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Moverare, Johan J. "Microstresses and anisotropic mechanical behaviour of duplex stainless steels /." Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek699s.pdf.
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Wei, Jianfei [Verfasser]. "Anisotropic Distortion of High Alloyed Tool Steels During Gas Quenching and Tempering / Jianfei Wei." Aachen : Shaker, 2004. http://d-nb.info/117261458X/34.
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Menard, Corentin. "Imagerie ultrasonore dans des aciers anisotropes dont les propriétés élastiques sont incertaines : application au contrôle des assemblages soudés du domaine nucléaire." Electronic Thesis or Diss., université Paris-Saclay, 2021. http://www.theses.fr/2021UPASG027.
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En contrôle non-destructif par ultrasons, la qualité de l’imagerie échographique repose sur l’adéquation entre le modèle direct de propagation des ondes élastiques et la propagation dans le milieu physique. C’est notamment le cas des structures anisotropes, comme les soudures en acier du domaine nucléaire, où la méconnaissance de l’anisotropie au moment de l’inspection peut conduire à des images très dégradées et inexploitables. Cette dégradation est d’autant plus marquée que l’anisotropie d’une soudure est fortement inhomogène en raison de la croissance dendritique de la matière au moment de son refroidissement. La fiabilité des diagnostics en imagerie ultrasonore requiert alors de bien connaître les propriétés du matériau au moment de l’inspection.Dans cette thèse, une méthode adaptative basée sur une procédure d’optimisation est étudiée pour améliorer l’imagerie des soudures anisotropes du domaine nucléaire. On s’intéresse notamment à l’imagerie TFM (Total Focusing Method) dont l’intérêt principal est que le mode d’acquisition des signaux ne présuppose aucun a priori sur les propriétés du matériau. Dans la procédure d’optimisation, une première image est calculée à partir d’un modèle de reconstruction isotrope. Si l’image fait apparaître une indication au-dessus du niveau de bruit, un algorithme d’optimisation itère le calcul des images en faisant varier les paramètres du modèle de soudure jusqu’à maximiser l’amplitude de l’écho d’intérêt. Dans ce travail, l’optimisation est validée statistiquement avec des échos simulés, en s’appuyant sur des outils d’apprentissage machine qui permettent d’accélérer les temps de calcul. La procédure est également évaluée expérimentalement sur diverses soudures de complexité croissante. Dans chacun des cas, la procédure produit une image avec un rapport signal/bruit satisfaisant, tout en minimisant les erreurs de localisation des défautsIn non-destructive ultrasound testing, the quality of the imaging relies on the adequacy between a direct model of elastic wave propagation and the propagation in the physical medium. This is particularly the case for anisotropic structures, such as nuclear-domain welds, for which not knowing the anisotropy at the time of inspection can lead to severly degraded and unusable images. This degradation is all the more marked as the anisotropy of a weld is highly inhomogeneous, due to the dendritic growth of the material during its cooling. The reliability of an array imaging diagnosis therefore requires a good knowledge on the material at the time of inspection.In this thesis, an adaptive method based on an optimization procedure is studied in order to improve the imaging in nuclear anisotropic welds. We are especially interested in TFM (Total Focusing Method) imaging, whose acquisition principle does not rely on any foreknowledge on the material properties. In the optimization procedure, a first image is computed with an isotropic reconstruction model. If the image shows an indication above the noise level, an optimization algorithm iterates image computations by varying the parameters of the model that describes the structure, until the amplitude of the echo of concern is maximized. The optimization is statistically validated with simulated data, using machine learning tools to speed up computation times. This method is also evaluated experimentally on different welds of increasing complexity. In each case, the procedure produces an image with a high level of signal-to-noise ratio, while minimizing the defect localization error
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Cyril, Nisha S. "Anisotropy and Sulfide Inclusion Effects on Tensile Properties and Fatigue Behavior of Steels." Connect to full text in OhioLINK ETD Center, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1198808409.
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Thesis (M.S.)--University of Toledo, 2007.Typescript. "Submitted as partial fulfillment of the requirements for the Master of Science Degree in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 204-209.
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Fard, Samad Moemen Bellah. "Modelling anisotropy in electrotechnical steels." Thesis, Cardiff University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263551.
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Xue, Xin. "Modelling and control of twist springback in lightweight automotive structures with complex cross-sectional shape." Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/17766.
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Doutoramento em Engenharia MecânicaEste trabalho é dedicado à investigação dos mecanismos / fontes de retorno elástico torsional em estruturas automóveis leves e à identificação de formas de controlar este problema. Em primeiro lugar, para garantir uma correta modelação do retorno elástico torsional, foram utlizados os resultados de vários ensaios do material, incluindo diferentes solicitações de carga/descarga, assim como a utilização de modelos constitutivos adequados. O comportamento mecânico dos materiais submetidos a trajetórias simples e complexas de carga é descrito utilizando leis de encruamento e critérios de plasticidade anisotrópicos. Foi desenvolvido um novo dispositivo de ensaios de corte para os aços DP para realização de ensaios de inversão de carga. Foram realizados testes cíclicos de carga-descarga-carga de tração uniaxial e biaxial assim como testes de dobragem em três pontos em material pré -deformado com vista à determinação da degradação do módulo de elasticidade com o aumento de deformação plástica. O efeito da trajetória de deformação na determinação do valor inicial do módulo de elasticidade e a sua degradação foram registados e analisados. Em segundo lugar, foram selecionados como casos de estudo dois processos clássicos de deformação plástica de metais, nomeadamente embutidura de chapas de aço DP e dobragem por matriz rotativa de tubos de alumínio de parede fina e secção assimétrica, devido ao seu evidente efeito de retorno elástico torsional. Foi proposta uma definição melhorada de retorno elástico torsional baseada nos eixos principais de inércia da secção transversal. A relação entre o momento de torção e ângulo de torção foi introduzida para explicar a ocorrência de retorno elástico torsional. Para melhorar a robustez dos modelos numéricos, foram realizadas várias técnicas de modelação, incluindo a identificação de coeficiente de atrito, a restrição de acoplamento da superfície para mandril flexível utilizando um elemento conector articulado, e a correlação de imagens digitais. O mecanismo de retorno elástico torsional foi analisado tendo em conta a evolução de estado plano de tensão e a trajetória de deformação nos componentes após a enformação por deformação plástica. Em terceiro lugar, foi analisada e discutida a sensibilidade dos modelos constitutivos de materiais no que diz respeito à precisão da previsão do retorno elástico torsional. Além disso, foi investigada a influência dos parâmetros do processo de embutidura profunda (direção de material, “blank-piercing” e lubrificação) e dos parâmetros numéricos do processo de dobragem de tubos (restrição dos limites do mandril flexível e atrito nas zonas de contacto) no retorno elástico torsional. Finalmente, foram propostas duas estratégias de controlo para o processo de embutidura profunda, com base no raio da curvatura da matriz variável e na posição dos freios, para reduzir o retorno elástico torsional de duas peças “Cchannel” e “P-channel”, respetivamente. No caso de dobragem de tubos, o controlo do retorno elástico torsional foi alcançado pela otimização da função do mandril e inclusão de um assistente de impulso de carga. Estas estratégias de controlo, baseadas em FEA, apresentam-se como métodos alternativos para a redução do momento torsor e do retorno elástico torsional em termos de aplicações específicas.
This work is devoted to the investigation of the mechanism/source of twist springback in lightweight automotive structures and to the identification of ways to control this problem. Firstly, to ensure accurate twist springback modelling, a reliable test data of material behaviours under various loading /unloading conditions as well as appropriate constitutive models are necessary. The anisotropic yield criteria and hardening models were adopted to characterize the material behaviours under monotonic and complex strain paths. An enhanced simple shear device was developed to obtain the stress-strain behaviour under reversal loading of DP steels. Uniaxial and biaxial loadingunloading- loading cycle tests and the proposed three-point bend test with prestrained sheets, were conducted to determine the elastic modulus degradation with the increase of plastic strain. A significant effect of the loading strategy on the determination of the initial and the degradation of elastic modulus was observed and discussed. Secondly, two typical metal forming processes, namely deep drawing of DP steel sheets and mandrel rotary draw bending of asymmetric thin-walled aluminium alloy tube, were selected as case studies due to their evident twist springback. A more reasonable definition of twist springback with respect to the principal inertia axes of the cross-sections was proposed. The relationship between torsion moment and twist angle was introduced to explain the occurrence of twist springback. Several key modelling techniques including the friction coefficient identification, surface-based coupling constraint for flexible mandrel using HINGE connector element and digital image correlation were performed for improving the robustness of the numerical models. The mechanism of twist springback was analysed from the evolution of in-plane stress and deformation history in the components after forming. Thirdly, the sensitivities of material constitutive models to the accuracy of twist springback prediction were analysed and discussed. The influence of deep drawing process parameters (material direction, blank piercing and lubrication) and numerical parameters of tube bending (boundary constraint for flexible mandrel and interfacial friction) on twist springback are provided. Finally, two control strategies for deep drawing process, based on variable die radius and partial draw bead design, were proposed to reduce the twist springback of the C-channel and the P-channel, respectively. In case of tube bending, the control of twist springback was reached by the optimization of mandrel nose placement and inclusion of push assistant loading. These FEAbased control strategies appear to be alternative methods to reduce the unbalance torsion moment and the twist springback in terms of particular case.
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Daniel, Dominique. "Prediction of elastic and plastic anisotropy in deep drawing steels." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74533.
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Yield stresses and r-values were measured as a function of inclination with respect to the rolling direction on thirty-one steels selected from high strength low alloy (HSLA), Al-killed (AKDQ), interstitial free (IF1 and IF2) and rimmed (RIM) types. Modul-r and electromagnetic acoustic (EMAT) techniques were employed to determine the elastic anisotropy in terms of the angular variation of Young's modulus and the ultrasonic velocities, respectively. Orientation distribution functions (ODF's) were also measured for these steels in their as-received states and after deformation in tension and in drawing. The various initial textures and their evolutions along the latter strain path are analyzed in terms of the 4- and 6-ear behaviours commonly observed during the forming of cylindrical cups.The series expansion method was employed for predicting the elastic and plastic anisotropies from the initial texture data. Comparison with the experimental measurements of Young's modulus indicates that the so-called elastic energy method can accurately reproduce the elastic anisotropy if the single crystal elastic constants are appropriately chosen within their ranges of uncertainty. The systematic evaluation of various grain interaction models for predicting the polycrystal plastic anisotropy reveals that the "pancake" relaxed constraint model is a more accurate predictor of the behaviour than the Taylor, Sachs-Kochendorfer, or other relaxed constraint models. The best quantitative agreement is obtained when the critical resolved shear stress (CRSS) ratio for glide on the $ {112 } langle 111 rangle$ and $ {110 } langle 111 rangle$ systems is 0.95 (except for the AKDQ and IF2 grades, for which values of 0.90 and 1.0, respectively, are preferred).
