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Li, You-Sheng. "Heat capacity measurements of Sr₂RuO₄ under uniaxial stress". Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16591.
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The most-discussed pairing symmetry in Sr₂RuO₄ is chiral p-wave, pₓ ± p[sub]y, whose degeneracy is protected by the lattice symmetry. When the lattice symmetry is lowered by the application of a symmetry-breaking field, the degeneracy can be lifted, potentially leading to a splitting of the superconducting transition. To lift the degeneracy, the symmetry breaking field used in this study is uniaxial stress. Uniaxial stress generated by a piezo-electric actuator can continuously tune the electronic structure and in situ lower the tetragonal symmetry in Sr₂RuO₄. Previous studies of magnetic susceptibility and resistivity under uniaxial stress have revealed that there is a strong peak in T[sub]c when the stress is applied along the a-axis of Sr₂RuO₄. In addition, it has been proposed that the peak in T[sub]c coincides with a van Hove singularity in the band structure, and measurements of Hc₂ at the maximum T[sub]c indicate the possibility of an even parity condensate for Sr₂RuO₄ at the peak in Tc. In this thesis, the heat capacity approach is used to study the thermodynamic behavior of Sr₂RuO₄ under uniaxial stress applied along the crystallographic a-axis of Sr₂RuO₄. The first thermodynamic evidence for the peak in T[sub]c is obtained, proving that is a bulk property. However, the experimental data show no clear evidence for splitting of the superconducting transition; only one phase transition can be identified within the experimental resolution. The results impose strong constraints on the existence of a second phase transition, i.e. the size of the second heat capacity jump would be small or the second T[sub]c would have to be very close to the first transition. In addition to these results, I will present heat capacity data from the normal state of Sr₂RuO₄. The experimental results indicate that there is an enhancement of specific heat at the peak in T[sub]c, consistent with the existence of the van Hove singularity. The possibility of even parity superconductivity at the maximum T[sub]c has also been investigated. However, the heat capacity measurements are shown to be relatively insensitive to such a change, so it has not been possible to obtain strong and unambiguous evidence for whether it takes place or not.
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Barber, Mark E. "Uniaxial stress technique and investigations into correlated electron systems". Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/15429.
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In the repertoire of an experimental condensed matter physicist, the ability to tune continuously through features in the electronic structure and to selectively break point-group symmetries are both valuable techniques. The experimental technique at the heart of this dissertation, uniaxial stress, can do both such things. The thesis will start with a thorough discussion of our new technique, which was continually developed over the course of this work, presenting both its unique capabilities and also some guidance on the best working practices, before moving on to describe results obtained on two different strongly correlated electron materials. The first, Sr2RuO4, is an unconventional superconductor, whose order parameter has long been speculated to be odd-parity. Of interest to us is the close proximity of one of its three Fermi surfaces to a Van Hove singularity (VHs). Our results strongly suggest that we have been able to traverse the VHs, inducing a topological Lifshitz transition. T[sub]c is enhanced by a factor ~2.3 and measurements of H[sub](c2) open the possibility that optimally strained Sr2RuO4 has an even-parity, rather than odd-parity, order parameter. Measurements of the normal state properties show that quasiparticle scattering is increased across all the bands and in all directions, and effects of quantum criticality are observed around the suspected Lifshitz transition. Sr3Ru2O7 has a metamagnetic quantum critical endpoint, which in highly pure samples is masked by a novel phase. Weak in-plane magnetic fields are well-known to induce strong resistive anisotropy in the novel phase, leading to speculation that a spontaneous, electronically driven lowering of symmetry occurs. Using magnetic susceptibility and resistivity measurements we can show that in-plane anisotropic strain also reveals the strong susceptibility to electronic anisotropy. However, the phase diagram that these pressure measurements reveal is consistent only with large but finite susceptibility, and not with spontaneous symmetry reduction.
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Campbell, Brendan Anthony. "Annealing, uniaxial stress and isotope effects in radiation damaged diamond". Thesis, King's College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408149.
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Hartnett, S. J. "Uniaxial stress/DLTS studies on deep level defects in n-GaAs". Thesis, University of Sussex, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361362.
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Mitra, Abhijit. "LABORATORY INVESTIGATION OF COAL PERMEABILITY UNDER REPLICATED IN SITU STRESS REGIME". OpenSIUC, 2010. https://opensiuc.lib.siu.edu/dissertations/124.
