Dissertations / Theses on the topic 'In-Situ tensile'
To see the other types of publications on this topic, follow the link: In-Situ tensile.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'In-Situ tensile.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Lee, Kok Loong. "Deformation behaviour of Cu-Cr in-situ composite." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/11077.
Full textAbstract:
With the increasing requirements for higher strength materials with high electrical conductivity, a lot of interest has been paid to develop Cu-based composites in the last 25 years. These composites have superior tensile strength, combined with good electrical conductivity, to that exhibited by pure Cu and conventional Cu alloys. To date, much of the research carried out on this composite has focused on the mechanical and electrical properties of the as processed material. However, there is a basic lack of understanding of the way in which the properties may change or degrade during service. Without this knowledge, these composites cannot be fully and safely exploited. Thus the objective of this study was to investigate the thermo-mechanical behaviour of a Cu-Cr composite, and the nature and extent of any damage mechanisms occurring within the composite over a wide range of experimental conditions. Neutron diffraction was used to investigate the deformation behaviour of the individual phases in the composite and their interaction through elastic and plastic loading at room temperature. For the composite, a fairly good agreement was observed in the phase strains predicted by the Eshelby theory and measured by neutron diffraction. In-situ tensile tests in the SEM were also performed to study the damage mechanism of the composite. Tensile and creep tests were carried out in air and in vacuum over a wide range of temperatures. To provide data for comparison with the composite material, pure Cu specimens were tested whenever possible. Creep resistance increases significantly with the introduction of Cr fibres into Cu. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. Damage characteristics and distributions were found to be similar during tensile and creep testing.
2
Lind, Jonathan F. "In-situ High-Energy diffraction Microscopy Study of Zirconium Under Uni-axial Tensile Deformation." Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/301.
Full textAbstract:
The ability to predict a material's performance while being subject to complex thermo-mechanical processing is of great importance for material design and implementation in the real world. A material's behavior and performance has been shown to depend on its underlying microstructure. Recent advances in x-ray-based characterization of bulk microstructures while in service has lead to validation and constraints of models used for predictive responses. Specifically the use of Near-Field High Energy X-ray Diffraction Microscopy (nf-HEDM) with Forward Modeling Method (FMM) to obtain spatially-resolved microstructures and microtextures has been a breakthrough in fully characterizing bulk materials in-situ. New advanced data processing methods have been applied to nf-HEDM diffraction images to assist in fidelity of microstructure reconstructions returned via the FMM. Here we present the development and results of one study of pure Zirconium as it is subjected to several states of uni-axial loading. The local feature tracking, including tensile twin nucleation and void formation, as well as global evolution is discussed.
3
Eriksen, Lars. "Combined EBSD-Investigations and In-situ Tensile Tests of a Direct Metal Deposited Ti6Al4V-Alloy." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22438.
Full textAbstract:
Two blocks made of Ti6Al4V material produced by Norsk Titanium Components ned Direct Metal Deposition (DMD) production technology were delivered for this investigation. The main difference between the blocks was the different waiting time implemented in the production parameters. The different waiting time implied that the material were allowed to cool to a deisred Interpass Temperature (IT). The blocks are referred to as T200 and T600 after their lowest IT of <200 degrees celsius and 500-700 degrees celsius, respectively. Sintef Manufacturing Raufoss reported elongations of 5% and 8% in the deposition-direction of the two blocks, which was lower than the 10% elongation obtained for the building-direction. The objective was to find any explanations for the impaired ductility in the deposition-direction, and why T200 have a lower elongation than T600. To reveal differences in micro- macrostructure and deformation-mechanisms between the blocks was combined EBSD+In-situ. tensile tests the main tool. Complementary studies with optical microscopy of etched in-situ specimens were also performed.The work started with an extensive macroetching of different planes relative to the deposition-direction. This revealed a 3D-image of the epitaxially growing solidification structure of columnar prior beta grains. Measurements of grain size and morphology did not indicate significant differences between the blocks. Later was EBSD selected to prior beta grain boundaries for specimens at the center of the blocks. Measurements of the thickness of primary alfa phase also indicated small differences between the blocks. From this it was concluded that the different ITs lead to small differences in solidification structure and the amount of primary alfa phase in the center of the blocks.The EBSD + in-situ tensile tests were carried out for specimens fabricated from the blocks in the deposition direction, such that investigation could be performed in the XZ-plane. The force was applied parallel to the deposition direction X. The in-situ specimens in block T200 had a slightly higher position in the block giving a finer microstructure because of faster cooling rates. The T200 specimens also contained to deposition layers in contrast to only one in T600 specimens. This made a direct comparison difficult. However, from the four in-situ specimens investigated was the following concluded: specimens from T200 deformed more homogeneously on a macroscale. Correspondingly was more activity observed at prior beta grain boundaries for T600. The more active grain boundaries in T600 may result from the different cooling rates from the peak temperature. Slower cooling rates will give smaller prior beta grains decorated with more homogeneous alfa phase along the boundaries of T600 specimens. The frequently reported detrimental mismatch between soft and hard HCP-grains in titanium alloys were also observed. However, the orientation and morphology of these grains seems to play an important role. Cracks growing along prior beta grains were always located at the side having a non-Burgers orientation relationship. The lamellar basketweave microstructure also seem quite effective to stop cracks from growing further, because of the plates having distinct orientations.This work has also uncovered the transition in microstructure between the substrate plate and first deposition layer. The microstructure develops from a very fine bimodal plate structure, through a equiaxed region with small amounts of primary alfa phase, to early stages of the columnar beta grain configuration. The first columnar beta grains are very small in size compared to higher up in the block, and they contains very small amounts of primary alfa phase. However, the basketweave microstructure develops relatively close to the substrate plate.
4
Wang, Wenbo. "Failure Analysis of High Nickel Alloy Steel Seal Ring Used in Turbomachinery." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6635.
Full textAbstract:
The system of upper high nickel alloying steel seal ring and lower high nickel alloying steel seal ring, installed in the grooves of turbine, can extend out and fit with the wall of valve cage, resulting in forming a good seal under the pressure. In the project, the failure steel seal ring is considered. This situation had threatened the safety of the whole steam turbine system. The purpose of this study is to identify the failure cause of the steel seal ring used in nuclear steam turbines. New high nickel steel alloy seal ring was compared with the failed seal ring. The dimensions of macroscopic ring with clearly plastic deformation were measured using calipers. Surface morphology of ring was observed by optical microscopy through metallographic analysis. There is a lot of precipitation in the grain boundaries of used seal ring, along with smaller grain size than the new seal ring. To explore the composition of precipitation, scanning electron microscopy (SEM) with energy-dispersive spectrometer (EDS) were used. The results indicated that the concentration of titanium (Ti) and molybdenum (Mo) was higher in the precipitation of used seal ring. At the same time, the hardness and elastic modulus of used seal ring were reduced, measured by nanoindentation test. In-situ SEM tensile testing were used to record and analyze the generation of crack source and crack development under applied load. The reasons of the seal ring failure can be answered because of these experimental results at both macroscopic and microscopic scales.
The main reason of the seal ring failure is a combination of long-term stress and elevated temperature during turbine operation. Complex work environment caused recrystallization and recovery, resulting in grain refinement and secondary phase precipitation. Further embodiment, recrystallization and recovery caused the elastic modulus and hardness of used seal ring decrease. Moreover, a lot of secondary phase precipitates appeared at grain boundaries during use. The appearance of secondary phase precipitates become the weakest part of used seal ring. The applied load lead to seal ring failure from the formation of microvoids to microvoids aggregated becoming microcracks until to the appearance of cracks at macroscopic scale. These changes of microscopic structure ultimately reflected in critical plastic deformation of used seal ring.
5
Böhm, Jochen. "In situ tensile testing at the limits of X-ray diffraction a new synchrotron-based technique." Stuttgart Max-Planck-Inst. für Metallforschung, 2004. http://deposit.d-nb.de/cgi-bin/dokserv?idn=972182810.
Full text
6
Grippo, Christian P. (Christian Patrick) 1969. "Design and manufacturing of a tensile text machine for in-situ atomic force microscope mechanical testing." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89386.
Full text
7
Déprez, Pascal. "Contribution à l'étude de la forgeabilité et de la criquabilité des aciers de coulée continue." Valenciennes, 1993. https://ged.uphf.fr/nuxeo/site/esupversions/7bbe5533-fb40-4a89-a728-8816cc7f22f3.
Full textAbstract:
L’un des enjeux actuels de la sidérurgie concerne l'enfournement à chaud des produits de coulée continue avant laminage. Il devient donc primordial d'éviter l'apparition de criques d'origine thermique ou mécanique. Un essai de traction à chaud après refusion, sans phase de retour à la température ambiante, a été développé de façon à reproduire la microstructure des produits de coulée continue. Les résultats obtenus sur différentes nuances d'aciers ont permis de mettre en évidence des écarts significatifs de ductilité et de sensibilité à la crique, dans les gammes de températures concernées, entre les essais conventionnels par reausténisation et les essais après fusion in situ. Ces écarts se justifient par la taille des grains austénitiques, la répartition des ségrégations, la cinétique de formation de la ferrite ou encore l'aptitude à la recristallisation dynamique de l'austénite. L’influence du mode de solidification, de la teneur en carbone et de la présence d'éléments de microalliage tels le niobium et le vanadium a été étudiée. Les modes de rupture ont été analysés pour différentes conditions de déformation. Il a été montré que l'évaluation objective de la forgeabilité et de la criquabilité, nécessitait le recours à des essais prenant en compte l'histoire thermique du métal, en particulier pour les aciers présentant une réaction péritectique durant la solidification.
8
Babinský, Tomáš. "Rekrystalizace automatové oceli studované technikou in-situ SEM/EBSD." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378404.
Full textAbstract:
Placing recrystallization annealing in a manufacturing proces is often necessary in order to restore plasticity of worked blanks right before working products to its final shape. For better understanding of processes which are taking place in a material during annealing the use of in-situ techniques is favorable. Such observations enable us to watch changes in the materiál in real time at the original spot. Observations at grain-level are ideally made with scanning electron microscope – SEM by electron back-scattered diffraction – EBSD. The technique makes watching nucleation, growth and potential coarsening of recrystallized grains possible. Special construction of a tensile stage allows us to watch changes of a sample during tensile tests which can be used in observing influence of MnS inclusions on plasticity of free-cutting steels. Materials studied in this work are commonly used free-cutting steel 11SMnPb30 and its lead-free alternative 11SMnBi30.
9
Kasvayee, Keivan Amiri. "Microstructure and deformation behaviour of ductile iron under tensile loading." Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Material och tillverkning – Gjutning, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-28335.
Full textAbstract:
The current thesis focuses on the deformation behaviour and strain distribution in the microstructure of ductile iron during tensile loading. Utilizing Digital Image Correlation (DIC) and in-situ tensile test under optical microscope, a method was developed to measure high resolution strain in microstructural constitutes. In this method, a pit etching procedure was applied to generate a random speckle pattern for DIC measurement. The method was validated by benchmarking the measured properties with the material’s standard properties. Using DIC, strain maps in the microstructure of the ductile iron were measured, which showed a high level of heterogeneity even during elastic deformation. The early micro-cracks were initiated around graphite particles, where the highest amount of local strain was detected. Local strain at the onset of the micro-cracks were measured. It was observed that the micro-cracks were initiated above a threshold strain level, but with a large variation in the overall strain. A continuum Finite Element (FE) model containing a physical length scale was developed to predict strain on the microstructure of ductile iron. The materials parameters for this model were calculated by optimization, utilizing Ramberg-Osgood equation. For benchmarking, the predicted strain maps were compared to the strain maps measured by DIC, both qualitatively and quantitatively. The DIC and simulation strain maps conformed to a large extent resulting in the validation of the model in micro-scale level. Furthermore, the results obtained from the in-situ tensile test were compared to a FE-model which compromised cohesive elements to enable cracking. The stress-strain curve prediction of the FE simulation showed a good agreement with the stress-strain curve that was measured from the experiment. The cohesive model was able to accurately capture the main trends of microscale deformation such as localized elastic and plastic deformation and micro-crack initiation and propagation.
10
Mathisen, Martin Borlaug. "In-Situ Tensile Testing Combined with EBSD Analysis of Ti-6Al-4V Samples from Components Fabricated by Additive Layer Manufacture." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18905.
Full textAbstract:
ALM-based production of Titanium components shows great promise in supplying cost-effective products within industries such as energy, chemical processing and aerospace. In common for all is high quality demands. This necessitates extensive research into the intricacies of this production process. Complex microstructures comprised of columnar remnants of directionally solidified β-Titanium, with interior inhabited by colonies of finer α-plate structures were found in samples produced by layered plasma welding of alloy Ti-6Al-4V. Utilising the powerful characterisation tool of in-situ tensile tests combined with EBSD analysis allowed qualitative correlation between microstructural features and deformation characteristics. Non-uniform deformation occurs due to a strong variation of strain response between colonies. Prismatic and basal slip systems are active, with the prismatic systems contributing to the most severe deformation through coarse, widely spaced slip bands. Certain colonies behave as microstructural units, with easy slip transmission across the entire colony. Other colonies show significant deformation mismatch, with local build up of strain gradients and stress concentration. Segmentation occurs due to the growth morphology imposed by the columnar grains. Tensile tests perpendicular to columnar structures reveal strong deformation localization. Connections are made between the peculiarities of the production process and the observed microstructure and deformation mechanisms.
11
Hasan, Mahamudul. "In-situ martensite texture evolution and phase fractions of superelastic NiTi upon tensile loading using synchrotron hard x-ray diffraction." Bochum Europ. Univ.-Verl, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=3013895&prov=M&dok_var=1&dok_ext=htm.
