Дисертації з теми "Deformed materials"
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1
Rodrigues, Ferreira Elizabete. "Finite-amplitude waves in deformed elastic materials." Doctoral thesis, Universite Libre de Bruxelles, 2008. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210464.
Повний текст джерелаАнотація:
Le contexte de cette thèse est la théorie de l'élasticité non linéaire, appelée également "élasticité finie". On y présente des résultats concernant la propagation d'ondes d'amplitude finie dans des matériaux élastiques non linéaires soumis à une grande déformation statique homogène. Bien que les matériaux considérés soient isotropes, lors de la propagation d'ondes un comportement anisotrope dû à la déformation statique se manifeste. Après un rappel des équations de base de l'élasticité non linéaire (Chapitre 1), on considère tout d'abord la classe générale des matériaux incompressibles. Pour ces matériaux, on montre que la propagation d'ondes transversales polarisées linéairement est possible pour des choix appropriés des directions de polarisation et de propagation. De plus, on propose des généralisations des modèles classiques de "Mooney-Rivlin" et "néo-Hookéen" qui conduisent à de nouvelles solutions. Bien que le contexte soit tri-dimensionnel, il s'avère que toutes ces ondes sont régies par des équations d'ondes scalaires non linéaires uni-dimensionelles. Dans le cas de solutions du type ondes simples, on met en évidence une propriété remarquable du flux et de la densité d'énergie.
Dans les Chapitres 3 et 4, on se limite à un modèle particulier de matériaux compressibles appelé "modèle restreint de Blatz-Ko", qui est une version compressible du modèle néo-Hookéen.
En milieu infini (Chapitre 3), on montre que des ondes transversales polarisées linéairement, faisant intervenir deux variables spatiales, peuvent se propager. Bien que la théorie soit non linéaire, le champ de déplacement de ces ondes est régi par une version anisotrope de l'équation d'onde bi-dimensionnelle classique. En particulier, on présente des solutions à symétrie "cylindrique elliptique" analogues aux ondes cylindriques. Comme cas particulier, on obtient aussi des ondes planes inhomogènes atténuées à la fois dans l'espace et dans le temps. De plus, on montre que diverses superpositions appropriées de solutions sont possibles. Dans chaque cas, on étudie les propriétés du flux et de la densité d'énergie. En particulier, dans le cas de superpositions il s'avère que des termes d'interactions interviennent dans les expressions de la densité et du flux d'énergie.
Finalement (Chapitre 4), on présente une solution exacte qui constitue une généralisation non linéaire de l'onde de Love classique. On considère ici un espace semi-infini, appelé "substrat" recouvert par une couche. Le substrat et la couche sont constitués de deux matériaux restreints de Blatz-Ko pré-déformés. L'onde non linéaire de Love est constituée d'un mouvement non atténué dans la couche et d'une onde plane inhomogène dans le substrat, choisies de manière à satisfaire aux conditions aux limites. La relation de dispersion qui en résulte est analysée en détail. On présente de plus des propriétés générales du flux et de la densité d'énergie dans le substrat et dans la couche.
The context of this thesis is the non linear elasticity theory, also called "finite elasticity".
Results are obtained for finite-amplitude waves in non linear elastic materials which are first subjected to a large homogeneous static deformation. Although the materials are assumed to be isotropic, anisotropic behaviour for wave propagation is induced by the static deformation.
After recalling the basic equations of the non linear elasticity theory (Chapter 1), we first consider general incompressible materials. For such materials, linearly polarized transverse plane waves solutions are obtained for adequate choices of the polarization and propagation directions (Chapter 2). Also, extensions of the classical Mooney-Rivlin and neo-Hookean models are introduced, for which more solutions are obtained. Although we use the full three dimensional elasticity theory, it turns out that all these waves are governed by scalar one-dimensional non linear wave equations. In the case of simple wave solutions of these equations, a remarkable property of the energy flux and energy density is exhibited.
In Chapter 3 and 4, a special model of compressible material is considered: the special Blatz-Ko model, which is a compressible counterpart of the incompressible neo-Hookean model.
In unbounded media (Chapter 3), linearly polarized two-dimensional transverse waves are obtained. Although the theory is non linear, the displacement field of these waves is governed by a linear equation which may be seen as an anisotropic version of the classical two-dimensional wave equation. In particular, solutions analogous to cylindrical waves, but with an "elliptic cylindrical symmetry" are presented. Special solutions representing "damped inhomogeneous plane waves" are also derived: such waves are attenuated both in space and time. Moreover, various appropriate superpositions of solutions are shown to be possible. In each case, the properties of the energy density and the energy flux are investigated. In particular, in the case of superpositions, it is seen that interaction terms enter the expressions for the energy density and the energy flux.
Finally (Chapter 4), an exact finite-amplitude Love wave solution is presented. Here, an half-space, called "substrate", is assumed to be covered by a layer, both made of different prestrained special Blatz-Ko materials. The Love surface wave solution consists of an unattenuated wave motion in the layer and an inhomogeneous plane wave in the substrate, which are combined to satisfy the exact boundary conditions. A dispersion relation is obtained and analysed. General properties of the energy flux and the energy density in the substrate and the layer are exhibited.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
2
Divinski, Sergiy V., Jens Ribbe, Gerrit Reglitz, Yuri Estrin, and Gerhard Wilde. "Ultra-fast diffusion in severely deformed materials." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-190057.
Повний текст джерела
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Divinski, Sergiy V., Jens Ribbe, Gerrit Reglitz, Yuri Estrin, and Gerhard Wilde. "Ultra-fast diffusion in severely deformed materials." Diffusion fundamentals 11 (2009) 45, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A14008.
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4
Stojakovic, Dejan Doherty R. D. Kalidindi Surya. "Microstructure evolution in deformed and recrystallized electrical steel /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2728.
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Dalai, Biswajit. "Material characterization of AA7075-T651 deformed at different temperatures and strain rates." Licentiate thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-84325.
Повний текст джерелаАнотація:
In this licentiate thesis, the mechanical response and the microstructure evolution in aluminum alloy (AA) 7075 in its T651 heat treated state have been studied through mechanical tests at varied conditions of strain rate and temperature. First, compression tests were performed on AA7075-T651 samples at room temperature (RT), 100, 200, 300, 400 and 500 °C (melting temperature of AA7075 is ~635 °C) with two comparatively low strain rates of 0.01 and 1 s-1 using a Gleeble thermo-mechanical simulator. The effects of softening mechanisms, such as adiabatic heating, dynamic recovery (DRV) and dynamic recrystallization (DRX), on the flow stress level, strain rate sensitivity (SRS) and temperature sensitivity were analyzed over the entire range of deformation temperatures. Additionally, the extent of DRX with respect to temperature, strain rate and local strain was demonstrated and explained through electron back-scattered diffraction (EBSD) analysis. The deformation behavior of AA7075-T651 was then studied at high strain rates in the order of 102-103 s-1 at RT, 200, 300 and 400 °C using a Split-Hopkinson pressure bar (SHPB) setup complemented with an induction coil. Unlike in case of deformation at low strain rates, the unavailability of sufficient time for the dissipation of heat energy during deformation at high strain rates resulted in the formation of adiabatic shear bands (ASBs). Two types of ASB, namely distorted shear band (DSB) and transformed shear band (TSB) were characterized by their distorted-elongated and ultra-fine grain structures, respectively. A deformation path was established following the evolution of ASBs, micro-voids and micro-cracks leading to the fracture of the material. The effects of strain, strain rate and deformation temperature on the formation of ASBs and cracks were also discussed.
6
Zhai, Dawei. "Studies on Electron Dynamics in Deformed Graphene." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540985604827894.
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Vachhani, Shraddha J. "Stored energy maps in deformed metals using spherical nanoindentation." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51813.
Повний текст джерелаАнотація:
Microstructure changes that occur during the deformation and heat treatments involved in wrought processing of metals are of central importance in achieving the desired properties or performance characteristics in the finished products. However, thorough understanding of the evolution of microstructure during thermo-mechanical processing of metallic materials is largely hampered by lack of methods for characterizing reliably their local (anisotropic) properties at the sub-micron length scales. Recently, remarkable advances in nanoindentation data analysis techniques have been made which now make it possible to obtain quantitative information about the local mechanical properties of constituent individual grains in polycrystalline metallic samples. In this work, a novel approach that combines mechanical property information obtained from spherical nanoindentation with the complementary structure information measured locally at the indentation site, using Electron Backscattered Diffraction (EBSD), is used to systematically investigate the local structure-property relationships in fcc metals. This work is focused on obtaining insights into the changes in local stored energies of polycrystalline metallic samples as a function of their crystal orientation at increasing deformation levels. Furthermore, using the same approach, the evolution of mechanical properties in the grain boundary regions in these samples is studied in order to better understand the role of such interfaces during deformation and recrystallization processes. The findings provide valuable information regarding development of stored energy gradients in polycrystalline materials during macroscopic deformation.