The ODF coefficients of order greater than 4 were evaluated and calculated non-destructively from the anisotropy of the ultrasonic velocities of the lowest order symmetrical Lamb (S$ sb{ rm o}$) and shear horizontal (SH$ sb{ rm o}$) waves propagating in the rolling plane. The elastic energy method was employed, together with a decomposition of the texture into the principal preferred orientations. The calculated pole figures based on the ODF coefficients obtained in this way are similar to those derived from complete X-ray data. It is shown that the plastic properties of commercial deep drawing steels are predicted more accurately when the 4th and 6th order ODF coefficients are employed than when only the 4th order ones are used.
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Baselli, Silvia. "Study of the anisotropic sintering shrinkage of green iron and stainless steel." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/267476.
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Powder metallurgy (PM) is a near net-shape technology that guarantees excellent dimensional control and surface finishing in the production of parts with complex shapes. Press and sinter is the conventional PM process. The powder mix is compacted into rigid dies to obtain the so called green part that is subsequently sintered to promote the formation of metallic bonding between the powder particles. The differences in terms of geometrical and dimensional features between the green compact and the final part are related to the dimensional variations occurring during sintering, therefore, to preserve the cost effectiveness of the process, their in-depth knowledge is crucial. In this context, post- sintering machining should be limited to the realization of geometrical details that cannot be directly obtained through uniaxial cold compaction or to achieve strict tolerances required by specific applications. The dimensional changes in sintering that may be either shrinkages or swellings are affected by many parameters and, among them, we can consider: material, presence of lubricant and additives, green density, compaction strategy, sintering temperature and time, atmosphere, heating and cooling rate. Furthermore, the dimensional variations along the direction parallel to compaction (longitudinal, axial) are different from the dimensional variations in the compaction plane (transversal, radial) causing an anisotropy that depends, in addition to the mentioned parameters, on the geometry and the dimension of the part. At present, in absence of an adequate designing tool to account for the anisotropy, engineers rely on empirical methods often based on the trial-and-error approach.
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Baselli, Silvia. "Study of the anisotropic sintering shrinkage of green iron and stainless steel." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/267476.
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Powder metallurgy (PM) is a near net-shape technology that guarantees excellent dimensional control and surface finishing in the production of parts with complex shapes. Press and sinter is the conventional PM process. The powder mix is compacted into rigid dies to obtain the so called green part that is subsequently sintered to promote the formation of metallic bonding between the powder particles. The differences in terms of geometrical and dimensional features between the green compact and the final part are related to the dimensional variations occurring during sintering, therefore, to preserve the cost effectiveness of the process, their in-depth knowledge is crucial. In this context, post- sintering machining should be limited to the realization of geometrical details that cannot be directly obtained through uniaxial cold compaction or to achieve strict tolerances required by specific applications. The dimensional changes in sintering that may be either shrinkages or swellings are affected by many parameters and, among them, we can consider: material, presence of lubricant and additives, green density, compaction strategy, sintering temperature and time, atmosphere, heating and cooling rate. Furthermore, the dimensional variations along the direction parallel to compaction (longitudinal, axial) are different from the dimensional variations in the compaction plane (transversal, radial) causing an anisotropy that depends, in addition to the mentioned parameters, on the geometry and the dimension of the part. At present, in absence of an adequate designing tool to account for the anisotropy, engineers rely on empirical methods often based on the trial-and-error approach.
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Somkun, Sakda. "Magnetostriction and magnetic anisotropy in non-oriented electrical steels and stator core laminations." Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/55184/.
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Magnetostriction is a source of vibration and acoustic noise of electrical machines and it can be highly anisotropic even in non-oriented electrical steel. Understanding of magnetostriction under magnetisation and stress conditions present in stator core laminations can help predict the core vibration and radiated noise. Anisotropy of magnetostriction of a 0.50 mm thick non-oriented steel investigated in Epstein strips cut at angles to the rolling direction was much higher than the anisotropy of its magnetic and elastic properties because magnetostriction arises directly from magnetic domain processes. Magnetostriction of a disc sample of the 0.50 mm thick steel was measured under ID and 2D magnetisation and compared with that of a 0.35 mm thick steel with different anisotropy level. A 2D magnetostriction model and an analytical simple domain model were used to explain the experimental results. 2D magnetostriction is dependent on the magnetostrictive anisotropy and the ratios of the transverse to longitudinal magnetostriction. AC magnetostriction measured in the disc samples was larger than in the Epstein strips due to the form effect. An induction motor model core was constructed from the 0.50 mm thick steel for measurements of localised flux density and deformation. Core deformation due to Maxwell forces was calculated. Magnetostriction and specific power loss of the core material under magnetisation conditions present in the core was measured. The localised loss in the stator teeth, tooth roots and back iron differed from their average value by 52%, 19% and 36% due to the magnetic anisotropy. Magnetostriction was estimated to be about 55% and 80% of the radial deformation at the tooth root and back iron regions respectively. Stator teeth deformed asymmetrically and the magnitude of the space harmonics increased due to the magnetostrictive anisotropy. The measurement results inferred that 2D magnetostriction can be predicted from the magnetostrictive anisotropy and vice versa. Also, core deformation and vibration of large machines, where segmented stator core laminations are used, can be estimated analytically with the knowledge of 2D magnetostriction of the core material.
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Shinohara, Yasuhiro. "Effet d'une pré-déformation sur l'endommagement anisotrope d'un acier pour pipeline de grade API X100." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2014. http://pastel.archives-ouvertes.fr/pastel-01073824.
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Dans le cadre de cette étude, l'influence de la pré-déformation sur l'anisotropie du comportement plastique et sur la ténacité d'un acier API X100 pour pipeline a été abordée. Une étude expérimentale approfondie de la microstructure, des propriétés mécaniques et de l'endommagement du matériaux a été mise en oeuvre. Un modèle phénoménologique anisotrope combinant les écrouissagesisotrope et cinématique a été développé dans l'objectif de rendre compte du comportement ductile de cet acier à haute résistance. De plus, un modèle d'endommagement anisotrope a été établi pour représenter l'effet de pré-déformation sur la ductilité et la ténacité de cet acier. L'application des modèles à la flexion sous contrainte illustre, par exemple, l'effet négatif de la pré-déformation sur la charge limite (Moment de flexion maximum) supportée avant flambement du pipe.
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Ljungberg, Adam, and Nathalie Schmidt. "Deformationsstrukturer i ett duplext rostfritt stål (SAF 2507)." Thesis, Högskolan Dalarna, Materialteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:du-15770.
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För att kunna förbättra processer och användning av det duplexa rostfria stålet SAF 2507 måste dess deformationsegenskaper undersökas och förklaras. Genom EBSD-analyser har deformationsstrukturer och polfgurer tagits fram för att kunna beskriva materialets beteende vid deformation. Även Taylorfaktorer, E-moduler och Poissons tal har tagits fram för att kunna undersöka materialets anisotropi. Experimenten har utförts på prov av SAF 2507 som har deformerats plastiskt till olika töjningar. Det som undersökts är odeformerat prov, prov som dragits enaxligt till 7,7 % och 24,3 % töjning, samt ett prov som är cykliskt belastat till 3 % töjning. Det undersökta stålet tillverkas genom två olika metoder, men i denna rapport har enbart det extruderade stålet undersökts. Genom att jämföra hur stålets olika mekaniska egenskaper beter sig under plastisk deformation har resultatet blivit att stålets ferritfas beter sig anisotropt med en antydan till ökande isotropi vid ökande deformation. Austenitfasen beter sig däremot isotropt och blir varken mer eller mindre isotropt vid ökande deformation. Substrukturerna i ferritfasen ökar tydligt vid ökande deformation, och ses framför allt i austenitfasen efter 24 % deformation.In order to improve the processes and the use of the duplex stainless steel SAF 2507, its deformation properties has to be investigated and explained. Through EBSD-analysis deformation structures and pole figures have been developed to describe the behavior of the material during deformation. Also Taylor factors, Young’s modules and Poisson's ratio have been developed in order to investigate the material's anisotropy. The experiments have been performed on samples of SAF 2507 which has been plastically deformed at different strains. The strains studied are undeformed sample, samples drawn uniaxial drawn to 7.7 % and 24.3 % elongation, and one sample which is cyclically loaded to 3% elongation. The steel we have investigated is produced by two different methods, but in this report, only the extruded steel is investigated. By comparing how different mechanical properties of the steel behave during plastic deformation, the result shows that the steel’s ferrite phase behaves anisotropically with a hint of increasing isotropy when the deformation is increasing. The austenite phase behaves isotropic and does not become more or less isotropic with increasing deformation. The substructures in the ferrite phase are clearly increasing with increasing deformation, and are seen mainly in the austenite phase after 24 % deformation.
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Akbarzadeh, Abbas. "Effect of thermomechanical processing on microstructure, texture, and anisotropy in two Nb microalloyed steels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq29871.pdf.
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Hihat, Nabil. "Modèles quasi 3D pour l'analyse de structures présentant une anisotropie 3D." Thesis, Artois, 2010. http://www.theses.fr/2010ARTO0206/document.