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The cleat permeability of coal, a key to the success of any coalbed methane (CBM) recovery operation, is a dynamic parameter impacted by changes in effective stress and desorption-induced "matrix shrinkage". Most commonly-used theoretical models developed to predict CBM production as a result of permeability changes are based on the assumption that the deformation of a depleting coalbed is limited to the vertical direction; that is, the coal is under uniaxial strain conditions. However, most laboratory studies completed to estimate the changes in coal permeability have used triaxial state of stress, thus violating the underlying principles of the models. An experimental study was, therefore, undertaken to estimate the permeability variation of coal with a decrease in pore pressure under replicated in situ conditions where flow through coal, held under uniaxial strain conditions, was measured. Three samples were tested, one from the San Juan basin and the other two from the Illinois basin. The experimental results showed that, under uniaxial strain conditions, decreasing pore pressure resulted in a significant decrease in horizontal stress and increased permeability. The permeability increased non-linearly with decreasing pore pressure, with a small increase in the high pressure range, which increased progressively as the pressure dropped below a certain value. The experimental results were used to validate two theoretical models, namely the Palmer and Mansoori and Shi and Durucan, commonly used to project permeability variation with continued production. The models failed to provide good agreement with the experimental results below 300 psi, suggesting a shortcoming in the modeling philosophy. Although the measured permeability and stress changes were in qualitative agreement with the modeling results, both models predicted negative horizontal stresses at low pore pressures for one coal type, which was not supported by experimental results. The sorption-induced strain was also found to be significantly higher in the low pore pressure range, clearly suggesting a direct relationship between the sorption-induced strain and permeability. Moreover, the increase in permeability was different for the three coal types tested, with the largest increase for the core taken from maximum depth. Finally, a gradual increase in the logarithm of permeability was measured with reduction in horizontal stress. These results suggest a distinct advantage for deeper coals, which have generated limited interest to date, primarily due to the low initial permeability. Extending the deformation of a cylindrical rock sample loaded axially, a hypothesis was developed where coal undergoes maximum deformation at the middle of its length. Using this hypothesis, permeability variation with decreasing pore pressure was estimated and the established trend was used to modify one of the existing models. The agreement between laboratory results and the modified model showed definite promise for improving permeability projection capability.
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Rau, Georg. "Theory of the electronic and optical properties of GaAs/AlGaAs quantum wells under uniaxial stress". Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298423.
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Thapa, Romit. "Uniaxial and Biaxial Restraint in Concrete Pavement Undergoing Alkali-Silica Reaction". Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1533123602865294.
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Chen, Wen. "Uniaxial behaviour of suction caissons in soft deposits in deepwater". University of Western Australia. School of Civil and Resource Engineering, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0136.
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Suction caissons are a cost-effective alternative to traditional piles in deep to ultradeep waters. No design rule has been available on the axial capacity of suction caissons as part of the mooring system in soft sediments. In this research, a series of centrifuge tests were performed using instrumented model caissons, to investigate the axial capacity and radial stress changes around caissons during installation, consolidation and vertical pullout in normally consolidated, lightly overconsolidated and sensitive clays. Total pressure transducers instrumented on the caisson wall were calibrated for various conditions. The radial total stress acting on the external wall varied almost linearly during penetration and extraction of the caisson, with smaller gradients observed during post-consolidation pullout. Minimum difference was found in the penetration resistance and the radial total stress for caissons installed by jacking or by suction, suggesting that the mode of soil flow at the caisson tip is similar under these two types of installation. Observed soil heave showed that the soil particles at the caisson tip flow about evenly outside and inside the caisson during suction installation. Comparison was made between measurements and various theoretical predictions, on both the radial stress changes during caisson installation, and the radial effective stress after consolidation. Significant under-predictions on excess pore pressure changes, consolidation times and external shaft friction ratios were found for the NGI Method, based on the assumption that the caisson wall is accommodated entirely by inward motion of the clay during suction installation. Obvious over-predictions by the MTD approach were found in both stress changes and shaft capacity of the caissons. A simple form of cavity expansion method was found to give reasonable estimations of stress changes and post-consolidation external shaft friction. A model for predicting the penetration resistance of suction caissons in clay was evaluated. Upper and lower bound values of external shaft friction ratio during uplift loading after consolidation were derived. Uplift capacity of caissons under sustained loading and cyclic loading were investigated, revealing approximately 15 to 30% reduction of the capacity compared to that under monotonic loading. External shaft friction ratios and reverse end-bearing capacity factors were both found to be significantly lower than those under monotonic loading
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Sviridov, Viacheslav [Verfasser]. "Stress-Dependent Elastic Properties of Anisotropic Sedimentary Rocks: Uniaxial and Triaxial Experiments and Theoretical Modelling / Viacheslav Sviridov". Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1176638718/34.
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Coates, Terrence Joseph. "Effects of uniaxial tensile stress on magnetic flux leakage and magnetic Barkhausen noise around blind-hole pits in steel". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0002/MQ42600.pdf.
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Hartig, Jens. "Numerical investigations on the uniaxial tensile behaviour of Textile Reinforced Concrete". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-66614.
