of beam mechanics to calculate the dispersion characteristics of periodic structures. Subsequently, based on this dynamical beam formulation, we calculate the dispersion characteristics of one-dimensional and two-dimensional periodic media. A sufficiently high order development of the forces and moments of the structural elements is necessary to accurately describe the propagation modes of higher order. These results show that the calculations of the dispersion characteristics of structural systems can be approached with good accuracy by the dynamics of the discrete elements. Besides, non-classical behaviors can be captured not only by higher order expansion but also by higher gradient formulations. To that scope, we develop a higher gradient dynamic homogenization method with micro-inertia effects. Using this formulation, we compute the macroscopic constitutive parameters up to the second gradient, using two distinct approaches, namely Hamilton’s principle and a total internal energy formulation. We analyze the sensitivity of the second gradient constitutive terms on the inner material and geometric parameters for the case of composite materials made of a periodic, layered microstructure. Moreover, we show that the formulations based on the total internal energy taking into account higher order gradient terms give the best description of wave propagation through the composite. We analyze the higher order and micro-inertia contributions on the mechanical behavior of composite structures by calculating the effective static and dynamic properties of composite beams using a higher order dynamic homogenization method. We compute the effective longitudinal static response with higher order gradient, by quantifying the relative difference compared to the classical formulation of Cauchy type, which is based on the first gradient of displacement. We then analyze the propagation properties of longitudinal waves in terms of the natural frequency of composite structural elements, taking into account the contribution of micro-inertia. The internal length plays a crucial role in the contributions of micro-inertia, which is particularly significant for low internal length values, therefore for a wide range of materials used in structural engineering. The developed method shows an important size effect for the higher gradients, and to remove these effects correction terms have been incorporated which are related to the quadratic moment of inertia. We analyze in this context the influence of the correction terms on the static and dynamic behavior of composites with a central inclusion
Appiah, Kwadwo Ampofo. "Microstructural and microanalytical characterization of laminated (C-SiC) matrix composites fabricated by forced-flow thermal-gradient chemical vapor infiltration (FCVI)". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/14910.
Testo completoDelcuse-Robert, Laura. "Processing effects on the structure and behavior of Nickel based alloys produced by additive manufacturing". Electronic Thesis or Diss., Université de Lorraine, 2021. https://docnum.univ-lorraine.fr/public/DDOC_T_2021_0355_DELCUSE.pdf.
Testo completoRegarding its high strength at high temperature, Inconel 718 is widely used in aerospace field. With additive manufacturing, novel structure such as auxetic structure should be produced in Inconel 718 and offered new opportunities in a wide range of industrial application. Under impact loading, the high energy absorption capacity of auxetic material allows new possibilities mainly on safety issues for transport vehicles. The current work is developed through this problematic. First, the geometrical parameters of a re-entrant honeycomb structure were optimised by applying a Taguchi method and a parametrical study on computational modelling. The influence of the laser powder bed fusion parameters (L-PBF) were also tackled on thin-walled cellular structures in Inconel 718. The building direction and the laser energy density were varying to determine their effect on the porosity and print accuracy on thin strut. Then, the mechanical behaviour of the optimised re-entrant honeycomb structures was studied under tension and compression loading to identify the kinetic of deformation of the structure. To reproduce this mechanical behaviour, the compression behaviour of the Inconel 718 printed into horizontal (XY) and vertical (ZX) building direction was investigated using quasi-static and dynamic strain rates, between 10-3 s-1 and 2500 s-1. A Johnson-Cook model was determined considering the effect of the building direction on the mechanical properties. The anisotropy of the printed Inconel 718 depends on the building direction and was revealed by a microstructural study. By using EBSD orientation map and BSE micrographs, it was found that the horizontal building direction (XY) mainly provided equiaxed grain as compared to columnar grain for vertical building direction (ZX). In addition, a microstructure gradient was observed for both building directions from the border to the volume, divided into three zones (i) border, (ii) transition and (iii) centre. According to the microstructural analysis, a novel modelling approach on the yield stress was developed based on the grain size of the Inconel 718. A numerical model of the auxetic structure was developed using Abaqus software, under dynamic compression loading. The behaviour law of the printed Inconel 718 is then validated by this model, reproducing the mechanical behaviour of the auxetic structure at the macroscopic scale
Bossy, Etienne. "Influence des caractéristiques de microstructures nitrurées sur l’initiation d’écaillage en surface par fatigue de contact". Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI095.