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Les travaux présentés dans cette thèse s'inscrivent dans le cadre de l'analyse et la modélisation de la distribution du champ magnétique dans les machines électriques à circuit magnétique feuilleté avec des tôles à grains orientés. L'anisotropie des tôles magnétiques des transformateurs induit des phénomènes 3D complexes au niveau des joints magnétiques où les tôles se chevauchent. Concernant l'augmentation de l'efficacité énergétique des machines tournantes, de nouvelles structures à base de tôles à grains orientés font leur apparition. Néanmoins, simuler finement en 3D un paquet de tôles minces recouvertes d'un isolant de quelques microns d'épaisseur conduit à des temps de calculs très importants.Dans cette optique, nous présentons une méthode d'homogénéisation dont le but est de définir les caractéristiques magnétiques équivalentes d'un empilement quelconque de tôles et d'entrefers. Sa formulation est basée sur la minimisation de l'énergie et la conservation du flux magnétique. Les résultats de cette méthode appliquée à un joint magnétique de transformateur à joints step-lap sont confrontés à des mesures expérimentales et à un modèle élément fini 3D. Ce dernier requiert de connaître les caractéristiques magnétiques des tôles dans les directions de laminage, transverse et normale. La détermination de la perméabilité des tôles dans la direction normale est problématique et constitue un point original de notre étude. Deux méthodes, analytique et numérique, s'appuient sur les mesuresd'un banc de caractérisation en régime statique pour déterminer cette perméabilité normaleThis thesis focuses on the analysis and the modeling the magnetic flux distribution in electrical machines with anisotropic laminated magnetic circuit. The anisotropy of magnetic sheets in transformers induces complex 3D phenomena in step-lap magnetic joints where the sheets are overlapped. Moreover, in order to increase the energy efficiency of rotating machines, new structures based on grain-oriented electrical steel are developed.However, an accurate 3D simulation of a laminated core with thin sheets and insulation of a few microns leads to very large computation time. In this context, we present a homogenization method, which purpose is to define the equivalent magnetic characteristics of any laminated core made of sheets and air gaps. Its formulation is based on the energy minimization and the magnetic flux conservation. The results of this method applied to a step-lap magnetic joint are compared with experimental measurements and a 3D finite element model. The latter requires to know the magnetic characteristics of the sheets in the rolling, transverse and normal directions. The determination of the sheets permeability in the normal direction is problematic and it constitutes an original point of our study.Two methods, analytical and numerical, based on measurements obtained with a static characterization bench makes possible the determination of the normale permeability
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Fansi, Joseph. "Prediction of DP steel fracture by FEM simulationsusing an advanced Gurson model." Phd thesis, Paris, ENSAM, 2013. http://pastel.archives-ouvertes.fr/pastel-00944529.
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This numerical investigation of an advanced Gurson-Tvergaard-Needleman (GTN) model is an extension of the original work of Ben Bettaieb et al. (2011). The model has been implemented as a user-defined material model subroutine (VUMAT) in the Abaqus/explicit FE code. The current damage model extends the previous version by integrating the three damage mechanisms: nucleation, growth and coalescence of voids. Physically based void nucleation and growth laws are considered, including an effect of the kinematic hardening. These new contributions are based and validated on experimental results provided by high-resolution X-ray absorption tomography measurements. Also, the numerical implementation of the kinematic hardening in this damage extension has obliged to readapt the classical triaxiality definition. Besides, a secondary fracture initiation criterion based on the ultimate average inter-cavities distance has been integrated to localize and quantify with good accuracy the strain distribution just before the material fails apart. The current damage model is applied in industrial conditions to predict the damage evolution, the stress state and the fracture initiation in various tensile thin flat sheet geometries and the cross-die drawing tests.
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Buzit, Sebastien. "Evolution of crystallographic textures and TRIP effects in stainless steel AISI 304." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/19584.
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Rajhi, Wajdi. "Anisotropie induite par l'endommagement ductile : mécanismes physiques, modélisation et simulation numérique." Thesis, Troyes, 2014. http://www.theses.fr/2014TROY0027/document.
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L’objectif de ce travail est de développer une modélisation prédictive du comportement et de la rupture ductile des matériaux métalliques à anisotropies initiales et induites par l’endommagement. La thermodynamique des processus irréversibles est utilisée comme cadre pour la formulation proposée. Le modèle de comportement est élastoplastique anisotrope avec écrouissage non linéaire isotrope et cinématique en grandes déformations plastiques, avec une théorie non associée à normalité associée, basée sur des normes de contraintes quadratiques. L’endommagement ductile anisotrope est décrit par un tenseur du second ordre symétrique dont l’évolution est décrites par des relations de type Lemaitre-Desmorat. Le couplage fort comportement-endommagement est réalisé dans le cadre de l’hypothèse de l’équivalence en énergie totale où l’effet de l’endommagement sur le comportement est introduit par un tenseur « effet d’endommagement » d’ordre quatre symétrique de type Murakami. Après une caractérisation expérimentale des mécanismes physiques de l’endommagement dans l’acier AISI 316L, le modèle de comportement avec endommagement a été identifié. Une fois discrétisé et implémenté dans le code de calcul de structures ABAQUS/Explicit®, une étude paramétrique et de nombreuses simulations numériques de l’endommagement anisotrope en mise en forme de quelques structures ont été réalisées et discutées en détailThe objective of this work is to develop a predictive modeling of behavior and ductile fracture of metallic materials with initial anisotropy and induced by the ductile anisotropic damage. Thermodynamics of irreversible processes is used as a framework for the proposed formulation. The model is anisotropic elastoplastic with non-linear isotropic and kinematic hardening under large plastic strains. It is formulated in the framework of the non-associative plasticity theory with associative normality rule and based on quadratic equivalent stress. The anisotropic ductile damage is described by a symmetric second-rank tensor whose evolution is described by Lemaitre /Desmorat type relationships. The strong damage-behavior coupling is done under the assumption of total energy equivalence where the effect of the anisotropic damage is introduced by a fourth-rank symmetric damage-effect tensor of Murakami kind.After an experimental characterization of the main physical mechanisms of anisotropic damage in stainless steel AISI 316L, the behavior model with damage has been identified. Once discretized and implemented in the computer code ABAQUS / Explicit ®, a parametric study and many numerical simulations of anisotropic damage in some metal forming processes have been carried out and discussed in detail
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Gullberg, Daniel. "Influence of composition, grain size and manufacture process on the anisotropy of tube materials." Thesis, Uppsala University, Department of Engineering Sciences, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-125336.
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A problem with cold pilgered tubes for OCTG applications is that they can get anisotropic properties with regard to yield strength. One source of anisotropy is texture that is developed during the cold deformation. EBSD measurements have been made on several austenitic stainless steels with different deformations to see what influence the composition has on the texture formation. The same measurements were used to study the influence of grain size on texture formation. The conclusion was that the composition can have an impact on the texture and hence has potential to also affect the anisotropy. The differences in texture cannot be associated with a specific alloying element, but is rather a synergetic effect. It was also concluded that grain structure has no strong influence on texture formation. An evaluation of three different tool designs used for cold pilgering was made. The designs evaluated are referred to as design A, B and C. EBSD measurements showed large deviations in texture in the middle of the wall compared to close to the surface of pilgered OCTG. However, the measurements showed no large differences between the three designs and the texture could not be coupled to the anisotropy.
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Massé, Thomas. "Study and optimization of a high carbon steel flat wires." Paris, ENMP, 2010. http://www.theses.fr/2010ENMP1672.
Full textAbstract:
Cette thèse porte sur la modélisation par éléments finis des procédés de mises en forme à froid, que sont le tréfilage et le laminage. Tout d'abord le comportement mécanique des aciers haut carbone a été mesuré grâce à une large campagne d'essais expérimentaux tout au long de cette gamme de mise en forme et une progressive anisotropie mécanique a été observée au cours du tréfilage. Puis, la simulation numérique du tréfilage et du laminage a été réalisée à l'aide de FORGE2005®. Le résultat principal concerne la prédiction de l'élargissement en fin de laminage qui est très imprécise avec une loi isotrope (sous estimation de la largeur de 10%). Cette sous-estimation passe à 5% avec une loi de comportement anisotrope. Ensuite, une troisième partie a porté sur l'étude microstructurale couplée à une analyse des mécanismes d'endommagement des aciers perlitiques au cours du tréfilage et du laminage. L'anisotropie mécanique provient de l'alignement des colonies de perlite au tréfilage et par l'apparition d'une orientation cristallographique préférentielle. Trois mécanismes d'endommagement ont pu être identifiés au cours du tréfilage. Lors du passage au laminage, les cinétiques de propagation de l'endommagement sont modifiées. La simulation a permis d'apporter des informations supplémentaires et de valider les observations expérimentales. Enfin, des calculs d'optimisation du tréfilage ont été effectués et ont permis d'étudier la sensibilité des fonctions objectifs (endommagement et force de tréfilage) aux paramètres d'optimisation (géométrie de filière). De plus, cette étude a mis en évidence que les solutions optimales diffèrent en fonction du choix de la fonction coût et qu'il est possible de diminuer l'endommagement sans trop augmenter la force de tréfilage et le risque de ruptureThis thesis deals with the numerical simulation of cold forming processes, i. E. Wire drawing and rolling. First, high carbon steel mechanical behaviour was measured from experiments throughout this range of steel forming and a progressive mechanical anisotropy has been observed during drawing. Secondly, numerical simulations, with FORGE2005®, have been run to simulate the material behaviour during wire drawing and rolling. The main results show that the widening prediction, with an isotropic behaviour law, is not accurate with an underestimation of 10% on the total width. This underestimation is only 5% when an anisotropic behaviour is used. Then, a microstructural study coupled with an analysis of damage mechanisms was done on high carbon pearlitic steels during wire drawing and rolling. The mechanical anisotropy comes from the orientation of the pearlitic colonies in the drawing, and by the emergence of a preferential crystallographic texture. Three damage mechanisms have been identified during drawing. During rolling, damage expansion kinetics are changed because of heterogeneous strain. Simulation enabled to bring further information and to validate previous experimental observations. Finally, drawing optimization calculations have been performed and enabled to study the sensitivity of the cost functions (damage and drawing force) to optimization parameters (drawing die geometry). Moreover this study highlighted that optimal solution depends on the choice of the cost function and identified an opportunity to reduce damage by reducing the die angle without increasing the axial stresses and the fracture risk
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Tankoua, Yinga Franck. "Transition ductile-fragile des aciers pour gazoducs : Étude quantitative des ruptures fragiles hors plan et corrélation à l’anisotropie de microtexture." Thesis, Paris, ENMP, 2015. http://www.theses.fr/2015ENMP0014/document.