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In the present work, the load-bearing behaviour of Textile Reinforced Concrete (TRC), which is a composite of a fine-grained concrete matrix and a reinforcement of high-performance fibres processed to textiles, exposed to uniaxial tensile loading was investigated based on numerical simulations. The investigations are focussed on reinforcement of multi-filament yarns of alkali-resistant glass. When embedded in concrete, these yarns are not entirely penetrated with cementitious matrix, which leads associated with the heterogeneity of the concrete and the yarns to a complex load-bearing and failure behaviour of the composite. The main objective of the work was the theoretical investigation of effects in the load-bearing behaviour of TRC, which cannot be explained solely by available experimental results. Therefore, a model was developed, which can describe the tensile behaviour of TRC in different experimental test setups with a unified approach. Neglecting effects resulting from Poisson’s effect, a one-dimensional model implemented within the framework of the Finite Element Method was established. Nevertheless, the model takes also transverse effects into account by a subdivision of the reinforcement yarns into so-called segments. The model incorporates two types of finite elements: bar and bond elements. In longitudinal direction, the bar elements are arranged in series to represent the load-bearing behaviour of matrix or reinforcement. In transverse direction these bar element chains are connected with bond elements. The model gains most of its complexity from non-linearities arising from the constitutive relations, e. g., limited tensile strength of concrete and reinforcement, tension softening of the concrete, waviness of the reinforcement and non-linear bond laws. Besides a deterministic description of the material behaviour, also a stochastic formulation based on a random field approach was introduced in the model. The model has a number of advantageous features, which are provided in this combination only in a few of the existing models concerning TRC. It provides stress distributions in the reinforcement and the concrete as well as properties of concrete crack development like crack spacing and crack widths, which are in some of the existing models input parameters and not a result of the simulations. Moreover, the successive failure of the reinforcement can be studied with the model. The model was applied to three types of tests, the filament pull-out test, the yarn pull-out test and tensile tests with multiple concrete cracking. The results of the simulations regarding the filament pull-out tests showed good correspondence with experimental data. Parametric studies were performed to investigate the influence of geometrical properties in these tests like embedding and free lengths of the filament as well as bond properties between filament and matrix. The presented results of simulations of yarn pull-out tests demonstrated the applicability of the model to this type of test. It has been shown that a relatively fine subdivision of the reinforcement is necessary to represent the successive failure of the reinforcement yarns appropriately. The presented results showed that the model can provide the distribution of failure positions in the reinforcement and the degradation development of yarns during loading. One of the main objectives of the work was to investigate effects concerning the tensile material behaviour of TRC, which could not be explained, hitherto, based solely on experimental results. Hence, a large number of parametric studies was performed concerning tensile tests with multiple concrete cracking, which reflect the tensile behaviour of TRC as occurring in practice. The results of the simulations showed that the model is able to reproduce the typical tripartite stress-strain response of TRC consisting of the uncracked state, the state of multiple matrix cracking and the post-cracking state as known from experimental investigations. The best agreement between simulated and experimental results was achieved considering scatter in the material properties of concrete as well as concrete tension softening and reinforcement wavinessDie vorliegende Arbeit beschäftigt sich mit Untersuchungen zum einaxialen Zugtragverhalten von Textilbeton. Textilbeton ist ein Verbundwerkstoff bestehend aus einer Matrix aus Feinbeton und einer Bewehrung aus Multifilamentgarnen aus Hochleistungsfasern, welche zu textilen Strukturen verarbeitet sind. Die Untersuchungen konzentrieren sich auf Bewehrungen aus alkali-resistentem Glas. Das Tragverhalten des Verbundwerkstoffs ist komplex, was aus der Heterogenität