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Holzer, Jakub. "Měření mechanických vlastností tenkých vrstev metodou bulge test." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-387730.
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Main objective of this diploma thesis is to finish a construction of the Bulge test apparatus for measurement of thin films, perform first tests on commercially available Si3N4 membranes and bilayer membrane with aluminium. First part of the thesis is focused mainly on literature review of current knowledge regarding this topic and other methods of thin films testing. Experimental part deals with construction of apparatus, methodology of data evaluation and results of the measurement. The thin films of interest are fabricated as amorphous silicon nitride or bilayer of mentioned nitride and either aluminium, titanium or Ta-B-C layer. The apparatus has been built in house in collaboration with Institute of Scientific Instruments of CAS. Both reliability and repeatability of this method has been tested on over 160 measurements of commercially available membrane. The results of measurements are compared with literature and nanoindentation test. More detailed data analysis is currently under development with colleagues at Institute of Physics of Materials. It has been proven beyond doubt that Bulge test method and constructed apparatus are suitable for the measurement of several mechanical properties of thin films.
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Valášek, Daniel. "Stanovení mechanických charakteristik povlaků impulsní excitační metodou." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442844.
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This diploma thesis deals with the determination of the Young’s modulus of coatings using the impulse excitation technique (IET). The theoretical part of the thesis describes Cold and Thermal Spray technology, theoretical foundations of the impulse excitation technique and models of composite materials. The experimental part of the thesis deals with the determination of the tensile modulus of copper coating created by Cold Spray technology. The impulse excitation technique has been used to measure fifteen samples with coating thickness ranging approximately from 0,4 to 2 mm. Results from this measurement were evaluated using five composite models to establish the Young’s modulus of the applied coating. The best results were achieved by using the composite model based on rule of mixtures (ROM).
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Colom, diego Adai. "From eye lens cells to lens membrane proteins : Development and application of a hybrid high-speed atomic force microscopy/optical microscopy setup." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4033.
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Je utilise le AFM et le HS-AFM pour étudier les caractéristiques mécaniques du cellule du cristallin et aussi des protéines de membrane de la cellule, AQP0 et Connexon. L’énergie d'interaction de la AQP0 est -2.7 kBT, très nécessaire pour former les microdomaines de jonctions (junctional microdomain). Aussi c' est la première fois qu il est possible de voir des protéines individuel et son mouvement en cellules vivants. La formation de microdomaines est important pour la transparence du cristallin, et le AQP1 ne le peux faireI used the AFM and HS-AFM for characterise the eye lens and the eye lens membrane protein, AQP0 and connexon.A QP0-AQP0 interaction energy is -2.7kBT, it is important for the formation of junctional microdomains, which keep the distance between the cells lens and lens transparency. this is the first report which is present time the visualization of unlabelled membrane proteins on living cells under physiological conditions. AQP1 can not maintain the lens transparency because it does not form junctional microdomains
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Gupta, Mohit Kumar. "Design of Thermal Barrier Coatings : A modelling approach." Doctoral thesis, Högskolan Väst, Avd för maskinteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-7181.
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Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating's final thermal and mechanical properties, and the service lives of the coatings. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.
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Ševc, Jan. "Studené asfaltové směsi s R-materiálem." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-240090.
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The thesis is focused on the use of R-material into cold asphalt mixtures. It deals with cold recycling and with input materials for this technology. It verifies properties of R-material and residues of bituminous binder. It also verifies properties of designed cold asphalt mixtures by the probative controls (indirect tensile strenght and water resistance). Furthermore is focused on the experimental measurement of selected mixtures to ensure more characteristics. The amount of homogenity of R-material, quantity and quality of residues bituminous binder is essential for positive results.
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Quince, Zachery. "Optical coherence elastography for the measurement of anterior segment biomechanical properties." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/236255/2/Zachery%2BQuince%2BPhD%2BThesis%282%29.pdf.
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This thesis developed a novel optical coherence elastography method to characterise tissue biomechanical properties in the anterior eye. The developed method applies a static force to deform the tissue and combines optical coherence tomography imaging with image processing to track the deformation and extract tissue mechanical properties. This project represents the first step towards developing a clinically viable method to comprehensively measure the mechanical properties of the anterior segment of the eye.
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Tarabeux, Justine. "Prédiction de la polymération et des propriétés mécaniques de pièces céramiques élaborées par stéréolithographie - Optimisation du procédé." Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0111.
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Ces travaux de thèse portent sur la maîtrise des caractéristiques dimensionnelles et mécaniques de pièces céramiques obtenues par stéréolithographie. L’objectif est d’être capable de prédire ces caractéristiques afin d’obtenir des pièces conformes dès la première fabrication. La stratégie a été de développer un modèle de simulation numérique capable de prédire l’exposition, la profondeur et la demi-largeur de polymérisation, ainsi que le module d’Young des pièces crues obtenues en fonction des paramètres du procédé. Ce modèle numérique intègre le phénomène de diffusion et est calibré pour chaque système à l’aide d’essais expérimentaux. Afin de pouvoir accéder aux propriétés élastiques effectives des pièces crues, un modèle de simulation par calculs éléments finis couplé à la technique d’homogénéisation a été développé. Ce modèle a été validé en comparant les résultats obtenus par simulation et les valeurs de module d’Young déterminées expérimentalement. Le caractère isotrope des propriétés élastiques dans le plan perpendiculaire à la direction de construction des pièces a ainsi été démontré. Sur la base des données fournies par les modèles numériques, une approche d’optimisation du procédé a été mise en oeuvre pour l’obtention de pièces crues conformes. Ainsi, des expositions élevées sont à privilégier pour assurer la faisabilité de la fabrication, des expositions faibles pour assurer la haute qualité dimensionnelle des pièces et des expositions intermédiaires pour assurer une grande productivité. Les pièces denses ont ensuite été considérées. Les propriétés élastiques et la contrainte à la rupture ont été déterminées avec des mesures ultrasonores et des essais de flexion bi-axiale. Une tendance similaire entre l’exposition maximale globale et les propriétés mécaniques a été mise en évidence, i.e. plus l’exposition maximale globale est élevée, plus les valeurs de module d’Young et de contrainte à la rupture sont élevées. Le travail d’optimisation pour l’obtention de pièces frittées en alumine montre que les expositions élevées sont à privilégier pour assurer de bonnes propriétés mécaniquesThis thesis work focuses on the control of the dimensional and mechanical characteristics of ceramic parts produced by stereolithography. The goal is to be able to predict these characteristics using a numerical model in order to manufacture parts in accordance with specifications, from the first production. The strategy was to develop a numerical simulation model capable of predicting exposure, cure depth and half width of polymerization, as well as Young's modulus of the green parts obtained, according to process parameters. This numerical model integrates the diffusion phenomenon and is calibrated for each system using experimental tests. In order to access the effective elastic properties of the green parts, a finite element simulation model, coupled with the homogenization technique, has been developed. This model was validated by comparing the results obtained by simulation and the experimentally determined Young's modulus values. The isotropic nature of the elastic properties in the plane perpendicular to the direction of construction of the pieces has thus been demonstrated. On the basis of data provided by the numerical models, an optimization approach has been performed to obtain compliant green parts. Thus, high exposures are preferred to ensure feasibility of manufacturing, low exposures to ensure high dimensional quality of parts and intermediate exposures to ensure high productivity. The elastic properties and the tensile stress of dense parts were determined by ultrasonic measurements and biaxial flexion tests. A similar trend between the overall maximum exposure and mechanical properties has been demonstrated, i.e. higher overall maximum exposure leads to higher Young's modulus and tensile strength values. The optimization work on sintered alumina parts showed that high exposures are preferred to ensure good mechanical properties
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Zhan, Haifei. "Numerical characterization of the mechanical properties of metal nanowires." Thesis, Queensland University of Technology, 2013. https://eprints.qut.edu.au/63475/1/Haifei_Zhan_Thesis.pdf.
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Nanowires (NWs) have attracted appealing and broad application owing to their remarkable mechanical, optical, electrical, thermal and other properties. To unlock the revolutionary characteristics of NWs, a considerable body of experimental and theoretical work has been conducted. However, due to the extremely small dimensions of NWs, the application and manipulation of the in situ experiments involve inherent complexities and huge challenges. For the same reason, the presence of defects appears as one of the most dominant factors in determining their properties. Hence, based on the experiments' deficiency and the necessity of investigating different defects' influence, the numerical simulation or modelling becomes increasingly important in the area of characterizing the properties of NWs. It has been noted that, despite the number of numerical studies of NWs, significant work still lies ahead in terms of problem formulation, interpretation of results, identification and delineation of deformation mechanisms, and constitutive characterization of behaviour.
Therefore, the primary aim of this study was to characterize both perfect and defected metal NWs. Large-scale molecular dynamics (MD) simulations were utilized to assess the mechanical properties and deformation mechanisms of different NWs under diverse loading conditions including tension, compression, bending, vibration and torsion. The target samples include different FCC metal NWs (e.g., Cu, Ag, Au NWs), which were either in a perfect crystal structure or constructed with different defects (e.g. pre-existing surface/internal defects, grain/twin boundaries).
It has been found from the tensile deformation that Young's modulus was insensitive to different styles of pre-existing defects, whereas the yield strength showed considerable reduction. The deformation mechanisms were found to be greatly influenced by the presence of defects, i.e., different defects acted in the role of dislocation sources, and many affluent deformation mechanisms had been triggered. Similar conclusions were also obtained from the compressive deformation, i.e., Young's modulus was insensitive to different defects, but the critical stress showed evident reduction. Results from the bending deformation revealed that the current modified beam models with the considerations of surface effect, or both surface effect and axial extension effect were still experiencing certain inaccuracy, especially for the NW with ultra small cross-sectional size. Additionally, the flexural rigidity of the NW was found to be insensitive to different pre-existing defects, while the yield strength showed an evident decrease.
For the resonance study, the first-order natural frequency of the NW with pre-existing surface defects was almost the same as that from the perfect NW, whereas a lower first-order natural frequency and a significantly degraded quality factor was observed for NWs with grain boundaries. Most importantly, the <110> FCC NWs were found to exhibit a novel beat phenomenon driven by a single actuation, which was resulted from the asymmetry in the lattice spacing in the (110) plane of the NW cross-section, and expected to exert crucial impacts on the in situ nanomechanical measurements. In particular, <110> Ag NWs with rhombic, truncated rhombic, and triangular cross-sections were found to naturally possess two first-mode natural frequencies, which were envisioned with applications in NEMS that could operate in a non-planar regime. The torsion results revealed that the torsional rigidity of the NW was insensitive to the presence of pre-existing defects and twin boundaries, but received evident reduction due to grain boundaries. Meanwhile, the critical angle decreased considerably for defected NWs.