Full textAbstract:
La bonne ténacité des aciers pour gazoducs aux basses températures est nécessaire pour éviter la propagation de fissures de manière catastrophique. Cette étude vise à améliorer la compréhension physique et l'évaluation quantitative du comportement à rupture des aciers pour gazoducs laminés à chaud, en nous intéressant plus particulièrement aux températures au pied de la transition ductile-fragile .La résilience de ces aciers est généralement validée à l'aide d'essais dits drop weight tear tests (DWTT), après lesquels le faciès de rupture doit contenir moins de 15% de zone fragile. Pour les aciers mis en forme par laminage thermomécanique (TMCP), des ruptures fragiles hors plan, comme le délaminage (qui se propage dans le plan de laminage de la tôle), et la rupture fragile en biseau le long des plans dits thêta (inclinés de 40° autour de la direction de laminage par rapport au plan de laminage) apparaissent dans la transition ductile-fragile. Ces modes de rupture, observés lors des essais de résilience (DWTT, Charpy) et de ténacité (CT), affectent la résistance à la rupture de ces aciers.L'anisotropie de l'écoulement plastique, puis celle de la sensibilité à la rupture par clivage ont été caractérisées en fonction de la température, à l'aide d'essais de traction sur des éprouvettes lisses et entaillées conçues pour cette étude. L'analyse mécanique de ces essais à l'aide de calculs par éléments finis a permis de déterminer des contraintes critiques de clivage dans les directions perpendiculaires au plan de laminage et aux plans thêta. Les valeurs obtenues dans ces directions sont de 25% inférieures à celles correspondant aux directions de laminage et travers long.L'anisotropie de la contrainte critique de clivage a été quantitativement corrélée à l'anisotropie de microtexture du matériau. Des entités appelées « facettes de clivage potentielles » ont été définies et mesurées dans cette étude, comme des régions contenant un plan {100} défavorablement orienté et dans lesquelles les fissures de clivage se propagent sans être arrêtées. Par exemple, un plan contenant 20% de facettes de clivage potentielles aurait une contrainte critique de clivage de 20% moins élevée qu'un plan présentant seulement 10% de facettes de clivage potentielles.La taille et la forme de ces facettes de clivage potentielles évoluent avec la déformation plastique. Par conséquent, la contrainte critique de clivage est affectée par l'historique de déformation. Dans le cas du délaminage, les facettes de clivage potentielles s'allongent au cours d'un chargement dans la direction travers long, conduisant à une augmentation de leur taille effective et par conséquent à une diminution (qui peut atteindre 30%) de la contrainte critique de clivage dans le plan de la tôle. Cette diminution facilite in fine l'apparition du délaminage. De plus, la présence de micro-fissures ductiles facilite la rupture par délaminage en modifiant l'état de contrainte local. Un critère a ainsi été proposé pour prédire numériquement l'amorçage du délaminage dans des éprouvettes de traction et/ou de résilience Charpy.L'application de cette approche à des échantillons traités thermiquement et à des échantillons pré-déformés a montré que la sensibilité au délaminage pouvait être contrôlée en modifiant la texture locale initiale du matériauHigh toughness of pipeline steels at low temperature is required to avoid catastrophic propagation of brittle crack. The aim of the study is to improve physical understanding and quantitative assessment of the toughness behavior of hot-rolled pipeline steels, focusing on the lower part of the ductile to brittle transition temperature range.The impact toughness of these steels is commonly validated using drop weight tear tests (DWTT), on the basis of fracture surfaces that must exhibit less than 15% of brittle fracture appearance. In thermomechanical control processed steels, brittle out-of-plane cracks such as delamination (which propagates along the rolling plane), and brittle tilted fracture (BTF) along theta-planes (tilted around RD by 40° with respect to rolling plane), have been characterized in the ductile to brittle transition temperature range, for both industrial (DWTT) and laboratory Charpy impact tests. In both cases, as well as in fracture toughness tests, such brittle out-of-plane cracking has been shown to impair the impact toughness.The anisotropy in plastic flow and sensitivity to cleavage fracture has been characterized as a function of temperature, by using tensile tests on specifically designed smooth and notched specimens. From finite element mechanical analysis of these tests, critical cleavage stresses normal to the rolling plane and the theta-plane are considerably lower (around 25%) than for planes normal to the rolling and transverse directions.The anisotropy in critical cleavage stress has been quantitatively correlated to microtexture anisotropy. So-called “potential cleavage facets” have been defined and measured in this study, as regions with unfavorably oriented {100} planes, which are taken as unit crack paths for cleavage propagation. A sample containing 20% of potential cleavage facets had a critical cleavage stress 20% lower than a sample with only 10% of potential cleavage facets.The size and shape of these potential cleavage facets evolve during plastic deformation. Therefore, the critical cleavage stress was found to be affected by plastic strain history. In the case of delamination, potential cleavage facets along the rolling plane were elongated during loading, their area was increased and the corresponding critical cleavage stress decreased by around 30% with respect to the undeformed case. This made delamination cracking easier. Moreover, the presence of a ductile crack at the initiation site of delamination locally modified the stress state and also facilitated delamination occurrence. A criterion has been developed to numerically predict the onset of delamination in tensile and Charpy specimens.Application of this approach to heat-treated and to prestrained specimens eventually showed that it was possible to modify the sensitivity to delamination by strongly modifying the initial microtexture anisotropy
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Beese, Allison M. "Experimental investigation and constitutive modeling of the large deformation behavior of anisotropic steel sheets undergoing strain-induced phase transformation." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67576.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 139-146).
The strain-induced phase transformation from austenite to martensite is responsible for the high strength and ductility of TRansformation-Induced Plasticity (TRIP)- assisted steels. The large deformation behavior of conventional steels is governed by crystallographic slip. In the case of TRIP steels, the phase transformation provides an additional microstructural deformation mechanism, which has a particularly strong effect on the strain hardening response at the macroscopic level. This thesis work develops a new plasticity model for TRIP steels that accounts for the effect of phase transformation. In particular, the large deformation behavior of 1.5mm thick stainless steel 301LN sheets at room temperature is studied in detail. Several techniques for quantifying the martensite volume fraction are evaluated including micrography, X-ray diffraction, neutron diffraction, magnetic saturation, and magnetic permeability measurements. The latter is then used to measure the evolution of the martensite content throughout mechanical experiments. The experimental program for different stress states includes experiments for uniaxial tension, uniaxial compression, equi-biaxial tension, pure shear, and transverse plane strain tension. The resulting experimental data demonstrate the influence of both the stress triaxiality and Lode angle parameter on the austenite-to-martensite transformation kinetics. A stress-state dependent transformation kinetics evolution equation is proposed which describes the martensite content as a function of plastic strain, the stress triaxiality, and the Lode angle parameter. Furthermore, a phenomenological plasticity model is developed comprising an anisotropic yield function, an isotropic hardening law, and a nonlinear kinematic hardening law with initial back stress. The isotropic hardening law expresses the increase in deformation resistances as a function of the plastic strain and the martensite content and is directly coupled with the stress-state dependent transformation kinetics equation. As a result, the model is able to describe the experimentally observed effect of stress state on the macroscopic hardening response. The constitutive model is implemented into a finite element program and used to simulate all experiments performed. The model predictions agree well with the experimental results for a wide range of stress states and for both specimens with homogeneous and heterogeneous stress and strain fields.
by Allison M. Beese.
Ph.D.
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Steckmeyer, Antonin. "Caractérisation et modélisation du comportement mécanique à haute température des aciers ferritiques renforcés par dispersion d'oxydes." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00819136.
Full textAbstract:
Le renforcement par dispersion d'oxydes nanométriques permet, d'une manière générale, d'améliorer la résistance mécanique des matériaux métalliques. Il autorise donc une augmentation de leur température maximale d'utilisation. De nombreux travaux de recherche sont menés au Commissariat à l'Énergie Atomique et aux Énergies Alternatives sur les aciers ODS, pour Oxide Dispersion Strengthened steels. S'inscrivant dans le cadre du développement du nucléaire civil de quatrième génération, ces travaux ont pour but de qualifier un matériau pouvant être utilisé en tant que matériau de gainage combustible à une température de 650℃. Ce travail de thèse a pour objectif d'améliorer la compréhension des propriétés mécaniques des aciers ODS, en cherchant d'une part à caractériser et à modéliser leur comportement en fluage, et d'autre part à caractériser leur nisotropie de comportement et à en identifier l'origine. Pour cela, de nombreux essais mécaniques ont été effectués entre 20℃ et 900℃ sur une nuance d'acier ODS ferritique de composition nominale Fe-14Cr1W0,26Ti + 0,3Y2O3 . Cette nuance a été élaborée au CEA, par mécanosynthèse puis extrusion à chaud, sous la forme d'une barre ronde. Les résultats obtenus démontrent la grande résistance mécanique à haute température de l'acier ODS étudié. Ils mettent également en évidence une forte dépendance de la ductilité et de la résistance du matériau vis-à-vis de la vitesse de sollicitation. Sur la base des différentes caractérisations expérimentales réalisées, un modèle de comportement macroscopique uniaxial a été développé. S'appuyant sur la description de trois écrouissages cinématiques et d'un terme de restauration statique, ce modèle démontre une capacité remarquable à reproduire le comportement mécanique du matériau en traction, en fatigue, en fluage et en relaxation. Par ailleurs, la caractérisation de l'anisotropie mécanique de la nuance d'acier ODS étudiée s'avère dépendre de la température. Deux modélisations polycristallines différentes ont été mises en place afin de reproduire cette anisotropie de comportement à partir des textures cristallographique et morphologique du matériau. Le désaccord observé entre les prévisions de ces modèles et les résultats expérimentaux conduit à formuler d'autres hypothèses sur la déformation des aciers ODS.
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Millan, Mirabal Leysmir Adriana. "Contribution à la caractérisation et à la modélisation 3D de l'anisotropie des aciers électriques à grains orientés en vue du calcul des pertes aux extrémités des turbo-alternateurs." Electronic Thesis or Diss., Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILN013.