der Matrix und der Garne sowie der unvollständigen Durchdringung der Garne mit Matrix resultiert. Das Hauptziel der Arbeit ist die theoretische Untersuchung von Effekten und Mechanismen innerhalb des Lastabtragverhaltens von Textilbeton, welche nicht vollständig anhand verfügbarer experimenteller Ergebnisse erklärt werden können. Das entsprechende Modell zur Beschreibung des Zugtragverhaltens von Textilbeton soll verschiedene experimentelle Versuchstypen mit einem einheitlichen Modell abbilden können. Unter Vernachlässigung von Querdehneffekten wurde ein eindimensionales Modell entwickelt und im Rahmen der Finite-Elemente-Methode numerisch implementiert. Es werden jedoch auch Lastabtragmechanismen in Querrichtung durch eine Unterteilung der Bewehrungsgarne in sogenannte Segmente berücksichtigt. Das Modell enthält zwei Typen von finiten Elementen: Stabelemente und Verbundelemente. In Längsrichtung werden Stabelemente kettenförmig angeordnet, um das Tragverhalten von Matrix und Bewehrung abzubilden. In Querrichtung sind die Stabelementketten mit Verbundelementen gekoppelt. Das Modell erhält seine Komplexität hauptsächlich aus Nichtlinearitäten in der Materialbeschreibung, z.B. durch begrenzte Zugfestigkeiten von Matrix und Bewehrung, Zugentfestigung der Matrix, Welligkeit der Bewehrung und nichtlineare Verbundgesetze. Neben einer deterministischen Beschreibung des Materialverhaltens beinhaltet das Modell auch eine stochastische Beschreibung auf Grundlage eines Zufallsfeldansatzes. Mit dem Modell können Spannungsverteilungen im Verbundwerkstoff und Eigenschaften der Betonrissentwicklung, z.B. in Form von Rissbreiten und Rissabständen untersucht werden, was in dieser Kombination nur mit wenigen der existierenden Modelle für Textilbeton möglich ist. In vielen der vorhandenen Modelle sind diese Eigenschaften Eingangsgrößen für die Berechnungen und keine Ergebnisse. Darüber hinaus kann anhand des Modells auch das sukzessive Versagen der Bewehrungsgarne studiert werden. Das Modell wurde auf drei verschiedene Versuchstypen angewendet: den Filamentauszugversuch, den Garnauszugversuch und Dehnkörperversuche. Die Berechnungsergebnisse zu den Filamentauszugversuchen zeigten eine gute Übereinstimmung mit experimentellen Resultaten. Zudem wurden Parameterstudien durchgeführt, um Einflüsse aus Geometrieeigenschaften wie der eingebetteten und freien Filamentlänge sowie Materialeigenschaften wie dem Verbund zwischen Matrix und Filament zu untersuchen. Die Berechnungsergebnisse zum Garnauszugversuch demonstrierten die Anwendbarkeit des Modells auf diesen Versuchstyp. Es wurde gezeigt, dass für eine realitätsnahe Abbildung des Versagensverhaltens der Bewehrungsgarne eine relativ feine Auflösung der Bewehrung notwendig ist. Die Berechnungen lieferten die Verteilung von Versagenspositionen in der Bewehrung und die Entwicklung der Degradation der Garne im Belastungsverlauf. Ein Hauptziel der Arbeit war die Untersuchung von Effekten im Zugtragverhalten von Textilbeton, die bisher nicht durch experimentelle Untersuchungen erklärt werden konnten. Daher wurde eine Vielzahl von Parameterstudien zu Dehnkörpern mit mehrfacher Matrixrissbildung, welche das Zugtragverhalten von Textilbeton ähnlich praktischen Anwendungen abbilden, durchgeführt. Die Berechnungsergebnisse zeigten, dass der experimentell beobachtete dreigeteilte Verlauf der Spannungs-Dehnungs-Beziehung von Textilbeton bestehend aus dem ungerissenen Zustand, dem Zustand der Matrixrissbildung und dem Zustand der abgeschlossenen Rissbildung vom Modell wiedergegeben wird. Die beste Übereinstimmung zwischen berechneten und experimentellen Ergebnissen ergab sich unter Einbeziehung von Streuungen in den Materialeigenschaften der Matrix, der Zugentfestigung der Matrix und der Welligkeit der Bewehrung
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Zhang, Xuesong, i n/a. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion". Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051104.153239.
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Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.
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Zhang, Xuesong. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion". Thesis, Griffith University, 2003. http://hdl.handle.net/10072/365777.
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Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.Thesis (Masters)
Master of Philosophy (MPhil)
School of Engineering
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Souza, Márcio Alves Sodré de. "Efeito da tensão mecânica no ruído de baixa frequência de transistores SOI planares e tridimensionais". Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-15072016-142254/.