This study has provided a comprehensive and deep investigation on the mechanical properties and deformation mechanisms of perfect and defected NWs, which will greatly extend and enhance the existing knowledge and understanding of the properties/performance of NWs, and eventually benefit the realization of their full potential applications. All delineated MD models and theoretical analysis techniques that were established for the target NWs in this research are also applicable to future studies on other kinds of NWs. It has been suggested that MD simulation is an effective and excellent tool, not only for the characterization of the properties of NWs, but also for the prediction of novel or unexpected properties.
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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.
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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.
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Oumarou, Noura. "La caractérisation mécanique de systèmes film-substrat par indentation instrumentée (nanoindentation) en géométrie sphère-plan." Thesis, Vandoeuvre-les-Nancy, INPL, 2009. http://www.theses.fr/2009INPL001N/document.
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L’indentation instrumentée (nanoindentation) est une technique d’analyse des données expérimentales utilisées pour atteindre les propriétés mécaniques de matériaux (dureté H, module de Young E) pour lesquels les techniques classiques sont difficilement applicables voire non envisageables. Ces paramètres mécaniques sont issus de l’exploitation de la seule courbe expérimentale charge-décharge. L’analyse de cette dernière repose sur des nombreux modèles reportés dans la littérature (Oliver et pharr, Field et Swain, Doener et Nix, Loubet et al.) qui considèrent la décharge purement élastique. De nombreuses expériences que nous avons menées, sur divers types de matériaux massifs (aciers inoxydables AISI304, AISI316, AISI430; aciers rapides HSS652; verre de silice SiO2) et revêtus de films minces de TiN et TiO2 ont montré que les propriétés mécaniques (E et H), déduites de la méthode de Oliver et Pharr, dépendent du pourcentage de la courbe de décharge considéré, de la charge appliquée et du rayon de la pointe. De plus, pour un système film-substrat, la technique est en général utilisée pour atteindre les propriétés in-situ du film ou du substrat, alors que la méthode de dépouillement fournit des paramètres composites qu’il faut ensuite déconvoluer. Dans la recherche d’une stratégie simple, permettant d’accéder au module élastique d’un film « dur » pour les applications mécaniques, nous avons fait appel à la simulation numérique. Le code de simulation numérique utilisé, est basé sur la méthode des éléments de frontière. Nos investigations numériques utilisant l’indentation sphérique nous ont permis de mettre en évidence un certain nombre de résultats utiles pour l’analyse des données expérimentales. Nous avons commencé par montrer que aussi bien pour un matériau massif homogène élastoplastique que pour un système film dur – substrat élastoplastique, la relation [delta]=a2/R demeure valable (R étant le rayon de l’indenteur, a le rayon de l’aire projetée de contact). Cela permet de représenter les résultats de l’essai d’indentation sphérique par la courbe pression moyenne F/[pi]a2- déformation a/R . Au début du chargement, la pente cette courbe est proportionnelle au module de Young du film tandis que la pente initiale de la courbe de décharge est proportionnelle au module d’élasticité du substrat. Une relation entre le déplacement de l’indenteur et [delta] , puis une méthode d’analyse d’indentation ont été établies. Enfin, la procédure a été validée numériquement et expérimentalement sur les données issues de l’indentation de divers combinaisons film-substrat (TiN/AISI430, TiN/HSS652 et TiO2/HSS652) avec succèsDepth sensing Indentation (nanoindentation) is an experimental technique increasing retained for the assessment of the mechanical properties of materials (hardness H, Young's modulus E) for which common homogeneous mechanical tests can not be performed or are extremely difficult to perform. The mechanical parameters are obtained from the indentation curve (the plot of the load vs penetration depth during both load and unload). Usually, some methodology reported in the literature (Oliver and pharr, Field and Swain, Doener and Nix, Loubet and al.) are used in order to assess E and H. We have performed a number of experiments on homogeneous materials (stainless steel AISI304, AISI316, AISI430; high-speed steel HSS652; glass SiO2) as well as a film-substrate system (TiN/AISI430, TiN/HSS652, TiO2/HSS652). Applying the Oliver and Pharr methodology, E end H vary with the applied load as well as the percentage of used unload curve retained for the analysis, as reported in the literature. Besides, in the case of the film-substrate system, only composite parameters are obtained instead of the in-situ films properties. In order to establish a simple strategy for the determination of the elastic modulus of a hard coating, we have carried out many simulations using a boundary element based numerical tool. Then a number of useful results have been identified. The well known elastic relation [delta]=a2/R between the relative approach [delta], the projected contact radius a and the punch radius R, remain valid in the plastic range for homogeneous as well as film-substrate specimens. This allows data indentation to be represented in term of mean pressure F/[pi]a2 vs indentation strain a/R . The initial slope of the loading part of the latter curve is proportional to the elastic modulus of the film, while the slope of the initial part of the unloading curve is proportional to the substrate elastic modulus. Our indentation procedure anlysis has been validated experimentally on a number of samples (TiN/AISI430, TiN/HSS652, TiO2/HSS652) after having established a relation between the punch displacement and the relative approach [delta]
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Farbos, Baptiste. "Structure et propriétés de carbones anisotropes par une approche couplant analyse d’image et simulation atomistique." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0331/document.
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Des techniques combinées d'analyse/synthèse d'images et de simulation atomistique ont permis d’étudier la nanostructure/-texture de matériaux carbonés anisotropes et denses de type pyrocarbone (PyC) laminaire hautement texturé. Des représentations atomiques d’un PyC laminaire rugueux tel que préparé (AP) ainsi que d’un PyC laminaire régénéré AP et après plusieurs traitements thermiques (HT) ont été reconstruites pour mieux caractériser ces matériaux. Ces modèles comportent des domaines graphéniques de quelques nanomètres, joints entre eux par des lignes de défauts formées de paires de cycles à 5 et 7 carbones dans le plan et par des dislocations vis et des atomes tétravalents entre les plans. Les modèles les plus ordonnés ont des domaines plus étendus et un plus faible taux de connexions inter-plan. Les propriétés mécaniques et thermiques prédites à partir de ces modèles sont proches de celles du graphite et augmentent avec la cohérence intra-plan et la densité de connexions inter-plans. Des modèles de graphène polycristallins ont aussi été générés. Ils sont apparus, du point de vue structural et des propriétés mécaniques, très proches des feuillets de carbones des PyCs. Ils ont permis d'étudier la réorganisation structurale se produisant au cours du HT : formation de lignes de défauts, réparation de lacunes, … Il s'agit d'un premier pas vers l'étude de la graphitation des PyCs. La méthode de reconstruction a enfin été adaptée à l'étude de l'évolution structurale d'un graphite au cours de son irradiation par les électrons. Cela a permis d'observer à l'échelle atomique la création et la propagation des défauts au cours de l'irradiationCombined images analysis/synthesis techniques and atomistic simulation methods have allowed studying the nanostructure/-texture of anisotropic dense carbons of the highly textured laminar pyrocarbon (PyC) type.Atomic representations of an as-prepared (AP) rough laminar PyC as well as a regenerative laminar PyC AP and after several heat treatments (HT) were reconstructed to better characterize these materials.The models contain nanosized graphene domains connected between them by line defects formed by pairs of rings with 5 and 7 carbons inside layers and by screw dislocations and fourfold atoms between layers. The most ordered models have larger domains and a lower percentage of connections between the layers.Mechanical and thermal properties predicted from these models are close to those of graphite and increase with the coherence inside layers and the density of connections between layers.Models of polycrystalline graphene were also generated, showing structure and mechanical properties very close to those of the carbon layers extracted from PyCs. The structural reorganization occurring during the HT of such materials was studied: thinning of line defects and vacancy healing were observed. This represents a first step towards the study of the graphitization of PyCs.The reconstruction method was eventually adapted to study the structural evolution of a nuclear-grade graphite during its irradiation by electrons, allowing us to observe how defects are created and propagate during irradiation
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Chartier, Caroline. "Caractérisation des propriétés mécaniques du tissu cutané par élastographie impulsionnelle haute fréquence : applications en dermatologie et en cosmétique." Thesis, Tours, 2017. http://www.theses.fr/2017TOUR3304/document.
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L’exploration du tissu cutané est aujourd’hui limitée par le peu de méthodes dites quantitatives permettant de décrire objectivement les propriétés mécaniques du tissu cutané. L’élastographie permet une exploration locale d’un milieu et offre la possibilité pour certaines méthodes d’estimer quantitativement le module d’élasticité (module d’Young). Nous avons mis au point une technique d’élastographie ultrasonore impulsionnelle haute fréquence 1D (HF-TE) et haute résolution permettant une description micrométrique des propriétés mécaniques du tissu cutané pour des applications en cosmétique et en dermatologieNowadays, exploration of cutaneous tissue is limited by the few number of available approaches, known as quantitative methods, allowing an objective description of the mechanical properties of skin tissue. Elastography allows a local exploration of a medium and offers the possibility for some strategies to quantitatively estimate the modulus of elasticity (Young’s modulus). A 1-D high-frequency ultrasonic transient elastography method (HF-TE) allowing a micrometric description of the mechanical properties of skin tissue has been designed for cosmetic and dermatological applications. An experimental system of high-frequency transient elastography has been developed : software, hardware and measurement methodology. The HF-TE technique has been validated using simulation and measurements in monolayer and bilayer calibrated phantoms developed in the laboratory. The Young’s modulus values measured in monolayer media were then compared with those measured by two others dynamic techniques
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Villey, Richard. "Nanorhéologie des liquides confimés : application à la nanomécanique des couches minces." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10249/document.
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Lorsque deux solides séparés par un liquide se rapprochent, le drainage s’accompagne de forces visqueuses normales aux parois. Si elles sont très rapprochées, de l’ordre de quelques nanomètres, les parois sont indentées par ces forces : c’est le "confinement élastique". Indenter un solide par un liquide permet de supprimer l’adhésion, qui limite la résolution en termes de module d’Young des tests classiques d’indentation par un solide, surtout pour les films supportés minces et mous, par exemple des élastomères d’épaisseur micrométrique. Or leurs propriétés, qui peuvent sensiblement différer des propriétés en volume, sont essentielles dans des domaines aussi variés que la microfluidique, l’électronique ou l’usure mécanique. Nous présentons les calculs qui relient les forces normales aux propriétés mécaniques du liquide et des parois lors d’un confinement élastique. Les résultats sont comparés à des expériences de nanorhéologie réalisées sur une machine à forces de surface très sensible. Cette sensibilité nous permet de montrer que l’effet du confinement élastique se manifeste même sans film mou déposé : cela implique que la rhéologie apparente d’un liquide confiné est toujours affectée par les déformations des parois, même très rigides.Nous montrons enfin que nous pouvons effectivement mesurer avec précision des modules d’Young autour du MPa dans des films d’élastomères de quelques centaines de nanomètres à quelques micromètres d’épaisseur. Si le module de stockage ne varie presque pas avec l’épaisseur, un module de pertes apparaît, augmentant sensiblement lorsque l’épaisseur diminue, témoignant d’une visco-élasticité que nous attribuons à la présence d’une couche interfacialeWhen two solids separated by a liquid layer are moving towards each other, the resulting drainage is associated with viscous forces normal to the walls. If these are very close to each other (several nanometers), they are indented by these forces : this is the notion of “elastic confinement”. Indenting a solid by a liquid solves the problem of adhesion, which limits the ability of classical indentationtests to provide accurate measurements on Young’s modulii. Adhesion is especially problematic for soft thin films, for example micrometric layers of elastomers, which mechanical properties can strongly differ from the bulk, but are of the highest importance in various fields such as microfluidics, electronics or mechanical wear. We present here the calculations which link the solid and liquid mechanical properties to the resulting forces in a liquid indentation test. The corresponding results are compared to nanorheology experiments using a very sensitive Surface Force Apparatus. Its sensitivity enables us to show that the elastic confinement is also measurable without any soft films, which implies that a confined liquid apparent rheology is always affected bythe deformations of even very rigid confining walls. Finally, we demonstrate that we are indeed able to measure precisely Young’s modulii in the MPa range for films as thin as several hundreds of nanometers. While the storage modulii are found to be almost independent ofthe film thicknesses, we identify the presence of loss modulii increasing with decreasing thicknesses. We attribute this unexpected viscoelastic behaviour to the presence of an interfacial layer
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Gerstädt, Adrian, and Emil Morgén. "Mekaniska egenskaper hos mjuka heterogena biomaterial : Tillämpning på polyuretanskum." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-10349.