Full textAbstract:
Récemment, les gestionnaires de réseau et de système de transmission, comme le Réseau européen des gestionnaires de réseau de transport d'électricité (ENTSO-E), mettent en place des réglementations pour étendre la plage de fonctionnement des équipements connectés au réseau électrique. Les principaux objectifs de ces modifications sont : d'augmenter la flexibilité du réseau en le rendant capable de supporter des variations de fréquence et de tension (dues aux modifications de l'équilibre des puissances active et réactive) et de faciliter l'intégration et la production d'énergie renouvelable. Cependant, de nombreux équipements installés et raccordés au réseau n'ont pas été conçus pour être exploités dans ces plages de fonctionnement et leur utilisation dans ces conditions peut avoir un impact négatif sur le cycle de vie des équipements, en particulier dans les turbo-alternateurs.Les grands turbo-alternateurs, utilisés pour la production d'électricité dans les centrales nucléaires et hydroélectriques, sont impactés par ces nouvelles réglementations. Cet impact est particulièrement observé aux extrémités de ces machines électriques où les pertes fer sont susceptibles d'augmenter significativement. Ces pertes peuvent entraîner des échauffements, notamment des points chauds, qui peuvent conduire à la fusion de l’isolation entre les tôles du noyau du stator, provoquant ainsi des courts-circuits et des dommages irréversibles à l'équipement. Afin de pouvoir analyser et limiter l'impact des mécanismes physiques mis en jeu, la société EDF s’appuie sur des simulations numériques tridimensionnelles de la machine électrique pour calculer les pertes pour différents régimes de fonctionnement.Une partie de ce travail a déjà été réalisée au laboratoire L2EP, où le logiciel d'analyse par éléments finis code_Carmel a été adapté pour le calcul des pertes dans le noyau du stator et des pertes joule dans les modèles tridimensionnels. Cependant, la complexité physique des propriétés des circuits magnétiques aux extrémités des turbo-alternateurs doit être prise en compte pour obtenir des résultats fiables. En effet, compte tenu du schéma tridimensionnel du chemin du flux magnétique et des propriétés fortement anisotropes du circuit magnétique en acier électrique à grains orientés (GO), la description des pertes fer nécessite des modèles de matériaux magnétiques anisotropes précis combinés à une modélisation numérique efficace.Dans le cadre de ce travail de thèse, des modèles anisotropes dédiés aux aciers GO, notamment pour décrire la loi de comportement et les pertes fer, ont été étudiés puis implémentés dans un environnement de simulation par éléments finis (FEM) au sein du logiciel code_Carmel. La mise en œuvre a été validée par rapport à des données expérimentales obtenues sur un acier GO de qualité industrielle conventionnelle généralement utilisée dans les turbo-alternateurs. De plus, un démonstrateur expérimental a été développé pour étudier plus finement le comportement magnétique d'un empilement de tôles GO soumis à des excitations de flux magnétique 3D non conventionnelles. Un modèle numérique du démonstrateur expérimental a été développé et étudié, incluant les modèles de matériaux anisotropes, en comparant le comportement global du matériau GO ainsi que les pertes de fer dans l'échantillon d'intérêt.Les résultats montrent que, dans des configurations d'attaque de flux magnétique non conventionnelles, en particulier avec une attaque de flux magnétique normale au plan de laminage, les caractéristiques anisotropes de l’acier GO peuvent influencer la distribution du flux magnétique dans l'empilement de tôles étudié ainsi que les pertes de fer associées. Notamment, et comme attendu, les pertes par courants de Foucault classiques constituent la contribution majeure aux pertes fer dans l’empilement de tôles étudiéesRecently, network and transmission system operators like the European Network of Transmission System Operators of Electricity (ENTSO-E) have started to create regulations to extend the range of operation of the equipment connected to the electrical grid. The main purposes of these changes are: to increase the flexibility of the grid by making it able to withstand variations of frequency and voltage (due to alterations in the active and reactive power balance), and to ease the integration of renewable energy generation. However, many of the installed equipment connected to the grid have not been conceived to be exploited in these operating ranges and their use under these conditions will have a negative impact, especially on the turbo-generators life cycle.Large turbo-generators, used for the generation of electricity in nuclear and hydroelectric power plants, are affected by these new regulations. This impact is especially evident at end-regions of these electrical machines, where the iron losses are likely to increase significantly. These losses can lead to overheating, in particular hot points which can lead to the melting of the insulation layers between the lamination of the stator core, causing short-circuits and irreversible damage to the equipment. To be able to analyze and limit the impact of the involved physical mechanisms, the EDF Company works with tridimensional numerical simulations of the electrical machine to calculate the losses under different regimes of operation.Part of this work has already been realized in the L2EP laboratory, where the finite element analysis software code_Carmel have been adapted for the calculation of core losses and joule losses in tridimensional models. However, the physical complexity of the magnetic circuit properties at the end-regions of turbo-generators must be accounted for, in order to have reliable results. Indeed, considering the tridimensional pattern of the magnetic flux path and the strongly anisotropic properties of the magnetic circuit made from grain oriented electrical steel (GOES), the description of the iron losses requires accurate anisotropic magnetic material models combined with an efficient numerical modelling.In the framework of this PhD work, anisotropic GOES models, related to the behavior law and iron losses, have been studied and successfully implemented in a finite element method (FEM) simulation environment within the software code_Carmel. The implementation has been validated against experimental data achieved on an industrial conventional GO grade typically used in turbogenerators. Also, an experimental demonstrator has been developed to investigate more closely the magnetic behavior of a lamination stack made of GOES under non-conventional 3D magnetic flux excitations. A numerical model of the experimental demonstrator has been developed and studied with the implemented material models by comparing the global behavior of GOES as well as the iron losses in the sample of interest.The results show that under non-conventional magnetic flux attack configurations, especially with a magnetic flux attack normal to the lamination plane, the anisotropic characteristics of the GOES can influence the magnetic flux distribution within the lamination stack and the associated iron losses. In particular, the classical eddy current losses constitute, as expected, the most significant contribution of the total iron losses in the GOES laminations
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Sapezanskaia, Ina. "Deformation mechanisms of metastable stainless steels accessed locally by monotonic and cyclic nanoindentation." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/398401.
Full textAbstract:
Metastable austenitic stainless steels feature an abundance of different deformation mechanisms, which
contribute to the distinguished mechanical properties of these alloys. However, these properties are
known to depend on the local microstructure and also are highly anisotropic. Furthermore, deformation is
expected to be different for the bulk and the surface of a sample. In this sense, a discrete study is not
trivial.
The present work aims at investigation of the main deformation mechanisms and their gradual evolution,
by employing controlled deformation of individual austenite grains via monotonic and cyclic
nanoindentation. The corresponding loading–unloading curves have given extensive information about
underlying mechanical properties, which could be related to an exhaustive reconstruction of the
deformation substructure, both in surface and bulk, by different small scale characterization techniques.
Amongst others, features such as time-dependent deformation, reversible phase transformation under
load, crystalline anisotropy and grain size influences, besides plasticity transmission and fatigue behavior
have been found and analyzed.Los aceros inoxidables austeníticos metaestables pueden experimentar una amplia gama de mecanismos de deformación diferentes, los cuales contribuyen a sus extraordinarias propiedades mecánicas. Sin embargo, estas propiedades dependen de la microestructura y son altamente anisotrópicas. Además, la deformación es diferente en la superficie y en el interior de una muestra. Por lo tanto, un estudio detallado no resulta trivial. El objetivo de este trabajo es el estudio de los principales mecanismos de deformación, así como de su desarrollo gradual. Para ello se han realizado ensayos de nanoindentación, tanto monotónica como cíclica, los cuales han permitido la deformación controlada de granos austeníticos preseleccionados. Las curvas de carga y descarga de los ensayos de nanoindentación han proporcionado amplia información sobre el comportamiento mecánico del acero, la cual se ha podido correlacionar con la reconstrucción detallada de las subestructuras de deformación, tanto a nivel superficial como en el interior, la cual se ha llevado a cabo mediante técnicas de caracterización a escala microscópica. Entre otros, se encontraron y estudiaron fenómenos como las transformaciones de fase reversibles bajo carga, la influencia tanto de la anisotropía cristalina como del tamaño de grano, mecanismos dependientes del tiempo, junto con la transmisión de plasticidad y la respuesta a fatiga.
Les aciers inoxydables austénitiques métastables sont le siège de différents mécanismes de déformation qui sont à l'origine des propriétés mécaniques qui distinguent ce type d’alliages. Cependant, ces dernières, dépendant de la microstructure locale, sont fortement anisotropes. Par ailleurs, la déformation d'un échantillon massif serait différente de celle obtenue en surface. De ce fait, une étude détaillée trouve tout son intérêt. Le présent travail vise donc à identifier les principaux mécanismes de déformation et de leur évolution progressive, en se basant sur une déformation contrôlée de grains austénitiques individuels par des tests mécaniques de nanoindentation monotoniques et cycliques. Les courbes correspondantes au chargement-déchargement révèlent des informations détaillées sur les propriétés mécaniques sous-jacentes qui pourraient être liées à une étude complète de la structure de déformation en surface et en volume par différentes techniques de caractérisation à une échelle très fine. La déformation en fonction du temps, les phénomènes de transformation de phase réversible sous charge, l'anisotropie cristalline, l'influences de la taille des grains, la transmission de la plasticité et la tenue en fatigue ont été mis en évidence et étudiés.
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Arthington, Matthew Reginald. "Photogrammetric techniques for characterisation of anisotropic mechanical properties of Ti-6Al-4V." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:51e4f4d9-75e2-4784-9fbf-103d07496e23.
Full textAbstract:
The principal aims of this research have been the development of photogrammetric techniques for the measurement of anisotropic deformation in uniaxially loaded cylindrical specimens. This has been achieved through the use of calibrated cameras and the application of edge detection and multiple view geometry. The techniques have been demonstrated at quasi-static strain rates, 10^-3 s^-1, using a screw-driven loading device and high strain rates, 10^3 s^-1, using Split Hopkinson Bars. The materials that have been measured using the technique are nearlyisotropic steel, anisotropic cross-rolled Ti-6Al-4V and anisotropic clock-rolled commercially pure Zr. These techniques allow the surface shapes of specimens that deform elliptically to be completely tracked and measured in situ during loading. This has allowed the measurement of properties that could not have been recorded before, including true direct stress and the ratio of transverse strains in principal material directions, at quasi-static and elevated strain rates, in tension and compression. The techniques have been validated by measuring elliptical prisms of various aspect ratios and independently measuring interrupted specimens using a coordinate measurement machine. A secondary aim of this research has been to improve the characterisation of the anisotropic mechanical properties of cross-rolled Ti-6Al-4V using the techniques developed. In particular, the uniaxial yield stresses, hardening properties and the associated anisotropic deformation behaviour along the principal material directions, have all been recorded in detail not seen before. Significant findings include: higher yield stresses in-plane than in the through-thickness direction in both tension and compression, and the near transverse-isotropy of the through-thickness direction for loading conditions other than quasi-static tension, where significant anisotropy was observed.