8
Guo, Shuo. "Evaluation of deformed MnS in different industrial steels by using electrolytic extraction." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217880.
Повний текст джерелаАнотація:
The inclusions have a different chemical composition and give the steel different mechanical properties. These inclusions affect several properties of steel. In order to understand how the inclusions will affect the steel properties, the electrolytic extraction of 3D investigate method is applied on the steel grade of 42CrMo4. Then follow with Scanning Electron Microscope (SEM) observation. Steel samples from both ingot and rolling with and without heat treatment are observed and compared with different ratios. The result shown that, heat treatment can be applied for removing carbides successfully. And most inclusions are belonging to Type RS which is rod like MnS. The percentage of broken particles can be up to 80%, which means that the reason for the inclusions broken should be find. And heat treatment can affect the characteristics of elongated MnS.
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Patra, Anirban. "Modeling the mechanical behavior and deformed microstructure of irradiated BCC materials using continuum crystal plasticity." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50366.
Повний текст джерелаАнотація:
The mechanical behavior of structural materials used in nuclear applications is significantly degraded as a result of irradiation, typically characterized by an increase in yield stress, localization of inelastic deformation along narrow dislocation channels, and considerably reduced strains to failure. Further, creep rates are accelerated under irradiation. These changes in mechanical properties can be traced back to the irradiated microstructure which shows the formation of a large number of material defects, e.g., point defect clusters, dislocation loops, and complex dislocation networks. Interaction of dislocations with the irradiation-induced defects governs the mechanical behavior of irradiated metals. However, the mechanical properties are seldom systematically correlated to the underlying irradiated microstructure. Further, the current state of modeling of deformation behavior is mostly phenomenological and typically does not incorporate the effects of microstructure or defect densities.
The present research develops a continuum constitutive crystal plasticity framework to model the mechanical behavior and deformed microstructure of bcc ferritic/martensitic steels exposed to irradiation. Physically-based constitutive models for various plasticity-induced dislocation migration processes such as climb and cross-slip are developed. We have also developed models for the interaction of dislocations with the irradiation-induced defects. A rate theory based approach is used to model the evolution of point defects generated due to irradiation, and coupled to the mechanical behavior. A void nucleation and growth based damage framework is also developed to model failure initiation in these irradiated materials. The framework is used to simulate the following major features of inelastic deformation in bcc ferritic/martensitic steels: irradiation hardening, flow localization due to dislocation channel formation, failure initiation at the interfaces of these dislocation channels and grain boundaries, irradiation creep deformation, and temperature-dependent non-Schmid yield behavior. Model results are compared to available experimental data.
This framework represents the state-of-the-art in constitutive modeling of the deformation behavior of irradiated materials.
10
Wang, Lei. "Study of the microstructure and mechanical properties of TWIP steels deformed by ECAP." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/458883.
Повний текст джерелаАнотація:
In the current thesis, two TWIP steels with different chemical composition were successfully subjected to Severe Plastic Deformation with Equal Channel Angular Pressing (ECAP) at warm temperature (300°C), using a die with internal angle Ф= 90°, and an outer arc of curvature Ф=37°. The maximum strain around 4 (i.e. four pass of ECAP) and a ultra-fine grain size microstructure was obtained. Additionally, one pass of ECAP at room temperature was also tried for one of investigated TWIP steel. The microstructure was detected through different techniques, more specifically, Optical microscope (OM), Electron backscatter diffraction (EBSD), and Transmission electron microscopy (TEM). In the mean time, the mechanical properties before and after ECAP procedure with respect to micro-hardness and micro-tensile test were performed as well.
Furthermore, in order to better understand the corresponding tensile mechanical property, as well as the effect of microstructure on twinning capability, the strain hardening behavior was analyzed and well associated with the corresponding microstructure obtained by EBSD and TEM.
Microstructure detection reveled that both two investigated TWIP steels in heat treated condition exhibit a relatively homogeneous microstructure composed of equiaxed grain. After ECAP procedure at 300°C, for both two TWIP steels, the grains are elongated and the grain size decrease sharply, especially after the first pass. The microstructure of each pass sample consists of three different features: new formed grain, twin boundaries and subgrains. The fraction of twin boundaries reduce with increase number of passes, as well as low angle grain boundaries. It can be concluded that the subgrains gradually form the new grains. The twin thickness also showed a reducing trend. The TEM micrographs demonstrated the exist of twins in ECAPed condition. More specifically, in heat treated samples, straight and not tangled dislocations can be found. After one pass, relatively wide twins with low fraction of second twin system is the main feature; after two passes of ECAP, the second twin system is more abundant while the twin thickness is lower; after four passes,
extremely thin twins and subgrains were formed. The texture detected by EBSD showed in the heat treated condition that both two TWIP steels exhibit Brass and Goss as dominant component. After ECAP process, the dominant component move gradually from A1* to B . In terms of mechanical properties, the micro-hardness, the yield strength and the ultimate tensile strength increase significantly while the ductility and tensile toughness show a downward trend during ECAP procedure for both two TWIP steels. The strain hardening capability in heat treated condition is much higher than the ECAPed sample and
the reasons are analyzed.En la presente tesis, se sometió a dos aceros TWIP de composición diferente a procesos de Severa Deformación Plástica (SPD) por presión en canal angular de sección constante (ECAP), a 300oC. Para ello, se utilizó una matriz con un angulo interno Ф=90° y un arco exterior con un curvatura Ф=37°. Se llegó a aplicar una deformación alrededor de 4, correspodiente a 4 pases de ECAP, consiguiendo microestructuras de grano ultrafino. Además, se consiguió deformar a temperatura ambiente uno de los aceros mediante la aplicación de un pase de ECAP. Las microestructuras fueron caracterizadas mediante la aplicación de diferentes técnicas, más concretamente microscopía óptica (OM), difracción de electrones retrodispersados (EBSD) y microscopía electrónica de transmisión (TEM). Asmismo, las propiedades mecánicas previas y posteriores a la deformación por ECAP fueron determinadas por microdureza y ensayos de microtracción. Con el fin de comprender la interrelación entre las propiedades mecánicas, la microstructura y la capacidad de maclar del material, el comportamiento de endurecimiento por deformación se analizó en base a las microestructuras obtenidas por EBSD y TEM. La caracterización microestructural reveló que los dos aceros TWIP investigados presentaban una microestructura homogénea de granos equiáxicos en su condition de recocido. Tras la deformación por ECAP a 300ºC, ambos aceros presentaron granos alargados con un afino de grano pronunciado, sobretodo después del primer pase. La microestructura tras cada uno de los pases se caracteriza por la presencia de nuevos granos, subgranos y maclas. La fracción de los límites de macla se reduce con un aumento del número de pases, de la misma manera que la fracción de límites de grano de ángulo bajo, concluyéndose que los subgranos se transforman gradualmente en nuevos granos. It can be concluded that the subgrains gradually form the new grains. El espesor de la maclas también mostró una tendencia decreciente con el número de pases. Las micrografías por TEM demostraron la presencia de maclas para las probetas deformadas por ECAP, a pesar de la temperatura a la que se llevó a cabo el proceso. En particular, las probetas recocidas se detectaron dislocaciones rectas y sin enmarañamiento. Después de un pase, las maclas que aparecían eran relativamente anchas con poco maclado secundario. Tras dos pases, el maclado secundario aumenta, con una reducción del espesor de las maclas. Después de cuatro pases, se observan maclas extremadamente finas y gran formación de subgranos. La textura, caracterizada por EBSD mostró que en la condición de recocido ambos aceros mostraban componentes Brass y Goss dominantes. Tras la deformación por ECAP, el componente dominante se movió gradualmente de A1* a B. En lo relativo a las propiedades mecánicas, tanto la microdureza, como el límite elástico y resistencia máxica aumentaron con el número de pases, a la vez que la ductilidad y tenacidad disminuían. Por otro lado, el enduremiento por deformación era máximo para la condición de recocido, aunque dada la gran deformación aplicada en cada pase, el material seguía reteniendo capacidad de endurecer después de uno y dos pases de deformación por ECAP.
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Phillips, Patrick J. "Advanced defect characterization via electron microscopy and its application to cyclically deformed Ni-based superalloy R104." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1330915484.