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Neste trabalho é apresentado um estudo do efeito da tensão mecânica uniaxial e biaxial no ruído de baixa frequência nos transistores SOI planares e tridimensionais (MuGFETs de porta tripla) com diferentes orientações cristalográficas, além de um estudo das características analógicas nos transistores planares e tipo MuGFET de porta tripla. Nos transistores planares, o estudo do ruído de baixa frequência demonstrou uma melhora para os transistores tensionados no regime de saturação, independente do comprimento de canal, entretanto para a região linear, a tensão mecânica somente reduziu o ruído para um comprimento de canal pequeno (160nm). Nas características analógicas, foi utilizado o recurso da simulação numérica bidimensional para obtenção dos resultados. Os resultados mostram que os transistores tensionados são capazes de promover um melhor desempenho na transcondutância, na ordem de um aumento no mínimo de 40% , indicando para comprimentos longos de canal (910 nm) uma aumento de 56% para tensão mecânica biaxial e o oposto para a uniaxial (45%) (160 nm): entretanto, na condutância de saída, a tensão mecânica de forma geral promove uma maior degradação, aumento de 3% para um transistor uniaxial e aumento de 105% para o transistor biaxial. No ganho intrínseco de tensão, mais uma vez os transistores tensionados melhoraram de desempenho: contudo, neste caso, melhor resultado foi para o transistor biaxial, chegando a 5 dB de ganho. Nos transistores de porta tripla, a análise do ruído foi realizada nos transistores tensionados e convencionais operando em saturação e, de forma geral, a tensão mecânica piora o ruído de baixa frequência em uma ordem de grandeza para o transistor estreito, ocorrendo apenas uma melhora quase imperceptível num transistor largo ou quase planar. Na análise do ruído para os transistores rotacionados para a região linear, apresentaram dependência 1/f, com o ruído governado pela flutuação do número de portadores associado à flutuação na mobilidade: a tensão mecânica piora o ruído, entretanto, adicionando a rotação do substrato, ocorre uma melhora do ruído devido à redução das armadilhas de interface, ocasionando numa melhor interface lateral. Para dispositivos largos, o plano de topo sofre um aumento da concentração das armadilhas, piorando a interface superior devido a rotação do substrato, resultando um pior ruído. Nas características analógicas, os transistores de MuGFETs de porta tripla com tensão mecânica e substrato rotacionado foram estudados, onde a rotação do substrato em 45º mais a presença da tensão mecânica promoveram uma piora nos resultados, principalmente na transcondutância, onde a piora variou de 45 % até 15 %, para um dispositivo estreito (20 nm ) e um largo (870 nm).This work presents a study of the uniaxial and biaxial mechanical stress effect on low frequency noise in planar and three-dimensional SOI transistors (triple gate) with different crystal orientation, and an study of analog parameters in planar and for triple gate MuGFET. In planar transistor, the study of low frequency noise showed an improvement in low frequency noise for strained transistors in saturation regime, regardless of the channel length, however for the linear regime, the mechanical stress only reduced the noise in a small channel length (160nm). In the analog characteristics was used the feature of two-dimensional numerical simulation for the expansion of the results. The results shows that the strained transistors are capable to promoting a better performance in transconductance in a order at least 40%, indicating for a long channel lengths (910nm) an improvement of 56% in favor of biaxial stress and the opposite to uniaxial (45%) (160nm), however in the output conductance, the mechanical stress promotes higher degradation, ranging from 3% to uniaxial transistor and 105% for biaxial transistor. The intrinsic voltage gain, the strained transistors improved the performance, but in this case a best result was found for the biaxial strain reaching 5 dB. In triple gate transistors, the analysis of noise was performed on strained and conventional operating in saturation, and generally the worsening of mechanical stress on the low frequency noise in a order of magnitude for the marrow transistor, occurring only barely perceptible improvement seen in wider transistor or quasi-planar. The noise analysis for rotated transistors in linear region, showed a 1/f noise characteristic governed by the carrier number of fluctuations associated with fluctuations in mobility, the mechanical stress worsens the noise, however, by adding the substrate rotation occurs improves noise due to reduction of interface traps leading to a better sidewall interface. For larger devices the top plane suffer an increase of interface traps, worsening the top interface due to rotation of the substrate, causing a worse noise. In the analog characteristics, the triple gate MuGFETs transistors with mechanical stress and rotated substrate were studied, where the rotation of the substrate in 45º plus mechanical stress promoted a worsening of the results, particularly in the transconductance, where the worsening ranged from 45% up to 15% for a narrow device (20 nm) and a large (870 nm).
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Sharma, Henu. "Theoretical studies of PbTiO3 and SrTiO3 under uniaxial mechanical constraints combining firstprinciples calculations and phenomenological Landau theory". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI078.