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Sharma, Shiv. "Investigation of elastic anisotropy and texture of austenitic stainless steel weld metal using diffraction and self-consistent modelling." Thesis, Open University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522292.
Full textAbstract:
Welding of austenitic stainless steels is a prominent process in several industrial sectors including nuclear, aerospace, chemical and process. During finite element modelling of weld properties, it is assumed that the weld metal is homogeneous. During the modelling process weld metal is assigned the same elastic constants as that of parent metal. This can introduce erroneous results during the calculation of strains. Weld metal is usually highly anisotropic due to directional solidification. Weld metal also possessesty pical fibre texture as the grains grow along the maximum thermal gradient when cooling and the result is long, columnar grains. These grains usually have a particular crystallographic direction along the solidification direction. Weld metals usually have [0011 crystallographic planes along the solidification direction, and it has been termed as [0011 fibre texture. The resulting fibre texture due to solidification has an important consequence on weld metal properties. Depending on the grain orientations, different mechanical properties are observed as compared with an ideal homogeneous and isotropic material. Different types of austenitic weld metals have been investigated in this work. The mechanical response of different types of weld metal, in different directions has been analysed using in-situ tension/compression and neutron diffraction. It has been observed that the Young's modulus for the weld metal is direction dependent. These variations have been explained on the basis of texture investigation using the electron backscatter diffraction (EBSD) technique. The texture results have been correlated with the material response and it has been observed that the more pronounced the crystallographic texture, the more anisotropic is the material response under applied loading. Finally, the directional Young's modulus has also been calculated from elasto-plastic self-consistent modelling using Hutchinson's formalism (using the FORTRAN sub-routine written by Carlos Tome).
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Scharnweber, Michael. "Initiierung und Ausbreitung kurzer Ermüdungsrisse in ein- und zweiphasigem Edelstahl." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-143798.
Full textAbstract:
In der vorliegenden Arbeit wurden Untersuchungen zum Initiierungs- und Ausbreitungsverhalten kurzer Ermüdungsrisse in einem austenitischen sowie einem austenitisch-ferritischen Edelstahl durchgeführt. Dazu erfolgten zyklische Verformungsexperimente sowohl ex situ als auch in situ im Rasterelektronenmikroskop. Die Auswertung der Experimente erfolgte im Rasterelektronenmikroskop sowohl abbildend in verschiedenen Modi als auch über Rückstreuelektronenbeugungsmessungen. Bezüglich der Rissinitiierung wurde eine Häufigkeitsverteilung der Rissinitiierungsorte für beide Stähle erstellt. Die dabei ermittelte stark unterschiedliche Häufigkeit für die transkristalline Rissinitiierung in der austenitischen Phase konnte mit der unterschiedlichen Textur und Mikrostruktur der beiden Stähle in Zusammenwirken mit den elastischen Eigenschaften der beiden Phasen erklärt werden. Für die Rissausbreitung wurde gezeigt, dass eine Korrelation zwischen der Risslänge und der Rissausbreitungsrate besteht, aus der hervorgeht, dass die Übergangsrisslänge zwischen den Bereichen der mikrostrukturell und mechanisch kurzen Risse etwa einen Korndurchmesser beträgt. Anhand der in situ Messung der (plastischen) Rissöffnung und -scherung wurden die Unterschiede im Rissausbreitungsverhalten in den verschiedenen Phasen herausgearbeitet. Für die austenitische Phase ergibt sich dabei ein öffnungsdominierter und für die ferritische Phase ein scherungsdominierter Mechanismus. Die im Ferrit auftretenden zwei unterschiedlichen Ausprägungen der Oberflächenrisspfade („rau“ und „glatt“) konnten mit der Orientierung der jeweils risstragenden Körner korreliert werden. In Zusammenwirken mit der beobachteten Systematik der Anordnung der Gleitspuren um kurze Risse im Ferrit sowie einer Analyse der Spannungsverteilung um die Rissspitze wurde ein Modell des Rissausbreitungsmechanismus\' erstellt sowie die bisher in der Literatur vorherrschende These des Einfachgleitens widerlegt. Schließlich konnte die Barrierenwirkung von Korn- und Phasengrenzen sowohl anhand der Messung der Rissausbreitungsrate als auch der plastischen Rissöffnung bzw. -scherung gezeigt und daraus Rückschlüsse auf die Ausdehnung der plastischen Zone vor der Rissspitze gezogen werden. Gleichzeitig wurde dabei die Korrelation zwischen Rissausbreitungsrate und plastischer Rissöffnung bzw. -scherung nachgewiesen.
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Harant, Martin. "Výroba dílce hydroformováním a její optimalizace." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-402525.
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The project deals with analysis and optimization of the geometry of the stamped part produced by the pillow hydroforming. The blank consists of two sheets of steel DC01, which is welded by laser beam. The forming process can cause excessive thinning and cracking of the part. By evaluation of mechanical tests is created material model, which is the basis for numerical simulation created in software PAM-STAMP. The outputs are analysis which provide information about critical points, failure pressure, limiting deformations and prediction of springback. Validity of the numerical simulation is verified by comparison with the experimentally obtained data. The comparative criterions are the failure pressure and the material thickness at various locations. Based on the results of the numerical simulation, the optimization of the geometry is created. The optimization uses different values of radius at the crack point.
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Akcaoglu, Fehmi Umit. "Investigating The Effect Of Deformation And Annealing Texture On Magnetic Anisotropy In Low-c Steel Sheets By Magnetic Barkhausen Noise Method." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615569/index.pdf.
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Deformation and annealing texture in the cold rolled low carbon steels is important for sheet metal forming operations and service performance. The aim of this study is to non-destructively investigate the effect of texture on magnetic anisotropy. Various samples having different textures and residual stress states, due to different % reduction in thickness, annealing and stress relieving treatment, were prepared. Texture maps were obtained by Magnetic Barkhausen noise measurements performed with 100 steps between the ranges of 00-3600 on the surface. Microstructure investigation by optical &scanning electron microscopy
hardness and tension tests were performed
and texture was determined by X-Ray diffraction method. The results were compared, evaluated and discussed to establish relationship between texture and magnetic Barkhausen Noise emission.
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Lings, Martin L. "Contributions to the understanding of deep excavations in stiff clay and stiffness anisotropy also pile shaft friction and sand-steel interfaces." Thesis, University of Bristol, 2008. http://hdl.handle.net/1983/6fc1f459-b593-4b23-9059-9de25b8aae05.
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Lasota, Tomáš. "Computational Modelling of Mechanical Behaviour of "Elastomer-Steel Fibre" Composite." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-234188.
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Tato práce se zabývá výpočtovými simulacemi zkoušek jednoosým tahem a tříbodovým ohybem kompozitního vzorku složeného z elastomerové matrice a ocelových výztužných vláken orientovaných pod různými úhly, jakož i jejich experimentální verifikací. Simulace byly provedeny pomocí dvou různých modelů - bimateriálového a unimateriálového výpočtového modelu. Při použití bimateriálového modelu, který detailně zohledňuje strukturu kompozitu, tzn. pracuje s matricí a jednotlivými vlákny, je zapotřebí vytvořit model každého vlákna obsaženého v kompozitu, což přináší řadu nevýhod (pracná tvorba výpočtového modelu, řádově větší množství elementů potřebných k diskretizaci v MKP systémech a delší výpočetní časy). Na druhé straně v unimateriálovém modelu se nerozlišují jednotlivá vlákna, pracuje se pouze s kompozitem jako celkem tvořeným homogenním materiálem a výztužný účinek vláken je zahrnut v měrné deformační energii. Porovnání experimentů se simulacemi ukázalo, že bimateriálový model je v dobré shodě s experimenty, na rozdíl od unimateriálového modelu, který je schopen poskytnou odpovídající výsledky pouze v případě tahového namáhání. Z tohoto důvodu byl hledán způsob, který by umožnil rozšířit unimateriálový model o ohybovou tuhost výztužných vláken. V roce 2007 Spencer a Soldatos publikovali rozšířený unimateriálový model, který je schopen pracovat nejen s tahovou, ale i ohybovou tuhostí vlákna. Představený obecný model je však založen na Cosseratově teorii kontinua a jeho praktické využití je pro jeho složitost nemožné. Proto byl vytvořen zjednodušený model (částečně podle Spencera a Soldatose) s vlastní navrženou formou měrné deformační energie. Za účelem ověření nového unimateriálového modelu s ohybovou tuhostí vláken byly odvozeny všechny potřebné rovnice a byl napsán vlastní konečno-prvkový řešič. Tento řešič je založen na Cosseratově teorii kontinua a obsahuje zmíněný anizotropní hyperelastický unimateriálový model zahrnující ohybovou tuhost vláken. Vzhledem k tomu, že v případě Cosseratovy teorie jsou při výpočtu potřebné i druhé derivace posuvů, bylo nutné použít tzv. C1 prvky, které mají spojité jak pole posuvů, tak jejich prvních derivací. Nakonec byly provedeny nové simulace s využitím vlastního řešiče, které ukazují, že tuhost vláken lze u nového unimateriálového modelu řídit odpovídající materiálovou konstantou. V závěru práce je pak diskutováno, zda je nový unimateriálový model s ohybovou tuhostí schopen poskytnout stejné výsledky jako model bimateriálový, a to jak při tahovém tak i ohybovém namáhání kompozitního vzorku.
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Liu, Shibo. "Numerical and experimental study on residual stresses in laser beam welding of dual phase DP600 steel plates." Thesis, Rennes, INSA, 2017. http://www.theses.fr/2017ISAR0003/document.