Повний текст джерела
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Zeng, Zhipeng. "Deformation Behaviour, Microstructure and Texture Evolution of CP Ti Deformed at Elevated Temperatures." Doctoral thesis, Stockholm : Skolan för industriell teknik och management, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10404.
Повний текст джерела
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Shea, Lauren. "Microstructural and textural analysis of naturally deformed granulites in the Mount Hay block of central Australia: Implications for the rheology of polyphase lower crustal materials." Thesis, Boston College, 2019. http://hdl.handle.net/2345/bc-ir:108578.
Повний текст джерелаАнотація:
Thesis advisor: Seth C. KruckenbergQuantitatively describing the deformational behavior (i.e. the rheology) of lower crustal materials has proven challenging due to the highly variable nature of structural and compositional fabrics in the lower crust. Further, many flow laws describing the rheology of monophase aggregates are experimentally derived and do not necessarily apply to polyphase materials, such as gabbro, that dominate the lower crust. Here, we present the results of integrated microstructural analysis and electron backscatter diffraction (EBSD) textural analysis from exhumed lower crustal granulites in the Mount Hay block of central Australia. The preservation of heterogeneous mafic and felsic granulites containing monophase and/or polyphase mixtures of anorthite, pyroxene, and quartz (interlayered on the mm- to m-scale) make this region uniquely suited for advancing our knowledge of the processes that affect deformation and the rheology of the lower crust. Forty-two samples from distinct structural and compositional domains were chosen to compare the microstructural record of deformation, the development of crystallographic textures, and to provide estimates of lower crustal rheology and deformation conditions. Full thin-section maps of crystallographic texture were produced using EBSD methods. The resultant orientation maps were processed to characterize crystallographic textures in all constituent phases, and all other quantifiable aspects of the rock microstructure (e.g., grain size, grain shape, misorientation axes). The EBSD analysis reveals the presence of strong crystallographic preferred orientations (CPO) in nearly all constituent phases, suggesting deformation dominated by dislocation creep. Differential stresses during deformation are calculated using grain size piezometry for all major phases, and range between 34-54 MPa in quartz within monophase layers. Two-pyroxene geothermometry was used to constrain deformation temperatures to ca. 780-810 C. Based on the estimated CPO patterns, stress, and temperature, we quantify strain rates and effective viscosities of all major phases through application of monophase flow laws. Monophase strain rates range from 2.10 x 10-12 s-1 to 1.56 x 10-11 s-1 for quartz, 4.68 x 10-15 s-1 to 2.48 x 10-13 s-1 for plagioclase feldspar, 1.56 x 10-18 s-1 to 1.64 x 10-16 s-1 for enstatite, and 5.66 x 10-16 s-1 to 1.00 x 10-14 s-1 for diopside. The determined flow law variables used for monophase calculations were subsequently applied to two different models – the Minimized Power Geometric model of Huet et al. (2014) and the Asymptotic Expansion Homogenization (AEH) method of Cook (2006) – in order to calculate a bulk aggregate viscosity of the polyphase material. At a strain rate of 10-14 s-1, polyphase effective viscosities for our samples range from 3.07 x 1020 to 2.74 x 1021 Pa·s. We find that the bulk viscosity of heterogeneous, gabbroic lower crust in the Mount Hay region lies between that of monophase plagioclase and monophase quartz, and varies as a function of composition. These results are consistent with past modeling studies and geophysical estimates
Thesis (MS) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences
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WANG, QIAOLING. "Modelling plastic behaviour and fracture occurrence in HCP metal sheets deformed in a wide range of temperatures and stress states." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3423182.
Повний текст джерелаАнотація:
Titanium and magnesium alloys both have hexagonal closest packed (HCP) structure with limited slip systems. This structure lead to two features: low formability at room temperature and the anisotropy influence on the mechanical characteristics and fracture behaviour. Therefor, the plastic behaviour and fracture occurrence need to be investigated at elevated temperature and different specimen orientations.
The approach comprises a joint use of experimental and numerical techniques. In terms of experiments, on the one hand, the plastic behaviour was studied and analyzed on the basis of a large number of tensile tests carried out on smooth specimens in a wide range of temperature and strain rate; the fracture behaviour was studied and analyzed by carrying out tensile tests on different specimen geometries as well as Nakajima tests, in order to reproduce various stress states, identified by the related stress triaxiality and deviatoric stress parameters; on the other hand, the alloy microstructure was analyzed on the tested specimens to explain the mechanical characteristic and anisotropy behaviour, including Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Back Scatter Diffraction (EBSD) techniques and micro-hardness testing. In terms of numerical modelling, on the basis of the large number of experimental results, numerical simulations were implemented in the Ls-DynaTM code environment using a dynamic-implicit analysis with a coupled thermo-mechanical solution procedure to reproduce the sheet anisotropic plastic behaviour and fracture characteristics. The yield criterion and damage model were studied and modified to predict the experimental results.
Specifically, for Ti6Al4V titanium alloy, the heating of the alloy below the β-transus temperature is recognized to enhance its formability, reducing the flow stress and increasing the ductility. However, to investigate the effect of the sheet anisotropy on the material flow behaviour and plastic instability at varying temperature and strain rate, uniaxial tensile tests were carried out in a wide range of testing temperatures (from room temperature to 800°C) and strain rates (0.01, 0.1, 1 s-1) to assess the anisotropy effects. Strain hardening, strain rate sensitivity, and Lankford coefficients were evaluated as a function of the testing parameters and specimen orientation. Furthermore, a numerical model of the uniaxial tensile tests was developed and calibrated making use of the Barlat-Lian-1989 yield criterion and a hardening rule, which was adapted to take into account the anisotropic behaviour at different temperatures. It was proved that the developed model was capable of predicting the strain localization in the specimen gauge length due to plastic instability as well as its thickness distribution at varying temperature and strain rate. To investigate the influence of the sheet anisotropy on the material failure, tensile tests on smooth and notched specimens, shear tests and Nakajima-type tests carried out at varying temperature and rolling direction. The fracture strain is measured and the effect of the specimen orientation and stress state is identified. The coupling of the Barlat-Lian 1989 anisotropic yield criterion and GISSMO damage model was introduced to predict the fracture occurrence and capture its anisotropic characteristics. The two models were calibrated on the basis of an extensive experimental campaign. In order to validate the proposed approach, tests not used in the calibration phase were used, and the comparison between experimental and numerical results was carried out in terms of fracture characteristics at varying temperature and rolling direction. It was proved that the proposed modelling was able to satisfactorily reproduce the different fracture characteristics arising as a consequence of the sheet anisotropy and testing temperature.
Regarding AZ31B magnesium alloy, the same tests carried out on smooth specimen at the range of temperatures from room temperature to 300°C at 0.1 s-1 to evaluate the anisotropy influence on the mechanical and microstructural characteristics. The Lankford coefficients, ultimate tensile strength, diffuse necking strain and fracture strain values were evaluated as a function of the testing temperature and specimen orientation. Furthermore, microstructural features were analyzed as well as micro-hardness was measured for each testing condition to assess the post-deformation characteristics. To describe the fracture behaviour of AZ31 magnesium alloy sheets as a function of the temperature, stress state, and rolling direction. The same fracture tests were carried out at room temperature, 100°C and 300°C using different specimen geometries cut at different orientations with respect to the sheet rolling direction. The fracture strain values were measured making use of the Digital Image Correlation (DIC) approach and the fracture surfaces qualitatively characterized by means of stereoscopy and SEM. Afterwards, the AZ31 fracture locus as a function of the stress state, temperature and rolling direction was constructed. To analytically predict the fracture locus, a temperature-dependent parameter was added to the Modified Mohr Coulomb (MMC) fracture criterion; the newly proposed criterion was calibrated on the basis of the experimental data obtained from the tests previously mentioned, proving to be suitable to predict the AZ31 fracture locus for tension-dominated regions at varying temperature.
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Castro, Güiza Gabriel Mauricio. "Efeito da deformação a quente sobre a microestrutura, dureza e cinética de precipitação de um aço maraging C300." reponame:Repositório Institucional da UFSC, 2015. https://repositorio.ufsc.br/xmlui/handle/123456789/162730.