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Dans cette thèse, nous présentons des études théoriques de matériaux pérovskites sous con-trainte mécanique uniaxiale en combinant les calculs de premier principe DFT ainsi quela théorie phénoménologique de type Landau. Les pérovskites ABO3 forment une classetrès importante de matériaux fonctionnels, qui peuvent présenter un large éventail de pro-priétés (e.g., supraconductivité, magnétisme, ferroélectricité, multiferroïcité, transitionsmétal-isolant. . . ) grâce aux petites distorsions d’ une même structure prototype cubique.Bien que ces composés aient été largement étudiés expérimentalement et théoriquement, ilreste encore des questions importantes et non résolues concernant les effets de contraintesuniaxiales. Au cours de ces dernières années, l’ ingénierie de contrainte a été décrite commeune approche originale pour ajuster les propriétés ferroélectriques pérovskites ABO3. Alorsque les effets de tension épitaxié-biaxiale et pression la hydrostatique, sont plutôt bien com-pris dans cette classe de matériaux, très peu est connu en ce qui concerne l’ effet des con-traintes mécaniques uniaxiales. Notre étude est motivée par ce manque de compréhensionactuelle de l’ effet de tension et compression uniaxiale, qui a été jusqu’à présent presquetotalement négligé. Deux composés prototypes sont étudiés dans le détail: PbTiO3 etSrTiO3. Après une introduction générale sur les composés ABO3 et les calculs techniques(ab initio et modèle phénoménologique de Landau), nous avons étudié l’ effet de contraintesmécaniques sur ces matériaux dans notre thèse.PbTiO3 est un composé ferroélectrique prototypique et également l’ un des composantsmère de la solution solide Pb(Zr,Ti)O3 (PZT), qui est le piézoélectrique le plus largementutilisé dans des applications. Pour PbTiO3, nous avons montré que indépendammentde la contrainte mécanique uniaxiale appliquée, le système conserve un état fondamentalpurement ferroélectrique avec la polarisation alignée, soit le long de la direction de lacontrainte (en phase FEz) ou bien le long d’ un des axes pseudo-cubique, qui lui estperpendiculaire (phase de FEx). Cela contraste avec les cas de contraintes mécaniquesisotropes ou bi-axial, pour qui de nouvelles phases combinant des modes ferroélectriqueset antiferrodistortives ont déjà été décrites. Sous contrainte uniaxiale, PbTiO3 passe d’unétat fondamental FEx sous compression à un état fondamental FEz en tension au-delà d’une tension critique !czz! +1%. Sous contrainte uniaxiale, PbTiO3 présente soit un étatfondamental FEx sous compression ("zz < 0) ou un état fondamental de FEz sous tension("zz > 0). Cependant, ici, un brusque saut des paramètres structuraux est prévu sousdes contraintes de compression et de traction à des valeurs critiques "zz! +2 GPa et −8GPa. Ce comportement semble similaire à celui pré-prédit sous pression isotrope négativeet pourrait se révéler utile en pratique pour améliorer la réponse piézoélectrique dans lesnano-composants.Le deuxième composé intéressant est SrTiO3. Il a été largement étudié au cours desdernières décennies, en raison de ses propriétés exceptionnelles à basse température. Dansce travail, nous avons élargi nos précédentes études de PbTiO3, en explorant théorique-ment les effets de pression sur la perovskite SrTiO3, combinant les premiers principes decalculs et un modèle phénoménologique de type Landau. Nous avons discuté de l’évolutiondes fréquences des phonons de SrTiO3 des trois cas de contraintes isotrope, uniaxial ettensions biaxiaux en utilisant les calculs de premier principe. Nous confirmons des travauxexpérimentaux précédents sur SrTiO3 que ça soit en contrainte épitaxiée ou sous pressionhydrostatique. Enfin, nous avons calculé de diagramme de phase de SrTiO3 sous contrainteuniaxiale, obtenue à partir de la théorie de Landau que nous avons comparé aux calculsde premier principeIn the present thesis we present theoretical studies of perovskite compounds under uniax-ial mechanical constraints combining first-principles DFT calculations approach and phe-nomenological Landau theory. ABO3 perovskites form a very important class of functionalmaterials that can exhibit a broad range of properties (e.g., superconductivity, magnetism,ferroelectricity, multiferroism, metal-insulator transitions. . . ) within small distortions ofthe same simple prototype cubic structure. Though these compounds have been exten-sively studied both experimentally and computationally, there are still unresolved issuesregarding the effect of pressure. In recent years, strain engineering has reported to bean original approach to tune the ferroelectric properties of perovskite ABO3 compounds.While the effect of epitaxial biaxial strain and hydrostatic strain is rather well understoodin this class of materials, very little is yet known regarding the effect of uniaxial mechanicalconstraints. Our study is motivated by the little existing understanding of the effect ofuniaxial strain and stress, that has been up to now almost totally neglected. Two proto-type compounds are studied in detail: PbTiO3 and SrTiO3. After a general introductionon ABO3 compounds and calculations techniques (ab initio and phenomenological Landaumodel), we studied the effect of mechanical constraints in these compounds in our thesis.PbTiO3 is a prototypical ferroelectric compound and also one of the parent components ofthe Pb(Zr,Ti)O3 solid solution (PZT), which is the most widely used piezoelectrics. ForPbTiO3, we have shown that irrespectively of the uniaxial mechanical constraint applied,the system keeps a purely ferroelectric ground-state, with the polarization aligned eitheralong the constraint direction (FEz phase) or along one of the pseudocubic axis perpen-dicular to it (FEx phase). This contrasts with the case of isotropic or biaxial mechanicalconstraints for which novel phases combining ferroelectric and antiferrodistortive motionshave been previously reported. Under uniaxial strain, PbTiO3 switches from a FEx groundstate under compressive strain to FEz ground-state under tensile strain, beyond a critical strain !czz! +1%. Under uniaxial stress, PbTiO3 exhibits either a FEx ground state undercompression ("zz < 0) or a FEz ground state under tension ("zz > 0). Here, however, anabrupt jump of the structural parameters is also predicted under both compressive andtensile stresses at critical values "zz! +2 GPa and −8 GPa. This behavior appears similarto that predicted under negative isotropic pressure and might reveal practically useful toenhance the piezoelectric response in nanodevices.The second compound of interest is SrTiO3. It has been widely studied in the past decadesdue to its unusual properties at low temperature. In this work, we have extended ourprevious investigations on PbTiO3 by exploring theoretically the pressure effects on per-ovskite SrTiO3 combining the first-principles calculations and a phenomenological Landaumodel. We have discussed the evolution of phonon frequencies of SrTiO3 with the threeisotropic, uniaxial and biaxial strains using first-principles calculations. We also reproducethe previous work done in SrTiO3 with epitaxial strain and hydrostatic strain. Finally,we have calculated the phase diagram of SrTiO3 under uniaxial strain, as obtained fromLandau theory and discussed how it compares with the first-principles calculations
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Gonzales, Manny. "The mechanochemistry in heterogeneous reactive powder mixtures under high-strain-rate loading and shock compression". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54393.