Full text
12
Zhong, Zhengye [Verfasser]. "In situ tensile investigations on AA 7020-T6 using synchrotron diffraction for texture, lattice strain and defect density studies / Zhengye Zhong." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2015. http://d-nb.info/1078695237/34.
Full text
13
Dessolier, Thibaut. "Effet de la température sur les hétérogénéités de déformation plastique dans les alliages de magnésium." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI094/document.
Full textAbstract:
L’objectif de cette étude est de quantifier la contribution intra et intergranulaire lors d’une sollicitation à haute température d’un alliage de magnésium (AZ31). Afin de répondre à cette problématique scientifique, un essai de traction in situ à haute température dans un MEB a été mis en place. Un important travail de développement a été réalisé autour de cet essai afin de lever un nombre de verrous technique conséquent. Ces verrous expliquent en partie pourquoi il existe aujourd’hui peu d’étude in situ à haute température sur des alliages de magnésium. Un marqueur local ayant la forme d’une microgrille a été déposé sur notre échantillon étant donné que celui-ci n’offre aucun contraste local pour la corrélation d’image numérique (CIN). Afin le dépôt du marqueur local, une cartographie EBSD a été réalisée. À l’aide des joints de grains issus de la carte EBSD, on peut venir superposer les joints de grains aux champs de déformation issue de la CIN.À l’aide des essais de traction in situ à haute température, on a pu mettre en avant l’effet de la température sur les différents mécanismes de déformation actif. Tout ce travail de développement nous permet ainsi de pouvoir localiser les hétérogénéités de déformation plastique à la fois en fonction de l’évolution de la déformation et pour plusieurs températures. D’après les essais menés, on a pu mettre en évidence le fait que plus la température est élevée, que plus les hétérogénéités de déformation plastique se localisent au voisinage des joints de grains. Basé sur une hypothèse cœur/manteau, on a pu venir quantifier la contribution intergranulaire, et mettre en avant que celle-ci devenait plus importante avec la températureThe aim of this study is to quantify the intra and intergranular contribution of the deformation during a high temperature micromechanical test on a magnesium alloy (AZ31). In order to answer this scientific issue, we have developed an in situ tensile test at high temperature within a SEM. It has required a significant preparation work in order to push the current technical limits of this type of test on magnesium alloy. These technical limits can partly explain why there are currently few in situ studies at high temperature on magnesium alloys. A local marker in the form of a microgrid was placed on our sample as it does not provide any local contrast for digital image correlation (DIC). Before the deposition of the microgrid, EBSD mapping was made. Using the grain boundaries from the EBSD, we can superimpose the deformed grain boundaries on the strain map from the DIC.Using high temperature in-situ tensile tests, we were able to highlight the effect of the temperature on the different active deformation mechanisms. This whole development work enables us to locate the plastic deformation heterogeneities both according to the evolution of the deformation and for several temperatures. From the tests conducted, it has been shown that the higher the temperature, the more heterogeneous the plastic deformation heterogeneities are located in the vicinity of the grain boundaries. Based on a heart/coat hypothesis, we were able to quantify the intra and intergranular contribution, and show that it became more important with temperature
14
Sasaki, Layla. "Influence du vieillissement sur la résistance à la fissuration par fatigue à haute température d'alliages de titane pour mâts-réacteurs." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2018. http://www.theses.fr/2018ESMA0006/document.
Full textAbstract:
La conception de moteurs aéronautiques plus performants soumet les alliages de titane constitutifs des mâts-réacteurs à des contraintes thermiques et mécaniques plus sévères. Ces matériaux doivent d’une part être qualifiés en termes de tolérance aux dommages. D’autre part, l’exposition prolongée de ces alliages de titane à des températures élevées en service pose la question de leur vieillissement métallurgique. Le dimensionnement et la maintenance de telles aérostructures doit ainsi prendre en compte l’ensemble de ces deux problématiques cruciales.Dans ces travaux, le comportement cyclique ainsi que la résistance à la fissuration par fatigue d’alliages de titane de différentes nuances (TA6V, Ti 6242 et Ti 17) et de différentes microstructures, ont été étudiés en fonction du degré de vieillissement. L’effet du vieillissement se traduit essentiellement par une augmentation des vitesses de propagation à forte valeur du facteur d’intensité de contrainte, à température ambiante. Dans un second temps, une démarche de caractérisation poussée de ce phénomène mettant en œuvre des sollicitations variées, à différentes échelles et associées à des analyses fractographiques a été appliquée. Ceci a permis de proposer un scénario d’endommagement avant et après vieillissement pour l’alliage le plus affecté par l’exposition en température, le Ti 17. Ce scénario montre après vieillissement l’apparition d’un mode d’endommagement « statique » en lien avec un processus de rupture puis décohésion intralamellaire, sans modification notable du comportement cyclique. Enfin, une approche d’équivalence temps-température est proposée pour décrire la cinétique de dégradation des propriétés mécaniques consécutive au vieillissementThe conception of more efficient aircraft engines induces increased stress and temperature levels on the titanium alloys constitutive of the engine pylon. On the one hand, these materials have to be qualified in terms of damage tolerance. On the other hand, the long term high temperature exposure of these titanium alloys gives also rise to the question of thermal aging and metallurgical stability. Hence, the dimensioning as well as the maintenance of such aerostructures need to be considered in the light of both these critical issues.In the present work, the cyclic behavior as well as the fatigue crack resistance of different titanium alloys (TA6V, Ti 6242 et Ti 17), with various microstructures were studied after different aging conditions. Aging induces mainly an increase in crack growth rates at high values of the stress intensity factor, at room temperature. Subsequently, a thorough characterization procedure of this phenomenon was undertaken,including various types of loadings, at different scales and associated with fractographic analyses. The results allowed to suggest a damage scenario before and after aging, in the case of the alloy most affected by aging: theTi 17 alloy. This scenario shows the occurrence of a « static » mode of failure, which is linked to a damage process associated with intralamellar fracture and decohesion, without noticeable changes in the cyclic behavior. Finally, a time-temperature equivalency approach was developed to describe the kinetics of degradation of the mechanical properties induced by aging
15
Willeman, Héloïse. "Multi-scale characterization of deformation mechanisms of poly-ether-ether-ketone (PEEK) under tensile stretching." Electronic Thesis or Diss., Lyon, INSA, 2023. http://www.theses.fr/2023ISAL0006.
Full textAbstract:
L’objectif de cette thèse est d’établir le scénario multi-échelles de déformation du PEEK lorsqu’il est sollicité en traction uniaxiale. Préalablement à la mise en oeuvre d’échantillons de deux grades commerciaux de PEEK, les propriétés thermiques et mécaniques de ces matériaux ont été caractérisées. La température d’oubli thermodynamique ainsi que la sensibilité aux vitesses de refroidissement ont été établies. Des éprouvettes de traction ont été obtenues à partir de plaques thermocompressées, procédé choisi pour obtenir des morphologies les plus isotropes possibles. Les propriétés mécaniques en traction ont ensuite été caractérisées au-dessus et au-dessous de la transition vitreuse de la phase amorphe (Tg). Grâce à un dispositif expérimental fabriqué sur mesure, des essais de traction à deux températures distinctes au-dessous et au-dessus de Tg ont été suivis par diffusion des rayons X aux petits (SAXS) et grands angles (WAXS) pour caractériser les déformations à l’échelle des empilements lamellaires et à l’échelle de la maille cristalline. Simultanément, le champ de déformation a été mesurée par corrélation d’images (DIC) afin de comparer la déformation macroscopique et microscopique. Pour les deux températures, les lamelles tendent à s’orienter perpendiculairement à la direction de traction (TD). Ce mécanisme d’orientation local (que nous appelons « modèle de réseau de chaînes ») est induit par la transmission des contraintes par les chaînes amorphes reliant les lamelles cristallines adjacentes. Au-dessus de Tg, l’allongement local est plus faible que l’allongement macroscopique dans les lamelles perpendiculaire à TD, ce qui implique que les lamelles inclinées doivent être cisaillées. L’évolution de la distribution d’orientation des lamelles appuie ce résultat. Une morphologie fortement orientée est finalement obtenue quelle que soit la température. Cependant, le profil d’endommagement est différent. En-dessous de Tg, le profil de diffusion centrale indique l’existence de petites entités (lamelles ou crystallites) orientées aléatoirement. A hautes température, le matériau est fibrillaire et présente des cavitésThe aim of this PhD work is accessing the microscopic deformation mechanisms of bulk poly-ether-ether-ketone (PEEK) under tensile stretching. Beforehand, the thermal and mechanical properties of two commercial grades of PEEK were characterized. Tensile specimens were then compression-molded to obtain morphologies as isotropic as possible and characterized below and above the glass transition temperature. Deformations at the scales of lamellar stacks and of the crystalline unit cell have been characterized by small and wide-angle X-ray scattering (SAXS and WAXS) performed in-situ during tensile tests. Simultaneously, the strain field within the samples was followed by digital image correlation (DIC) in order to compare microscopic and macroscopic strains. At both temperatures, lamellae tend to orient perpendicular to the tensile direction (TD). This orientation mechanism (which we denote as ‘Chain Network model’) is driven by the amorphous chains which transmit the stress between adjacent lamellae. The tensile strain in lamellar stacks perpendicular to TD is lower than the macroscopic tensile strain, which must be compensated by increased shear in inclined stacks. Some differences of behavior have been observed depending on the test temperature, especially at high deformation. A highly oriented morphology is ultimately obtained in all cases. However, the central scattering profiles changes with testing temperatures. Below Tg, the presence of small entities randomly oriented is indicated. Above Tg, the material is fibrillar and contains cavities
16
Pinto, Cristiane Franco. "Analise da união e dos tecidos dentais (esmalte/dentina) adjacentes as restaurações com sistemas adesivos contendo fluoreto apos desafios cariogenicos in situ e in vitro." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287811.
Full textAbstract:
Orientador: Marcelo GianniniTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
Made available in DSpace on 2018-08-15T12:58:19Z (GMT). No. of bitstreams: 1 Pinto_CristianeFranco_D.pdf: 8181087 bytes, checksum: 41321386cc6d99055932efad6dad9919 (MD5) Previous issue date: 2010
Resumo: O objetivo deste estudo foi avaliar sistemas adesivos, tecidos dentais adjacentes (esmalte ou dentina) às restaurações e a união formada entre os adesivos e as estruturas dentais frente aos desafios cariogênicos in situ e in vitro. Para o estudo foram utilizados dentes bovinos e blocos dos tecidos dentais (esmalte e dentina) que foram restaurados com dois sistemas adesivos e resina composta. No estudo in situ; 11 voluntários utilizaram dispositivos palatinos contendo 2 amostras do grupo controle (substrato hígido sem preparo cavitário) de esmalte e dentina, e 6 amostras restauradas com os sistemas adesivos Clearfil Protect Bond (PB) ou One-Up Bond F Plus (OP) (em fases distintas) e com o compósito Filtek Z350. O desafio cariogênico consistiu de 2 fases (cada fase com um adesivo), sendo cada fase de 14 dias com intervalo de 10 dias entre elas. Os voluntários utilizaram solução de sacarose a 20%, 8X/dia e dentifrício fluoretado 3X/dia. Após cada etapa, o biofilme dental formado foi coletado e analisado. As amostras foram analisadas através de Microscopia de Luz Polarizada (MLP) e Microdureza Knoop para observação da extensão da lesão de cárie. Para o estudo in vitro foi realizado o preparo dos substratos e foram restaurados em esmalte e em dentina seguindo os grupos experimentais: 1-adesivo PB sem desafio cariogênico (DC); 2- adesivo PB com DC; 3- adesivo OP sem DC; 4- adesivo OP com DC. A partir dos blocos dentais restaurados foram obtidos espécimes para o ensaio de resistência da união com formato de paralelepípedos (palitos) e fatias para análise da interface da união em Microscopia Eletrônica de Transmissão (MET). Os espécimes (palitos ou fatias) foram submetidos à ciclagem de pH durante 8 dias. O resultado do ensaio de microdureza em esmalte e dentina mostrou maiores valores para PB nas profundidades mais superficiais e as imagens de MLP mostraram uma menor extensão da área de desmineralização para o adesivo PB que para o adesivo OP. Na análise bacteriológica, o adesivo PB levou a menor quantidade de colônias de Streptococcus totais e do grupo mutans em esmalte. A resistência de união não foi afetada pela ciclagem de pH e foi semelhante em esmalte para ambos adesivos, entretanto, em dentina, o adesivo PB apresentou maior resistência de união que o adesivo OP. Os adesivos produziram hibridização nos tecidos dentais, sem formações de fendas na interface de união. Concluiu-se que o adesivo PB produziu menor extensão de desmineralização dos substratos dentais após o desafio cariogênico e maior microdureza Knoop nas profundidades mais superficiais. Em algumas condições deste estudo, o adesivo PB reduziu a formações de colônias bacterianas. Embora a união formada pelos adesivos em esmalte foi semelhante, o adesivo PB mostrou maior resistência de união em dentina.