Повний текст джерелаАнотація:
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia dos Materiais, Florianópolis, 2015.Made available in DSpace on 2016-05-24T17:42:41Z (GMT). No. of bitstreams: 1 338223.pdf: 6331702 bytes, checksum: 075fbdd17c9b549656a64a1a28f177d4 (MD5) Previous issue date: 2015
Os aços maraging são uma classe especial de aços com alta resistência e tenacidade. Apesar das suas excelentes propriedades, suas aplicações são limitadas devido ao seu alto custo de produção. Com o propósito de encontrar novos processos para melhorar as propriedades mecânicas deste aço, foram analisados os efeitos produzidos pelo forjamento a quente sobre a microestrutura, dureza e cinética de precipitação de um aço maraging C300. Para isto, corpos de prova prismáticos foram deformados sem lubrificação usando diferentes condições de forjamento, e depois foram analisados nas condições como forjado e envelhecido usando diferentes técnicas de caracterização, tais como: microscopia ótica, ensaios de dureza, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios X e dilatometria. Os resultados experimentais mostraram que se obteve um importante refinamento da largura dos blocos de martensita quando o forjamento produziu uma austenita não recristalizada ou parcialmente recristalizada. Adicionalmente, os espécimes nos quais a martensita foi produzida a partir de uma austenita não recristalizada apresentaram um endurecimento mais rápido e uma maior quantidade de austenita reversa do que as amostras restantes. Estes fatos sugerem que houve uma aceleração significativa nas reações de precipitação e de formação de austenita reversa nas amostras cuja martensita foi produzida a partir de austenita não recristalizada. Finalmente, se detectou um acréscimo da dureza no estado como forjado nas amostras deformadas a quente, cujo valor máximo foi de 8% nas condições de maior redução de altura. Este endurecimento foi reduzido durante o envelhecimento devido provavelmente à ação da recuperação da subestrutura da martensita.
Abstract : Maraging steels are special steels with high strength and high toughness. Despite their desirable properties, their applications are limited due to their high production cost. In order to discover new processes that improve the mechanical properties of this alloy, the kinetical and microstructural changes induced by hot forging in a maraging C300 steel were analysed. Prismatic samples were deformed without lubrication using several forging conditions, and then were analysed in both the as forged and aged stages employing different techniques such as: optical microscopy, hardness testing, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and dilatometry. The experimental results showed that an important refinement of the martensite block width was obtained when hot working produced either work-hardened or partially recrystallized austenite. In addition, the specimens in which the martensite phase was produced from a work-hardened austenite hardened faster in the early stages of precipitation than non-deformed ones. Besides, the amount of austenite in the former samples was higher than the one found in the latter. These two facts suggest that a significant acceleration of the precipitation and reverted austenite formation reactions might be taking place in the samples where hot forging produced a work-hardened austenite. Finally, an increase in hardness was observed in the hot worked samples, which maximum value was 8% in the most deformed specimens. This raise was partially eliminated during aging, probably due to the recovery of the martensite substructure.
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Nguyen, Thuy Thi My. "Development of a second-order inelastic analysis method accounted for construction stage effects on the behaviour of prestressed steel structures." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/117967/8/Thi_Nguyen_Thesis.pdf.
Повний текст джерелаАнотація:
This research developed a new method to investigate the construction stage effects on the behavior of pre-stressed steel structures. Any changes of structural geometry and/or material properties are properly accounted and evaluated stage-by-stage during the whole construction. Therefore, the structural responses are properly predicted. Any instability and excessive deflection of structural members or the possibility of structural collapse during construction can be avoided.
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Godoy, López Pablo Roberto. "Estudio Microestructural y Calorimétrico de una Aleación Superelástica Cu-11.8%p.Al-0.5%.p.Be una Deformada a Distintas Temperaturas." Tesis, Universidad de Chile, 2010. http://www.repositorio.uchile.cl/handle/2250/103782.
Повний текст джерелаАнотація:
Existe una familia de aleaciones que presentan un comportamiento llamado Memoria de Forma, las cuales después de una deformación plástica, recuperan su forma original. La recuperación se da tras un tratamiento térmico calentando el material produciéndose el Efecto de memoria de forma o EMF o al retirar la carga que produce la deformación al material dentro de un rango de temperatura, fenómeno llamado generalmente súper elasticidad o SE. Ambos tipos de recuperación de la forma tienen origen en la Transformación Martensítica, un cambio de fase que ocurre por efectos de la temperatura o la deformación. La aleación Cu-11,8 %p. Al-0,5 %p. Be presenta el comportamiento de memoria de forma mencionado anteriormente, es por esto que el estudio de esta aleación es interesante debido al amplio campo probable de aplicaciones. El objetivo de esta memoria es estu- diar el efecto de distintos niveles de deformación impuesta por compresión a distintas temperaturas, en el rango superelástico y post-superelástico, y de tratamiento térmicos postdeformación, sobre la microestructura de una aleación superelástica Cu-11,8 %p.Al-0,5 %p.Be. Así, se realizaron ensayos de compresión hasta diferentes valores de deformación (10 valores diferentes) a distintas temper- aturas (5, 20, y 50◦C) y aplicaron tratamientos térmicos a algunas de las probetas deformadas, para evaluar la recuperación en longitud por estos tratamientos. Se analizó por DSC probetas altamente deformadas (15 %), para avanzar en el estudio e interpretación de peaks de transformación encon- trados fuera de las zonas típicas en recientes ensayos de tracción de alta deformación. Además se analizó por microscopia óptica probetas altamente deformadas (12 %), y se determinó la fracción y comportamiento de fases en función de la temperatura del ensayo de compresión. Finalmente se re- alizó un análisis fractográfico utilizando un microscopio óptico estereoscópico. Una vez realizados los ensayos y análisis, se logró concluir una dependencia de la temperatura del ensayo de compre- sión en el comportamiento mecánico y microestructural. Se determinó que el nivel de deformación post-descarga es mayor en los casos que la temperatura del ensayo es menor. Asimismo la concentración de martensita retenida, tiende a aumentar con el aumento de la temperatura del ensayo, debido al aumento de la concentración de dislocaciones a menores temperaturas de deformación.
Se determinó que para grandes deformaciones la acumulación de dislocaciones produce que la energía necesaria para lograr la transformación de martensita a austenita aumente considerablemente, además de impedir la transformación de ambas fases a las temperaturas típicas de transformación.
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Durán, Correa Alicia Isabel. "Transformaciones microestructurales y amortiguamiento interno en una aleación Cu-Al-Be deformada en el rango post- superelástico." Tesis, Universidad de Chile, 2014. http://www.repositorio.uchile.cl/handle/2250/116431.
Повний текст джерелаАнотація:
Magíster en Ciencias de la Ingeniería, Mención MecánicaEl efecto de superelasticidad y memoria de forma presentada por las aleaciones con memoria de forma está relacionado con una transformación martensítica inducida por esfuerzo. Por otro parte, en una aleación Cu-11,8%p.Al-0,5%p.Be policristalina, la cual presenta un comportamiento superelástico a temperatura ambiente, se ha observado que tal comportamiento se extiende hasta aproximadamente 3-4% de elongación; para deformaciones mayores, en el llamado rango post-superelástico (RPSE) se tiene, al retirar la carga, martensita retenida y deformaciones permanentes. En el RPSE se han detectado ciclos de histéresis, asociados a amortiguamiento interno. El objetivo de esta tesis es estudiar las transformaciones microestructurales de una aleación Cu-11,8% p. Al-0,5% p. Be deformada por tracción en el RPSE, para obtener información acerca del mecanismo de amortiguamiento interno en ese rango. Se empleó una aleación Cu-11,8%p.Al-0,5%p.Be producida por Trefimetaux (Francia), bajo la forma de alambres de 3,4 mm de diámetro. Trozos de 100 mm de longitud se sometieron a un envejecimiento convencional a 100ºC por 24 h. Con algunos de esos trozos se realizaron ensayos de tracción (carga-descarga), hasta distintas deformaciones (εim= 0 - 10,7 %) a temperatura ambiente y a una velocidad de deformación de 10 mm/min. Durante los ensayos se midió la temperatura superficial de las probetas, Tp. Se determinaron curvas esfuerzo-deformación σ-ε y temperatura-deformación Tp-ε para un único ciclo de carga-descarga por probeta. A muestras deformadas se les aplicó metalografía óptica. Por calorimetría diferencial de barrido (DSC) se analizaron muestras para distintos εim, aplicando tres ciclos de enfriamiento-calentamiento (-100 a +500°C), a 10°C/min. En las curvas σ-ε se observaron los habituales rangos para estas aleaciones: elástico, superelástico, y post-superelástico. De esas curvas, se determinaron los siguientes valores de propiedades, valores que en general son concordantes con resultados previos: módulo de Young E= 82 GPa, esfuerzo de transformación σT= 237 MPa, y esfuerzo de fractura σF= 692 MPa para una elongación de 10,7%, aproximadamente. Se estableció que la deformación asociada al inicio del RPSE corresponde a εLSE= 3,8%, aproximadamente. Por otra parte, la forma de las curvas Tp-ε presentan rangos, en términos de esfuerzos, que coinciden con aquellos observados en las curvas σ-ε. El análisis metalográfico reveló que las probetas deformadas en el RPSE presentaron martensita retenida en una matriz de austenita. Así, al aumentar la deformación impuesta, se verificó que, después de descargar, la fracción en volumen de la austenita (fV) es decreciente y la de martensita retenida (fVM) es creciente. El análisis por DSC de las probetas deformadas en el RPSE, mostró máximos calorimétricos en el rango inicial de bajas temperaturas del primer ciclo térmico, los cuales son consistentes con que a mayor εim, mayor es la fVM retenida y menor la de austenita. Además, al pasar por primera vez las muestras DSC por el rango de altas temperaturas, se observaron máximos por sobre los 450°C asociados a alguna forma de recuperación. Así, en los dos ciclos térmicos siguientes ya se tenían máximos calorimétricos de baja temperatura asociados a fV cercanos a 1. También se observó que el amortiguamiento interno aumenta con la εim en el RPSE. Esto se puede explicar por que, a mayor εim habrá más martensita y menos austenita, y es sabido que el amortiguamiento interno en la martensita para aleaciones con memoria de forma es mayor que en la austenita. De esta manera, el mecanismo de amortiguamiento que prevalece en el RPSE corresponde a aquel de la martensita.