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This work presents a systematic study of the mechanochemical processes leading to chemical reactions occurring due to effects of high-strain-rate deformation associated with uniaxial strain and uniaxial stress impact loading in highly heterogeneous metal powder-based reactive materials, specifically compacted mixtures of Ti/Al/B powders. This system was selected because of the large exothermic heat of reaction in the Ti+2B reaction, which can support the subsequent Al-combustion reaction. The unique deformation state achievable by such high-pressure loading methods can drive chemical reactions, mediated by microstructure-dependent meso-scale phenomena. Design of the next generation of multifunctional energetic structural materials (MESMs) consisting of metal-metal mixtures requires an understanding of the mechanochemical processes leading to chemical reactions under dynamic loading to properly engineer the materials. The highly heterogeneous and hierarchical microstructures inherent in compacted powder mixtures further complicate understanding of the mechanochemical origins of shock-induced reaction events due to the disparate length and time scales involved.
A two-pronged approach is taken where impact experiments in both the uniaxial stress (rod-on-anvil Taylor impact experiments) and uniaxial strain (instrumented parallel-plate gas-gun experiments) load configurations are performed in conjunction with highly-resolved microstructure-based simulations replicating the experimental setup. The simulations capture the bulk response of the powder to the loading, and provide a look at the meso-scale deformation features observed under conditions of uniaxial stress or strain. Experiments under uniaxial stress loading reveal an optimal stoichiometry for Ti+2B mixtures containing up to 50% Al by volume, based on a reduced impact velocity threshold required for impact-induced reaction initiation as evidenced by observation of light emission. Uniaxial strain experiments on the Ti+2B binary mixture show possible expanded states in the powder at pressures greater than 6 GPa, consistent with the Ballotechnic hypothesis for shock-induced chemical reactions. Rise-time dispersive signatures are consistently observed under uniaxial strain loading, indicating complex compaction phenomena, which are reproducible by the meso-scale simulations. The simulations show the prevalence of shear banding and particle agglomeration in the uniaxial stress case, providing a possible rationale for the lower observed reaction threshold. Bulk shock response is captured by the uniaxial strain meso-scale simulations and is compared with PVDF stress gauge and VISAR traces to validate the simulation scheme. The simulations also reveal the meso-mechanical origins of the wave dispersion experimentally recorded by PVDF stress gauges.
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Duffrene, Lucas. "Comportement viscoélastique d'un verre silico-sodocalcique dans le domaine des températures intermédiaires : approche phénoménologique et modélisation en triaxialité". Paris, ENMP, 1994. http://www.theses.fr/1994ENMP0515.