Full textAbstract:
Le procédé de soudage laser est largement utilisé dans les travaux d'assemblage, en particulier, dans ledomaine de l'industrie automobile. L'acier dual phase DP600 est un acier à haute résistance qui permet deréduire le poids de l'automobile dans le cadre de l'allègement des structures. Notre travail s' estessentiellement basé sur l'évaluation des contraintes résiduelles générées dans l'acier DP600 lors du soudagepar laser. Deux approches ont été réalisées. L'approche expérimentale a été réalisée à l'aide de méthodes derayon X et par neutrons pour calculer les contraintes résiduelles. L'approche de simulation a été réalisée parcouplage de différentes formulations numériques.Numériquement, le formalisme de la mécanique continue a été utilisé par des simulations par éléments finis(FEM) pour analyser et évaluer les contraintes résiduelles. Sur la base de tests de traction expérimentaux, lemodèle constitutif élasto-thermo-plastique de l'acier DP600 a été identifié. L'écrouissage du matériau a étéétudié par la loi de Ludwik et de Voce. A partir de résultats experimentaux, un modèle a été proposé et lesrésultats analysés en utilisant une loi de mélange martensite (écrouissage Ludwik) et ferrite (adoucissementde Voce). De même, nous avons étudié la sensibilité à la température en utilisant plusieurs modèles :Johnson-Cook, Khan, Chen. A partir de cette étude, nous avons proposé un modèle de sensibilité à tatempérature. Enfin, un modèle de sensibilité à la déformation plastique, à la vitesse de déformation issu destravaux d'A.Gavrus et un modèle d'anisotropie planaire définit par la théorie de Hill ont été ajoutés.Une méthode d'automate cellulaire (CA) 2D a été programmée pour simuler l'évolution de la microstructurelors de la solification liée au processus de soudage laser. Dans ce modèle, les phénomènes de nucléationavec prise en compte de l'orientation de la croissance, de la concentration et de la vitesse de croissance àl'interface solide/liquide, l'anisotropie de la tension de surface, de la diffusion, ainsi que la fraction desphases en présence ont été pris en compte. De plus, les équations de conservation ont été étudiées en détail etanalysés. Les résultats ainsi que le champ de température issu du modèle FEM ont été importés dans lemodèle CA. En comparant la simulation et les résultats expérimentaux, de bonnes concordances ont ététrouvées.Par la suite, nous avons réalisés un couplage des deux modèles CA et FEM. Concernant le procédé laser, lesrésultats du modèle par éléments finis ont été analysés. La géométrie de l'échantillon, la source de chaleur,les conditions aux limites, le comportement thermo-mécanique de l'acier dual phase DP600 telles que laconductivité, la densité, la chaleur spécifique, l'expansion, l'élasticité et la plasticité sont introduites. Lesmodèles d'analyse du terme d'écrouissage, de la sensibilité à la vitesse de déformation, de la sensibilité à latempérature, de l'anisotropie plastique et de l'anisotropie élastique ont été simulés. Les fractions volumiquesconcernant ta nature des deux phases en présence ont été également étudiées.Les résultats numériques finaux tes contraintes résiduelles ont été étudiées. Les comparaisons avec desmesures experimentales ont montré à la fois quels phénomènes étudiés sont prépondérants et tes effets moinsinfluents sur l'évaluation des contraintes résiduelles. Les résultats tes plus probants ont montré des bonnesconvergences entre l'approche numérique et expérimentale. Ces résultats confortent la robustesse du modèlenumérique developpéLaser welding process is widely used in assembly work of automobi le industry. DP600 dual phase steeis a high strength steel to reduce automobile weight. Residual stresses are produced during laser weldingDP600. Continuum mechanics is used for analyzing res idual stresses by finite element simulation.Based on experimental tensile tests, the DP600 steel constitutive model are identified. The hardening termaccording to Ludwik law, Voce law and a proposed synthesis model are studied. The temperature sensitivityof Johnson-Cook, Khan, Chen and a proposed temperature sensitivity model are investigated. The strain ratesensitivity model proposed by A. Gavrus and planar anisotropy defined by Hi ll theory are also used.Cellul ar Automaton (CA) 20 method are programed for the simulation of solidification microstructureevolution during laser welding process. The temperature field of CA are imported from finite element analysimodel. The analysis function of nucleation, solid fraction, interface concentration, surface tension an isotropy,diffusion, interface growth ve locity and conservation equations are presented in detail. By comparing thesimulation and experimental results, good accordances are found.Modelling by a finite element method of laser welding process are presented. Geometry of specimen, heatsource, boundary conditions, DP600 dual phase steel material properties such as conductivity, density, specifiheat, expansion, elasticity and plasticity are introduced. Models analyzing hardening term, strain ratesensitivity, temperature sensitivity, plastic an isotropy and elastic an isotropy are simulated.The numerical results of laser welding DP600 steel process are presented. The influence of hardening term,strain rate sensitivity, temperature sensitivity and anisotropy on residual stresses are analyzed. Comparisonwith experimental data show good numerical accuracy.Keywords: Laser Welding, DP600, Residual Stress, Cellular Automaton, Hardening, Temperature sensitivity,Strain Rate Sensitivity, Anisotropy, Mixture dual phase law
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SILVA, JUNIOR SILVERIO F. da. "Determinação de tensões em materiais estruturais pelo ensaio magnetoelástico." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11294.
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Made available in DSpace on 2014-10-09T12:50:24Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:01:55Z (GMT). No. of bitstreams: 1 10893.pdf: 14774524 bytes, checksum: 8546584bc4571566ee6628fd4e1e4914 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Dang, Van Truong. "Etude numérique statistique des champs locaux de contraintes en surface de polycristaux cubiques et hexagonaux en élasticité." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2016. http://www.theses.fr/2016ESMA0003/document.
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Les premiers stades d'endommagement par fatigue au sein des matériaux métalliques polycristallins sont pilotés par les champs mécaniques locaux se développant à l'échelle des grains en surface. La formation de bandes de glissement persistantes est souvent à l'origine des fissures de fatigue. Cette localisation de la plasticité cyclique apparaît au sein de grains d'un polycristal dans lequel les champs de contraintes élastiques peuvent être fortement hétérogènes en fonction de la microstructure granulaire et de l'anisotropie élastique cristalline. La majeure partie de ce travail est consacrée à évaluer puis à analyser statistiquement les champs de contraintes au sein des grains de surface de polycristaux. Ce travail s'est concentré sur la réponse élastique des matériaux considérés afin d'étudier l'activation du glissement plastique et sa variabilité, puis, de façon un peu moins directe, ses conséquences vis-à-vis de la formation des fissures de fatigue. La méthodologie retenue est basée sur la simulation numérique en champs complets par éléments-finis de la réponse élastique d'un ensemble d'agrégats polycristallins dont les orientations cristallographiques sont tirées aléatoirement.Deux matériaux très différents du point de vue de l'élasticité cristalline et des systèmes de glissement ont été choisis comme support de l'étude. Le premier est l'acier inoxydable austénitique 316L à structure cubique à faces centrées et le second l'alliage de titane TA6V à structure hexagonale compacte. Les distributions de la cission résolue au sein d'ensembles de grains de surface, par classe d'orientation, sont analysées en relation avec les configurations cristallographiques locales afin d'identifier celles qui favorisent - ou au contraire inhibent - l'activation du glissement plastique. Les résultats obtenus, dans le cas du TA6V, suggèrent notamment une activation plus précoce et importante du glissement basal devant le glissement prismatique. De plus, la stratégie de simulation a été adaptée pour rendre compte de la présence de zones texturées appelées « macrozones » dont l'influence sur l'activation de plasticité peut être qualitativement prédite. L'activation du glissement dans le TA6V est également étudiée expérimentalement par la réalisation d'un essai in situ sous MEB où la précocité du glissement basal est constatée.Cet essai a également permis de caractériser la cinétique d'activation des différents types de glissements. Ces données, couplées aux statistiques des cissions simulées, permettent une estimation de la cission résolue critique sur les 2 types de glissementThe first stages of fatigue damage in metallic polycrystalline materials are governed by local mechanical field at the grain scale. Fatigue crack initiation is often related to the emergence of persistent slip band at surface.Localization of cyclic plasticity occurs within grains of polycristals in which elastic stress field can be highly heterogeneous due to the granular microstructure and crystalline anisotropic elasticity. The main goal of this study is to evaluate and analyse statistically the stress fields in surface grains of polycristals. In this work, the elasticregime only is considered in order to study the subsequent activation of plastic slip and its variability. The possibleconsequences regarding crack formation are also addressed but in a lesser extent. The methodology is based on fullfield finite element numerical simulation of the elastic response of a set of polycrystalline aggregates in which grains orientation is chosen randomly.The two materials chosen for this study exhibit different characteristics regarding crystal elasticity and slip systems.The first one is an austenitic stainless steels 316L (face centered cubic) and the second one a titanium alloy TA6V(hexagonal close packed). The distribution of resolved shear stress within several sets of surface grains, for different classes of crystal orientation, are analysed in relation to local crystallographic configurations in order to identify those which promote - or prevent from - plastic slip activation. For TA6V, the results suggest in particular that basal slip is activated earlier than prismatic slip. In addition, the simulation strategy has been modified tomodel the presence of some sharp band-like crystallographic textures named “macrozones” whose influence has been qualitatively predicted. Plastic slip activation in TA6V is also studied experimentally. In situ tensile test using SEM has shown the earlier activation of basal slip. Experimental data has been combined with simulated distribution of resolved shear stress in order to estimate the critical resolved shear stress of basal and prismatic slip systems
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Lindell, David. "Process-microstructure-corrosion interrelations for stainless steel." Doctoral thesis, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-159072.
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Stainless steels were first developed in the early 20th century and have since then emerged as a very diverse class of engineering materials. Along with steels having new combinations of properties, there is a continuous development of new technologies allowing the material to be produced in a faster and more energy effcient manner. A prerequisite for new technologies to be adapted quicklyis a fundamental understanding of the microstructure evolution throughout theprocess chain. The first part of this thesis has been dedicated to the annealing and pickling processes from a process-microstructure perspective. In the second part the concept of utilising crystallographic texture as a way to attain microstructures with new combinations of properties has been evaluated. In the first part, annealing can be regarded as a high temperature oxidation process, resulting in chromium depletion that necessitate subsequent chemical pickling. Chemical pickling, on the other hand, is basically a wet-corrosion process and hence more difficult for highly corrosion-resistant grades. The chromium depleted layer was found to be enriched in austenite in case of duplex stainless steel UNS S32205 (Paper I) and this may inuence the pickling process. Proper pretreatment like shot-blasting dramatically increases the pickling rate because it provides the pickling acid with access to the chromium depleted layer (Paper II). Oxidation kinetics for S30400 in conditions relevant to strip annealing do not seem to be affected by the choice of air/oxygen as oxidiser even though the latter results in substantially higher water content (Paper III). This gives new possibilities regarding both cost savings and increased throughput. In the second part, the effect of crystallographic texture on resistance towards corrosion of S31603 in a solution of FeCl3 and AlCl3 in ethanol/glycerol and in 30 vol% H2SO4 is investigated. In the former, high density surfaces {1111} and {100} are less prone for pit nucleation, however the effect is relativelysmall. In H2SO4 pronounced crystallographic anisotropy is observed inwhich the corrosion rate increase in the order {111} < {110} ≤ {100} (Paper IV).For corrosion at high temperatures, chromium diffusion is governed by randomhigh angle boundaries with ~20—55° misorientation. The possibilities to alter the texture in austenitic stainless steels by means of warm-rolling and annealing has been evaluated for S30403 and S31603. During warm-rolling, both steels develop the copper-type texture in contrast to the brass-type texture observedat room temperature. However only S30403 is prone to recrytallise cube texture during subsequent annealing (Paper V).QC 20150121
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KUMAR, SHARMA PANKAJ. "EXPERIMENTAL AND NUMERICAL STUDIES ON SPRINGBACK OF 2-PLY AND 3-PLY LAMINATE COMPOSITES OF ALUMINIUM AND STAINLESS STEEL." Thesis, 2023. http://dspace.dtu.ac.in:8080/jspui/handle/repository/20390.