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Morlier, Joseph. "METHODES D'ANALYSE DES DEFORMEES MODALES PAR TRAITEMENT DU SIGNAL POUR LE DIAGNOSTIC IN SITU DE STRUCTURES." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2005. http://tel.archives-ouvertes.fr/tel-00078449.
Повний текст джерелаАнотація:
Cette thèse s'inscrit dans la thématique de l'évaluation non destructive en génie civil et plus particulièrement le diagnostic in situ de structure. Elle a pour but d'une part d'étudier l'aspect théorique de la détection et la caractérisation de défaut seulement à partir des données issues de l'analyse modaleet d'autre part d'identifier le meilleur outil pratique pour acquérir ces données modales. On s'est donc attaché à développer des méthodes d'analyse des déformées modales par traitement du signal afin de caractériser les défauts structuraux mais aussi d'essayer de quantifier la qualité des assemblages. Nous avons, à ces fins, mis en oeuvre des outils numériques de simulation (MEF) et des algorithmes d'analyse (ondelettes, dimension fractale, réseaux de neurones) sous Matlab permettant d'automatiser le diagnostic. La validation s'est aussi bien effeectuée sur des déformées simulées, mais aussi sur
des déformées issues de la bibliographie et finalement sur des déformées expérimentales d'un portique de dimension laboratoire (en utilisant un vibromètre laser à balayage).
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Carvalho, Marcelo Parmentier. "An?lise de tens?es e deforma??es em estruturas termopl?sticas usando o m?todo de elementos finitos." Pontif?cia Universidade Cat?lica do Rio Grande do Sul, 2007. http://tede2.pucrs.br/tede2/handle/tede/3105.
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Previous issue date: 2007-12-13A aplica??o dos materiais polim?ricos em nosso cotidiano tem sido grandemente difundida em raz?o de caracter?sticas como a excelente combina??o de baixa massa espec?fica e elevada rigidez, e a possibilidade de moldar pe?as nas mais variadas formas. ?, pois de fundamental import?ncia que o projetista disponha de ferramentas de aux?lio para a an?lise e otimiza??o que possibilitem dimensionar de modo r?pido e seguro a pe?a a ser fabricada, considerando os requisitos estruturais, caracter?sticas funcionais e restri??es impostas pelo processo de fabrica??o. Dentro deste contexto, o presente trabalho tem por objetivo desenvolver um modelo computacional para an?lise de tens?es e deforma??es em cadeiras pl?sticas tipo monobloco confeccionadas em resina de polipropileno. O modelo computacional baseia-se no M?todo dos Elementos Finitos e foi desenvolvido usando o pacote comercial SolidWorks/CosmosWorks 2007. Ensaios experimentais est?ticos e din?micos da cadeira, segundo a Norma NBR 14776, foram realizados no Laborat?rio de Ensaios Eletroeletr?nicos da PUCRS LABELO, visando ? valida??o do modelo desenvolvido. Igualmente, ensaios experimentais de tra??o e flex?o, segundo as Normas NBR 9622, ASTM D 638 e ASTM D 790, foram realizados em corpos de prova confeccionados com material retirado da cadeira. Estes ensaios forneceram as caracter?sticas mec?nicas do material, necess?rias ?s simula??es computacionais. Simula??es de carregamento e vincula??o foram executadas mostrando a validade do modelo computacional desenvolvido para a an?lise de tens?es e deforma??es da cadeira.
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Мисловська, М. С. "Розрахунок статичних і динамічних характеристик модифікованої конструкції пристрою автоматичного врівноважуючого пристрою". Master's thesis, Сумський державний університет, 2018. http://essuir.sumdu.edu.ua/handle/123456789/71740.
Повний текст джерелаАнотація:
Об’єкт дослідження – процес навантаження і деформування багатошарових композитних торових оболонок.
Мета роботи – полягає в розробці методики розрахунку термопружного напруженого стану композитних торових оболонок високого тиску.
Методи дослідження – для розв’язання термопружної незв'язаної задачі застосовуються метод сплайн-колокацій, метод Фур’є, метод рядів Тейлора, метод ортогональної прогонки. На основі даних методів cтворений алгоритм і мовою програмування VISUALFORTRAN складена програма розрахунку напружено-деформованого стану багатошарових торових оболонок від дії статичного та температурного навантаження. Для розв’язання деяких із розглянутих задач також використовувався метод скінченних елементів, який реалізовано в програмному комплексі ANSYS.
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Brambila, Evandro Hendler. "Estudo do defeito tipo rechupe em tubos de cobre de trocadores de calor." Pontifícia Universidade Católica do Rio Grande do Sul, 2008. http://hdl.handle.net/10923/3320.
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Previous issue date: 2008In this work was experimentally analyzed the process of radial deformation in copper pipes submitted to a thermomechanical cycles in heat exchangers. The main objective is the study of the dent formation in order to understand the cause of the deformation. A simulator was build using R-22 as a fluid refrigerant to repeat the process of formation the dent. The external frost formation on the tube was made in the artificial way. The defrost was made by hot gas method, same as occurred in commercial applications. Control devices and sensors were used to measure data and control variable process to analyse the gradual formation of the dent, relating the intensity of the deformation with the severity of pressure cycle and temperature. The properties of the new tube, expanded tube and the defective tube were evaluated by microstructure analysis, tensile and indentation tests, observing the different behavior of the material to each state of mechanical processing. With the results achieved it was possible to verify that the layer thickness of the ice has great influence in the dent deformation, and the curves of the evaporator are less subject to the dent formation than pipes. The increase of pressure drop in the evaporator has directly influence on the temperatures of the system, which shows one accented loss of efficiency. The dent occurrence always is located near the entry of the fluid refrigerant. Finally, the correlation between bad operational practices and the absence of periodic cycles of defrost induce the formation the dent defect.
Neste trabalho foi analisado experimentalmente o processo de deformação radial em tubos de cobre que estão submetidos a ciclos termomecânicos em trocadores de calor. O objetivo principal consiste no estudo da formação do defeito tipo rechupe, visando entender a origem da deformação. Para a repetição do processo de formação do defeito, construiu-se uma bancada de testes utilizando o fluido refrigerante R-22, semelhante ao que ocorre em aplicações comerciais. A formação da camada de gelo externa ao tubo de testes foi feita de maneira artificial, ocorrendo o degelo por vapor superaquecido, retratando o que ocorre na prática. Foram utilizados instrumentos de controle e de coleta de dados para a comprovação da gradual formação do rechupe, relacionando a sua intensidade com a severidade dos ciclos de pressão e temperatura. As propriedades do tubo novo, expandido e do tubo defeituoso foram avaliadas com a análise da microestrutura, ensaios de tração e indentação, observando as diferentes respostas do material cada estado de processamento mecânico. Com os resultados obtidos foi possível verificar que a espessura da camada de gelo possui grande influência na deformação tipo rechupe, e que as curvas dos evaporadores estão menos sujeitas a formação do defeito que os tubos.O aumento da perda de carga no evaporador influencia diretamente as temperaturas do sistema, retratando uma acentuada perda de eficiência. A ocorrência do rechupe está sempre localizada próxima a entrada do fluido refrigerante. Finalmente, a correlação entre a má prática operacional, a ausência de ciclos periódicos de degelo, induz a formação do defeito tipo rechupe.