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Denna rapport behandlar genomförandet av ett examensarbete på högskolenivå inom maskinteknik vid Högskolan i Borås. Examensarbetet har utförts hos SP Sveriges Tekniska Forskningsinstitut AB, enheterna SP Safety – Mechanical Research i Borås och Göteborg samt Food and Bioscience i Göteborg. Den största delen av arbetet har utförts vid sektionen Mechanical Research Göteborg. Målet med examensarbetet var att kombinera analys av experimentell bilddata från konfokalmikroskopi och mekanisk lastdata från en dragcell som gradvis deformerar ett polyuretanskum med modellering av skummets mekaniska egenskaper med hjälp av finita elementmetoder (FEM). Syftet var att bestämma elasticitetsmodul och Poissons tal. En viktig del av projektet var också att säkerställa hög repeterbarhet och möjliggöra vidareutveckling av metodiken genom att skapa rutiner för hur de olika delmomenten i arbetscykeln bäst utförs. Polyuretanskum, liksom många andra mjuka heterogena biomaterial saknar i dagsläget uppmätta eller beräknade mekaniska egenskaper. Därför finns potential för att den framtagna metodiken kommer till användning för att bestämma materialparametrar och analysera beteenden för fler av dessa material. Genom att bestämma materialparametrarna är det sedan möjligt att¬ utföra hållfasthetsberäkningar på sådana material, och korrelera materialparametrarna till processparametrarna vid tillverkningen för att optimera materialets egenskaper. Studien började med att ett prov av polyuretanskum placerades i en dragcell där det utsattes för en kraft så att det gradvis deformerades. Med hjälp av ett konfokalmikroskop kan hela deformationsprocessen följas i hög upplösning. De framtagna bildserierna analyserades sedan med hjälp av DaVis, en mjukvara som genomför så kallad digital image correlation-analys, med vars hjälp lokala förskjutningar kunde bestämmas. För att kunna utföra FEM-beräkningar delades materialstrukturen in i elementnät med hjälp av den fritt tillgängliga programvaran OOF2. Elementnät och förskjutningsdata importerades sedan till Matlab och insticksmodulen CalFEM. Med hjälp av CalFEM konstruerades en materialmodell med elasticitetsmodul och Poissons tal som inparametrar. Valideringskriterium användes för att säkerställa korrektheten i finita elementanalyserna. Elasticitetsmodulen bestämdes till 4.6 MPa och Poissons tal till 0.33 ± 0.06. Med tillgängliga data kunde inte modellen användas för att uppskatta båda parametrarna samtidigt. Poissons tal bestämdes genom manuell analys av bildserierna. Metodiken kan förbättras och vidareutvecklas genom att analysera fler provbitar för att ta hänsyn till lokala fluktuationer i materialstrukturen, samt avbilda provet i tredimensioner. Tredimensionell avbildning skulle också möjliggöra konstruktion av en tredimensionell beräkningsmodell av materialet.This bachelor thesis deals with the implementation of a degree in mechanical engineering at the University of Borås. The thesis work has been conducted at SP Technical Research Institute of Sweden AB at the departments SP Safety – Mechanical Research in Borås and Gothenburg and Food and Bioscience in Gothenburg. The major part of the work has been done at the Mechanical Research department in Gothenburg. The aim of the thesis work was to combine analysis of experimental image data from confocal laser scanning microscopy and mechanical load data from a tensile cell that gradually deforms a polyurethane foam with modelling of the mechanical properties of the foam using finite element methods (FEM). The purpose was to determine Young’s modulus and Poisson's ratio. A crucial part of the project was also to facilitate a high degree of repeatability and further development of the method through establishing routines and best practices for how to implement different parts of the method. There is currently a lack of measured or calculated properties for polyurethane foams, as is the case also for many other soft heterogeneous biomaterials. This implies that the developed method has potential use for determining material parameters and analyzing behavior also for other materials of this type. Determining the material parameters facilitates strength calculations on these materials and makes it possible to correlate material parameters to process parameters during manufacturing to optimize material performance. The polyurethane foam was placed in a tensile cell, exposed to a force and slowly, gradually deformed. Using a confocal microscope, the entire deformation process can be observed at high resolution. The obtained image series were then analyzed using DaVis, a software that can perform so called digital image correlation analysis where local displacements could be determined. In order to perform the finite element calculations, the material structure was divided into an element mesh using the software OOF2. The element mesh and displacement data were then imported to Matlab and the plugin module CalFEM. Using CalFEM, a material model involving Young’s modulus and Poisson’s ratio was created. Young’s modulus was determined to be 4.6 MPa and Poisson’s ratio 0.33 ± 0.06. Using the available data, the model was insufficient to determine both parameters simultaneously. Therefore, Poisson’s ratio was determined through manual analysis of the image series. The method can be improved and further developed mainly by analyzing several samples to account for local fluctuations in the material structure and by using three-dimensional imaging methods. The latter would also open up for creating a three-dimensional model of the material.
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Grosser, Peter, Carolin Siegel, Christoph Neinhuis, and Thea Lautenschlaeger. "Triumfetta cordifolia: A Valuable (African) Source for Biocomposites." NC State University, 2018. https://tud.qucosa.de/id/qucosa%3A33826.
Full textAbstract:
The tradition of using naturally occurring plant fibers is still alive in Africa. In the Uíge province of northern Angola, bast fibers from Triumfetta cordifolia serve as the basis for everyday objects, such as baskets, mats, fishing nets, and traditional clothing. The fibers exhibit a Young’s modulus of 53.4 GPa and average tensile strength of 916.3 MPa, which are comparable to those of commercial kenaf fibers. These values indicate a high potential for use as a reinforcement in biocomposites. Based on this promising mechanical and physical profile of individual fibers, different biocomposites were produced with polylactide (PLA) as a matrix. The obtained composites were analyzed mechanically, physically, and visually. Unidirectionally arranged PLA/33% T. cordifolia composites with continuous fibers showed the highest Young’s modulus (10.79 GPa ± 1.52 GPa) and tensile strength (79.37 MPa ± 14.01 MPa). These composites were comparable to those of PLA/30% hemp composites (10.9 GPa and 82.9 MPa, respectively) and therefore have economic potential.
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Проценко, Олена Борисівна, Елена Борисовна Проценко, Olena Borysivna Protsenko, Вікторія Володимирівна Ємельяненко, Виктория Владимировна Емельяненко, and Viktoriia Volodymyrivna Yemelianenko. "The analysis of the elastic properties of armchair and zigzag single-walled carbon nanotubes." Thesis, Sumy State University, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20630.
Full textAbstract:
Computation simulation is a powerful tool for predictiong the mechanics models of elastic properties of armchair and zigzag single-walled nanotubes. The aim of this work is investigation and comparison of Young’s modulus, shear modulus and Poisson’s
ratio variations of armchair and zigzag tubes as functions of diameter. We obtained a set of concise, closed form expressions for the size-dependent elastic modulus, shear modulus and Poisson’s ratio of armchair (n, n) and zigzag (n, 0) nanotubes, which are basic for constructing mathematical models of elastic properties of SWNTs. We investigated armchair nanotubes with chirality (3, 3)–(40, 40) and zigzag (3, 0)–(40, 0) with diameters 4,2–54,2 Å and 2,4–31,3 Å respectively. We calculated Young’s modulus to be 0,26–2,95 TPa for armchair and 0,5–3,7 TPa for zigzag nanotubes. The shear modulus calculated for armchair nanotube appeared to be in the range of 0,2–2,0 TPa and for
zigzag one in the range of 0,2–2,7 TPa. Specifically, it was inverse dependences of Young’s modulus and shear modulus on diameter. The Poisson’s ratio was in range from 0,28 to 0,42 and from 0,27 to 0,39, respectively. Results of this research can be
used for design, analysis and evaluating of nanotubes unctioning and creating new materials based on CNTs.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20630
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Jackman, Henrik. "Mechanical behaviour of carbon nanostructures." Doctoral thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32041.
Full textAbstract:
Abstract Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in future nanoelectromechanical systems and for many other applications. The extraordinary properties are however only attained by perfectly crystalline CNTs and quickly deteriorate when defects are introduced to the structure. The growth technique affects the crystallinity where in general CNTs grown by arc-discharge are close to perfectly crystalline, while CVD-grown CNTs have large defect densities. Mechanical deformation also affects these properties, even without introducing defects. When CNTs are bent they behave similarly to drinking straws, i.e. they buckle or ripple and their bending stiffness drops abruptly. In this thesis, the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers (VACNFs) has been studied by performing force measurements inside electron microscopes. Cantilevered CNTs, and VACNFs, were bent using a force sensor, yielding force-deflection curves while their structure was imaged simultaneously. We have found that CNTs grown by arc-discharge have a high enough crystallinity to possess a Young’s modulus close to the ideal value of 1 TPa. CVD-grown CNTs possess a Young’s modulus that is about one order of magnitude smaller, due to their large defect density. The VACNFs are yet another order of magnitude softer as a result of their cup-stacked internal structure. We also found that a high defect density will increase the critical strain for the rippling onset and the relative post-rippling stiffness. Multi-walled CNTs with a small inner diameter are less prone to ripple and have a larger relative post-rippling stiffness. Our findings show large variations in the onset of rippling and the bending stiffness before and after rippling. These variations open up possibilities of tailoring the mechanical properties for specific applications.Baksidetext Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in nanoelectromechanical systems (NEMS), and many other applications. In this thesis the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers has been studied by performing force measurements inside electron microscopes. We have found that the mechanical behaviour is very sensitive to the defect density and the internal structure of the CNTs. The extraordinary properties are only attained by defect free CNTs and quickly deteriorate if defects are introduced to the structure. Mechanical deformations also alter these properties. Single-walled CNTs behave similarly to drinking straws when bent, i.e. they buckle, while the inner tubes of multi-walled CNTs prevent buckling. Instead a more distributed rippling pattern is created for multi-walled CNTs. Both these deformation behaviours will cause an abrupt drop in the bending stiffness, which is detrimental for many applications. The findings in this work will have implications for the design of future NEMS.