Abstract: The aim of this study was to evaluate adhesive systems, mineralized dental tissues (enamel and dentin) around restorations and the bonding formed by adhesives and dental structures in conditions of cariogenic challenge in situ and in vitro. This study used dental blocks (enamel/ dentin) from bovine teeth, which were restored with adhesive systems and a resin composite. For the in situ study: volunteers (n=11) wore intra-oral appliance containing 2 dental fragments without restoration (enamel or dentin) and six dental blocks with restorations made with self-etching primers Clearfil Protect Bond (PB) or One-up Bond F Plus (OP) (in two phases) and the Filtek Z350 composite: The cariogênico challenge was performed in two phases of 14 days (each phase with one adhesive). The volunteers dropped 20% sucrose solution 8x/day and used fluoridated dentifrice 3x/day. After each phase, the biofilm was collected and analyzed. The samples were analyzed by cross-sectional microhardness and polarized light microscopy (PLM) to determine the demineralization depth. For the in vitro study, bovine were prepared and bonded in enamel and dentine with Clearfil Protect Bond (PB) or One-Up Bond F Plus (OP) and restored with Filtek Z-350 composite resin, according to the groups: 1- PB without CC; 2- PB with CC; 3- OP without CC; 4- OP with CC. Restored teeth were sectioned in order to obtain sticks for microtensile bond strength or slabs for transmission electron microscopy. The specimens were submitted to pHcycling, which consisted of DE (8h/day) and RE (16h/day) cycles at 37ºC during days. Microhardness analysis showed that the enamel and dentin around restorations PB had higher values in superficial depths, and the PLM showed that PB resulted in lower demineralization depth than OP. The biofilm investigation indicated that PB produced lower number of bacterial colony of Streptococcus totais and mutans in enamel. The results showed that the pH-cycling regimen did not affect the bond strength to enamel or dentin for both adhesives; however, the bond strength to dentin was higher for PB. The adhesives produced hybridization and no gaps formation in both dental tissues. In conclusion, PB adhesive may result in lower enamel demineralization around restoration and higher microhardness in superficial depths. In some conditions, PB adhesive reduced the number of bacterial colony. Although the adhesives in enamel formed similar bonded interfaces, PB produced higher bond strength to dentin than OP.
Doutorado
Dentística
Doutor em Clínica Odontológica
17
Tahir, Muhammad. "Development of Novel Blends based on Rubber and in-situ Synthesized Polyurethane-urea." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-232718.
Full textAbstract:
Polyurethane and the analogous ‘polyurethane-urea’ are high performance polymeric materials having remarkable properties such as high stiffness, abrasion and tear strengths. In many studies, the low strength rubbers have been blended with various types of polyurethanes for new and improved materials. However, until now, the reported heterogeneous blends offer only a narrow temperature range of application due to the high temperature softening of their polyurethane (-urea) phase. In addition, the conventional solution-or melt-blending methods are time and energy intensive, which tend to forfeit the economical realization of the reported blends. In contrast to earlier studies, a simplified reactive blending process is suggested to synthesize polyurethane-urea via a prepolymer route during blending with rubbers to obtain novel elastomeric materials having extended performance characteristics.
The reactive blending process is opted to prepare blends based on nitrile butadiene rubber (NBR) and in-situ synthesized polyurethane-urea (PUU). The blending is carried out in an internal mixer at a preset temperature of 100°C. The critical temperatures of the reactive blending process are determined from the chemo-rheological analysis of a premix, composed of a 4,4′-diphenylmethane diisocyanate (MDI)/polyether (PTMEG) based prepolymer admixed with 1,3-phenylene diamine (mPD). The prepared NBR/PUU blends exhibit highly improved mechanical properties. Contrary to previous reports, the reinforced dynamic-mechanical responses of the novel blends remain stable till very high temperatures (≥180°C).
The influence of diamine type on the in-situ synthesized polyurethane-urea and the performance of prepared blends are investigated. Four different diamines, namely 1,3-Phenylene diamine, 1,4-Bis(aminomethyl)benzene, 4,4′-Methylene-bis(2-chloroaniline) and 4,4ʹ-(1,3-Phenylenediisopropylidene)bisaniline, are selected to chain extend the prepolymer to PUU during blending with NBR. The chemical and domain structure of the PUUs are found to greatly influence the reinforced tensile and dynamic-mechanical responses of the NBR/PUU 70/30 blends.
The PUU (based on MDI/PTMEG prepolymer and mPD) is blended with polar (CR, XNBR) and nonpolar (NR, EPDM, sSBR) rubbers. PUU compatibilizes with all the rubbers irrespective of their polarity and reinforces their tensile and dynamic-mechanical characteristics. The use of blends in industrial applications, for example, in a truck tire tread compound and as a roller covering material, is examined. In a simplified tire tread formulation, the carbon black for NR-CB composite is partially replaced with an equivalent quantity of PUU for NR/PUU-CB composite of similar hardness. The dynamic mechanical investigations reveal that the energy dissipation and strain dependent softening is high in NR-CB as compared to the NR/PUU-CB composite. In another application, NBR/PUU blend is successfully tested as a rubber roller covering material. The tested blend-covered roller retains its structural integrity and develops less heat build-up as compared to the silica filled NBR-covered roller. This shows a substantial suitability of the blend-covered rollers for film, printing and textile processing machinery.
These novel blends are considered to be the promising new materials for many commercial applications including wheels, rubber rollers, belts or pump impellers.
18
Millot, Coraline. "Multi-scale characterization of deformation mechanisms of bulk polyamide 6 under tensile stretching below and above the glass transition." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0028/document.
Full textAbstract:
Notre étude a porté sur la compréhension microscopique des mécanismes de déformation du polyamide 6 (PA6) à l’état massif. Par des traitements thermiques appropriés, on a obtenu un jeu d’échantillons présentant des microstructures semi-cristallines variées, avec différentes formes cristallographiques (allotropes : α, γ ou β), différents taux de cristallinité (de 24 à 35%), différentes périodes de l’empilement des lamelles cristallines (de 7 à 12nm), ceci pour deux masses moléculaires différentes. Les propriétés mécaniques en traction ont été caractérisées au-dessus et au-dessous de la transition vitreuse de la phase amorphe (Tg). Les différents matériaux présentent des différences notables de comportements. Le taux de cristallinité semble être le facteur prédominant au-dessus de Tg, mais d’autres facteurs sont à prendre en compte en dessous de Tg, comme la forme cristalline et la morphologie lamellaire (épaisseur et facteur de forme). Grâce à un dispositif expérimental fabriqué sur mesure, des essais de traction ont été suivis par diffusion des rayons X aux petits (SAXS) et grands angles (WAXS) sur la ligne D2AM, ESRF, pour caractériser les déformations à l’échelle des empilements lamellaires et à l’échelle de la maille cristalline. Dans les échantillons présentant principalement de la phase cristalline β, les lamelles tendent à s’orienter perpendiculairement à la direction de traction (TD). Ce mécanisme d’orientation local (que nous appelons « modèle de réseau de chaînes ») est induit par la transmission des contraintes par les chaînes amorphes reliant les lamelles cristallines adjacentes. L’allongement local est plus faible que l’allongement macroscopique dans les lamelles perpendiculaire à TD, ce qui implique que les lamelles inclinées doivent être cisaillées. De plus, la phase β se transforme en phase α aux fortes extensions. Dans les échantillons présentant principalement de la phase α (la plus rigide), au-dessus de Tg, dans le régime élastique, les chaînes tendent d’abord à s’orienter perpendiculairement à TD, ce qui implique que les lamelles s’orientent parallèlement à TD (« modèle de lamelles rigides »). Ensuite, dans le régime plastique, une majeure partie des lamelles se réoriente perpendiculairement à TD, comme dans le « modèle de réseau de chaînes », tandis qu’une fraction mineure reste orientée parallèlement à TD. Une morphologie fibrillaire fortement orientée est finalement obtenue pour tous les échantillons quelle que soit la températureMechanical properties of bulk polyamide 6 (PA6) have been studied in relation to microscopic deformation mechanisms. By applying various thermal treatments, sets of samples with different semi-crystalline microstructures, namely various crystalline allotropic forms (denoted α, γ and β) and different values of the crystallinity index (from 24 to 35%) and of the long period of the lamellar stacks (from 7 to 12 nm), have been obtained, for two different molecular masses. Mechanical properties have been measured in the linear (viscoelastic) and nonlinear (plastic) regimes below and above the glass transition of the amorphous phase (Tg). Differences of behavior have been observed depending on the microstructure. While the crystallinity index seems to be the predominant factor affecting the mechanical behavior above Tg, other structural parameters such as the crystalline form and the lamellar morphology (thickness and aspect ratio) have to be taken into account below Tg. Deformations at the scales of lamellar stacks and of the crystalline unit cell have been characterized by small and wide angle X-ray scattering (SAXS and WAXS) performed in-situ during tensile tests. In samples with predominantly β phase, lamellae tend to orient perpendicular to the tensile direction (TD). This orientation mechanism (which we denote as ‘Chain Network model’) is driven by the amorphous chains which transmit the stress between adjacent lamellae. The tensile strain in lamellar stacks perpendicular to TD is lower than the macroscopic tensile strain, which must be compensated by increased shear in inclined stacks. Also, at high extension ratios, the β phase transforms into α phase. In samples with predominantly α phase and above Tg, morphology changes are more complex. In a first step, chains orient perpendicular to TD, which implies that lamellar planes tend to orient parallel to TD, possibly due to their high aspect ratio (denoted as ‘Rigid Lamella’ model). In a second step, beyond the yield, a major fraction of crystallites then reorients normal to TD, i.e. chains themselves become parallel to TD, while a minor fraction remains oriented along TD. A highly oriented fibrillar morphology is ultimately obtained in all cases
19
Pazat, Alice. "Chemical Modification of Graphite-based Derivates and Their Uses in Elastomer Nanocomposites." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1050/document.
Full textAbstract:
L'objectif de la thèse a été d'explorer différentes voies de dispersion de charges graphitiques dans des élastomères de type polyisoprène dans le but d'améliorer les propriétés mécaniques et barrière. Pour augmenter les interactions entre le graphite et l'élastomère et donc diminuer les interactions entre charges, les charges graphitiques ont été modifiées chimiquement. Le graphite a été préalablement oxydé pour obtenir du graphite oxydé (GO) contenant des groupements époxyde, hydroxyle et acide carboxylique, susceptibles de servir comme sites d'ancrage de molécules et de chaînes polymères. Afin d'améliorer la compatibilité du GO avec la matrice polyisoprène, des amines et des alkoxysilanes ainsi que des chaînes polyisoprène ont été greffées sur le GO. Des taux de greffage variant de 4 à 50 % en poids ont été obtenus selon la technique de fonctionnalisation utilisée. Une expansion thermique du GO a aussi été étudiée et a conduit à la formation d'une structure graphitique poreuse. Des composites polyisoprène contenant 15 pce de ces charges graphitiques modifiées ont ensuite été préparés et ont montré une diminution de la perméabilité à l'air (-70 % pour les composites graphite traité thermiquement, par rapport à ceux chargés uniquement en noir de carbone) ainsi qu'une amélioration des propriétés mécaniques. Enfin, l'utilisation de liquides ioniques comme agents dispersants a été étudiée. Des composites caoutchouc-graphite avec 1 % en poids de liquides ioniques ont montré un renforcement plus élevé (+ 25 % pour la contrainte à 300 % d'élongation) tout en conservant un allongement à la rupture similaire par rapport à des composites contenant uniquement du noir de carboneThe aim of this study was the investigation of various dispersion methods for graphite-based fillers in elastomers such as polyisoprene, to enhance mechanical and barrier properties. To increase graphite-rubber interactions and so decrease filler-filler aggregation, graphite-based fillers have been chemically modified. Graphite was previously oxidized into graphite oxide (GO), bearing epoxide, hydroxyl and carboxylic acid groups, which could further act as anchor sites for molecules and polymer chains. To increase the compatibility between GO and the polymeric matrix, amines and alkoxysilanes, as well as polymer chains, were grafted on GO. Grafting contents between 4-50 wt% were obtained, depending on the functionalization technique which was used. A thermal modification path of GO was also investigated and led to the formation of porous graphite structure. Polyisoprene composites containing 15 phr of these graphite-based fillers were prepared and showed decreased air permeability (-70 % for composites containing thermally-treated graphite filler, as compared to those containing carbon black only) as well as enhanced tensile properties. Finally, the use of ionic liquids as dispersing agents was investigated. Natural rubber – graphite composites with 1 wt% of ionic liquid displayed enhanced reinforcement (+ 25 % for the stress at 300 % strain) while maintaining similar strain at break to composites containing carbon black only
20
Böhm, Jochen [Verfasser]. "In situ tensile testing at the limits of X-ray diffraction : a new synchrotron-based technique / Institut für Metallkunde der Universität Stuttgart ... Vorgelegt von Jochen Böhm." Stuttgart : Max-Planck-Inst. für Metallforschung, 2004. http://d-nb.info/972182810/34.
Full text
21
Pushkareva, Marina. "Study of Void Growth in Commercially Pure Titanium." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35667.