Testo completoEnergy performance enhancement in the transport industry leads manufacturers to lighten their systems. As a result, the contacting parts are more and more stressed. Where cracks were previously initiated on inclusions in sub-surface, more and more surface defects appear. In order to guarantee and improve the performance of the parts under rolling contact fatigue, gas nitriding treatment is widely used. This thermochemical treatment enhances the steel surface properties by introducing residual stresses and increasing its hardness. Although this treatment is widely studied, crack initiation phenomenon are still grey areas. Nitrided steels present a network of intergranular precipitations of cementite that are significantly harder than steel. Their role has been highlighted in the case of crack propagation but their role in initiation remains hypothetical. In addition, in some cases, surface defects coexist with subsurface fatigue. The model and experiments presented in this study provide answers on these issues. The fatigue behavior is modeled using a finite element model coupled with Dang Van fatigue criterion. The modelization of nitrided steel, and particularly of its material properties, is complex. Given the property gradient between the surface and the bulk material, the resistance limits are indeed different. Independently tested, it is shown that neither surface nor bulk parameters can correctly model the fatigue behavior of the whole material. It is necessary to take into account the property gradient to model a fatigue response corresponding to the experimental observations. In this study the gradient of fatigue properties, difficult to measure, is similar to the micro-yield stress, more accessible. This model highlight the reason for the coexistence of surface defects and subsurface fatigue in the studied case. Indeed, although the load is highly located on the surface, the decrease of property material in the subsurface causes the appearance of deep areas undergoing fatigue. Realized experiments highlight the role of cementite precipitates on initiation of cracks. Their over-presence near microcracks confirms indeed their disruptive role of the involved phenomena. These carbide boundaries, which elastic behavior is similar to that of steel, seem to speed up the initiation. This is explained by the incompatibility of deformations in the microplastic field around precipitates. This incompatibility causes the de-cohesion of these elements thus generating microcracks. These microcracks can cross the cementite precipitates, circumvent it or more rarely propagate in steel. In the end, the proposed model predicts the fatigue response behavior of nitrided steel. The hypotheses formulated on the role of carbide precipitation in the literature seem to be verified experimentally and allow to propose scenarios proposed based on experimental observations and realists physical considerations
Müller, Guillaume. "Conception, élaboration et caractérisation de matériaux de composition et de microstructure innovants pour les micro-piles à combustible à oxyde solide". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00833281.
Testo completoBoulvert, Jean. "Traitements acoustiques à porosité contrôlée pour atténuation optimale". Thesis, Le Mans, 2020. http://www.theses.fr/2020LEMA1033.
Testo completoThis thesis exploits some of the new possibilities offered by additive manufacturing to design and optimize treatments for sound attenuation consisting in porous materials. Additive manufacturing allows to control individually each pore of a material. The porous treatment design process is turned upside down: instead of searching through a catalogue of existing materials to solve a problem, it is possible to directly design the right material by adjusting its microstructure. This research is part of a plan to reduce aircraft engine noise but extends beyond the aeronautical field, both theoretically and in terms of possible applications. A predicting method of the acoustic behaviour of porous materials produced by additive manufacturing and taking into account the impact of manufacturing defects is first introduced. Porous materials with controlled graded properties are then studied. A method for optimizing microstructural or manufacturing parameters is developed. The ability of graded porous materials to attenuate frequencies too low to be attenuated by non-graded materials is then proven and the optimal gradient for broadband attenuation is defined. The impact of the wall thickness of the pores along with the impact of transverse propagation inside porous materials is studied. Finally, a metaporous treatment allowing broadband and sub-wavelength absorption is developed. The results of this research can be applied to create porous treatments with a high noise attenuation. The analytical and numerical models used in this research are based on the hypothesis of porous materials acoustically behaving as equivalent fluids. The results are physically analyzed and experimentally validated through impedance tube testing of specimens produced by additive manufacturing
Boulesteix, Rémy. "Densification du grenat d'yttrium et d'aluminium pur ou dopé sous forme de céramiques transparentes : relation entre microstructure et propriétés optiques : élaboration de matériaux à gradient de concentration en néodyme". Limoges, 2009. http://www.theses.fr/2009LIMO4040.