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Souza, Antonio Lourenço Batista de. "Análise do comportamento termomecânico e da evolução microestrutural durante a laminação de tiras a quente de aços C-Mn via DEFORM™ 3D." Universidade Federal de São Carlos, 2015. https://repositorio.ufscar.br/handle/ufscar/7169.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Improving the steel processing is a major focus of the metallurgical industry because the need of materials and products with lower weight and more strength, in addition to increasingly stringent specifications imposed by buyers. The knowledge and kinetic control of the phenomena that occur during hot processing such as recrystallization, precipitation and grain growth are mandatory for the grain size refinement, which is a parameter that determines the properties of semi-finished products. In hot strip rolling the material is subjected to deformation schedules consisting of five to seven passes, with rolling mill arranged one in front of the other, performing a continuous operation. Over the years, several paths have been followed to investigate the industrial processing. One can cite as examples the use of pilot plants, physical simulations, and numerical simulations. The objective of this study was, therefore, to model the process of the hot strip rolling, enabling the analysis of how the process parameters such as temperature, strain, strain rate and austenitic grain size evolve during rolling of the C-Mn steels, using the commercial software DEFORM™ 3D developed for forming processes analysis. Seven rolling passes of an industrial process described were simulated. The results shown a good agreement of the load and temperature levels attained during simulation with the literature values, indicating that the model used to represent the industrial rolling process is suitable. The numerical reconstruction of processing shows clearly the presence of the strain, temperature and strain rate gradients during hot strip rolling mill, generating microstructural gradients. The evolution of rolling process minimizes the gradients, but some ones still remain at the end of rolling process. Thus, this study shows the effectiveness of the model to predict the evolution of the microstructure in a hot rolling process.
Aperfeiçoar o processamento dos aços é um dos principais focos da indústria metalúrgica devido à necessidade de materiais mais resistentes e produtos com menor peso, além das especificações cada vez mais rigorosas impostas pelos compradores. O conhecimento e controle da cinética dos fenômenos que ocorrem durante o processamento mecânico a quente como a recristalização, a precipitação e o crescimento de grão são mandatórios para o refinamento do tamanho dos grãos, o qual é um parâmetro que determina as propriedades dos produtos semiacabados. No processo de laminação de tiras a quente o material é submetido a sequências de deformação constituídas de cinco a sete passes, realizando uma operação contínua. Vários caminhos têm sido seguidos para investigar o processamento industrial, podem-se citar como exemplos a utilização de plantas pilotos, a simulação física e a simulação numérica. O objetivo deste trabalho foi, portanto, modelar o processo de laminação de tiras a quente, possibilitando analisar como os parâmetros do processo tais como temperatura, deformação, taxa de deformação e tamanho de grão austenítico evoluem durante a laminação de aços C-Mn, utilizando o software DEFORM™ 3D, desenvolvido para análises de processos de conformação. Foram simulados sete passes de laminação de um processo industrial descrito na literatura. Os resultados mostraram uma boa concordância entre os valores de carga e temperatura simulados com os valores medidos na planta industrial, indicando que o modelo utilizado para representar o processo é adequado. A reconstrução numérica do processamento mostra claramente a presença de gradientes de deformação, de temperatura e de taxa de deformação durante a laminação de tiras a quente, gerando gradientes microestruturais. A evolução da laminação minimiza os gradientes, todavia alguns ainda permanecem no final da laminação. Esse estudo mostrou a eficácia do modelo em predizer a evolução microestrutural do aço em um processo de laminação a quente.
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Sousa, S?rgio Barros de. "Desenvolvimento de um prot?tipo para an?lise din?mica da dureza de superf?cies met?licas." Universidade Federal do Rio Grande do Norte, 2010. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12723.
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Previous issue date: 2010-03-30In this paper we developed a prototype for dynamic and quantitative analysis of the hardness of metal surfaces by penetration tests. It consists of a micro-indenter which is driven by a gear system driven by three-rectified. The sample to be tested is placed on a table that contains a load cell that measures the deformation in the sample during the penetration of micro-indenter. With this prototype it is possible to measure the elastic deformation of the material obtained by calculating the depth of penetration in the sample from the difference of turns between the start of load application to the application of the load test and return the indenter until the complete termination of load application. To determine the hardness was used to measure the depth of plastic deformation. We used 7 types of steel trade to test the apparatus. There was a dispersion of less than 10% for five measurements made on each sample and a good agreement with the values of firmness provided by the manufacturers.
Nesse trabalho ? desenvolvido um prot?tipo para an?lise din?mica e quantitativa da dureza de superf?cies met?licas atrav?s de ensaios de penetra??o. Ele consiste de um micro-penetrador que ? movimentado por um sistema de engrenagens guiado por tr?s pinos retificados. A amostra a ser ensaiada ? colocada sobre uma mesa que cont?m uma c?lula de carga que mede a deforma??o na amostra durante a penetra??o do micro-penetrador. Com esse prot?tipo ? poss?vel medir a deforma??o el?stica do material obtida pelo c?lculo, atrav?s de software, da profundidade da penetra??o na amostra a partir da diferen?a de voltas entre o in?cio de aplica??o de carga at? a aplica??o total da carga de teste e o retorno do indentador at? a completa finaliza??o da aplica??o de carga. Para determina??o da dureza foi utilizada a medida da profundidade de deforma??o pl?stica. Foram utilizados 07 tipos de a?os comerciais para teste do aparato. Verificou-se uma dispers?o inferior a 10% para cinco medi??es efetuadas em cada amostra e uma boa concord?ncia com os valores de dureza fornecidos pelos fabricantes.
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Quirant, Jérôme. "SYSTEMES DE TENSEGRITE ET AUTOCONTRAINTE :QUALIFICATION, SENSIBILITE ETINCIDENCE SUR LE COMPORTEMENT." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2000. http://tel.archives-ouvertes.fr/tel-00174699.
Повний текст джерелаАнотація:
Les Systèmes de Tenségrité sont des systèmes innovants dans le domaine duGénie Civil. Leur esthétique est une source d'inspiration nouvelle pour les architectes. Ce
sont des systèmes réticulés, spatiaux et en état d'autocontrainte.
La première partie de ce manuscrit est l'occasion de présenter les diverses phases de leur
conception. La recherche de forme, notamment, amène à rechercher les géométries
particulières permettant l'instauration d'un état de sollicitation interne qui va rigidifier le
système.
La deuxième partie propose, pour une géométrie autocontrainte donnée, de déterminer tous
les états d'autocontrainte qui respectent la rigidité unilatérale des câbles. Ces états
conformes permettent de mettre en état d'autocontrainte l'ensemble de la structure. Leur
influence sur le comportement est évaluée pour réaliser un dimensionnement.
La troisième partie est consacrée à une étude de la sensibilité de ces systèmes aux
imprécisions de fabrication des éléments. Elle doit permettre, après une étude plus précise
de fiabilité, de compléter les Eurocodes pour des systèmes innovants qui n'ont pas été pris en
compte dans les règlements. Enfin, une étude de la mise en autocontrainte des systèmes est
proposée. Elle montre que l'assemblage des systèmes de tenségrité peut se faire dans une
géométrie non-autocontrainte, avec seulement quelques câbles actifs permettant la mise en
tension de la structure.
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Freitas, Neto Ramiro Gomes de. "Estudo da recristaliza??o do a?o inoxid?vel Lean Duplex LDX2101? submetido a diferentes graus de redu??o por lamina??o a frio." PROGRAMA DE P?S-GRADUA??O EM CI?NCIA E ENGENHARIA DE MATERIAIS, 2016. https://repositorio.ufrn.br/jspui/handle/123456789/21472.