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To meet the requirement of materials having higher tensile strength to weight ratio
along with corrosion resistance, the 2-ply and 3-ply clad sheets of aluminium and
stainless steel are being utilized in domestic applications, manufacturing of automotive
sheet metal parts, shipbuilding, and other industries. Metal clad sheet composites are a
different kind of composite material where alternating metal layers are bonded together
with inter-metallic bond.
The sheet metal components manufactured by forming processes may undergo some
geometrical changes due to the phenomenon of springback. The behaviour of
springback during bending of 2-ply and 3-ply clad sheet metals is very complex due to
the combination of sheets of different mechanical properties and thicknesses.
Accurate prediction of springback in clad sheets in a bending operation will help in
improving the die design by involving springback compensation. It would facilitate the
optimum selection of materials, blank design, and other design variables so as to
manufacture parts with minimum springback. In the present work, an analytical method
has been developed that predicts the amount of springback in bending of clad sheet
using input parameters from stress-strain diagrams of sheet materials like tensile
properties, strain hardening exponent and anisotropy of parent sheets. The total bending
moment in the analytical model at a cross sectional plane is calculated from the bending
stresses for different layers. Springback is calculated by superimposing the effect of a
negative bending moment of the same magnitude so as to simulate the unloading
phenomenon. Numerical simulations have also been done for the simulation of V bending of clad sheet using Abaqus software based on FEM (finite element method).
Experimental work has also been carried out and compared with the simulation and
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analytical results. The data from stress-strain plots for the parent and clad sheets was
generated using computerized UTM. The parent and clad sheets are characterized using
tensile properties, strain hardening exponent and anisotropy. The typical yield strengths
(0.2% offset) of clad sheets for the tensile specimens oriented at 0°, 45° and 90° are
observed to be 115MPa, 117MPa and 114MPa for a 2-ply and 153.5MPa, 174MPa and
176 MPa for a 3-ply sheet, respectively. A set of three punch profile radii was used to
conduct V-bending experiments for the measurement of springback on a computerized
UTM. The results from the analytical model and FEM simulation are seen found to be
in close agreement with the experimental results. It is observed that an increase in punch
profile radius causes a significant increase in springback for both 2-ply and 3-ply clad
sheets. For a 2-ply clad sheet, the bend samples (with AA1050 as inner layer ) which
are oriented at 45° to the rolling direction, the experimental values of springback, higher
than the other two orientations, are observed to be 4.12 and 4.88 with punch profile
radii of 15mm and 20mm, respectively. In case of a 3-ply clad sheet, the bend samples
(with SS304 as inner layer) oriented at 90° to the rolling direction, the experimental
values of springback higher than the other two orientations, are found to be 5.15° and
6.10° with punch radii of 15mm and 20mm, respectively. Similar trend of results is
obtained with analytical and simulation techniques. FE simulation results are closer to
the values of experimental results than the analytical model results. The analytical
model assumes a plane strain condition and neglects the neutral axis shift. These
assumptions are not made for the simulation. Also, a more robust material model is
used in FE simulations.
The effect of sheet setting on the die is also investigated in this work. Effect of the
position of aluminium sheet at both inner and outer layers is studied. Sheet setting
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conditions affect the values of springback due to the tensile strength variations and
different bending radii during V-bending operations. For both the sheet settings, the
residual stresses as predicted Abaqus simulations are in good agreement with the
experimental results except for a few cases.
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PRAKASH, VED. "EFFECT OF PUNCH PROFILE RADIUS ON SPRINGBACK OF EXTRA DEEP DRAW QUALITY STEEL IN U - BENDING AND IT'S FEA SIMULATION." Thesis, 2016. http://dspace.dtu.ac.in:8080/jspui/handle/repository/14552.
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Huang, Seng-Jie, and 黃聖傑. "A Study on Pseudo-Elastic Analysis for Aseismic Capacity of Multiple-Story Steel Frame Considering the Effect of Material Anisotropy." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/87261243899701329473.
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碩士國立臺灣大學
土木工程學研究所
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This paper is to study the effect of anisotropic property of steel for seismic capacity of steel frame. Due to anisotropic property of steel plate, the yielding stress and ultimate strain is much lower in the through-thickness direction than in rolling direction of steel plate. However, there is an impact on the column faces of beam-column connections for the application of anisotropic steel members in the steel frame. Because beam members of beam-column connection by the effect of moment produce tension and pressure on column faces of beam-column connections, column faces of beam-column connections under tension are prone to a result of lamellar tearing in the through-thickness direction of column with anisotropic property. The tensile strength, shear capacity, moment resisting capacity, and ductility of column members and beam members will significantly go down and even induce serious damage of steel frame if column faces produce lamellar tearing. The paper is to make use of reducing yielding stress of steel beams and columns for simulating the steel anisotropic mechanical behavior on the effect of stress for assessing seismic capacity of steel frame. Therefore, there are different reduction ratios of yielding stress to simulate differences of anisotropic property of steel member on the effect of seismic capacity of steel moment-resisting frames. Adopting methods of assessing seismic capacity of this research include Pseudo-elastic approach method and pushover analysis to obtain the structure nonlinear behavior as the analysis and comparison of seismic capacity. There is an assumption that structure behavior is linear firmly for the theory of Pseudo-elastic approach method. Firstly, it is essential to carry out members forces of structure under design earthquake by static analysis or dynamic analysis. Then, gradually enlarge the design earthquake, and thus members forces of structure will be amplified by the same scale. The structure behavior will not become inelastic until the first plastic hinge of the structure appears. According to the energy conservation principle, exceeding the elastic strain energy range of the total energy can be converted into the corresponding plastic energy by using Pseudo-elastic approach method with assumption of linear structure to figure out structure nonlinear behavior in the relationship of base shear and roof lateral displacement. Finally, the yielding lateral force, ultimate lateral force, ductility ratio, and collapsed ground acceleration of the structure can be worked out as the seismic capacity assessment index of the structure. Due to Pseudo-elastic analysis method with the advantages of rapidity, simplicity and convenience on assessing the seismic capacity of structures, this study will make use of the Pseudo-elastic analysis method and pushover analysis of ETABS software to assess the impact of seismic capacity of multi-storey steel moment-resisting frames with differences of anisotropic property of steel member. According to analysis result, do with the comparison and evaluation in order to understand the differences of steel properties between isotropic and anisotropic for impact of seismic capacity of steel frames.
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Scharnweber, Michael. "Initiierung und Ausbreitung kurzer Ermüdungsrisse in ein- und zweiphasigem Edelstahl." Doctoral thesis, 2013. https://tud.qucosa.de/id/qucosa%3A28094.
Full textAbstract:
In der vorliegenden Arbeit wurden Untersuchungen zum Initiierungs- und Ausbreitungsverhalten kurzer Ermüdungsrisse in einem austenitischen sowie einem austenitisch-ferritischen Edelstahl durchgeführt. Dazu erfolgten zyklische Verformungsexperimente sowohl ex situ als auch in situ im Rasterelektronenmikroskop. Die Auswertung der Experimente erfolgte im Rasterelektronenmikroskop sowohl abbildend in verschiedenen Modi als auch über Rückstreuelektronenbeugungsmessungen. Bezüglich der Rissinitiierung wurde eine Häufigkeitsverteilung der Rissinitiierungsorte für beide Stähle erstellt. Die dabei ermittelte stark unterschiedliche Häufigkeit für die transkristalline Rissinitiierung in der austenitischen Phase konnte mit der unterschiedlichen Textur und Mikrostruktur der beiden Stähle in Zusammenwirken mit den elastischen Eigenschaften der beiden Phasen erklärt werden. Für die Rissausbreitung wurde gezeigt, dass eine Korrelation zwischen der Risslänge und der Rissausbreitungsrate besteht, aus der hervorgeht, dass die Übergangsrisslänge zwischen den Bereichen der mikrostrukturell und mechanisch kurzen Risse etwa einen Korndurchmesser beträgt. Anhand der in situ Messung der (plastischen) Rissöffnung und -scherung wurden die Unterschiede im Rissausbreitungsverhalten in den verschiedenen Phasen herausgearbeitet. Für die austenitische Phase ergibt sich dabei ein öffnungsdominierter und für die ferritische Phase ein scherungsdominierter Mechanismus. Die im Ferrit auftretenden zwei unterschiedlichen Ausprägungen der Oberflächenrisspfade („rau“ und „glatt“) konnten mit der Orientierung der jeweils risstragenden Körner korreliert werden. In Zusammenwirken mit der beobachteten Systematik der Anordnung der Gleitspuren um kurze Risse im Ferrit sowie einer Analyse der Spannungsverteilung um die Rissspitze wurde ein Modell des Rissausbreitungsmechanismus\' erstellt sowie die bisher in der Literatur vorherrschende These des Einfachgleitens widerlegt. Schließlich konnte die Barrierenwirkung von Korn- und Phasengrenzen sowohl anhand der Messung der Rissausbreitungsrate als auch der plastischen Rissöffnung bzw. -scherung gezeigt und daraus Rückschlüsse auf die Ausdehnung der plastischen Zone vor der Rissspitze gezogen werden. Gleichzeitig wurde dabei die Korrelation zwischen Rissausbreitungsrate und plastischer Rissöffnung bzw. -scherung nachgewiesen.