Full textAbstract:
The ductile fracture process, which consists of the nucleation, growth and coalescence of microvoids, was extensively studied for materials deforming homogeneously. For materials with a non-homogeneous deformation behavior, such as those having hexagonal closed packed (HCP) crystal structure, experimental and numerical data is lacking. Therefore, the fracture properties of materials with such HCP structure, like titanium (used in aerospace and biomedical applications), zirconium (nuclear industry) and magnesium (manufacturing industry) are not well understood. The main research objective of this Ph.D. thesis is to better understand the mechanisms governing fracture in commercially pure (CP) titanium. In particular, the effect of grain orientation on void growth is investigated. The fracture process of CP titanium was visualized in model materials containing artificial holes. These model materials were fabricated using a femtosecond laser coupled with a diffusion bonding technique to obtain voids in the interior of titanium samples. Diffusion bonding was carried out either above or below the phase transformation temperature resulting in different microstructures. Changes in void dimensions during in-situ straining were recorded in three dimensions using x-ray computed tomography. Void growth obtained experimentally was compared with the Rice and Tracey model which predicted well the average void growth. However, a large scatter in void growth was observed experimentally and was explained in terms of differences in grain orientation which was confirmed by crystal plasticity simulations. It was also shown that grain orientation has a stronger effect on void growth than intervoid spacing and material strength. Intervoid spacing, however, appears to control whether the intervoid ligament failure is ductile or brittle. While this study showed a good agreement between experiments and simulations on average, there is no direct void growth comparison for particular grain orientations. In a follow-up study, an experimental approach was developed to directly relate the growth of a void to its underlying grain orientation. This is achieved by first annealing CP titanium samples below the α-β phase transformation temperature, then performing electron backscatter diffraction iii (EBSD) and finally diffusion bonding the samples together. Samples were then tested in x-ray tomography. This study showed the importance of the local state of strain on void growth. Crystal plasticity simulations that take into account the particular grain orientation and the local state of strain were found to predict well experimental void growth. Crystal plasticity simulations confirmed that the orientation of the voidcontaining grain is more important than the orientation of surrounding grains and more important than the volume fraction of voids, in order to determine void growth. This thesis on the growth and coalescence of voids is important to validate and improve the predictions of ductile fracture models and to design new materials with improved fracture properties.
22
Saraiva, Letícia Oliveira. "Influência da umidade e temperatura intrabucais na resistência de união de sistemas adesivos convencionais de dois passos à dentina : estudo in situ." Programa de Pós- Graduação em Odontologia da UFBA, 2008. http://www.repositorio.ufba.br/ri/handle/ri/11031.
Full textAbstract:
Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-04-23T18:30:00Z
No. of bitstreams: 2
Dissertacao Leticia Saraiva2.pdf: 1296302 bytes, checksum: 1e07502c1e338a38db482de4808d32f7 (MD5)
Dissertacao Leticia Saraiva1.pdf: 179952 bytes, checksum: cf1d7c8753ea10452ef96eb6607fddad (MD5)Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-05-16T18:04:08Z (GMT) No. of bitstreams: 2 Dissertacao Leticia Saraiva2.pdf: 1296302 bytes, checksum: 1e07502c1e338a38db482de4808d32f7 (MD5) Dissertacao Leticia Saraiva1.pdf: 179952 bytes, checksum: cf1d7c8753ea10452ef96eb6607fddad (MD5)
Made available in DSpace on 2013-05-16T18:04:08Z (GMT). No. of bitstreams: 2 Dissertacao Leticia Saraiva2.pdf: 1296302 bytes, checksum: 1e07502c1e338a38db482de4808d32f7 (MD5) Dissertacao Leticia Saraiva1.pdf: 179952 bytes, checksum: cf1d7c8753ea10452ef96eb6607fddad (MD5) Previous issue date: 2008
O presente estudo teve como objetivos avaliar o efeito das condições de temperatura e umidade relativa intrabucais na resistência de união à dentina de dois sistemas adesivos convencionais de dois passos (Single Bond 2/SB2 e One Step Plus/OSP), e avaliar a umidade e a temperatura presentes nas regiões de incisivos e molares superiores. Sessenta fragmentos dentários foram esterilizados, fixados em moldeiras de acetato individualizadas, e posicionados in situ em um voluntário para serem restaurados com resina composta, sendo aleatoriamente divididos em seis grupos, de acordo com o sistema adesivo e com a condição de temperatura e umidade: G1 – SB2 na condição ambiental de um consultório odontológico; G2 – SB2 na condição da região de incisivos; G3 – SB2 na condição da região de molares; G4 – OSP na condição ambiental de um consultório odontológico; G5 – OSP na condição da região de incisivos e G6 – OSP na condição da região de molares. Em todas as condições, foram obtidas e registradas a temperatura e a umidade relativa do ar no momento e no local em que as restaurações foram produzidas, usando um termo-higrômetro digital. Após ensaio de microtração, os dados do teste de resistência de união foram submetidos à análise estatística (ANOVA - 2 fatores/ Teste de Tukey, α=5%) e os valores médios em MPa foram: G1 = 20,2 (7,6); G2 = 23,0 (6,5); G3 = 22,7 (6,0); G4 = 29,0 (5,8); G5 = 29,7 (4,9) e G6 = 27,7 (4,8). Os resultados demonstraram que os grupos que utilizaram o OSP (G4, G5 e G6) apresentaram médias semelhantes entre si (p=0,67) e maiores do que os grupos que utilizaram o SB2 (G1, G2 e G3) (p=0,001), também semelhantes entre si (p=0,67). Foi observado que as condições de temperatura presentes nas regiões intrabucais (incisivos e molares) foram semelhantes entre si, e maiores que a condição ambiental do consultório odontológico. A condição de umidade na região de molares foi superior à condição na região de incisivos, e esta foi maior do que a condição presente no ambiente do consultório odontológico. As condições de temperatura e umidade intrabucais não influenciaram a resistência de união dos sistemas adesivos simplificados à dentina. O sistema adesivo One Step Plus apresentou melhores resultados que o sistema Single Bond 2, independentemente das condições de umidade e temperatura.
Salvador
23
Ehsan, Dina. "Stress-free titanium-based thin films for inner ear microphones : The last missing part of a technology for totally implantable hearing aid implants." Thesis, Linköpings universitet, Tunnfilmsfysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-169705.
Full textAbstract:
An implantable hearing aid device is being developed by a project group which is part of an EU initiative. This device contains a diaphragm consisting of a submicron thick freestanding titanium film, which should be free of internal stresses. Stress is the force exerted per unit cross-sectional area of the film and it can impair the functionality and performance of the device. The stress that evolves in a thin film during deposition at a substrate is compressive or/and tensile and affects the bending that occurs of the substrate due to the lateral force applied to the substrate by the stressed film. The goal of this diploma work was to contribute to the understanding of in situ stress evolution in a micron thick titanium film and thereby by tuning different physical parameters to obtain minimal residual stress in the films after growth. Titanium films were deposited on silicon sistrates using DC magnetron sputtering. The stress in the material varied, by tuning different physical parameters such as working pressure, power, distance between magnetron and the sample and substrate bias. For this thesis, firstly two different series were done; one where the changing parameter was the distance between the sample and the magnetron and one where it was the working pressure. Later a last series were done to see what effect the bias has on the stress. A multi-beam optical sensor system (MOS) was used to measure the stress in real-time during deposition. X-ray diffraction (XRD) was later used to make post-deposition stress measurements to verify the stress obtained from the MOS. However, the MOS shows the stress evolution in real time and XRD shows a ’final’ average value that can be compared with the stress obtained from MOS-data when the deposition is finished. The results showed that the stress goes from compressive to tensile as the working pressure and the distance between the magnetron and the sample increases. There are other factors, such as the temperature/heating in the main chamber, base pressure of the main chamber, cleaning of the sample and also where the argon gas is let in to the process chamber (in this project called the main chamber (MC)), that influences the results. This will in turn influence the repeatability of the data/measurements, since these effects can affect the process of nucleation and coalescence. The stress evolution can change if a bias is applied during the initial stage of the deposition process when the film has still not grown thick. This is could be due to the bias not having much of an impact on the stress evolution when the film is thicker and thereby more porous.
24
Zaragoci, Jean-François. "Simulation numérique directe multiphasique de la déformation d’un alliage Al-Cu à l’état pâteux – Comparaison avec des observations par tomographie aux rayons X in situ en temps réel." Thesis, Paris, ENMP, 2012. http://www.theses.fr/2012ENMP0088/document.
Full textAbstract:
La fissuration à chaud est un défaut majeur rencontré en solidification des alliages d'aluminium. Elle est liée à l'incapacité du liquide de s'écouler dans les zones où des porosités sont présentes, ne permettant pas de les refermer avant qu'elles gagnent en volume. Pour comprendre la fissuration à chaud, il est crucial de développer nos connaissances du comportement mécanique de la zone pâteuse. Pour cela, il est très utile d'effectuer des expériences de microtomographie aux rayons X et des simulations mécaniques sur des volumes élémentaires représentatifs. Dans cette thèse, nous proposons de coupler les deux approches en initialisant une simulation par éléments finis grâce à des données de microtomographie issues d'un test de traction isotherme d'un alliage d'aluminium-cuivre à l'état pâteux. Cette approche originale nous donne directement accès à la réalité expérimentale et permet des comparaisons des évolutions numérique et expérimentale de l'éprouvette. Nous expliquons dans un premier temps comment obtenir la représentation numérique à l'aide de l'algorithme des marching cubes et de la méthode d'immersion de volume. Nous présentons ensuite notre modèle numérique qui s'appuie sur une résolution monolithique des équations de Stokes. Une fois le champ de vitesse obtenu dans l'ensemble des phases solide, liquide et gazeuse, nous utilisons une méthode level set dans un formalisme eulérien afin de faire évoluer la morphologie de notre échantillon numérique. Malgré la simplicité du modèle, les résultats expérimentaux et numériques montrent un accord raisonnable en ce qui concerne la propagation de l'air à l'intérieur de l'échantillonHot tearing is a major defect arising during solidification of aluminium alloys. This defect is associated with the inability of liquid to feed areas where voids have started to appear, not allowing to heal small defects before they grow bigger. To understand hot tearing, it is mandatory to develop a good knowledge of the semi-solid mechanical behaviour. It is thus very useful to carry out X-ray microtomographies experiments and mechanical simulations on representative elementary volumes. In this work, we couple the both approaches by initialising a finite element simulation with the help of microtomography data obtained during an isothermal tensile testing of an aluminium-copper alloy in the mushy state. This innovative approach gives a direct access to the experimental reality and allows comparisons of numerical and experimental evolutions of the sample. We explain in a first time how to get the numerical representation thanks to a marching cubes algorithm and the immersed volume method. Then, we present our numerical model for which we solve the Stokes equations in a monolithic way. Once the velocity computed in all the solid, liquid and gaseous phases, we use a level set method in a Eulerian formalism to obtain the morphological evolution of our numerical sample. Despite the model simplicity, numerical and experimental results show a reasonable agreement concerning the air propagation inside the sample
25
Cristofari, François. "Etude du comportement et de la résistance mécanique d'un pancréas bioartificiel pour l'homme. Caractérisation expérimentale et simulation numérique." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0055.
Full textAbstract:
Afin de traiter les patients atteint de diabète de type 1, un pancréas bioartificiel permettant d’encapsuler des cellules produisant de l’insuline a été développé : il est constitué de membranes poreuses qui les isolent des anticorps du patient, tout en permettant le passage du glucose et de l’insuline. Avant sa mise sur le marché, il est nécessaire de vérifier que son comportement mécanique lui permet d’être implanté chez l’homme sans risque pour le patient. La résistance des membranes sous chargement mécanique est donc étudiée en particulier. Leur structure est d’abord mise en évidence par microscopie électronique à balayage et nanotomographie à rayons X. Des essais de traction sont ensuite effectués à l’échelle macroscopique et à l’échelle microscopique, l’utilisation de techniques de mesure de champs par corrélation d’images permettant de caractériser les déformations des membranes à chaque échelle. En parallèle, une modélisation numérique par éléments finis est développée en se basant sur les caractéristiques microstructurales et mécaniques des membranes. Une méthodologie de comparaison entre le comportement prédit par le modèle et le comportement expérimental des membranes est alors proposée et utilisée. Les résultats de cette étude sont finalement considérés pour juger de la possibilité d’utiliser ce dispositif en phase cliniqueIn order to treat type 1 diabetics, a bioartificial pancreas has been developed. It consists in the encapsulation of insulin producing cells: it is made of porous membranes which isolate cells from patient antibodies, allowing the glucose and the insulin to pass through. Before its commercialization, it is necessary to verify that its mechanical behavior allows it to be implanted in a human body without any risk for the patient. The mechanical strength of the membranes under loading is therefore studied. Their structure is first obtained using scanning electron microscopy and X-ray nanotomography. Tensile tests are then done at both macroscopic and microscopic scales, digital image correlation techniques being used to characterize the membranes at each scale. At the same time, a numerical model using finite element method is built based on the microstructural and mechanical characteristics of the membranes experimentally identified. A methodology to compare the experimental and numerical results behavior of the membranes is proposed and used. The results of the study are finally considered to assess the possibility to use the device in clinic phase
26
Bo, Arixin. "Investigation of the mechanical and electron interaction properties of layered titanate nanowires." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/105649/4/Arixin_Bo_Thesis.pdf.
Full textAbstract:
This project reports first-hand knowledge on the mechanical and electron interaction properties of titanate nanowires which possess a broad range of applications. Using experimental techniques, the mechanical bending and tensile behaviours of individual nanowires are analysed from which a time-dependant recovery and an atypical reversible defect motion of the nanowires are observed. Applying electron beam irradiation, joint formation between two titanate nanostructures is demonstrated with the underlying mechanisms explained. The electron-titanate interaction phenomenon is also shown to be a practical tool for tailoring structures at nanoscale.
27
Lin, Sen. "Deformation-Induced Martensitic Transformation and Mechanical Properties of Duplex and Austenitic Stainless Steels : A Synchrotron X-Ray Diffraction Study." Thesis, KTH, Metallografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-233334.