Testo completoHuc, Delphine. "Hiérarchisation des facteurs contribuant à la croissance des bulles dans des fromages à pâte pressée non cuite par une approche multi-échelles". Phd thesis, Université Rennes 1, 2013. http://tel.archives-ouvertes.fr/tel-00931927.
Testo completoLiu, Meishuai. "Study on microstructural and crystallogarphic characteristics of phase transformation induced by ECP in annealed Cu-40%Zn alloy". Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0210.
Testo completoA thorough investigation has been conducted on the microstructural and crystallographic features of Electric Current Pulse (ECP) treated Cu-40%Zn alloys. The phase transformation orientation relationship (OR) and its correlation with crystal defects have been studied and the formation mechanisms of ECP induced crystal defects in the parent phase and the sub-structures in the β precipitates were also analyzed. The α to β heating phase transformation can be induced by ECP treatment with the formation of fine β precipitates that can be remained to the room temperature. With the increase of the electric current density, the amount of precipitates is increased and the formation sites increase from α grain boundaries to grain interiors. The β precipitates follow different ORs depending on the formation site. The grain boundary β phase obeys the Kurdjumov-Sachs (K-S) OR; whereas the intragranular β respects the Nishiyama-Wasserman (N-W) OR. In the former sites, the {111}α /<11̅0>α dislocations are observed, whereas in the latter, the {111}α/<112̅>α stacking faults are found. Transformation strain analyses revealed that under the K-S OR the maximum lattice deformation required is a shear on the {111}α /<11̅0>α slip system, whereas under the N-W OR the maximum deformation is a shear on the {111}α /<112̅>α system. Thus the existing {111}α /<11̅0>α dislocations along the α grain boundaries provide pre-strain required by the transformation via the K-S path, whereas the {111}α /<112̅>α stacking faultsboarded by {111}α /<112̅>α partial dislocations offer pre-strain facilitating the transformation via the N-W path. Different types of crystal defects are formed in the α matrix by the ECP treatments depending on the current density. At low density, large amount of {111}α /<112̅>α stacking faults and then nano twins are produced in the α matrix. At high density, dislocation nets are formed near the β precipitates that are composed of edge typed {111}α /< 11̅0 >α perfect dislocations and the Frank typed dislocations. The volume misfit between the α and the β phase analyzed with transformation deformation reveals that the transformation from α to β requires an expansion along [11̅0]α direction and a contraction along [111]α direction. The former results in the appearance of the {111}α /<11̅0>α edge typed dislocation arrays in front of the {31̅1}α broad faces and the latter induces the formation of the Frank typed dislocations in front of the {121}α broad faces. Thus, dislocation nets formed along the edges of the broad faces of the β precipitates where the two kinds of dislocations meet. Furthermore, the β precipitates contain two kinds of nano-sized and diffuse atomic clusters with the structure obeying the Burgers OR and with the ω structure obeying the Blackburn OR with the β matrix. They were each formed through a two-stepped atomic displacement. For the structure, the first step is the atomic shuffle of each second {110}β plane in the <11̅0>βdirection and the second is a structure change mainly by a shear on the {11̅2}β /<1̅11>β. For the ω structure, the first is an atomic shuffle on each second and third {112̅}β plane in the ±[111]β directions and then normal strains in three mutually perpendicular directions (<111>β, <112̅>β and <11̅0>β). The concomitant appearance of the two structures lies in the fact that the volume increase accompanying the formation can be canceled by the volume decrease accompanying the ω distortion, which minimizing the transformation strain energy. The results of this work provide fundamental information on the Cu-40%Zn alloys for interpreting the impact of the crystal defects on the solid phase transformation ORs, on the formation of various types of crystal defects induced by the ultra-rapid phase transformation and on the formation mechanisms of sub structures in the product phase
Ben, Elhaj Salah Sami. "Modélisation non-locale et stochastique de matériaux à fort gradient de propriétés par développement asymptotique". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2019. http://www.theses.fr/2019ESMA0018.