Artikel 2 Image formation mechanisms tidigare som manuskript, nu publicerad: urn:nbn:se:kau:diva-16425 (MÅ 150924)
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Fredriksson, Tore. "Carbon Nanotubes : A Theoretical study of Young's modulus." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32351.
Full textAbstract:
Carbon nanotubes have extraordinary mechanical, electrical, thermal andoptical properties. They are harder than diamond yet exible, have betterelectrical conductor than copper, but can also be a semiconductor or evenan insulator. These ranges of properties of course make carbon nanotubeshighly interesting for many applications. Carbon nanotubes are already usedin products as hockey sticks and tennis rackets for improving strength and exibility. Soon there are mobile phones with exible screens made fromcarbon nanotubes. Also, car- and airplane bodies will probably be mademuch lighter and stronger, if carbon nanotubes are included in the construction.However, the real game changers are; nanoelectromechanical systems(NEMS) and computer processors based on graphene and carbon nanotubes.In this work, we study Young's modulus in the axial direction of carbonnanotubes. This has been done by performing density functional theorycalculations. The unit cell has been chosen as to accommodate for tubes ofdierent radii. This allows for modelling the eect of bending of the bondsbetween the carbon atoms in the carbon nanotubes of dierent radii. Theresults show that Young's modulus decreases as the radius decreases. Ineect, the Young's modulus declines from 1 to 0.8 TPa. This eect can beunderstood because the bending diminishes the pure sp^2 character of thebonds.These results are important and useful in construction, not only when usingcarbon nanotubes but also when using graphene. Our results point towardsa Young's modulus that is a material constant and, above a certain criticalvalue, only weakly dependent on the radius of the carbon nanotube.Graphene can be seen as a carbon nanotube with innite radius.
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CUPERTINO, LEANDRO FONTOURA. "MODELING YOUNGS MODULUS OF NANOCOMPOSITES THROUGH COMPUTATIONAL INTELLIGENCE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15391@1.
Full textAbstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Materiais compósitos são a base de muitos produtos, devido à sua capacidade de aperfeiçoar certas propriedades. Recentemente, a utilização de nanocargas na fabricação de compósitos vem sendo amplamente estudada, pois a partir de concentrações baixas de nanocargas, as propriedades começam a melhorar, possibilitando a criação de materiais leves e com uma grande gama de propriedades. Uma das propriedades mecânicas mais estudadas é o módulo de Young, que mensura a rigidez de um material. Alguns dos modelos existentes para essa propriedade em nanocompósitos pecam na precisão ou são limitados em função da fração máxima de nanopartículas admissível no modelo. Outros se adequam apenas a uma determinada combina ção de matriz/carga preestabelecida. O objetivo deste trabalho é utilizar Redes Neurais Artificiais como um aproximador capaz de modelar tal propriedade para diversas matrizes/cargas, levando em consideração suas características, sem perder a precisão. A validação do aproximador é realizada comparando o resultado com outros modelos propostos na literatura. Uma vez validada, utiliza-se Algoritmos Genéticos em conjunto com tal rede para definir qual seria a configuração ideal para três casos de estudo: um que maximize o valor do módulo de Young, outro que maximize o módulo relativo e um terceiro que maximize o módulo relativo e minimize a quantidade de carga utilizada, diminuindo os custos de projeto. As técnicas de Inteligência Computacional empregadas na modelagem e síntese de materiais nanoestruturados se mostraram boas ferramentas, uma vez que geraram uma boa aproximação dos dados utilizados com erros inferiores a 5%, além de possibilitarem a determinação dos parâmetros de síntese de um material com o módulo de Young desejado.
Composite materials became very popular due to its improvements on certain properties achieved from the mixture of two different components. Recently, the use of nanofillers in the manufacture of composites has been widely studied due to the improvement of properties at low concentrations of nanofillers, enabling the creation of lightweight materials. Some of the existing models for the Young modulus of the nanocomposites have low accuracy or are limited in terms of the maximum filler fraction possible. Others are appropriate only for a given combination of matrix and filler. The objective of this work is to use Artificial Neural Networks as a function approximation method capable of modeling such property for various matrix/nanofillers, taking into account their characteristics, without losing accuracy. The validation of this approximator is performed comparing its results with other models proposed in the literature. Once validated, a Genetic Algorithm is used with the Neural Network to define which would be the ideal setting for three case studies: one that maximizes the value of composite’s Young’s modulus, other that maximizes the relative modulus and a third one that maximizes the relative modulus and minimizes the amount of load used, reducing the cost of project. Computational Intelligence techniques employed on the modeling and synthesis of nanostructured materials proved to be adequate tools, since it generated a good approximation of the data with errors lower than 5%, and determined the material’s parameters for synthesis with the desired Young’s modulus.
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Stewart, Robert L. Stewart. "EFFECTS OF POROSITY AND TEMPERATURE ON THE MECHANICALPROPERTIES OF HOLEY GRAPHENE SHEETS." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1533046679055161.
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Bodel, William. "The relationship between microstructure and Young's modulus of nuclear graphite." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-relationship-between-microstructure-and-youngs-modulus-of-nuclear-graphite(ac5fe868-cefb-4f0c-8b22-a8904bc97da5).html.
Full textAbstract:
In addition to its role as moderator within British nuclear reactors, polycrystalline graphite is also a major structural component of the core, enabling access for control rods, coolant gas and fuel. Aging processes, primarily fast neutron irradiation and radiolytic oxidation lead to distortion of the graphite components and property changes which ultimately reduce the material's effectiveness and can lead to component failure.Despite much research into the material, graphite behaviour under irradiation conditions is not fully understood and has resulted in an overestimation of the extent of component failures in Magnox reactors, and a subsequent underestimation of component failures in the following generation Advanced Gas-cooled Reactors (AGRs). A greater understanding of the material is therefore required in order to make more informed evaluations as part of on-going safety cases. Young's modulus is one property which varies as a complex function of radiolytic oxidation and fast neutron irradiation dose; this work investigates investigate the Young's modulus behaviour of nuclear grade graphites through property measurement and microstructural characterisation. Physical properties are dependent on microstructure, which is in turn a result of the manufacturing processes and raw materials used in its fabrication. Because of this, this thesis begins with a microstructural study of AGR graphite artefacts from varying points during the manufacturing process and post-irradiation, utilising X-ray diffraction to observe changes in crystallinity, microscopy to directly observe the microstructure and pycnometry to gauge porosity variations. Increases in crystallinity towards graphitisation are seen, with a subsequent decrease after irradiation; and significant changes are observed from inspection of optical and scanning electron micrographs. Young's modulus property data are obtained using a combination of static and dynamic techniques to accumulate data from a variety of techniques. An experiment designed to track changes to the speed of sound under compressive load was carried out on Magnox and AGR graphite, showing different behaviour between the grades, and variation with irradiation.A final series of tests combine compressive testing with in-situ microscopy to try and better understand the reasons behind this varied in behaviour and relate microstructural changes to graphite behaviour under compressive loading.
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Cheng, Kamyin. "Effective Young's Modulus of rigid particles in Gelatin composites." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59901.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 50).
In many biological systems, small rigid parts are embedded in deformable tissues to perform different biological functions. This study examines the effects of adding rigid filler particles inside deformable material. More specifically, a series of experiments led to eventual understanding of the relationship between effective Young's Modulus of material and volume fraction of rigid particles. The deformable material used in this study is gelatin, a readily available consumer product. It was found that the higher the volume fraction, the higher the Young's Modulus value for the composite material. In addition, it was found that cyclic loading with high strain and high volume fraction may cause stress stiffening or stress softening, while cyclic loading with small strain and small volume fraction yields linear elastic behavior. Furthermore, the effect of strain rate on material behavior was examined. Unfortunately the sample size was too small to draw definite conclusion. Finally, the reusability of particles was explored, and the results suggested that particles in composites are reusable so long as the composite did not undergo high strain compression.
by Kamyin Cheng.
S.B.
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Ткач, Геннадій Федорович, Геннадий Федорович Ткач, Hennadii Fedorovych Tkach, Віталій Зіновійович Сікора, Виталий Зиновьевич Сикора, Vitalii Zinoviiovych Sikora, Андрій Миколайович Буштрук, Андрей Николаевич Буштрук, and Andrii Mykolaiovych Bushtruk. "Зміни величини модуля Юнга та жорсткості поперечного перетину стегнової кістки в динаміці репаративного остеогенезу." Thesis, Сумський державний університет, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42223.
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Модуль Юнга, або модуль пружності є інтегрованим показником, який відображає
якість кісткової тканини та має переважне значення для показників еластичності органу, тобто
залежить в першу чергу від якості органічної складової. Проте, колагенові волокна у кісткові
тканині знаходяться у тісному зв’язку з мінералом гідроксиапатиту, тому зміна
співвідношення або якості зазначених складових мають значний вплив на величену модуля
Юнга. Жорсткість поперечного перетину кістки відображає здатність кісткової тканини до
супротиву та має більшу залежність від якості мінеральної складової. Не зважаючи на велику
кількість досліджень змін даних показників в процесі росту кісток, їх динаміка в процесі
репаративної регенерації в залежності від віку тварин вивчена недостатньо.
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Nortemann, Markus. "Characterisation of Young's modulus and loss factor of damping materials." Thesis, Nelson Mandela Metropolitan University, 2014. http://hdl.handle.net/10948/d1021036.