Full textAbstract:
Metastable austenitic and duplex stainless steels are widely used materials in industrial anddomestic applications, owing to their attractive characteristics such as good corrosion resistanceand favorable mechanical properties. Both types of steel experience enhanced mechanicalproperties during plastic deformation due to the formation of the martensite phase from theparent austenite phase, this is called deformation-induced martensitic transformation (DIMT).It is therefore of technical interest to study the transformation mechanism and its impact onmechanical properties for a better understanding and ultimately for developing new materialswith improved performance in certain applications. In the present thesis, two austenitic stainless steels (201Cu, HyTens® 301) and two duplexstainless steels (FDX25®, FDX27®) were investigated. Samples were tensile tested during insitusynchrotron radiation experiments performed at the Cornell High Energy SynchrotronSource (CHESS), Ithaca, USA. Tests were performed at both room temperature and at elevatedtemperatures. The collected diffraction data were then processed by software such as Fit2D andMATLAB. Quantitative phase fraction analysis based on the direct comparison method wasperformed successfully. Microstructural analysis of samples before deformation and after thefull tensile testing was also performed using electron microscopy. The deformation induced martensitic transformation took place in HyTens 301, FDX25 andFDX27, but in 201Cu the austenite was stable during the tensile tests conducted here. The a’-martensite formed in a significantly higher fraction than the ε-martensite in all alloys. At roomtemperature, the critical stress levels for martensitic transformation were 490 MPa, 700 MPaand 700MPa for HyTens 301, FDX25 and FDX27, respectively.
28
Hägerström, Helene. "Polymer Gels as Pharmaceutical Dosage Forms : Rheological Performance and Physicochemical Interactions at the Gel-Mucus Interface for Formulations Intended for Mucosal Drug Delivery." Doctoral thesis, Uppsala University, Department of Pharmacy, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3538.
Full textAbstract:
Drug delivery to the nasal and ocular mucosa faces several obstacles. One of these is from the effective clearance mechanisms present in the nose and eye. Polymer gels with suitable rheological properties can facilitate the absorption of poorly absorbed drugs by increasing the contact time of the drug with the mucosa. This has been attributed to the rheological and mucoadhesive properties of the gel. The main objective of this thesis was to investigate the importance of these features for the anticipated in vivo contact time, here exemplified by the ocular and nasal routes of administration.
The in situ gelling polymer gellan gum was found to have a favourable rheological and in vivo performance. When administered in the nasal cavity of rats, a gel was formed that could remain at the site of administration for up to 4 hours. In addition, the epithelial uptake and transfer of a 3 kDa fluorescein dextran was higher than for a mannitol solution. Therefore, it was concluded that a gellan gum formulation should be a promising strategy for nasal drug delivery.
The potential mucoadhesive properties of a variety of polymer gels were investigated using a rheological method and by measuring the tensile force required to detach the gel from a mucosa. With both methods the rheological properties of the gel were a determining factor for the results obtained. The rheological method was found to have several limitations. One of these was that a positive response, interpreted as mucoadhesion, was only seen with weak gels. The tensile method could, in contrast, detect strengthening of the mucus only for strong gels. However, this method reflects the in vivo performance of the gel better than the rheological method.
Finally, dielectric spectroscopy was explored as a tool for investigating the likelihood of intimate surface contact between the gel and the mucus layer. This novel approach involved determining the ease with which a charged particle can pass the gel-mucus interface layer, and may enable the study of the events at the interface closer to the molecular level, than is possible with the rheological and tensile strength methods.
29
Chaudemanche, Samuel. "Caractérisation in situ de l'endommagement volumique par Spectroscopie Raman et rayons X de différents polypropylènes déformés en traction uniaxiale." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0263/document.
Full textAbstract:
L'utilisation de matériaux polymères a su s'imposer au cours du 20ième siècle, en remplaçant ou se combinant aux matériaux métalliques, pour des applications mécaniques toujours plus techniques. La grande diversité des propriétés physiques des polymères est intimement lié à leur forte complexité microstructurale, qui malgré leur utilisation massive reste, au demeurant, encore très incomprise. Afin de mieux comprendre les évolutions microstructurales aux échelles nano et micrométrique dont résultent le comportement macroscopique il est nécessaire de développer de nouvelles techniques de caractérisation in situ. Ce travail fait état de l'utilisation de la spectroscopie Raman couplée au système VidéoTractionTM afin d'obtenir des informations microstructurales de la déformation de polymère semi-cristallins. Pour cela, des polypropylènes de formulations diverses ont été étudiés, permettant de souligner le rôle joué par la matrice et les charges organiques et minérales dans le processus de déformation plastique. Des mesures in situ de l'orientation des chaînes macromoléculaires déterminées in situ par Raman ont été confirmées, au synchrotron Petra III d'Hambourg, par une expérience couplant le système VidéoTractionTM-Raman à un dispositif de diffusion des rayons X aux grands angles. L'endommagent volumique des matériaux a été étudié post mortem par Tomographie X et radiographie X. Les améliorations apportées au système VidéoTractionTM-Raman ainsi qu'une étude de la diffusion de la lumière incohérente de nos matériaux au cours de leurs déformations ont permis l'établissement d'un critère de mesure de l'endommagement volumique in situ par RamanThe use of polymer materials - replacing or combining with metallic materials - has successfully established itself in the 20th century for increasingly technical mechanical applications. The great diversity of polymers physical properties is closely related to their high microstructural complexity, which is still very misunderstood despite their massive use. The development of new techniques for in situ characterization allows to better understand the microstructural evolutions on nanoscale and micrometer scale which affect the macroscopic behavior. This work report the use of Raman spectroscopy coupled with the VideoTractionTM system in order to obtain information about the microstructural deformation of polymer. Various formulations of polypropylene were studied to highlight the role played by the polypropylene matrix and the organic and mineral fillers in the plastic deformation process. The in situ measures of the macromolecular chains' orientation determined by Raman were confirmed by the performing of an experimental setup coupling the Raman-VideoTractionTM system with a device of Wide angle X-ray scattering. The volume damage of material was studied post mortem using X-ray tomography. The improvements made to VideoTractionTM-Raman system and a study of the incoherent light scattering of our materials enabled the setting of a Raman criterion for measuring in situ the volume damage. The studies carried out to evaluate in situ macromolecular orientation and volume damage highlight the existence of competition between these two processes. The degree of influence of organic and mineral fillers in this competition within the polypropylene matrix was determined
30
Ben, Hafsia Khaoula. "Identification des micro-mécanismes de déformation du PET amorphe et semi-cristallin in situ au cours d’un essai mécanique." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0081/document.
Full textAbstract:
Selon leur formulation et leur mise en forme et grâce à leur complexité microstructurale induite, les polymères thermoplastiques bénéficient d’une grande diversité de propriétés thermomécaniques. Cependant, l’évolution de la microstructure de ces matériaux au cours de leur utilisation reste difficile à identifier. Afin de mieux comprendre les modifications microstructurales ayant lieu au cours de sollicitations thermomécaniques, différentes techniques non destructives de caractérisation en temps réel et in situ ont été développées. Dans ce contexte, un Poly (Ethylène Téréphtalate) (PET) amorphe et semi-cristallin a été étudié afin de mettre en évidence l’effet de la microstructure sur les propriétés macroscopiques du matériau. Pour ce faire, plusieurs couplages de techniques expérimentales de caractérisation ont été mis en œuvre tels que la spectroscopie Raman et la diffraction/diffusion des rayons X couplées au système de VidéoTraction™ ou la spectroscopie Raman couplée à la calorimétrie différentielle à balayage (DSC) pour une caractérisation des micromécanismes de déformation et du comportement thermique du matériau respectivement. Le suivi de différentes bandes vibrationnelles judicieusement identifiées a permis d’établir un nouveau critère robuste et capable de mesurer avec exactitude le taux de cristallinité du matériau ou de remonter aux températures caractéristiques de sa morphologie (Tg, Tc, Tcc, Tf) grâce aux informations extraites d’un spectre Raman. De plus, un système de caractérisation relaxationnelle par un couplage de la spectroscopie diélectrique dynamique avec un essai de traction a été utilisé afin de mettre en évidence l’effet de la mobilité moléculaire sur la déformation élasto-visco-plastique du PET. D’un point de vue mécanique, les principaux micromécanismes de déformation ont été étudiés en temps réel pendant un essai de traction à différentes températures et vitesses de déformation vraies constantes : l’orientation macromoléculaire, l’endommagement volumique, le développement de mésophase et la cristallisation induite sous contrainte, ont été observés et quantifiés in situ en utilisant les couplages précédents au synchrotron Petra III de Hambourg et au synchrotron Elettra de Trieste. En parallèle, une étude de la mobilité moléculaire (paramètre déterminant à la prédominance de tel ou tel micromécanisme de déformation) a été menée via des analyses relaxationnelles réalisées au cours de la déformation du matériau. En complément, des expériences en temps réel, des études post mortem par les techniques précédemment citées et par radiographie X, microscopie électronique à balayage et tomographie X ont été réalisées afin d’apprécier l’influence de la relaxation mécanique du PETAccording to their formulations and forming processes and thanks to the complexity of their induced microstructure, thermoplastic polymers show a wide range of thermomechanical properties. However, the identification of the evolution of the microstructure of these materials during their use remains difficult. To better understand the microstructural changes occurring during thermomechanical loadings, various in situ and non-destructive techniques of characterization have been used. In this context, a Poly (Ethylene Terephthalate) (PET) amorphous and semi-crystalline was studied in order to highlight the effect of the microstructure on the macroscopic properties of the material. This way, different coupling systems combining several experimental characterization techniques have been implemented such as Raman spectroscopy and X-rays diffraction/scattering coupled to the VidéoTraction™ system or Raman spectroscopy coupled with differential scanning calorimetry (DSC) for the characterization of the deformation micro-mechanisms and the thermal behavior of the material respectively. Monitoring specific vibrational bands thoroughly identified allowed the establishment of a new robust criterion which enables to accurately measure the crystallinity ratio of the material and the identification of the characteristic temperatures of its morphology (Tg, Tc, Tcc, Tm). In addition, a relaxational characterization system by coupling dynamic dielectric spectroscopy to a tensile test has been used in order to highlight the effect of molecular mobility on the elasto-visco-plastic deformation of PET. From a mechanical point of view, the main deformation micro-mechanisms have been studied in real time during a tensile test at different temperatures and constant true strain rates: macromolecular orientation, volume damage, development of mesophase and strain induced crystallization were observed and quantified in situ using the coupled characterization technics presented previously at Petra III (Hambourg) and Elettra (Trieste) synchrotrons. In parallel, a study of the molecular mobility (a determining parameter for the predominance of one deformation micromechanism to another) was conducted via relaxational analysis performed during the deformation of the material. In addition to in situ experiments, post mortem analysis by the previously mentioned technics and by X radiography, scanning electron microscopy and X tomography were performed to assess the influence of the mechanical relaxation of the polymer
31
Ben, Ramdane Camélia. "Etude et modélisation du comportement mécanique de CMC oxyde/oxyde." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0077/document.
Full textAbstract:
Les CMC oxyde/oxyde sont de bons candidats pour des applications thermostructurales. Le comportement mécanique et les mécanismes d’endommagement de deux composites alumine/alumine à renforts tissés bi- et tridimensionnels ont été étudiés et comparés. La microstructure de ces CMC à matrice faible a été caractérisée à partir de porosimétrie et de CND, tel que thermographie IR, scan ultrasonore et tomographie X, ce qui a permis de mettre en évidence la présence de défauts initiaux. Le comportement mécanique en traction, ainsi qu’en compression dansle cas du CMC à renfort bidimensionnel, dans la direction des fibres ainsi que dans la direction ±45°, aété étudié à température ambiante. Afin d’exploiter pleinement ces essais, nous avons eu recours à plusieurs méthodes d’extensométrie et de suivi d’endommagement, telles que la thermographie IR et l’émission acoustique. Les propriétés mécaniques à rupture ainsi que le module de Young du CMC à renfort bidimensionnel développé à l’Onera se sont avérées supérieures à celles disponibles dans la littérature. Les mécanismes d’endommagement des matériaux ont été déterminés à partir d’observations post mortem au MEB et d’essais in situ dans un MEB, ce qui a permis d’évaluer la nocivité des défauts initiaux. Enfin, l’étude du comportement mécanique de ces composites a permisde proposer un modèle d’endommagement tridimensionnel qui permettra de poursuivre le développement de ces matériaux grâce à du calcul de structure. A l’issue de cette thèse, des pistes d’amélioration des procédés d’élaboration et de choix d’instrumentation à utiliser pour les futures études, notamment en ce qui concerne le suivi d’endommagement, ont également été proposéesOxide/oxide CMCs are good candidates for thermostructural applications. Themechanical behaviour and damage mechanisms of two alumina/alumina composites with two andthree dimensional woven reinforcements were studied and compared. The microstructure of theseweak matrix CMCs was characterized by porosimetry and NDT methods, such as IR thermography,ultrasound scanning and X-ray tomography, which highlighted initial defects. The mechanicalbehaviour was studied through tensile tests, as well as compression tests in the case of the twodimensionalreinforced CMC. These tests were conducted at room temperature, in the fibres directionsand in the ±45° direction. In order to fully exploit these tests, several extensometry and damagemonitoring methods, such as IR thermography and acoustic emission, were used. Young’s moduli andmaximum stresses and strains of the two-dimensional reinforced CMC developed at Onera appearedto be higher than those available in the literature. The damage mechanisms of the materials weredetermined by post mortem SEM observations and in situ testing in a SEM, which made it possible toassess the nocivity of initial defects. Studying the mechanical behaviour of these composites finallyenabled the development of a three-dimensional damage model that will facilitate the furtherdevelopment of such materials, through finite element analysis. Finally, some improvements regardingthe manufacturing processes and the instrumentation for damage monitoring were suggested forfuture studies
32
Kasvayee, Keivan Amiri. "On the deformation behavior and cracking of ductile iron; effect of microstructure." Doctoral thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Material och tillverkning, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-36852.