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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
Os a?os inoxid?veis duplex s?o a?os altamente ligados caracterizados por uma estrutura bif?sica de ferrita-austenita obtida atrav?s de processos de conforma??o a quente ou tratamentos t?rmicos adequados ap?s os processos de conforma??o a frio. A presen?a de fra??es volum?tricas pr?ximas de ferrita e austenita na estrutura dos a?os duplex promove uma boa combina??o entre as propriedades de resist?ncia mec?nica e resist?ncia a corros?o. Uma das classes dos a?os duplex que vem se desenvolvendo nos ?ltimos anos ? o Lean duplex, que apresentam teores mais baixos de Cr, Ni e Mo, o que os torna mais baratos em compara??o com os austen?ticos. Para compensar a redu??o de Ni e Mo, elementos como Mn e N s?o adicionados em maior quantidade para proporcionar uma boa resist?ncia ? corros?o e conferir a estabilidade da austenita no a?o. Nos ?ltimos anos o n?mero de trabalhos relacionados ao a?o Lean duplex cresceu bastante devido ao interesse em se conhecer, desenvolver e aplicar cada vez mais essa classe de a?os. Uma das aplica??es que est? em alta ? a soldagem por difus?o no estado superpl?stico, e os a?os inox duplex possuem o comportamento superpl?stico, que exige microestruturas com gr?os pequenos e baixas taxas de deforma??o. Sendo assim, um estudo de recristaliza??o do a?o inoxid?vel Lean duplex 2101 como m?todo de refino de gr?o ? proposto para este trabalho. Diferentes lamina??es a frio, sendo elas 70, 80 e 90% de redu??o, foram empregadas no material para fornecer potencial termodin?mico para a recristaliza??o nos tratamentos t?rmicos em tr?s temperaturas, 900?C, 1000?C e 1100?C por tempos de 20 minutos, 1 e 2 horas. T?cnicas de microscopia ?ptica, eletr?nica de varredura, EDS, medidas magn?ticas, difra??o de raios-X, EBSD e microdureza foram empregadas para a caracteriza??o. Os resultados de medidas magn?ticas e microscopia ?tica indicam que h? acentuada ocorr?ncia de transforma??o induzida por deforma??o da austenita para martensita CCC, al?m de ind?cios da ocorr?ncia de outros mecanismos de deforma??o como macla??o mec?nica e deslizamento de discord?ncias, bem como ind?cios de zonas de austenita n?o transformada, aparentemente isenta de encruamento, conforme indicado pelos valores de microdureza, mesmo para redu??es de 90% na lamina??o a frio; aparentemente houve precipita??es de fases indesejadas tanto na ferrita quanto na austenita durante os tratamentos t?rmicos e aparente recristaliza??o total das amostras laminadas p?s tratamento t?rmico mesmo para os tempos mais curtos. Nas amostras analisadas por EBSD foram observados ind?cios de refino do gr?o austen?tico e uma tend?ncia de crescimento secund?rio da ferrita. Nas amostras recristalizadas identificou-se que para temperaturas e tempos de tratamento mais baixo as fra??es de ferrita se mostraram levemente maiores, enquanto que para temperaturas e tempos de tratamentos maiores as fra??es de austenita foram maiores.
Duplex Stainless Steel are an alloy based on Fe-Cr-Ni system characterized by biphasic structure of austenite-ferrite obtained through different thermomechanical cycles and they show good combination between mechanical (high tension strength and good tenacity) and corrosion resistance properties (stress corrosion cracking and pitting corrosion), besides good soldability. One of the Duplex Stainless Steel grades that is being developed in the last years is the Lean Duplex (LDSS) which have low addition of Cr, Ni, Mo and, for this, they are cheaper than austenitic and standard duplex stainless steel. To compensate the reduction of Ni and Mo, elements like Mn and N are added in larger quantities to give good corrosion resistance and ensure the stability of austenite. A possibility for application for LDSS is the manufacturing of components that are subjected corrosion conditions lesser severe for petrochemical industries, manufactured by diffusion bonding, taking advantage of superplastic behavior that these steels have since refined grains structure is present and low deformation rate are applied. Therefore, in this work was made a study of recrystallization of LDSS 2101, previously work hardened, as a method to refine grain. The material was subjected to different reduction degree by cold rolling (70, 80 and 90%), different heat treatments of recrystallization annealing in three temperatures (900, 1000 and 1100?C) and different times (20 min, 1 and 2 hours). The techniques of optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy, magnetic saturation measures, X-ray diffraction, Electron Backscattered Diffraction (EBSD) and Vickers micro hardness were employed in the microstructure characterization. The results of magnetic measures and optical microscopy show a sharp occurrence of strain induced martensite BCC (??) on austenite, besides evidences of occurrence of other deformations mechanisms such as deformation twins and dislocation glide, as well evidences of non-transformed austenite without work hardening, according to the hardness values, even for 90% reduction. Evidences of deleterious phases precipitation, as seen in SEM, were not confirmed by X-ray diffraction, which confirms the system thermodynamic simulation, which indicates phase precipitation such as ? and nitrides in temperature smaller than those used in this work. Preliminary analysis of EBSD samples indicates that recrystallization were not complete for 900?C and 20 minutes, as well a refined austenite grain structure and a trend for secondary recrystallization for ferrite. Optical microscopy also shows a trend to increase austenite over ferrite when temperature and time of recrystallization increased.
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Silva, Junior Francisco Alves da. "Avalia??o do efeito da adi??o de res?duo de borracha de pneu e brita calc?ria na formula??o de comp?sitos ciment?ceos." Universidade Federal do Rio Grande do Norte, 2014. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12867.
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Previous issue date: 2014-05-30Researches have shown that the introduction of rubber in concrete improves the features of its deformability, as well as contributes to environmental disposal of waste generated in the tire retreading process. Furthermore, there is a high availability of limestone within RN and CE country. Ignorance about this stone, does not allow its wide use as aggregate, leaving, this abundant supply idle. A composite of limestone gravel, with proportions of tire rubber waste which could be used as concrete would be an alternative to concrete for low applications. Therefore, this research aims to evaluate the characteristics of concrete containing limestone gravel and proportions of little aggregate replacement (sand) by tire rubber waste. To this goal, the material components of the concrete were characterized, concrete specimens with limestone gravel were made, from the dash 1.0: 2.5: 3.5, varying the water/cement ratio, and inserting a commercial plasticizer, without a proportion of residue, known as reference. From this, concrete with and without the presence of the additive in the same proportions were chosen, as well as these with the use of granite gravel, for being the most used. Selected the references, to these, replacements of little aggregate (sand) were added replaced by rubber waste from the tire retreading process, treated with 1M NaOH in proportions from 5.0 to 20.0 % by mass, cured and exposed to the semiarid environment. The results indicate the possibility of using limestone gravel in the concrete composition with workability correction using plasticizer. There was a decrease in the mechanical properties of the concrete with increments of waste rubber, but there is an improvement in toughness and deformability of the composite, which makes it interesting for the construction of non-structural concrete floors, as well as, the rubber waste delayed the hardening process, continuing to gain resistance after 28 days
Pesquisas t?m mostrado que a introdu??o de borracha no concreto melhoram as caracter?sticas de deformabilidade deste, assim como, contribuem para destina??o ambiental de res?duos gerados no processo de recauchutagem de pneus. Somado a isto, existe uma alta disponibilidade de rocha calc?ria no interior do RN e do CE. O n?o conhecimento desta pedra, n?o possibilita sua ampla utiliza??o como agregado, deixando, esta farta oferta ociosa. Um comp?sito de brita do tipo calc?ria, com propor??es de res?duo de borracha de pneu que pudesse ser utilizado como concreto seria uma alternativa para concretos destinados a baixas solicita??es. Logo, este trabalho possui como objetivo a avalia??o das carater?sticas de concretos contendo brita calc?ria e propor??es de substitui??o do agregado mi?do (areia) por res?duo de borracha de pneus. Para tanto, caracterizou-se os materiais componentes do concreto, confeccionou-se corpos de prova de concretos com brita calc?ria, a partir do tra?o 1,0: 2,5: 3,5, variando-se a rela??o ?gua/cimento, e inserindo-se um plastificante comercial, sem a propor??o de res?duo, chamados de refer?ncia. A partir deste, foram escolhidos nas mesmas propor??es concretos com e sem a presen?a do aditivo, assim como, estes com a utiliza??o da brita gran?tica, por ser a mais utilizada. Escolhidas as refer?ncias, a estas foram acrescidas substitui??es de parte do agregado mi?do (areia) por res?duo de borracha de pneu proveniente do processo de recauchutagem, tratados com NaOH 1 M, nas propor??es de 5,0 a 20,0 % em massa, curados e expostos ao ambiente semi?rido. Os resultados indicam a possibilidade de utiliza??o da brita calc?ria na composi??o do concreto com corre??o da trabalhabilidade utilizando-se plastificante. Observou-se uma diminui??o nas propriedades mec?nicas dos concretos com incrementos de res?duo de borracha, por?m existe uma melhora de tenacidade, e deformabilidade do comp?sito, o que o torna interessante para a constru??o de pisos de concretos n?o estruturais, assim como, o res?duo retardou o processo de endurecimento, continuando o concreto a ganhar resist?ncia, ap?s os 28 dias
28
Simmler, Urs. "PTC Creo Simulate 3.0." Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-171761.
Повний текст джерела
29
Bibhanshu, Nitish. "Thermo-Mechanical Processing of Third Generation γ – Titanium Aluminides". Thesis, 2019. https://etd.iisc.ac.in/handle/2005/4641.