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Given the importance of simulation techniques in automotive engineering, there is a lack of implementation regarding these techniques in the acoustics of damping materials for air-borne sound. Biot’s calculations have proven its abilities to simulate the acoustic characteristics of these damping materials. However, the characterisation of essential structural parameters, such as Young’s modulus and loss factor, in order to conduct Biot’s calculations have been inconclusive. Thus, the primary research objective of this study is to propose a new measurement system for the structural Biot parameters. After a comprehensive literature review has been undertaken on damping materials, as well as measurement apparatuses for Young’s modulus and loss factor of damping materials, two causes of measurement errors have been identified. Unknown stresses in measurement apparatuses and inhomogeneous, polytrophic and viscoelastic behaviour of specimens. A new measurement system that does not affect the specimens with unknown stresses and accounts for their complex behaviour required investigation. Non-contact ultrasound had been selected as a solution to determine the aforementioned parameters, since these methods do not necessarily touch or compress the specimen, which led to unknown stresses and neglection of the complex specimen behaviour with the aforementioned techniques. Although ultrasound had been used to determine structural parameters on various types of materials, it has never been used to measure soft porous damping materials. In order to find possible solutions, various sources using ultrasonics to investigate struc- tural parameters had been reviewed. In order to calculate structural parameters, the longitudinal and transversal wave velocity inside the specimen had to be determined. The main findings showed that non-contact ultrasound will be able to evaluate the Young’s modulus, loss factor as well as Poisson’s ratio. Consequently, it was shown that longitudinal velocity measurements could be conducted using well known transmission measurements. However, well known approaches would not be sufficient measuring the transversal wave velocity in soft damping materials. This problem was addressed with a special gas to be used, with lower sound speed velocity in the fluid than in the solid. Moreso, a new method determining the transversal wave velocity had been found, as it would enable the use of an even larger range of damping materials, especially ones with heavy frames and lower porosity. It will use refracted waves inside the specimen and the determination of the convertion position of the transversal to the longitudinal wave at the rear specimen surface. At the end of the study, hardware components were selected and a test rig was constructed, which should be able to prove that a determination of structural Biot parameters with non-contact ultrasound is possible with less errors instead of using mechanical transfer function systems. The development of measurement software as well as the testing of the measurement system and its validation was not under investigation in this dissertation. This study has expanded on the body of literature knowledge regarding non-contact ultrasound. Furthermore, a significant contribution has been made towards a new measurement system measuring Young’s modulus and loss factor which circumvents errors in mechanical transfer function systems. This will contribute to more precise simulations of damping materials and damped enclosures, which may ultimately result in enhanced efficiency of damping materials as well as the acoustic packaging of cars.
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Sampaio, Leonardo Fernandes. "Estudo de primeiros princípios de nanofios de inas submetidos a tensões extremas." Universidade Federal de Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/9249.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe ability to manipulate materials at the atomic scale turn it possible to look for materials at the nanoscale that can supersede the performance of their bulk counterparts in specific tasks. Nanowires, due to their unique structural characteristics, are natural candidates for electric or heat conducting devices. When these nanowires take part of a circuit, they can subjected to an external stress that can change their intrinsic properties. In this work, we will be studying the mechanical and electronic behavior of narrow InAs nanowires, with different diameters, when subjected to extreme external stress. Our calculations use the Density Functional Theory, and the local density approximation to the exchange and correlation potential, as implemented in the VASP code. Our results reveal that the InAs nanowires exhibit a mechanical behavior which depends on the external stress and the nanowire diameter. For the narrowest diameter, it shows an elastic behavior followed by the rupture of the wire. As the nanowires turn thicker, different responses to the external stress take place. When the first chemical bonds are broken, the nanowire changes between elastic behaviors with different Young modulus. When more and more chemical bonds are broken (for the thicker nanowires), the nanowires show a plastic behavior, before the rupture. For each of these mechanical regimes, the electronic band structure of the nanowires is also analysed.
Nanofios, devido às suas caracteristícas estruturais únicas, são candidatos naturais para dispositivos condutores de eletricidade e calor. Quando estes nanofios formam parte de um dispositivo, podem estar sujeitos a tensões externas que podem alterar as suas propriedades intrínsecas. Neste trabalho estudaremos o comportamento mecânico e eletrônico de nanofios de InAs com diferentes diâmetros quando sujeitos a tensões externas extremas. Nossos cálculos usam a Teoria do Funcional da Densidade dentro da aproximação da densidade local para o funcional de exchange e correlação, como implementado no código computacional VASP. Nossos resultados revelam que os nanofios de InAs exibem um comportamento mecânico que depende da tensão externa e do diâmetro do nanofio. Para o nanofio mais estreito, observa-se um comportamento elástico da curva de tensão vs elongação ( stress vs strain ), seguido de ruptura do fio. Quando os nanofios tornam-se mais espessos, diferentes respostas às tensões extremas são observadas. Quando as primeiras ligações químicas são quebradas, os nanofios mudam de regime elástico para outro, com diferentes valores de módulo de Young. Quando mais e mais ligações químicas são quebradas, sempre do centro para as bordas, os nanofios apresentam um comportamento plástico antes da ruptura. Para cada um destes regimes mecânicos estrutura de bandas dos nanofios é também analisada.
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Gemmiti, Christopher V. "Effect of Fluid Flow on Tissue-Engineered Cartilage in a Novel Bioreactor." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13963.
Full textAbstract:
Due to its relative avascularity, low cellularity and lack of an undifferentiated cell reservoir, articular cartilage has a limited capacity for self-repair when damaged through trauma or disease. Articular cartilage impairment and the resultant reduced joint function affects millions of people at a substantial cost. In the U.S. alone, over 20 million adults are afflicted with osteoarthritis, costing more than $65 billion per year in health care and lost wages. Surgical techniques have been developed to address small, focal lesions, but more critical sized defects remain without a viable solution. Tissue engineering strategies produce cartilage-like constructs in vitro containing living cells in the hope of replacing damaged cartilage and restoring joint function. However, these constructs lack both sufficient integration into the surrounding tissue following implantation and the mechanical properties capable of withstanding the demanding and complex in vivo loading environment.
Our central hypothesis is that exposure of engineered cartilage to fluid-induced shear stress increases the collagen content and mechanical properties (tensile and compressive). The overall objective of this project is to modulate the matrix composition and mechanical properties of engineered cartilage to be more like native tissue using a novel bioreactor. Improving the matrix components and mechanical stability of the tissue to be more similar to that of native tissue may aid in integration into a defect in vivo.
The central hypothesis was proven in that shear stress potently altered the matrix composition, gene expression and mechanical properties of both thick and thin engineered cartilage. Modulation was found to be highly dependent on shear stress magnitude, duration, and waveform and affected different matrix constituents and mechanical properties in disparate ways. Our overall objective was satisfied on the basis that the bioreactor created stronger engineered tissues, but with the caveat that the tissues showed an increase in presence of type I collagen. Such an effect would be undesirable for articular cartilage engineered tissues, but could be very beneficial in fibrocartilaginous tissues such as that found in the temporomandibular joint. In conclusion, the novel bioreactor system provides a flexible platform technology for the study of three-dimensional engineered tissues, not just articular cartilage.
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Geyin, Mertcan. "Micro-Scale Characterization of Quartzitic and Carbonate Sand Grains Using Nanoindentation." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/81274.
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Many offshore energy infrastructures are built on carbonate sands which are skeletal remains of marine organisms. Carbonate sands have a porous grain structure and are more compressible compared to quartzitic sand grains which are abundant in alluvial depositional environments. Consequently, there is a stark difference in material behavior of carbonate sands and it is difficult to characterize this distinct behavior with conventional methods. This study focuses on micro-scale characterization of carbonate and quartzitic sands to overcome this challenge. Experimental studies consist of nanoindentation tests performed on 17 different sands; 7 quartzitic and 10 carbonate sand samples. Mechanical properties of individual sand grains with different mineralogies are determined using nanoindentation. A force is applied by the nanoindenter on the grain surface and the load-displacement curve is developed. Modulus and hardness of individual sand grains are evaluated. Nanoindentation test results show that modulus and hardness of carbonate sands are significantly lower than quartzitic sands. For quartzitic grains, mechanical properties are relatively independent of indentation depth; whereas, for carbonate grains there is a considerable decrease in both Young's modulus and hardness values with increasing indentation depth. Results from this study can further be used for the evaluation of compressibility and strength characteristics of these two types of sands as part of a multi-scale analysis framework.Master of Science
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Rivera, Constantino Rigoberto. "Détermination des propriétés mécaniques des sables et des argiles en régime dynamique et cyclique aux faibles déformations." Châtenay-Malabry, Ecole centrale de Paris, 1988. http://www.theses.fr/1988ECAP0075.
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Étude dans le domaine des faibles déformations (10**(-5) pour les essais dynamiques, et 10**(-6) a 10**(-3) pour les cycliques), a travers trois paramètres principaux: module de Young, coefficient de poisson et coefficient d'amortissement. Rôle de la contrainte moyenne, indice des vides, saturation, histoire des contraintes. Pour argiles remaniées normalement consolidées, corrélation entre module de Young, limite liquide, indice de plasticité et coefficient de compressibilité. Comparaison entre régime dynamique et cyclique
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Henke, Anne E. "Young modules and Schur subalgebras." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301862.
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Brunetti, Carlotta. "Frequency-dependent response of snow in uniaxial compression and comparison with numerical simulation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7820/.
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La determinazione del modulo di Young è fondamentale nello studio della propagazione di fratture prima del rilascio di una valanga e per lo sviluppo di affidabili modelli di stabilità della neve. Il confronto tra simulazioni numeriche del modulo di Young e i valori sperimentali mostra che questi ultimi sono tre ordini di grandezza inferiori a quelli simulati (Reuter et al. 2013). Lo scopo di questo lavoro è stimare il modulo di elasticità studiando la dipendenza dalla frequenza della risposta di diversi tipi di neve a bassa densità, 140-280 kg m-3. Ciò è stato fatto applicando una compressione dinamica uniassiale a -15°C nel range 1-250 Hz utilizzando il Young's modulus device (YMD), prototipo di cycling loading device progettato all'Istituto per lo studio della neve e delle valanghe (SLF). Una risposta viscoelastica della neve è stata identificata a tutte le frequenze considerate, la teoria della viscoelasticità è stata applicata assumendo valida l'ipotesi di risposta lineare della neve. Il valore dello storage modulus, E', a 100 Hz è stato identificato come ragionevolmente rappresentativo del modulo di Young di ciascun campione neve. Il comportamento viscoso è stato valutato considerando la loss tangent e la viscosità ricavata dai modelli di Voigt e Maxwell. Il passaggio da un comportamento più viscoso ad uno più elastico è stato trovato a 40 Hz (~1.1•10-2 s-1). Il maggior contributo alla dissipazione è nel range 1-10 Hz. Infine, le simulazioni numeriche del modulo di Young sono state ottenute nello stesso modo di Reuter et al.. La differenza tra le simulazioni ed i valori sperimentali di E' sono, al massimo, di un fattore 5; invece, in Reuter et al., era di 3 ordini di grandezza. Pertanto, i nostri valori sperimentali e numerici corrispondono meglio, indicando che il metodo qui utilizzato ha portato ad un miglioramento significativo.
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Oh, Jung Joo. "Determination of Young's modulus of carbon nanotube using molecular dynamics (MDSS) simulation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FOh.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003.Thesis advisor(s): Young W. Kwon, James H. Luscombe. Includes bibliographical references (p. 53-57). Also available online.
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Ståhl, Martin. "Numerical modeling to complement wood tests." Thesis, Uppsala universitet, Tillämpad mekanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-207269.