Testo completoThe aim is to propose a macroscopic, deterministic and non-local model, constructed by scale transition for heterogeneous materials with high property gradients and containing a random distribution of inclusions. More precisely, the inclusions are distributed in an elastic matrix according to a stochastic ergodic process. Several non-local models exist in the literature, but they do not allow (or very little) to obtain non-local quantities and/or fields at the macroscopic scale from a scale-transition. Besides, it is often difficult to link the non-local parameters to the microstructure. To this aim, we developed a two-step approach.In the first stage, we combined the method of asymptotic developments with an energetic approach to reveal a second displacement gradient in the strain energy. The advanced model involves three homogenized elasticity tensors functions of the stochastic parameter and of the phase properties. As opposed to the literature, the model involves two characteristic lengths strongly linked to the microstructure. These lengths define two morphological representative elementary volumes on which full field simulations are performed in order to determine the macroscopic strain tensors at orders 0 and 1 involved in the formulation of the model. In order to test this first version of the model, numerical simulations were performed. The estimate of the classical part of the energy, coming from the local part of the fields, has been successfully compared to classical bounds for a composite bar consisting of a random distribution of two homogeneous and isotropic elastic materials. Then, numerical solving of the whole model including the non-local terms has been performed in the three-dimensional case. Two types of microstructures with increasing morphological complexity were used. The first ones are virtual microstructures generated from a given simple pattern randomly distributed throughout the structure and composed of a big inclusion circled by six identical small ones. The second are real microstructures of Ethylène-Propylène-Diène Monomère (EPDM) obtained by tomography and containing clusters of inclusions with complex structures.In order to obtain a macroscopic model that can be used for structure analysis, without any full field intermediate calculations, a second scale transition has been performed using stochastic variational homogenization tools in the ergodic case. More precisely, the Γ-convergence method has been used in order to have a convergence of energy rather than that of mechanical fields, aiming at keeping a strong microstructural content. In fine, the model is macroscopic, non-local, deterministic and strongly connected to the microstructure. Non-local effects are now accounted for by the presence of the second displacement gradient but also by the presence of the virtual (memory) displacement field of the inclusions. The link with microstructure is still manifest through the presence of the stochastic parameter and phase properties, but also by the presence of the asymptotic fractions of the inclusion phase in the material and in each of the morphological volumes defined by the model characteristic lengths. In order to prepare the use of the model for structure calculations, a non-local finite element enriched with Hermit-type interpolations was implemented in FoXtroT, the finite element solver of the Pprime Institute. This element takes into account the virtual (memory) displacement field related to inclusions as well as the gradients of the macroscopic and virtual displacement fields. The first numerical results on this aspect, to our knowledge never discussed in the literature, are promising
Jeyabalan, Karthikeyan. "Experimental study and prediction of microstructures and internal stresses during heat treatment of carburized and carbonitrided low-alloyed steels". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0379.
Testo completoCarbonitriding thermochemical treatments are used in automotive industry for improving fatigue and wear resistance of mechanical parts. These treatments aim to generate gradients of carbon and nitrogen in the surface aera of the piece by diffusion in the austenitic field, and with the following quenching the desired gradients of microstructures, mechanical properties, and compressive residual stresses on the surface are obtained. The objective of the PhD thesis is to better understand the effects of carbon and nitrogen gradients on the development of internal stresses during cooling in relationship with the phase transformations as well as on the residual stresses distributions after cooling. The approach consists first of the elaboration of laboratory samples with controlled carbon and nitrogen gradients representative of the parts. Then, the kinetics of phase transformations and the internal stresses evolutions have been analysed experimentally by in situ High Energy (synchrotron) X-ray Diffraction throughout the chemical composition gradients thanks to a specific new methodology. To our knowledge, it is the first time internal stresses can be measured in situ during cooling in gradient specimens. Unexpected results have been obtained in nitrogen enriched samples; it has been shown that the chronology of phase transformations between core and surface is inversed as compared to the more classical case of carburizing leading to completely inversed residual stress profiles with tensile stresses in the nitrogen enriched layer and compression in the core. It has been related to the acceleration of transformation kinetics in the nitrided layer that decreases its hardenability. A coupled thermal-metallurgical-mechanical model has been developed too to predict temperature evolutions, phase transformations kinetics, internal stresses evolutions as well as final microstructure, hardness and residual stress distributions in the gradient samples. The metallurgical model developed in a previous study has been implemented in the finite element code Zebulon. The thermomechanical behaviour law of the material is thermoelastoviscoplastic including transformation strains (volumic variations and transformation plasticity strains). All material parameters (thermomechanical and thermophysical parameters) are considered as temperature, phase and carbon and nitrogen dependent; they have been determined from experimental characterizations on carbon and nitrogen homogeneously enriched specimen and in house data. The simulations allowed to confirm and understand more in details the complex microstructure and internal stresses evolutions due to combined nitrogen and carbon gradients. The comparison between calculated and experimental results shows that the simulation gives the main tendencies of the experimental observations. The main discrepancies on the level of residual stresses are attributed to the underestimation of the retained austenite fractions as the present model does not take into account its stabilization during cooling
Maudet, Florian. "Couches nanostructurées par dépôt en incidence oblique : corrélations microstructure et propriétés optiques pour application aux traitements antireflets hautes performances dans le visible étendu et l'infrarouge". Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2295/document.