Full textAbstract:
This thesis focuses on the effect of microstructural variation on the mechanical properties and deformation behavior of ductile iron. To research and determine these effects, two grades of ductile iron, (i) GJS-500-7 and (ii) high silicon GJS-500-14, were cast in a geometry containing several plates with different section thicknesses in order to produce microstructural variation. Microstructural investigations as well as tensile and hardness tests were performed on the casting plates. The results revealed higher ferrite fraction, graphite particle count, and yield strength in the high silicon GJS-500-14 grade compared to the GJS-500-7 grade. To study the relationship between the microstructural variation and tensile behavior on macroscale, tensile stress-strain response was characterized using the Ludwigson equation. The obtained tensile properties were modeled, based on the microstructural characteristics, using multiple linear regression and analysis of variance (ANOVA). The models showed that silicon content, graphite particle count, ferrite fraction, and fraction of porosity are the major contributing factors that influence tensile behavior. The models were entered into a casting process simulation software, and the simulated microstructure and tensile properties were validated using the experimental data. This enabled the opportunity to predict tensile properties of cast components with similar microstructural characteristics. To investigate deformation behavior on micro-scale, a method was developed to quantitatively measure strain in the microstructure, utilizing the digital image correlation (DIC) technique together with in-situ tensile testing. In this method, a pit-etching procedure was developed to generate a random speckle pattern, enabling DIC strain measurement to be conducted in the matrix and the area between the graphite particles. The method was validated by benchmarking the measured yield strength with the material’s standard yield strength. The microstructural deformation behavior under tensile loading was characterized. During elastic deformation, strain mapping revealed a heterogeneous strain distribution in the microstructure, as well as shear bands that formed between graphite particles. The crack was initiated at the stress ranges in which a kink occurred in the tensile curve, indicating the dissipation of energy during both plastic deformation and crack initiation. A large amount of strain localization was measured at the onset of the micro-cracks on the strain maps. The micro-cracks were initiated at local strain levels higher than 2%, suggesting a threshold level of strain required for micro-crack initiation. A continuum Finite Element (FE) model containing a physical length scale was developed to predict strain on the microstructure of ductile iron. The material parameters for this model were calculated by optimization, utilizing the Ramberg-Osgood equation. The predicted strain maps were compared to the strain maps measured by DIC, both qualitatively and quantitatively. To a large extent, the strain maps were in agreement, resulting in the validation of the model on micro-scale. In order to perform a micro-scale characterization of dynamic deformation behavior, local strain distribution on the microstructure was studied by performing in-situ cyclic tests using a scanning electron microscope (SEM). A novel method, based on the focused ion beam (FIB) milling, was developed to generate a speckle pattern on the microstructure of the ferritic ductile iron (GJS-500-14 grade) to enable quantitative DIC strain measurement to be performed. The results showed that the maximum strain concentration occurred in the vicinity of the micro-cracks, particularly ahead of the micro-crack tip.Denna avhandling fokuserar på effekten av variationer i mikrostrukturen på mekaniska egenskaper och deformationsbeteende hos segjärn. För att undersöka dessa effekter, två olika sorter av segjärn, (i) GJS-500-7 och (ii) högkisellegerad GJS-500-14, gjutits till plattor av olika tjocklekar för att generera mikrostrukturvariationen. Mikrostrukturundersökning, samt drag- och hårdhetsprov gjordes på de gjutna plattorna. Resultaten visade att en högre ferritfraktion, grafitpartikelantal och sträckgräns i den högkisellegerade GJS-500-14-sorten jämfört med GJS-500-7. För att studera förhållandet mellan mikrostrukturell variation och spännings-töjningsbeteendet på makroskala, modellerades detta med hjälp av Ludwigson-ekvationen. De erhållna spännings-töjningsegenskaperna modellerades baserat på mikrostrukturell karaktäristika genom multipel linjärregression och variansanalys (ANOVA). Modellerna visade att kiselhalt, grafitpartikelantal, ferritfraktion och porfraktion var de viktigaste bidragande faktorerna. Modellerna implementerades i ett simuleringsprogram för gjutningsprocessen. Resultatet från simuleringen validerades med hjälp av experimentella data som inte ingick i underlaget för regressionsanalysen. Detta möjliggjorde att prediktera spännings-töjningsbeteendet och dess variation hos gjutna segjärns komponenter med liknande sammansättning och gjutna tjocklekar som användes i denna studie. För att kunna undersöka deformationsbeteendet på mikroskala utvecklades en metod för kvantitativ mätning av töjning i mikrostrukturen, genom DIC-tekniken (digital image correlation) tillsammans med in-situ dragprovning. I denna metod utvecklades en grop-etsningsprocess för att generera ett slumpvis prickmönster, vilket möjliggjorde DIC-töjningsmätning i matrisen och i området mellan grafitpartiklarna med tillräcklig upplösning. Metoden validerades genom benchmarking av den uppmätta sträckgränsen mot materialets makroskopiska sträckgräns mätt med konventionell dragprovning. Det mikrostrukturella deformationsbeteendet under dragbelastning karakteriserades. Under elastisk deformation avslöjade töjningsmönstret en heterogen töjningsfördelning i mikrostrukturen, och bildandet av skjuvband mellan grafitpartiklar. Sprickbildning initierades vid låg spänning och redan vid de spänningsnivåer som ligger vis ”knät” på dragprovningskurvan, vilket indikerar energidissipering genom både begynnande plastisk deformation och sprickbildning. Den lokala töjningen vis sprickinitiering skedde då den lokala töjningen översteg 2%, vilket indikerar att detta skulle kunna vara en tröskelnivå för den töjning som erfordras för initiering av mikro-sprickor. En kontinuum Finita Element (FE) modell utvecklades för att prediktera töjningen hos ett segjärn och dess fördelning i segjärns mikrostruktur. Materialparametrarna för denna modell optimerades genom att anpassa parametrarna i Ramberg-Osgood ekvationen. De predikterade töjningsfördelningarna jämfördes med de experimentell uppmätta töjningsmönstren uppmätta med DIC, både kvalitativt och kvantitativt. Töjningsmönstren överensstämde i stor utsträckning, vilket resulterade i att modellerna kunde anses vara validerade på mikronivå. För att kunna mäta töjningsmönster under dynamiska förlopp på mikronivå utvecklades en metod för att skapa prickmönster och att utföra in-situ CT provning i ett svepeletronmikroskop (SEM). Prickmönstret skapades genom avverkning med en fokuserad jonstråle (FIB), och provades på det ferritiska segjärnet (GJS-500-14 grad). Resultaten visade att maximal töjningskoncentration fanns i närheten av mikrosprickorna, framförallt framför sprickspetsen.
33
Barke, Derek Woolrich 1975. "An in situ test for stress corrosion damage and tension in bolts." Monash University, Dept. of Mechanical Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/7686.
Full text
34
Jousse, Florie. "Processus physico-chimiques à l'origine des différences d'efficacité des techniques de traitement de sols pollués aux hydrocarbures." Thesis, Bordeaux 3, 2016. http://www.theses.fr/2016BOR30030/document.
Full textAbstract:
De nos jours, la préservation de l’environnement est un enjeu majeur. Avant cette prise de conscience, de nombreux polluants ont été rejetés dans la nature. Parmi eux, les hydrocarbures sont très souvent rencontrés. Or, ils sont reconnus pour leur toxicité et leur persistance accrue. La mise en place de méthodes efficaces de dépollution est donc primordiale. Les méthodes classiques nécessitent l’excavation ou le pompage des zones contaminées, imposant un coût de dépollution élevé. C’est pourquoi des techniques de dépollution in-situ ont été développées afin de réduire ces coûts, tout en garantissant des rendements de dépollution efficaces. Les travaux menés durant cette Thèse ont permis de déterminer, pour plusieurs techniques de traitement, les facteurs limitants inhérents à la technique, mais aussi de quantifier le rôle du contact entre agents de traitement et zone polluée ou des effets densitaires. Les techniques in-situ utilisées sont : l’oxydation chimique in situ, le lavage par tensio-actifs, l’injection d’air (sparging) et le traitement thermique. Trois niveaux d’expérience ont été étudiés : le batch, la colonne et le pilote 3D. Les réacteurs fermés, ont permis la comparaison des oxydants en statiques face à une matrice plus ou moins riche en matières organiques. Les colonnes ont mis en avant l’influence du mode d'injection appliqué vis-à-vis des propriétés physico-chimiques des polluants (cinétique réactionnelle, pression de vapeur, température d’ébullition, etc.). Les pilotes 3D, d’un volume d’un 1 m3, ont permis de comparer les différentes techniques sur un milieu hétérogène présentant des zones peu perméables, difficiles à traiter. A partir des résultats acquis et de modélisation numérique des expériences, il est dorénavant possible de mieux ajuster la méthode de traitement et surtout de comparer différentes méthodes pour un contexte hydrogéologique donnéPollution of soils and aquifers by Diesel fuel compounds is a widespread remediation issue. Problems due to soil remediation are more and more difficult to treat. Hydrocarbons are often encountered. But they are known for their toxicity and increased persistence. The establishment of effective remediation methods is paramount. Conventional methods require excavation or pumping contaminated areas requiring a high abatement costs. That is why, in-situ remediation techniques have been developed to reduce these costs while ensuring efficient pollution control returns. The work done during this thesis has determined for several treatments, the limiting factors inherent the treatment, but also quantifies the role of contact between agents and pollutants or density effects. In-situ treatments are: in situ chemical oxidation, surfactants flushing, air sparging and thermic treatment. Three levels of experience were investigated: batch, column and 3D Pilot. Batchs, enabled the comparison of oxidants in sand and natural soil. The columns have highlighted the influence of the injection method applied occurs toward the physical and chemical properties of contaminants (reaction kinetics, vapor pressure, boiling temperature, etc.). 3D Pilot, have a volume of 1m3. They were used to compare the different treatments on a heterogeneous medium having low permeability zones, difficult to treat. From the results of numerical modeling and experiences, it is possible to adjust the treatment method and especially to compare different methods for a given hydrogeological context
35
Khosravani, Ali. "Application of High Resolution Electron Backscatter Diffraction(HR-EBSD) Techniques to Twinning Deformation Mechanism in AZ31 Magnesium Alloy." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3432.
Full textAbstract:
The application of high resolution electron backscatter diffraction (HR-EBSD) techniques has been used in order to study the evolution of geometrically necessary dislocation (GND). The tested materials were taken from AZ31 magnesium sheet which had strong basal texture. Because of low symmetry of the magnesium crystal lattice, the von Mises criteria cannot be satisfied by the three independent, easily activated, basal slips. The strain along the c-axis of the crystal must be accommodated by either twinning and/or slip systems. HR-EBSD data was taken in order to investigate these phenomena. The HR-EBSD results were post processed in order to resolve total GND density onto the observed possible slip systems. The first chapter of the investigation focused on the correlation between resolved GNDs with tensile twin nucleation, and the subsequent propagation path in the microstructure. For this purpose, 2.5 % strain was applied in a uniaxial compression test along the transverse direction (TD). Several fine scan were done at the boundaries where twin formed. The results show that in order for a twin to nucleate spontaneously at the grain boundaries, two criteria should generally be met: high angle grain boundaries (35-45°) and pile ups of basal slip system in neighboring grain at the other side of the boundary. Furthermore, once nucleation has initiated, twin propagation can occur through low angle grain boundaries (15-25°); if a twin reaches a high angle boundary, it will generally terminate at the boundary at low strain levels. A twin may pass through high angle boundaries with further deformation. In the second chapter, deformation of the AZ31 magnesium alloy was study for different strain paths. For this purpose, compression and tension in-situ tests were done and the texture and GND evolutions were investigated. The results show that the load paths, compression and tension, evolve the microstructure in different ways. Massive twin fractions were formed in compression, and higher GND contents were observed in tension tests. It was observed that at higher strain levels GND contents are roughly independent of the initial texture but the activation of slip systems at low strain strongly depends on initial structure. If the samples were loaded along RD, GND density increased sharply at low strain. In contrast, for the samples loaded along TD, GND increased moderately. A small amount of repetition is apparent in the two parts of the thesis due to them being formatted for individual publication as journal papers.
36
Hutin, Anthony. "Interactions entre molécules amphiphiles in situ et tensioactifs synthétiques pour la récupération d'huile réactive." Paris 6, 2013. http://www.theses.fr/2013PA066395.