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Pressure tests on wood have been conducted to determine its properties. The resultswere not as expected, and it is therefore difficult to obtain the parameters of thewood. This project examines how a specific defect in the wood sample affects theresult.The pressure test is simulated with numerical modeling. In the numerical model thecube’s top side is non-parallel with the bottom side, it is in other words somewhattilted.The results from the model agreed with the findings from some pressure tests. Withthose we can easily calculate the wood's properties. For other pressure tests, otherfactors might need to be examined before we can draw any conclusions.Tryckprover på trä har utförts för att ta reda dess egenskaper. Resultaten blev intevad som förväntades, och det blir därför svårt att få fram träets egenskaper. Dettaprojekt undersöker hur en viss defekt i träprovet påverkar resultatet.Tryckprovet simuleras med numerisk modellering. I modellen är kubens toppsida inteparallell med bottensidan, den är med andra ord något sned.Resultatet från modellen stämde med resultat från vissa tryckprover. Då kan man fåfram träets egenskaper. För andra tryckprover kan andra faktorer behöva undersökasinnan man kan dra några slutsatser.
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Luyken, Lewis. "Using intercalation to simulate irradiation damage of nuclear graphite." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/using-intercalation-to-simulate-irradiation-damage-of-nuclear-graphite(85ce1ebb-2981-4807-8cf8-4aedc4acea97).html.
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This thesis investigates the use of bromine intercalation of graphite as a method to simulate and investigate irradiation damage. In particular this study investigates the effects of intercalation on dimensional change on the macro and micro scales and how these changes combine to affect Young’s modulus. Highly Orientated Pyrolytic Graphite has been used to gather data as a close approximation to single crystal graphite. Three different grades of polycrystalline nuclear graphite have been used to investigate the effect of different microstructure on intercalation and subsequent property changes. The graphites have been characterized by optical microscopy, pycnometry and x-ray powder diffraction and texture measurements. A number of bespoke rigs were designed and manufactured to carry out sorption, tomography and laser vibrometry experiments.The results indicate that the rate of dimensional change for polycrystalline graphites is significantly lower than for single crystal graphites. Modelling of dimensional change suggests that the difference in expansion is due to closure of porosity. Closer investigation of the dimensional change within the microstructure shows that the majority of the dimensional change is driven by expansion of filler particles.The young’s modulus results show an initial increase in modulus followed by a decrease, which corresponds with empirical evidence for irradiated samples. It is postulated that the initial increase in modulus is due to crystal expansion and that the subsequent decrease is due to crack growth. After experimentation some samples show significant cracking which would appear to support this assertion.
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Vautrot, Mathieu. "Étude du comportement mécanique des matériaux dans des conditions étendues de vitesses et de températures : application à l'acier C68 dans le cas d'une opération de formage incrémental." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00795973.
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L'objectif de ce travail de thèse est la caractérisation et la modélisation du comportement thermo-mécanique d'un acier à haut taux de carbone dans des conditions de chargement identiques à celles d'un procédé de formage incrémental à 720°C. Le regain d'intérêt des industriels pour ce type de procédé provient du fait qu'ils sont moins énergivores et permettent un ratio matière valorisée sur matière brute intéressant pour des propriétés mécaniques améliorées de la pièce formée. Le recours à l'outil numérique devient aujourd'hui une solution intéressante pour optimiser au mieux la mise au point du procédé. Son application demande, entre autres, une description fine du comportement du matériau dans les conditions de sollicitations de celui-ci, c'est-à-dire sur une large plage de vitesses de déformation et de températures. Pour cela, une caractérisation du matériau est nécessaire dans ces conditions. Le comportement mécanique d'un acier à haut taux de carbone a été étudié au travers d'essais de traction quasi-statiques et dynamiques afin de déterminer la sensibilité du matériau à la température et à la vitesse de déformation. Cette caractérisation repose sur la combinaison novatrice d'un système de chauffage par induction contrôlé par pyrométrie et d'un système d'acquisition d'images numériques. Ce dernier est utilisé pour la détermination des déformations à partir des champs de déplacement obtenus par corrélation d'images. En particulier, les effets de la température sur le module d'élasticité, l'anisotropie et l'écrouissage isotrope ont été étudiés. Les résultats de ces essais ont ensuite constitué une base de données expérimentales pour l'identification des paramètres de divers modèles de comportement thermo-élasto-visco-plastique. Ces derniers sont plus ou moins complets selon le nombre de paramètres utilisés pour décrire le comportement du matériau sur l'ensemble du domaine étudié. Cela permet d'identifier le modèle avec le meilleur ratio qualité/coût-délai pour une application donnée. Chacun des modèles étudiés dispose donc d'un domaine de définition propre.
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Vernon, Marie. "On a construction of young modules." Thesis, University of Leicester, 2005. http://hdl.handle.net/2381/30531.
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Let n be a natural number and E an n-dimensional vector space over a field K. The symmetric group acts by place permutation on the tensor space E ⊗r. The Sigmar-module E⊗r can be decomposed into a direct sum of permutation modules Mlambda where lambda is a composition of r into at most n parts.;Each permutation module labelled by such a composition is isomorphic to one labelled be a partition of r into at most n parts, and therefore we assume that lambda is such a partition. The indecomposable direct summands of the permutation module M lambda are called Young modules, and they are labelled by partitions of r into at most n parts.;Throughout this thesis we consider the case where E has dimension two. For lambda a two-part partition of r, we explicitly decompose the module M lambda into a direct sum of Young modules by providing spanning sets for the Young modules.;Moreover, we consider the problem of finding a basis or an algorithm for a basis for the Young modules in this case and, although we have not been able to solve this in general, we give some conjectures and examples showing in which cases we can find a basis.
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Martinot, Emmanuelle. "Indentation de films élastiques complexes par des sondes souples." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00786422.
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La compréhension des mécanismes qui pilotent la transmission des contraintes aux interfaces déformables est au centre de nombreuses problématiques touchant des applications actuelles utilisant un film mince de polymère souple comme couche interfaciale. Arriver à caractériser de tels films fins est encore un défi aujourd'hui car l'analyse des mesures expérimentales destinées à extraire les contributions dues aux films est complexe et délicate et les techniques usuelles de caractérisation sont peu adaptées aux systèmes. Ce travail étudie la réponse mécanique de deux types de systèmes modèles au moyen de deux techniques de caractérisation différentes. Le premier système que nous avons élaboré et caractérisé mécaniquement par le test JKR, est constitué de films d'élastomère réticulé d'épaisseurs micrométriques (de 5 à 100µm) et déposés sur des wafers de silicium. Les mesures expérimentales ont été analysées par comparaison à un modèle semi-analytique récent proposé par E. Barthel dans le but d'extraire le module élastique de chaque film et de répondre à la question de savoir si l'épaisseur du film influe sur la valeur de ce module. Nous avons montré que ce modèle permet de rendre compte quantitativement du raidissement lié à la présence d'un solide supportant le film mais que la précision sur les mesures de modules de Young reste limitée (de l'ordre de 35 %).Le deuxième système modèle est constitué de brosses de polymères greffées (PDMS) par une extrémité à la surface de wafers de silicium et gonflées dans un bon solvant (47V20). Nous avons analysé la réponse mécanique dans plusieurs régimes de distance et de fréquence en utilisant un appareil à forces de surface (SFA) dans lequel on contrôle l'approche d'une sphère millimétrique d'un plan sur lequel sont greffées les polymères. En statique, nous avons vérifié que la réponse en compression était celle d'une brosse de type Alexander-de Gennes. En mode dynamique, quand la sphère est loin de la couche gonflée, nous avons vérifié que la réponse dissipative était celle d'un écoulement de Reynolds qui décrit normalement l'écoulement d'un fluide simple newtonien entre une sphère et un plan solide. Ceci nous a permis de montrer que l'écoulement du solvant pénètre partiellement à l'intérieur de la couche greffée sur une profondeur de l'ordre du tiers de l'épaisseur gonflée de la couche. Dans le régime ou les brosses sont comprimées, il n'y a pas d'accord entre les mesures réalisées et le modèle classique de Fredrickson et Pincus. Ceci s'explique par les expériences que nous avons réalisées sur un substrat nu (sans polymère) montrant pour la première fois la déformation des substrats solides qui sont indentés par l'écoulement de liquide et qu'il faut prendre en compte cette déformation dans les analyses de nanorhéologie. Finalement, une annexe est consacrée à la fabrication de surfaces hydrophobes silanisées optimisées en vue d'étudier le glissement d'un liquide simple et d'électrolytes à la paroi.
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Crocker, Janina. "Measurement of the Young's modulus of Hexoloy silicon carbide thin films using nanoindentation." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18414.
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Thin films of metals and ceramics are commonly used as the structural materials for microelectromechanical systems (MEMS). These systems are used for a wide range of applications that include sensors, displays, and portable power generators. Accurate measurement of the mechanical properties of these thin films is essential for the robust design of high-performance and reliable MEMS. In this thesis, the method of nanoindentation is used to characterize the elastic properties of thin films of Hexoloy-SG silicon carbide. This material is of particular interest for MEMS operating in harsh, hightemperature environments. Nanoindentation was performed using a commercial Hysitron TriboIndenter® equipped with a diamond Berkovich nanoindenter tip. During each nanoindentation test, the indenter was forced into the specimen by a calibrated load, while the indentation depth was recorded continuously with nanometer resolution. The first part of this thesis describes a detailed protocol for nanoindentation testing using the TriboIndenter® and discusses the calibration of the instrument using a quartz standard. The identification of errors due to drift, vibrations, and surface inhomogeneities is described in detail. This protocol was then used to test a 2.1 µm thick film of Hexoloy-SG silicon carbide film deposited on a 500 µm thick single-crystal silicon substrate. The film was tested with loads varying from 1,000 µN to 13,000 µN, such that the maximum indentation was always less than 10% of the film thickness. The nanoindentation load-displacement curves from a total of 155 individual indents were analyzed using three different methods to extract the value of the Young's modulus of the Hexoloy film. The first method, developed by Oliver and Pharr, is widely used in nanoindentation analysis, but does not account explicitly for the effects of the underlying substrate. It is valid strictly for monolithic materials. Therefore, refinements of the Oliver-Pharr method by King aDes structures formées de couches minces métalliques et céramiques sont couramment utilisées dans la conception de microsystèmes électromécaniques (MEMS). Ces derniers se retrouvent dans plusieurs domaines, tels que les capteurs, les vidéoprojecteurs et les systèmes de génération d'énergie portable. Pour concevoir des MEMS fiables, les propriétés mécaniques de ces couches minces doivent êtres connues précisément. Le but de cette thèse est d'utiliser la méthode de nanoindentation pour déterminer les propriétés mécaniques des couches minces de carbure de silicium Hexoloy-SG. Ce matériel à été développé pour des microsystèmes opérant dans des conditions thermiques et chimiques extrêmes. La nanoindentation a été réalisée par le système TriboIndenter® de Hysitron équipé d'une pointe Berkovich en diamant, de forme pyramidale à base triangulaire. Chaque indentation comprend un cycle charge/décharge durant lequel la pointe indentatrice est enfoncée et retirée du matériel par une force calibrée, tandis que la profondeur de l'indentation est surveillée continuellement au nanomètre près. La première partie de cette thèse décrit une procédure détaillée pour la nanoindentation avec le système TriboIndenter®, incluant la calibration de l'instrument utilisant une norme en quartz monolithique. Également, l'identification d'erreurs expérimentales reliées au système de nanoindentation dues à la dérive, aux vibrations et à la rugosité de l'échantillon et leurs mesures correctrices sont présentées. Par après, cette méthodologie a été utilisée pour tester les propriétés mécaniques d'une couche mince de Hexoloy-SG mesurant 2.1 µm d'épaisseur, déposée sur un substrat de silicium monocristallin comptant 500 µm d'épaisseur. La force exercée par l'indentateur sur l'échantillon varie de 1,000 µN à 11,000 µN, pour que la profondeur de l'indentation demeure en deçà de 10% de l'épaisseur totale de la co
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Chan, Wing Kin. "Intrinsic and extrinsic effects on Young's modulus of nanowire measured in nanobridge tests /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20CHANW.