Testo completoAnti-reflective (AR) coatings are widely used to improve the transmission of optical systems composed of window, lenses, separating filters,... In this thesis, the spectral ranges targeted are the extended visible [400-1800nm] and the mid infrared [3.7-4.8µm]. Thin film deposition nanostructuring method using oblique angle deposition (oblique angle deposition) PVD technique was chosen because it allows high performance AR to be considered over a wide wavelength range, by an industrial process. The introduction of porosity with the control of deposition angle is used to nanostructure the architecture of each layer and stack; a method for modifying and optimizing the optical properties of the constituent layers for optimal complete design. A mapping of the effective indices accessible by OAD has been identified for the three materials deposited (TiO2, SiO2 and Ge). However optical properties of these nanostructured layers differ greatly from those of dense layers due to the presence of anisotropy, index gradient, diffusion and absorption. Based on advanced microstructural, chemical and optical characterizations (AFM, SEM, TEM, FIB tomography, TEM tomography, EDX, EELS, spectrophotometry and generalized ellipsometry) a more complex analytical optical model coupled with finite element analyses (FDTD) is presented. All the work has enabled OAD to develop simple two-layer anti-reflective coatings that already demonstrate high levels of transmission, superior to existing (interferential) or work in progress (Moth-eyes) AR treatments
Thomas, Jonova. "Microstructural Phase Evolution In Laser Deposited Compositionally Graded Titanium Chromium Alloys". Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849610/.
Testo completoOzturk, Tugce. "Experimental and Computational Investigation of the Microstructure-Mechanical Deformation Relationship in Polycrystalline Materials, Applied to Additively Manufactured Titanium Alloys". Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/900.
Testo completoAntonysamy, Alphons Anandaraj. "Microstructure, texture and mechanical property evolution during additive manufacturing of Ti6Al4V alloy for aerospace applications". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/microstructure-texture-and-mechanical-property-evolution-during-additive-manufacturing-of-ti6al4v-alloy-for-aerospace-applications(03c4d403-822a-4bfd-a0f8-ef49eb65e7a0).html.
Testo completoArmattoe, Kodjo Mawuli. "Modélisation non-locale du comportement thermomécanique d'Alliages à Mémoire de Forme (AMF) avec prise en compte de la localisation et des effets de la chaleur latente lors de la transformation de phase : application aux structures minces en AMF". Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0053/document.
Testo completoIn this Phd thesis, thermo-mechanical models based on a nonlocal approach are proposed in order to describe the behavior of Shape Memory Alloys (SMA), taking into account localization and latent heat effects during phase transformation. These models are obtained as extensions of an existing local model. In order to describe the localization of phase transformation, the extension of the initial model consisted of rewriting it in a nonlocal context through the introduction of a new variable, defined as the nonlocal counterpart of the martensite volume fraction. The use of this model has required the development of a specific finite element in ABAQUS with the nonlocal martensite volume fraction as an additional degree of freedom. The simulations show the relevance of such an approach in the description of the phase transformation occurring in thin SMA structures subjected to thermo-mechanical loadings. To achieve the description of the latent heat effects, a heat balance equation with a source term depending on contributions of the phase transformation was added to the constitutive equations of the initial model. Even there, the use of the model required the development of a finite element which takes into account the thermo-mechanical coupling and considers the proposed formulation for the thermal balance. Numerical simulations have shown the delaying effect of the latent heat on phase transformation and the possible heterogeneous character of the phase transformation in this case. These effects are even more important as the strain rate is high