Full textAbstract:
Ce travail concerne la compréhension des interactions entre les tensioactifs naturels du brut (endogènes) et les tensioactifs synthétiques ajoutés dans le cadre de la récupération assistée du pétrole (EOR). Un brut réactif contient des molécules amphiphiles, asphaltènes et acides naphténiques, qui agissent comme des tensioactifs naturels en présence d'interface. Lors d'une opération EOR, la valeur du pH influe sur l'ionisation des fonctions acides et/ou basiques des tensioactifs naturels du brut les rendant globalement beaucoup plus hydrophiles ce qui augmente leur affinité pour l'interface. Nous avons montré qu'il existe une forte interaction entre un tensioactif anionique sulfoné (SDBS) et les tensioactifs in situ d'un brut lourd acide. Des tensions interfaciales ultra-basses (<10-3 mN/m) ont été obtenues à pH 11 avec un faible ajout de SDBS (~0,05 wt%). Différentes dynamiques de tensions interfaciales ont été mesurées en présence de SDBS aux pH extrêmes avec des effets transitoires importants. Ces effets sont le résultat du transfert des molécules du brut vers l'eau. Les transferts de masse des molécules amphiphiles du brut ont été mis en évidence par la mesure du pH de la phase aqueuse en contact avec le brut. En absence de SDBS, nous observons également le transfert des bases du brut à pH acide. Avec la prise en compte du comportement acido-basique du brut, nous avons mis au point un modèle qui permet de prédire l'évolution du pH final d'un solution aqueuse en contact avec une huile acido-basique en fonction des différents paramètres (acidité, pka,. . . )This work deals with the understanding of interactions between in situ (or indigenous) surfactants and added synthetic surfactants for Enhanced Oil Recovery (EOR). Heavy crude oils contain amphiphilic moclécules, such as asphaltenes and naphthenic acids, wich ar natural surfactants. Durinf an EOR operation, pH influences the ionization of acidic and/or basic species of crude oil making thm more hydrophylic that inscreases their affinity for the interface. In this study, we showed that there is a strong interaction between a sulfonated anionic surfactant (SDBS) and in situ surfactant of an acidic heavy oil. Ultra-low interfacial tensions (<10-3 mN/m) were obtained at pH 11 with a small addition of SDBS (~0,05 wt%). Different dynamics of interfacial tensions were measured in the presence of SDBS for extreme pH with significant transient effects. These are the result of transfers of molecules from crude oil to water. Mass transferrs of amphiphilic molecules from crude oil were highlighted by measuring the pH of the aqueous phase in contact with crude oil. Without SDNS, crude oil act as an acid oil with the transfer of acids at basic pH. In the presence of SDBS, we also observe the transfer of bases of crude oil at acidic pH. Taking into account the acid-base behavior of crude oil, we developed a model to predict the evolution of the final pH of an aqueous solution in contact with an acid-base oil according to different parameters (acidity, pka,. . . )
37
Pinho, Marco André de Berredo. "Efetividade in situ do Chlor-Xtra na dissolução do tecido pulpar em canais radiculares ovais." Universidade do Estado do Rio de Janeiro, 2013. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=6694.
Full textAbstract:
O objetivo deste estudo foi avaliar a dissolução do tecido pulpar pelo NaOCl contendo em sua composição agentes redutores da tensão superfical (Chlor-Xtra) quando comparados ao NaOCl convencional. Com esta finalidade 44 dentes unirradiculares humanos com tecido pulpar preservado em solução de formol a 10% foram agrupados em 22 pares de acordo com a semelhança de sua anatomia interna previamente avaliada por radiografias. Os canais foram instrumentados com sistema Protaper Universal e todo o processo de irrigação teve, além do tempo, seu volume e fluxo controlado por meio automatizado por meio do sistema Vatea Endodontic Iirrigation Device. Após cada canal que compunha um par ter sido instrumentado empregando-se uma das diferentes soluções testadas, as quais foram previamente avaliadas quanto a sua tensão superficial, ambos foram devidamente preparados e enviados para processamento e análise histológica. Cortes a 0,5, 1,2,3 e 4mm do ápice foram realizados, corados e fotografados. As imagens foram analisadas por meio do programa AxioVision a fim de estabelecer o percentual de tecido remanescente em relação à área total do canal nos segmentos estudados. As análises referentes a tensão superficial revelaram que o Chlor-Xtra demonstrou possuir significativamente menor tensão superficial quando comparado ao NaOCL convencional (p>0,05). A análise estatística por meio do test T student das áreas dos canais, demonstrou que o pareamento das amostras foi eficiente entre os grupo NaOCl e Chlor-Xtra (p>0,05). Em relação ao Percentual de Tecido Remanescente (PTR), os resultados revelaram por meio de análise feita pelo teste Kruskal-Wallis e o teste de correlação de Spearman que o nível de corte influencia significantemente o PTR (P<0,05).Por fim, o teste de Mann-Whitney indicou que o PTR não é influenciado pela solução irrigadora utilizada (P>0,05). A partir da análise dos resultados foi possível concluir que quanto mais apicalmente foi o nível de corte histológico dos canais estudados, maior foi o percentual de tecido pulpar remanescente independentemente da solução utilizada, portanto.não houve diferença significativa na qualidade do debridamento produzido pelas duas soluções testadas, desta forma indicando que a presença de agentes modificadores da tensão adicionados ao NaOCl não foi capaz de superar os resultados obtidos por soluções de NaOCl convencionais.Sodium hypochlorite solutions with added wetting agents are advertised to dissolve necrotic tissue in root canals faster than counterparts without lowered surface tension. This was tested in the current study using extracted, single-rooted teeth with oval canals that contained pulp tissue. Formerly vital extracted teeth (N = 44) with similar anatomy were radiographically paired and chemomechanically prepared. In one tooth, a 5.25% NaOCl solution with reduced surface tension was used, in the other a pure, technical-grade NaOCl solution of 5.25%. Percentage of remaining pulp tissue (PRPT) was histologically assessed in root cross-sections. The non-Gaussian raw data was subjected to Kruskal-Walis and Mann-Whitney U tests to verify the respective effect of level of cross-section and solution on the PRPT.The relationship between level of cross-section and PRPT was estimated by Spearman correlation test. Alpha-type error was set at 5%. The level of section significantly influenced the PRPT (P<0.05), whereas the PRPT was not influenced by the solution used (P>0.05). A significant inverse correlation was found between the level of section and PRPT (P<0.05, r = -0.330). The lower the distance to the apex, the higher the PRPT, regardless of the solution used.Contrary to the advertised statement, the dental solution with reduced surface tension did not dissolve vital pulp tissue in oval root canals any better than a conventional NaOCl solution of similar strength. Closer to the apex, pulp tissue dissolution is less efficient, irrespective of the solution.
38
Djeridi, Ikram. "Biodégradation des Hydrocarbures en milieux hypersalins : modes de transferts et réponses des communautés procaryotiques à une contamination pétrolière." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4053.
Full textAbstract:
Le devenir des hydrocarbures (HC) dans les environnements hypersalins constitue une problématique environnementale majeure. Ce travail pour objectifs (1) d’évaluer l’impact d’une pollution pétrolière sur les communautés microbiennes d’un milieu hypersalin, (2) de déterminer comment les archées hydrocarbonoclastes accèdent aux HC et, (3) de déterminer si la biodégradation est possible en conditions anaérobies dans ces environnements hypersalés. Nous avons démontré qu’une biodégradation modérée du pétrole est possible en milieu hypersalin environ 10 % de la fraction aliphatique du pétrole sont biodégradé. Une disparition progressive des composés aromatiques les plus légers est également observée, liée aux processus abiotiques. La dynamique des communautés procaryotiques montre un changement dans la structure de la communauté bactérienne autochtone des saumures. Une résistance à la contamination pétrolière a en revanche été observée pour les communautés archéennes des saumures. Dans une deuxième partie du travail, nous avons pu montrer, à l’aide d’une souche d’archée hyperhalophile modèle (Haloferax volcanii MSCN14), que les archées hydrocarbonoclastes de ces environnements mettent en oeuvre plusieurs mécanismes leur permettant d’augmenter la biodisponibilité des HC. Dans une dernière partie des travaux, nous avons testé les capacités d’une souche modèle (Hfx. volcanii MSNC 16) à dégrader les HC en anaérobiose. Si Hfx. volcanii MSNC16 est bien capable d’utiliser le fumarate comme accepteur terminal d’électrons, elle n’est en revanche pas capable de dégrader l’alcane testé (heptadécane) en absence d’oxygèneThe fate of hydrocarbons (HC) in hypersaline environments is an important environmental issue. This work aimed to (1) assess the impact of oil pollution on microbial communities of a hypersaline environment, (2) determine how hydrocarbonoclastic archaea can access to HC and (3) whether biodegradation is possible in these hypersaline environments in the absence of oxygen. We have shown that moderate oil biodegradation is possible under hypersaline conditions. In these conditions close to natural ones, about 10% of the aliphatic hydrocarbons were biodegrade. A gradual disappearance of the lighter aromatic compounds was also observed, but these losses were mainly due to abiotic processes. The monitoring of prokaryotic communities based on molecular fingerprints showed a change in the structure of the indigenous bacterial community. On the contrary, resistance to oil contamination was observed among the indigenous archaeal communities of brines. In the second part of this work, laboratory cultures of a hyperhalophilic archaeal strain (Haloferax volcanii MSCN14), allowed to demonstrate that, in hypersaline environments, hydrocarbonoclastic archaea use several strategies to increase the bioavailability of HC. Indeed, strain MSCN14 was capable of producing one or several biosurfactants during growth on different HC, and was adhering to the surface of the HC. In the last part of this work, we tested the capacities of a model archaeal strain (Hfx. volcanii MSNC 16) to degrade HC anaerobically. If Hfx. volcanii MSNC16 was able to use fumarate as a terminal electron acceptor, it was, however, not capable of degrading heptadecane in the absence of oxygen
39
Venturi, Linda. "Etude des propriétés de photoluminescence de nano-matériaux sous champ électrique intense." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR118.
Full textAbstract:
Dans cette thèse, la tomographie à sonde atomique assistée par laser est couplée in situ à un banc de photoluminescence (PL), où le rayonnement laser pulsé est utilize pour déclencher l’évaporation ionique des échantillons et, simultanément, pour activer l’émission à partir des centres optiquement actifs présents dans le matériau. Pour ce travail, deux matériaux différents ont été sélectionnés : des nano-aiguilles de diamant avec des défauts optiquement actifs intégrés (centres de couleur) et une hétérostructure multi-quantique (MQW) ZnO / (Mg, Zn)O, qui contient des émetteurs quantiques d’épaisseurs différentes. Grâce à cette configuration originale de photoluminescence, l’influence du champ électrique sur la structure fine de certains centres de couleur, noyés dans les nano-aiguilles de diamant, a été observée. La première étude s’est concentrée sur le centre neutre de vacance d’azote (NV0), qui est l’un des centres de couleur les plus étudiés dans la littérature. L’évolution de la signature optique NV0, en fonction du biais appliqué, a permis d’évaluer la contrainte mécanique (> 1 GPa) et le champ électrique agissant sur les pointes de diamant. Ces résultats démontrent une nouvelle méthode originale pour effectuer la piezo-spectroscopie sans contact des systems nanométriques sous une contrainte de traction uniaxiale, générée par le champ électrique. Cette méthode a également été appliquée à un autre centre de couleur, dont la nature n’est toujours pas claire dans la littérature, émettant à 2,65 eV, et plus sensible que les centres de couleur NV0 au champ de contrainte / déformation. Des nouveaux résultats sur ses propriétés opto-mécaniques ont été obtenus, mais son identité reste à comprendre. Le champ d’évaporation du diamant étant très élevé, les nano-aiguilles de diamant n’ont pas été analysées à l’aide de La-APT. Par conséquent, la technique couplée in situ a été appliquée afin d’étudier l’hétérostructure ZnO / (Mg, Zn) O MQW, en accédant à la structure, à la composition et à la signature optique de l’échantillon sondé dans une seule expérience. Les spectres de photoluminescence acquis par le spécimen au cours de son évaporation en cours représentent une source unique d’informations pour la compréhension du mécanisme de l’interaction lumière-matière et la physique de la photoémission sous champ électrique élevé. La corrélation des informations structurelles et optiques, liées à cette hétérostructure MQW, démontre que la technique couplée in situ peut chevaucher la limite de diffraction du laser PL et que, comme pour les nano-aiguilles de diamant, il est possible d’estimer le stress de traction induit. Les résultats obtenus par couplage in situ de la technique La-APT avec la spectroscopie PL montrent qu’un tel instrument est une technique innovante et puissante pour effectuer des recherches à l’échelle nanométrique. Pour cette raison, ce travail peut ouvrir de nouvelles perspectives pour une compréhension approfondie de la physique liée aux systèmes étudiés en parallèle avec l’amélioration continue de la configuration expérimentaleIn this thesis, the Laser-assisted Atom Probe Tomography is coupled in-situ with a photoluminescence (PL) bench, where the pulsed laser radiation is used to trigger the ion evaporation from the specimens and, simultaneously, to activate the emission from optically active centers present into the material. For this work, two different materials were selected: diamond nano-needles with embed- ded optically active defects (color centers) and a ZnO/(Mg,Zn)O multi-quantum-well (MQW) heterostructure, which contains quantum emitters of different thicknesses. Thanks to this original photoluminescence setup, the influence of the electric field on the fine structure of some color centers, embedded into the diamond nanoneedles, was observed. The first study focused on the neutral nitrogen-vacancy center (NV0), which is one among the most studied color centers in literature. The evolution of the NV0 optical signature, as a function of the applied bias, allowed to evaluate the mechanical stress (> 1 GPa) and the electric-field acting on diamond tips. These results demon- strate an original new method to perform contactless piezo-spectroscopy of nanoscale systems under uniaxial tensile stress, generated by the electric field. This method was applied also on another color center, which nature is still not clear in literature, emitting at 2.65 eV, and more sensitive than the NV0 color centers to the stress/strain field. New results on its opto-mechanical properties were obtained, but its identity still needs to be understood. Since the evaporation field of diamond is really high, the diamond nanoneedles were not analyzed using La-APT. Therefore the coupled in-situ technique was applied in order to study the ZnO/(Mg,Zn)O MQW heterostructure, accessing to the structure, composition and optical signature of the probed specimen in only one experiment. The photoluminescence spectra acquired by the specimen during its ongoing evaporation represents a unique source of information for the understanding of the mechanism of light-matter interaction and the physics of photoemission under high electric field. The correlation of the structural and optical information, related to this MQW heterostructure, demonstrates that the coupled in-situ technique can overlap the diffraction limit of the PL laser and that, as done for the diamond nanoneedles, is pos- sible to estimate the induced-tensile-stress. The results achieved by the in-situ coupling of the La-APT technique with the PL spec- troscopy show that such instrument is an innovative and powerful technique to perform research at the nanometric scale. For this reason, this work can open new perspectives for a deeply understanding of the physicics related to the studied systems in parallel with the continuous enhancement of the experimental setup
40
Park, Janghoon, Hyi Jae Kang, Hyogeun Gil, Kee-Hyun Shina, and Hyunkyoo Kang. "Roll-to-roll infrared and hot-air sintering of gravure-printed Ag layer based on in situ tension measuring and analysis." Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-222812.