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Saheli, Massih. "Elastic Modulus Determination of Krouse Specimens through Resonance using Simple Beam Theory." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1555140817600694.
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Ahmed, Tabassum. "Computing Wall Thickness and Young's Modulus of Carbon Nanotubes with Atomistic Molecular Dynamics Simulations." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103647.
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Carbon nanotubes (CNTs) are tubular structure of a layer or layers of carbon atoms. CNTs serve as a prototypical nanomaterial holding great promises for various basic and applied research applications in the fields of electrical, thermal, and structural materials owing to their superlative mechanical, thermal, electrical, optical, and chemical properties. Since the discovery of CNTs by Iijima in 1991, numerous researches have been conducted to quantify and understand the atomic origin of their high strength, exceptional thermal conductivity, and unique electrical properties. CNTs are also widely used as nanofillers in composite materials to enhance their mechanical properties such as fracture toughness and to serve as sensing agents. There is thus an imperative need to deeply understand the physical properties of CNTs and their responses to various models of deformations such as stretching, bending, twisting, and combinations thereof. In this thesis, we apply all-atom molecular dynamics simulations to study in detail the behavior of several single-walled, armchair CNTs under stretching and bending deformations, realized by imposing appropriate boundary conditions on the CNTs. The simulation results reveal unique scaling properties of the stretching and bending stiffness with respect to the CNT radius and length, which indicate that a single-walled CNT is best modeled as a thin cylindrical shell with a cross-sectional radius equal to the CNT radius and a constant wall thickness much smaller than the CNT radius. By studying the thermal fluctuations of carbon atoms on the CNT wall, the wall thickness is determined to be about 0.45~AA~for all the single-walled CNTs studied in this thesis and correspondingly, Young's modulus is estimated to be about 8.78 TPa for these CNTs.Master of Science
Carbon atoms are magic building blocks of our world and the basis of life on the earth, and likely in the universe too. They can also form amazing materials with dimensionalities ranging from 0 to 3. For example, carbon atoms can form soccer-ball like spherical structures called fullerenes, with 0 dimensionality. They can also form 1-dimensional tubular structures with only one wall (i.e., one layer of carbon atoms) or multiple walls, called carbon nanotubes (CNTs) that have diameters typically in the nanometer range and lengths as long as 0.5 meter. Carbon atoms also form graphene sheets, which can be regarded as 2-dimensional structures, and 3-dimensional materials including graphite and diamond. In this work, we model CNTs using the molecular dynamics simulation method, where the motion of each atom is resolved and controlled if needed. Specifically, we study CNTs under stretching by fixing one end while pulling the other end in the axial direction, or bending by pulling the middle of a CNT along the radial direction in its cross-section while fixing its two ends. By fitting the simulation results to the continuum mechanics models, we show that a CNT is best described as a thin cylindrical shell with a radius equal to the CNT radius and a wall thickness much smaller than the radius. At the end, the wall thickness of all the CNTs studied here is determined to be about $0.45times 10^{-10}$ meter and their Young's modulus is estimated to be about $8.78times 10^{12}$ Pa, confirming that CNTs are one of the strongest and stiffest materials.
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Kubavat, Harshal A. "The influence of crystallization on the mechanical and interfacial properties of active pharmaceutical ingredients." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548090.
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Ali, S. "Dynamic effect of Young's modulus on attachment and differentiation of mouse embryonic stem cells." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1467252/.
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Embryonic stem cells have generated much interest due to their ability to differentiate into any cell type within the body. This ability could potentially allow for scientists and engineers to develop a number of therapies for diseases, which currently have no cure such as Parkinson’s disease, Alzheimer’s disease and diabetes. However, the differentiation process itself is one of the major bottlenecks in developing potential therapies. Currently protocols involve the use of mixtures of growth factors in order to create a suitable soluble microenvironment for differentiation. These growth factors are often expensive, thereby limiting the potential for scale-up of cell bioprocesses. Much interest has thus been generated into other elements of the microenvironment that could improve differentiation efficiency. The field of mechanobiology in particular, has developed rapidly in recent years. The aim of this thesis was to investigate the effect of Young’s modulus on neuronal differentiation of mouse embryonic stem cells (mESC’s). Instead of treating differentiation as one long process, the decision was made to split the process into three stages. The first, involved the formation of neural precursors from mESC’s. This was followed by the formation of immature neurons from neural precursors. The final stage was to allow the immature neurons to develop into a mature neuronal subtype. The impact of Young’s modulus was split into three effects. One was the initial attachment of cells. The second was the expansion of cells into colonies. The third was the effect of Young’s modulus on enrichment of neuronal cells. It was found that physiologically soft materials favoured the formation of all three neuronal cell types (precursor, immature and mature). However, the exact effect of differentiation varied over the course of differentiation. Over the first and second stages, soft substrates favoured the initial attachment of cells without affecting enrichment. Over the final stage, however, soft substrates directly favoured maturation of immature neurons, without having a significant effect upon their attachment. Thus the effect of Young’s modulus on neuronal differentiation changes according to the level of cellular maturity. There have not been any previous studies, which have tried to characterise the effect of the mechanical microenvironment on differentiation in a stage-by-stage manner. These findings have many important implications in terms of regenerative medicine bioprocessing. Firstly the optimal conditions for cellular attachment are not always the same as the optimal conditions for increasing cell enrichment. By carefully fine-tuning the mechanical properties at each stage of differentiation, both cell yields and final enrichment could be increased substantially. Furthermore, different cell types will require different optimisation strategies. Finally, by better understanding the interaction between cells and their mechanical environment, these findings could allow for better future design of tissue engineering biomaterials for implantation of cells into target areas for cell therapies.
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Bakenne, Adetokunboh. "Deformation and modulus changes of nuclear graphite due to hydrostatic pressure loading." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/deformation-and-modulus-changes-of-nuclear-graphite-due-to-hydrostatic-pressure-loading(aa6b8fd6-1c9f-4e71-b0dc-b5150b67223d).html.
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Graphite is used within a reactor as a moderator and a reflector material. During fast neutron irradiation, the physical properties and dimensions of nuclear graphite are changed significantly. Graphite shrinkage could lead to disengagement of individual component and loss of core geometry; differential shrinkage in the graphite component could lead to the generation of internal stresses and component failure by cracking. The latter behaviour is complicated by the irradiation induced changes in Young's modulus and strength. These dimensional and modulus change have been associated with the irradiation-induced closure of many thousands of micro-cracks associated with the graphite crystallites due to crystal dimensional change. Closure of microcracks in nuclear graphite was simulated by external pressure (hydrostatic loading, deviatory stress and dynamic loading) and not by irradiation, whilst Young's modulus was measured to check if there was any correlation between the two mechanisms. A study of the deformation behaviour of polycrystalline graphite hydrostatically loaded up to 200MPa are reported. Gilsocarbon specimens (isotropic) and Pile Grade A (PGA) specimens are (anisotropic in nature) were investigated. Strain measurements were made in the axial and circumferential directions of cylindrical samples by using strain gauges. Dynamic Young's modulus was also investigated from the propagation velocity of an ultrasonic wave. Porosity measurements are made to determine the change in the porosity before and after deformation and also their contribution towards the compression and dilatation of graphite under pressure. Graphite crystal orientation during loading was also investigated by using XRD (X-ray diffraction) pole figures. Effective medium models were also investigated to describe the effect of porosity on graphite elastic modulus. All the graphite specimens investigated exhibited non-linear pressure- volumetric strain behaviour in both direction (axial and circumferencial). In most of the experiments, the deformation was closing porosity despite new porosity being generated. Under hydrostatic loading, PGA graphite initially stiff then it became less stiff after a few percent of volume strain and then after about ~20% volumetric strain they stiffen up again, whist Gilsocarbon showed similar behaviour at lower volumetric strain (~10-13%). Gilsocarbon was stiff than PGA; this behaviour is due to the fact that Gilsocarbon has higher density and lower porosity than PGA. During unloading, a large hysteresis was formed. The stressed grains are relieved; the initial closed pores began to reopen. It is suggested that during this stage, the volume of pore re-opening superseded the volume of pores closing, the graphite sample volume almost fully recovered. In the axial compression test, PGA perpendicular to the extrusion direction (PGA-AG) was less stiff than PGA parallel to the extrusion direction (PGA-WG); in the hydrostatic compaction test, the PGA-WG sample deformed more because it had to undergo a less complicated shape change. This is because the symmetry of their anisotropy is parallel to the symmetry of the sample. The Pole figures showed an evidence of slight crystal reorientation after hydrostatic loaded up to 200MPa. The effective medium model revealed the importance of porosity interaction in graphite during loading.
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Yamaguchi, M., Y. Yamada, Y. Goto, M. Shikida, and K. Sato. "Mechanical Properties of Silicon-Based Membrane Windows Applied for a Miniature Electron Beam Radiation System." IEEE, 2007. http://hdl.handle.net/2237/9570.
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Sun, Li. "Complex Unloading Model for Springback Prediction." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1298656444.
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RAMACHANDRAN, RAHUL. "A nonlinear stress sensitivity study on role of Coil-thrombus complex in reduction of idealized cerebral aneurysm wall stresses." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1202193853.
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Yescas, Jorge Arturo. "Vibrational study of agarose spheres of millimetric and micrometric size." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/vibrational-study-of-agarose-spheres-of-millimetric-and-micrometric-size(c4bf7877-f6cf-48b8-bed2-ece48e230c5d).html.