Повний текст джерелаАнотація:
The γ – TiAl based intermetallics are characterized by unique combination of the properties which
make these materials amenable for the application in gas turbines. However, due to problems
related to limited plasticity and strong solidification texture, the application of these materials is
limited to low pressure turbine regions. In order to utilize the full potential of these materials, new
chemistries have been developed, which are currently known as the third generation γ titanium
aluminides. Further it is desirable to optimize the processing conditions of these newly developed
materials, and provide a fundamental understanding of processing-microstructure relationship.
The present thesis deals with examining the thermo-mechanical processing response of
third generation titanium aluminides with nominal compositions Ti-45Al-5Nb-0.2B-0.2C and
Ti-45Al-10Nb-0.2B-0.2C. The study involves through-processing microstructural modification
and characterization. The entire work consists of four parts. In the first part, the solidification
microstructure and texture of the cast material and the modification brought due to hot isostatic
pressing (HIPping) has been investigated. A clear comparison has been brought out in terms of
niobium content of the alloys. Further, these alloys undergo complex phase transformations during
heating and cooling. In the second part of the study, the microstructural changes during phase
transformation have been investigated for both the alloys along with the oxidation behavior. The
difference in terms of Nb content leads to differences in the transformation temperature as well as
in oxidation response. In the third part of the study, thermo-mechanical processing (TMP) of the
cast plus HIPped alloys has been investigated by plotting strain rate sensitivity maps. The results
indicate that processing is easier in the domain of α phase, where in higher deviation from the
orientation relationship between the two constituent phases have been observed indicating the
occurrence of dynamic recrystallization. In the last part, an alternative route for processing has
been followed by including a pre-deformation heat treatment cycle to spheroidize the lamellae by
the thermal cycling. Such a microstructural feature is expected to provide a more amicable and
broader processing domain. The materials with prior spheroidised microstructure were subjected
to thermo-mechanical processing and a validation of the hypothesis has been carried out by
plotting the strain rate sensitivity maps. The predictions of the maps have been validated by
examining the microstructures of the as-deformed materials. Different possible pathways have
been proposed for tailoring suitable microstructures that would enable to design the appropriate
processing schedule for the third generation TiAl base intermetallics.
The thesis has been divided in to eight chapters. The first three chapters (chapters 1-3) are
dedicated to the introduction, a detailed review of the relevant literature and the experimental
methodologies followed in the present investigation. The investigations and the outcomes
pertaining to the present thesis, as described above, are detailed in the next four chapters (chapters
4-7). The overall outcome of the thesis is presented in chapter 8, along with the recommendation
for future investigations.
30
Nechaev, Yury S. "On the liquid-like local state in deformed metallic materials, relevance to physics of the diffusion and other anomalies." 2017. https://ul.qucosa.de/id/qucosa%3A31675.
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31
"Material performance and numerical modeling of HDPE deformed/reformed liners." Tulane University, 1996.
Знайти повний текст джерелаАнотація:
The objective of this research was to investigate short- and long-term performance of high density polyethylene deformed/reformed liners. This was achieved by; (i) performing experimental tests to identify the material properties, (ii) selecting an appropriate constitutive relationships for modeling the material, (iii) developing a finite element model for the liner system, (iv) comparing the finite element predictions with available analytical and experimental data, (v) predicting the service life of a HDPE liner under various loading conditions and life spans, and (vi) modifying current design practice Current design and installation practices of HDPE deformed/reformed liners have been based on either the design methodology used for flexible pipes or empirical methods extended from practical experience gained through in-situ installation. However, such methods generally produce conservative designs. Also these methods are incapable of accounting for some in-situ situations including the effect of many important parameters related to pipe, soil, and pipe/soil interface. In view of these limitations, this research has focused on the development of a finite element model for the liner system representing the complex geometry, non-homogeneous soil conditions, viscoelastic response of the liner material, and various loading conditions Based on the experimental and finite element modeling results, it was concluded that: (i) stress concentrations resulting from manufacturing and installation significantly influence the buckling resistance of a deformed/reformed liner system; (ii) the classical buckling equation was modified to estimate the critical buckling resistance of a HDPE liner under short-term external loads; (iii) the long-term critical buckling resistance of the HDPE liner material was found to be one-fourth of that of the critical resistance measured during short-term tests; (iv) the material properties of HDPE liners satisfied closely the requirements specified in plastics design handbook; (v) the standard test method for estimating the tensile properties of plastics (ASTM D 638) has been modified; (vi) a bedding angle of 120$\sp\circ$ was found to be the most critical and should be considered in the analytical design for long-term conditions; (vii) the condition of a completely deteriorated host pipe modeled in the finite element analysis indicated similar results to an unsupported HDPE liner tested in laboratory experiments; (viii) temperature in the liner system significantly affect its short-term performance in the field; (ix) analyses on the HDPE liner system for the service life conditions of up to 50 years showed satisfactory performance limits; and (x) use of flexible pipe design criteria for a deformed/reformed liner system may result in conservative designsacase@tulane.edu
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Sun, Roy Yu-Han, and 孫宇恆. "The Study for Anti-Corrosion Material of Deformed Bar in Reinforced Concrete Structure." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/75804162395623674925.
Повний текст джерелаАнотація:
碩士健行科技大學
土木工程系空間資訊與防災科技碩士班
104
In this study, the problem of Concrete Leakage causing the “Efflorescence”. The related testing to improve cement mortar formulations. There are 9 groups of 27 samples of cement with deformed bar mortar were setting in the wet environment (with electrical potential observed), these testing exam the degree of various admixture resist corrosion ability, which is solubilized of calcium hydroxide. Analysis on the corrosion potential impact for the efflorescence phenomenon. Experimental features of control parameters include: (1) Mixing Water of make Specimen, (2) Cement Admixture, (3) Coating Material on deformed bar. This research results showing that (1)while test specimen mixing with and soak in ionized water, can effectively reduce the corrosion potential of deformed bar; (2) Test specimen mixing with and soak in ionized water, and also coating deformed bar with XC, these specimens obtain minimum corrosion potential. (3) Test specimen immersion in drinking water, under the waterline and the bottom of container where we could find white sediment/precipitate. But test specimen soaking in ion water does not have this phenomenon. Above conclusions stated that ionized water does prevent the effect of deformed bar corrosion, i.e. “Efflorescence”
33
Peres, Ana Carla Reis e. Gonçalves Lopes. "O Método dos Avanços Sucessivos, desde a Fase de Projeto à Construção da Ponte." Master's thesis, 2016. http://hdl.handle.net/10362/34369.
Повний текст джерелаАнотація:
No processo de conceção de uma ponte, a escolha do método construtivo a adotar deve ser considerado e racionalizado logo nas primeiras fases do projeto. É um dos aspetos que mais condiciona e influencia a globalidade do processo de conceção e dimensionamento da ponte, sendo que, essa decisão decorre de uma profunda análise de vários fatores condicio-nantes, nomeadamente: o custo, a facilidade de execução, a segurança, o tempo de constru-ção e a capacidade técnica do empreiteiro.
A presente dissertação trata o caso da construção de pontes pelo método dos avanços sucessivos, com a execução de aduelas betonadas “in situ”, e, pretende reunir todos os dados e resultados obtidos, desde as fases de conceção e de desenvolvimento do projeto até à cons-trução da obra.
Num processo construtivo, deste tipo, pela existência de diversos intervenientes envolvi-dos, torna-se muitas vezes difícil conseguir efetuar a recolha de toda a informação produzida e fazer a análise sobre os resultados obtidos, não se tornando assim possível, tirar daí as devi-das conclusões, relativas às diferenças verificadas nas fases de projeto e obra e que por si re-velam a evolução de todo o processo.
Para o caso específico da Ponte sobre o rio Tinhela, pretende-se fazer a apresentação do projeto de execução, do projeto de faseamento construtivo, e ainda, dos resultados obtidos em obra, efetuar a análise e estabelecer a comparação entre os valores de projeto e os verifi-cados durante a construção.
Faz enfoque nos diversos modelos de cálculos utilizados, em cada uma das fases de desenvolvimento do projeto, função das necessidades e objetivos a atingir, quer em termos das solicitações atuantes, considerando os equipamentos construtivos disponíveis e adotados em obra, das capacidades resistentes dos materiais de construção utilizados e das metodologias e calendarização previstas no programa de trabalhos.
São analisados em pormenor os resultados obtidos no que diz respeito à anti-deformada e/ou plano de contraflechas para construção do tabuleiro da ponte e apresentam-se os registos obtidos em obra, tirando daí as devidas conclusões sobre as diferenças ocorridas.