Full textAbstract:
This study presents a method developed to achieve the roll-to-roll sintering of printed Ag patterns based on exposure to hot air, near-infrared, and mid-infrared sources. The sintering energy was quantified and evaluated based on theoretical and experimental calculations. Moreover, the effect of the sintering energy on the web tension was simultaneously consideredDieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
41
Shaoguang, Chen. "Experimental Investigation on Mechanical Properties of Nanospring Thin Films Fabricated by Glancing Angle Deposition Technique." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225556.
Full text
42
Guérin, Jean-Dominique. "Analyse des essais de compression et de traction des aciers après solidification in situ et des essais d'indentation des aciers phosphatés." Valenciennes, 1993. https://ged.uphf.fr/nuxeo/site/esupversions/b769f69b-4777-454d-94ad-c3bac6b6fab1.
Full textAbstract:
La mise en forme à chaud et à froid des aciers est étudiée avec deux types d'expérimentations : les essais à hautes températures des aciers juste après leur solidification et les essais à température ambiante des aciers phosphates. Le premier type d'expérimentation consiste à mener un essai de compression ou de traction à vitesse de traverse constante sur des éprouvettes, cylindriques pour l'essai de compression et axisymétriques à entaille circulaire pour l'essai de traction, en acier solidifie in situ. Il s'agit a partir des données expérimentales de caractériser le comportement de l'acier solidifie in situ teste. Une procédure d'essai est donc proposée et des modélisations analytiques permettent, d'une part, de déterminer le comportement élasto-thermo-viscoplastique de l'acier solidifie et, d'autre part, d'évaluer les contraintes et déformations caractéristiques dans les zones de l'éprouvette d'essai propices a l'apparition de criques. La comparaison des résultats obtenus analytiquement et par éléments finis, pour des essais de référence sur deux types d'acier, montre que les analyses proposées sont suffisamment précises pour identifier efficacement le comportement de l'acier solidifie situ. Le deuxième type d'expérimentation consiste à mener un essai d'indentation rotation sur une éprouvette cylindrique revêtue d'une ou plusieurs couches de frottement en phosphate ou stéarate de zinc. La spécificité du contact indenteur éprouvette durant la phase d'indentation de l'essai requiert une modélisation adéquate pour étudier le comportement de l'éprouvette sous la zone de contact. Un modèle par éléments finis local au contact est donc construit et des calculs sont menés pour des cas typiques de revêtements phosphates. Ce modèle par éléments finis s'avère apte à déterminer efficacement les répartitions de contraintes et de déformations dans l'éprouvette et il est ainsi opérationnel pour prédire l'efficacité du revêtement sans procéder à l'expérimentation.
43
Ornek, Cem. "Performance characterisation of duplex stainless steel in nuclear waste storage environment." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/performance-characterisation-of-duplex-stainless-steel-in-nuclear-waste-storage-environment(4db73e9b-c87c-40a6-9778-0b823b1c499f).html.
Full textAbstract:
The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.
44
RATHOD, CHANDRASEN. "DIFFRACTION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS AND SELECTED ENGINEERING COMPONENTS." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2892.
Full textAbstract:
Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
45
Fnaiech, Mustapha. "Contribution a l'etude "in situ" du glissement et de la montee des dislocations dans un compose semiconducteur (3/5) : insb." Toulouse 3, 1987. http://www.theses.fr/1987TOU30070.
Full textAbstract:
La these se compose de deux parties : etude du glissement des dislocations dans insb et etude de leur montee sous irradiation aux electrons. Le glissement est etudie par microscopie electronique. Mesure de la vitesse des dislocations et de la contrainte locale et comparaison avec les resultats obtenus par d'autres methodes. D'autre part, observation de l'apparition et de la croissance de defauts sous irradiation des electrons de 1 mev, dans un microscope a haute tension
46
MotsI, Glenda Tsholofelo. "In-situ scanning electron microscopy studies on the uniaxial tensile deformation mechanisms in Aluminium alloy 5083." 2014. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001710.
Full textAbstract:
M. Tech. Metallurgical Engineering.Aims to study tensile deformation mechanisms of aluminium alloy 5083 using in situ SEM techniques. The objectives to achieve this aim are: to investigate the effect of strain rate on mechanical properties ; investigating anisotropy mechanical properties at varying strain rates ; investigating microstructure anisotropy behaviour at varying strain rates and to investigate the influence of intermetallic particles during tensile deformation.
47
(11154630), George A. Warren. "Deformation Mechanisms in Unirradiated and Irradiated Iron Chromium Aluminum Identified by TEM in situ Tensile Testing." Thesis, 2021.
Find full textAbstract:
FeCrAl alloys are being investigated as candidate materials for replacing zirconium based alloys as nuclear reactor fuel cladding because of their superior high temperature oxidation resistance in steam environments. Unirradiated FeCrAl as well as Fe2+ ion irradiated FeCrAl to a peak dose of 20DPA were mechanically tested and compared against each other. Nanohardness tests were performed on both the unirradiated and irradiated conditions and it was found that the irradiated alloy was about 1GPa harder than its unirradiated counterpart. TEM in situ tensile tests were performed using the Bruker push to pull device alongside a PI95 Picoindenter on single crystals with grain orientations 001, 011 and 111. The unirradiated 001 grains tended to fail without yielding in a brittle manner while the irradiated 001 grain yielded and reached an ultimate tensile strength before failure. The unirradiated 011 grains behaved in a mixed manner, where one failed without yielding and one slipped many times before failing. The irradiated 011 grain yielded and failed quickly thereafter. The unirradiated 111 grain yielded, slipped and twinned before failing and both irradiated 111 grains slipped. Two general trends were observed. One, each unirradiated single grain was stronger than its irradiated counterpart. This trend is indicative of the ion irradiated microstructure facilitating bulklike mechanical behavior in the irradiated samples whereas the unirradiated samples exhibited mechanical size effects due to either the total lack of preexisting defects or the ability for existing defects to escape easily to the surface of the sample resulting in a pristine, defect free sample. Two, regardless of irradiation condition, the 001 grain orientation was brittle, the 011 grain orientation deformed in a mixed brittle/ductile manner and the 111 grain orientation was ductile through all tests. These results are indicative of the geometry of the BCC crystal structure and the slip system involving these orientations.
48
Mo°scicki, Marcin [Verfasser]. "In situ diffraction analysis of single grain behaviour during tensile straining of polycrystals / von Marcin Mościki." 2010. http://d-nb.info/1007453885/34.
Full text
49
Pantano, Maria, Leonardo Pagnotta, Horacio Espinosa, and Sergio Rizzuti. "Design and application of a novel microelectromechanical system for in situ SEM/TEM displacement controlled tensile testing of nanostructures." Thesis, 2012. http://hdl.handle.net/10955/1187.
Full textAbstract:
Scuola di Dottorato "Pitagora" Scienze Ingegneristiche, Dottorato di Ricerca in Ingegneria Meccanica Ciclo XXV, a.a. 2011-2012Since the 1920s, different methodologies have been developed especially for mechanical characterization of material samples with characteristic length on the order of micro/nanometers. In the present manuscript, the main of such methodologies are presented and compared, in order to provide guidelines for mechanical characterization at the micro/nanoscale, and to identify the most versatile and effective among them. These are based on complete and miniaturized tensile testing stages, developed on proper microelectromechanical systems (MEMS). Because of their small size (they lie onto silicon wafers with area smaller than 1mm2 and thickness of only few micrometers), such testing devices are particularly suitable to handle micro/nanosized components, and can fit inside the tight chamber of scanning/ transmission electron microscopes (SEM/TEM), for real-time imaging of sample deformation. However, the effectiveness of the tests they allow to perform can be compromised by some disturbing phenomena, like onset of instability, as reported in a certain kind of tensile testing devices. In particular, these devices become unstable as soon as the sample under investigation shows stress relaxation, after some strain has been applied. Nevertheless, it is very important to be able to detect such singularities, since they may allow a deeper comprehen sion of materials’ behavior. In the present work, the above mentioned instability issue is overcome through the design of a novel device for in situ SEM/TEM tensile testing of nanostructures under true displacement control. Like other stages, also the one presented herein consists of two main components: an actuator and a sensor, which are separated by a small gap for positioning of the specimen. Actuation is performed by a thermal actuator, which pulls the end of the sample attached to it. The other end of the sample is instead connected to a displacement sensor, which moves from its equilibrium position, as a consequence of the force transmitted to it by the specimen. However, the main novelty of the present design is the introduction of a feedback control loop. In particular, a controller, implemented within a software routine, receives as input the sensor output, and computes the voltage to be applied to an electrostatic actuator, in order to generate a rebalance force of electrostatic nature, thus bringing the sensor back to equilibrium. In this way, the end ofand this boundary condition removes any potential source of instability. The MEMS sensing and actuating structures were designed by the means of both analytical and numerical approaches, in order to provide sufficiently high deformation (up to about 50% strain) and forces (up to 100μN) to break a variety of material samples. Fabrication was carried out by an external foundry on the basis of the masks drawings, reported in the present manuscript. In order to guarantee a correct functioning of the device, a proper experimental apparatus was developed. This allowed electrical connection of all of the actuating and sensing parts with external instrumentation, including current pre-amplifiers, power supplies, a lock-in amplifier, and a data acquisition card, which was used as interface between the controller and the MEMS device. The effectiveness of the present experimental apparatus was proven through an application on silver nanowires, with about 70 nm diameter and 3-4 μm gage length. The corresponding results, in terms of Young modulus, fracture and yield strength, showed good agreement with data already available in the literature, obtained for samples with comparable size. Also the device ability to detect singularities in the sample characteristic was demonstrated, as emerges from a load drop recorded after yielding of a nanowire. As a conclusion, the present experimental apparatus can be considered for future in situ SEM/TEM tensile tests on other material samples, as well as for electromechanical tests, since the specimen results to be electrically isolated from the remaining of the device. Thus, very interesting properties, like piezoresistivity and piezoelectricity, could be evaluated.
Università degli Studi della Calabria
50
Tahir, Muhammad. "Development of Novel Blends based on Rubber and in-situ Synthesized Polyurethane-urea." Doctoral thesis, 2017. https://tud.qucosa.de/id/qucosa%3A30765.
Full textAbstract:
Polyurethane and the analogous ‘polyurethane-urea’ are high performance polymeric materials having remarkable properties such as high stiffness, abrasion and tear strengths. In many studies, the low strength rubbers have been blended with various types of polyurethanes for new and improved materials. However, until now, the reported heterogeneous blends offer only a narrow temperature range of application due to the high temperature softening of their polyurethane (-urea) phase. In addition, the conventional solution-or melt-blending methods are time and energy intensive, which tend to forfeit the economical realization of the reported blends. In contrast to earlier studies, a simplified reactive blending process is suggested to synthesize polyurethane-urea via a prepolymer route during blending with rubbers to obtain novel elastomeric materials having extended performance characteristics.
The reactive blending process is opted to prepare blends based on nitrile butadiene rubber (NBR) and in-situ synthesized polyurethane-urea (PUU). The blending is carried out in an internal mixer at a preset temperature of 100°C. The critical temperatures of the reactive blending process are determined from the chemo-rheological analysis of a premix, composed of a 4,4′-diphenylmethane diisocyanate (MDI)/polyether (PTMEG) based prepolymer admixed with 1,3-phenylene diamine (mPD). The prepared NBR/PUU blends exhibit highly improved mechanical properties. Contrary to previous reports, the reinforced dynamic-mechanical responses of the novel blends remain stable till very high temperatures (≥180°C).
The influence of diamine type on the in-situ synthesized polyurethane-urea and the performance of prepared blends are investigated. Four different diamines, namely 1,3-Phenylene diamine, 1,4-Bis(aminomethyl)benzene, 4,4′-Methylene-bis(2-chloroaniline) and 4,4ʹ-(1,3-Phenylenediisopropylidene)bisaniline, are selected to chain extend the prepolymer to PUU during blending with NBR. The chemical and domain structure of the PUUs are found to greatly influence the reinforced tensile and dynamic-mechanical responses of the NBR/PUU 70/30 blends.
The PUU (based on MDI/PTMEG prepolymer and mPD) is blended with polar (CR, XNBR) and nonpolar (NR, EPDM, sSBR) rubbers. PUU compatibilizes with all the rubbers irrespective of their polarity and reinforces their tensile and dynamic-mechanical characteristics. The use of blends in industrial applications, for example, in a truck tire tread compound and as a roller covering material, is examined. In a simplified tire tread formulation, the carbon black for NR-CB composite is partially replaced with an equivalent quantity of PUU for NR/PUU-CB composite of similar hardness. The dynamic mechanical investigations reveal that the energy dissipation and strain dependent softening is high in NR-CB as compared to the NR/PUU-CB composite. In another application, NBR/PUU blend is successfully tested as a rubber roller covering material. The tested blend-covered roller retains its structural integrity and develops less heat build-up as compared to the silica filled NBR-covered roller. This shows a substantial suitability of the blend-covered rollers for film, printing and textile processing machinery.
These novel blends are considered to be the promising new materials for many commercial applications including wheels, rubber rollers, belts or pump impellers.