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This PhD thesis is concerned with developing a methodology for early diagnosis of cancer by comparing the resonant frequencies in the amplitude spectra obtained during a vibration test using the AFM or, by comparing the stiffness properties of single cancerous and normal cells obtained using a resonant technique. As there is no reliable data in the literature to prove the existence of resonant frequencies of single cells, this work pioneers the search for resonant frequencies of related microspherical soft bodies using the AFM. Experiments to investigate the resonant behaviour of single cells depends on various parameters which are difficult to control; for example, the cell type, deciding at what stage the cell should be tested during the culturing process, determining the nucleus size, determining the cytoskeleton integrity and designing an appropriate vibration test setup among others. For this reason, agarose microspheres were selected to carry out preliminary work as these samples have similar properties to human cells and their resonances are affected by fewer variables. Although these micrometric spheres were tested under different conditions, no clear resonant behaviour was found at frequencies below 20 kHz and, only wide curves (interpreted as highly damped peaks of resonance) in the interval ranging from 20 kHz to 100 kHz were observed. By considering those curves as the quadrupole (Qp) vibration mode, approximate stiffness values for the agarose microspheres were found to be in between 37 kPa and 72 kPa. These values are similar to those obtained during an indentation test performed on the same samples whic¬¬h gave Young’s modulus values ranging from 10 kPa to 200 kPa. In order to gain a greater insight into the vibration test performed on microscopic samples, the research was extended to include agarose spheres of millimetric size. The characterization of these samples was carried out using an innovative purpose-built experimental setup. For the vibration test, a PZT based excitation device and a vibro-acoustic sensor were designed and constructed. The amplitude spectra of the vibration tests performed on millimetric samples consistently showed at least three peaks of resonance from which after the numerical simulation of the vibration test were interpreted as the quadrupole (Qp) and octupole (Op) vibration modes. Using this information, stiffness values for the samples ranging from 100 kPa to 700 kPa were calculated. In order to obtain the stiffness of the millimetric samples using a different technique, an experimental setup was constructed to perform a compression test. However, due to high viscoleasticity of the samples, it was not possible to obtain a standard compression curve necessary for their mechanical characterization. The results obtained from the tests on millimetric agarose samples demonstrate that spheres made of this material are able to provide measurable vibrational characteristics. Consequently, this methodology can be further implemented on micrometric samples and possibly on human cells to detect their resonant frequencies and equivalent stiffness values which can be used as a cancer marker. From the vibrational experiments on millimetric samples, it was noticed that the excitation mechanism plays an important role and for this reason future work is proposed to continue in this direction.
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Fintland, Trygve Westlye. "Measurements of Young's Modulus on Rock Samples at Small Amplitude and Low Frequency : RockHard Deformations." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13580.
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This thesis describes a new instrumental approach designed to measure the complex Young’s modulus on cylindrical samples 1 inch in diameter 2 inch long and typically in the range of 1-70 GPa. Excitation frequencies are from 11 Hz to 167 Hz. The setup is based on the Forced Deformation Method (Batzle et al., 2006) and is capable of measuring phase and magnitude of the dynamic stress and strain. An actuator provides an oscillating force from one end of the plug. Strain is measured on the cylindrical side with three strain gages evenly spaced around the circumference. The lowest recordable magnitude of strain is in the order of 10E-8. Force is measured by a piezoelectric transducer. Values are < 10 N. Plug sample measurements of the Young’s modulus values for Berea sandstone, Castlegate sandstone, Pierre shale, PEEK, and aluminium alloys (ALU-7075 and ALU-6061) are included. Reference material results are in accordance with published values. Some of the instrumentation needed is also given in detail in the previous work (Fintland, 2010).
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Karlsson, Tomas, and Johan Fromell. "Förstärkta strävor i trätakstolar för ökad tryckkapacitet : En laborativ undersökning." Thesis, Växjö University, School of Technology and Design, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-1545.
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I vissa takstolskonstruktioner kan det ibland uppstå stora tryckkrafter i diagonala reglar. I Sverige löser man oftast detta med hjälp av stagning tvärs diagonalen för att hindra utböjning i veka riktningen. Ibland när det är svårt att på plats trä in strävor på grund av utrymmesbrist och dylikt kan man spika eller skruva på en regel för att på så sätt förstärka den diagonala strävan. Detta examensarbete har undersökt två olika förstärkningsalternativ, rektangulärt- och T-tvärsnitt, med hjälp av reglar med dimension 45x95 mm2 vilka skruvas respektive spikas ihop. Detta har gjorts laborativt genom att trycka provkroppar i en provningsram och undersöka hur mycket den axiala kapaciteten ökar med förstärkning. De två olika förstärkningslösningarna bygger på att man på plats kan förstärka strävor med enkla medel.
Testbitarna har levererats till Växjö universitet och är av oklassat virke. Provbitarnas E-modul har undersökts för att på teoretisk väg undersöka hur stor axialkraftskapacitet den primära strävan har utan förstärkning. Provkroppar tillverkades och konditionerades i klimatrum, med temperaturen 20°C och 65 % RF, i ca tre veckor före provtryckning.
De laborativa värdena visar att den axiella kapaciteten ökar med 1,9 – 2,7 ggr för de rektangulära tvärsnitten och 2,5 – 4,0 ggr för T-tvärsnitten. Förstärkningsfaktorn är beroende av längd, förstärkningsalternativ och sammanfogning. Förstärkningseffektiviteten är högst för de längre strävorna.
In wooden roof trusses there sometimes may occur buckling in compressed web members. In most cases in Sweden this is solved by bracing between two webs to prevent buckling of the minor axis. Sometimes it is hard to brace between webs because of lack of space. Then it is possible to nail or screw a side member on the compressed web to increase the capacity. This diploma work has examined two different ways of bracing, rectangular cross section and T-bracing, with webs 45x95 mm2. Experimental tests have been made on compression webs and examine the bracing efficiency. It is important that the bracing alternatives are easy to use with simple tools.
Ungraded lumber were delivered to Växjö University. The Youngs modulus of the test pieces has been examined so the critical buckling load of the main member without bracing could be calculated theoretically. The lumber was conditioned to equilibrium moisture content of approximately 12 percent in a room maintained at 65 percent relative humidity and 20°C in three weeks before testing the critical buckling load.
The experimental results show that the critical buckling load increases with a factor of 1,9 – 2,7 for the rectangular cross sections and with a factor of 2,5 – 4,0 for the T-bracing. The bracing efficiency is dependent on length, bracing alternative and type of connectors.. The bracing efficiency increases for longer webs.
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Garcia, Giseli Cristina Ribeiro. "Estudo do comportamento ao dano por choque térmico de um concreto refratário, contendo agregados de andaluzita, sinterizado em diferentes temperaturas." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-27092012-122818/.
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O conhecimento da resistência ao dano por choque térmico de materiais refratários é uma das características mais importantes para determinar seu desempenho em muitas aplicações, pois quando os refratários são submetidos a abruptas e severas variações de temperatura, estes podem sofrer danos. A resistência ao dano por choque térmico de um material pode variar com o tamanho de grão, com o tipo e valor da tensão, com a taxa de carregamento e com outras condições de aplicação da tensão, ou seja, não é uma propriedade intrínseca do material. Os métodos correntemente utilizados para prever o comportamento da resistência ao dano por choque térmico são baseados nos trabalhos de Hasselman, responsável pelo estudo da determinação dos parâmetros de resistência ao choque térmico, R (oC), o parâmetro de resistência ao dano por choque térmico R\'\'\'\' (m), e o parâmetro de estabilidade da trinca sob tensão térmica Rst (m1/2.oC). As equações previstas por ele levam em consideração o módulo de Young, o módulo de ruptura, a energia de fratura e o coeficiente de expansão térmica do material a ser analisado. A resistência ao dano por choque térmico pode ser avaliada por meio de ciclos térmicos, isto é, sucessivos testes de aquecimento e subseqüente resfriamento, com análise da queda do módulo de Young a cada ciclo. Para prever e avaliar a resistência ao dano por choque térmico, amostras de um concreto refratário comercial fornecido pela IBAR (Indústrias Brasileiras de Artigos Refratários), foram sinterizadas a 1000ºC e 1450ºC por cinco horas. Essas temperaturas foram definidas em virtude de o concreto em questão apresentar agregados de andaluzita, que sofrem mulitização após 1280ºC. Logo esse concreto exibe um comportamento distinto em função da temperatura de tratamento térmico, pois seu agregado pode se transformar em mulita e sílica. Para esse estudo, amostras prismáticas sinterizadas a 1000ºC e 1450ºC, foram submetidas a ciclos de choque térmico, permanecendo 20 minutos no forno com temperatura de 1000ºC e subseqüente resfriamento em água circulante a 25ºC. Também foram realizadas análises de porosidade aparente, de absorção de água, de massa específica aparente, de difração de raios X e microscopia eletrônica de varredura. Foi verificado que os parâmetros de Hasselman previram que o refratário sinterizado a 1450ºC apresentaria menor resistência ao choque térmico, previsão esta confirmada pelos testes experimentais. Sendo assim é importante avaliar o comportamento do concreto refratário desde a temperatura ambiente até a temperatura de trabalho, a fim de que se conheçam todas as mudanças envolvidas, e que sejam evitados problemas que possam gerar prejuízos na instalação industrial e ao processo pertinente à sua aplicação.The thermal shock resistance of refractory materials is one of the most important characteristics that determine their performance in many applications, since abrupt and drastic differences in temperature can damage them. A material1s thermal shock resistance may vary according to grain size, the type and intensity of the stress to which it is subjected, the loading rate, and other loading conditions; hence, this resistance is not an intrinsic property of the material. The method currently employed to predict thermal shock behavior is based on the work of Hasselman, whose studies involved the determination of the parameters of thermal shock resistance, R (ºC), thermal shock damage resistance, R\"\" (m), and thermal stress crack stability, Rst (m1/2.ºC). Hasselman\'s equations take into consideration Young\'s modulus, the modulus of rupture, the energy at fracture and the coefficient of thermal expansion of the material under analysis. Resistance to thermal shock damage can be evaluated based on thermal cycles, i.e., successive heating and cooling cycles followed by an analysis of the drop in Young\'s modulus occurring in each cycle. In the present study, samples of a commercial refractory produced by IBAR (Indústrias Brasileiras de Artigos Refratários) were sintered at 1000ºC and 1450ºC for 5 hours to predict and evaluate their thermal shock resistance. These temperatures were chosen because this refractory contains andalusite aggregates that become mullitized at temperatures above 1280ºC. Therefore, this castable displays a particular behavior as a function of the heat treatment temperature, since its aggregates can transform into mullite and silica. In this study, prismatic samples from each sintering temperature were subjected to thermal shock cycles, soaking in the furnace for 20 minutes at a temperature of 1000ºC, and subsequent cooling in circulating water at 25ºC. Apparent porosity, water absorption, apparent density, X-ray diffraction and scanning electron microscopy analyses were also performed. It was found that Hasselman\'s parameters predicted that the refractory sintered at 1450ºC would show lower thermal shock resistance than the refractory sintered at 1000ºC, a prediction that was confirmed by the results of the thermal shock tests. Hence, is important to evaluate the behavior of refractory castables from ambient temperature to working temperature in order to be aware of all the changes that occur, thus avoiding problems leading to losses in industrial installations and in the processes involved in the specific applications of these refractories.