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Les opérations de mise en forme ou de traitement thermique (trempe, recuisson) sont généralement effectuées à des températures intermédiaires (500-650c) et à des niveaux de contraintes modérés pour lesquels le comportement mécanique du verre peut être décrit par une loi viscoélastique linéaire. L'objectif de la thèse est de réaliser une démarche expérimentale complète afin de modéliser le comportement viscoélastique en triaxialité d'un verre silico-sodocalcique. Les modules d'élasticité du verre ont été mesures par diffusion Brillouin dans le domaine de la transition. Des essais statiques de relaxation des contraintes et de fluage-recouvrance en cisaillement et en sollicitation uniaxiale ont été réalisés autour de la transition vitreuse. Ils permettent en particulier de montrer la dualité fluage-relaxation. Des essais dynamiques en cisaillement ont été également réalisés afin de montrer la correspondance statique-dynamique. Un développement de la théorie de la viscoélasticite par l'introduction des moments des spectres de relaxation et de retard ainsi que des constantes viscoélastiques permet d'obtenir des relations fondamentales entre les sollicitations uniaxiale, de cisaillement et de pression hydrostatique. Ainsi, dans le cadre du modèle de Maxwell généralisé, la partie hydrostatique du comportement viscoélastique est déterminée à partir des essais en sollicitation uniaxiale et par la connaisance du comportement en cisaillement. On montre également que la fonction de Kohlraush et le modèle de Perez ne conviennent pas pour décrire d'une manière phénomenologique le comportement viscoélastique du verre silico-sodocalcique. Le modèle de Maxwell généralisé est validé en comparant les résultats d'un calcul de structure avec un essai présentant un état de contraintes triaxiales complexes. Le modèle viscoélastique déterminé peut être étendu à la thermoviscoélasticite pour simuler les procédés de formage, de trempe des vitrages automobiles en verre silico-sodocalcique
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Zang, Yong Hua. "Contribution a l'etude des proprietes viscoelastiques de caoutchoucs reticules et de liquides polystyrenes". Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13225.
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Les mesures experimentales ont ete effectuees en cisaillement dynamique et en extension uniaxiale. La viscosite limite depend de la masse moleculaire moyenne en poids. La complaisance recouvrable peut etre decrite par une loi de melange. La frequence critique et le module de perte critique correspondant au passage du comportement newtonien au comportement pseudoplastique ont ete relies aux moments de la distribution des masses moleculaires. Cette etude conduit a un nouveau type de relation entre la contrainte et la deformation
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Barragán, Bryan Erick. "Failure and toughness of steel fiber reinforced concrete under tension and shear". Doctoral thesis, Universitat Politècnica de Catalunya, 2002. http://hdl.handle.net/10803/5905.
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La tesis se enmarca en la caracterización, a nivel material, de la fractura del hormigón reforzado con fibras de acero (SFRC) bajo solicitaciones de tracción y cortante, y sobre la determinación de parámetros que representan la tenacidad del material sometido a esos dos modos de carga. Asimismo, se han realizado ensayos hasta rotura por cortante de elementos estructurales a escala real, los cuales se han analizado utilizando formulaciones existentes en distintos códigos de diseño.El comportamiento a tracción uniaxial del hormigón reforzado con fibras de acero se caracteriza utilizando cilindros entallados, elaborados con hormigones de resistencia normal y alta, con y sin fibras de acero. La metodología se extiende también para testigos extraídos de elementos de mayor tamaño. Los resultados se utilizan para definir parámetros de tenacidad y resistencia equivalentes de post-pico utilizables para representar el comportamiento del material y para un posible diseño estructural. Además, se desarrolla un estudio paramétrico experimental, que considera diferentes variables del ensayo y forma de probetas, para definir una configuración confiable del ensayo. Se analizan los modos de rotura observados y se evalúa la respuesta tensión-ancho de fisura. Asimismo, se propone una relación tensión-apertura de fisura característica para el diseño y análisis estructural. El comportamiento a tracción uniaxial se compara también con el de flexión y tracción por compresión diametral.
La fractura por cortante se estudia a nivel material, en hormigones de resistencia normal y alta, con y sin fibras de acero, utilizando la configuración de cortante directo denominada push-off. Se analizan el modo de rotura y la respuesta tensión-desplazamiento. Además, se definen parámetros basados en la tenacidad y tensiones equivalentes de cortante para una posible utilización en el diseño estructural.
Con el fin de obtener resultados que validen la utilización de las fibras de acero como refuerzo de cortante y al mismo tiempo estudiar la fractura por cortante a nivel estructural, se han realizado ensayos a escala real sobre vigas de sección rectangular y en T. Se analizan las respuestas carga-flecha y carga-ancho de fisura de vigas rectangulares de hormigón reforzado con fibras de acero variando su altura y de vigas T variando las dimensiones del ala. Los resultados obtenidos experimentalmente se utilizan para verificar la aplicabilidad de los métodos de diseño existentes en el caso del hormigón reforzado con fibras de acero. Además, se presenta una propuesta para el diseño a cortante basada en la respuesta tensión-desplazamiento relativo obtenida a partir del ensayo push-off de cortante directo.
The thesis deals with the characterization of the failure of steel fiber reinforced concrete (SFRC) in tension and shear, on the material level, and the determination of parameters that represent the toughness in these two modes of failure. Tests have been performed on large-scale beams failing under shear failure, which have been analyzed using existing design code formulas. The toughness parameters determined from the material are used in the design against such failure.
The uniaxial tensile behavior of SFRC is characterized using notched cylinders of normal and high strength concretes, with and without steel fibers. The methodology is also extended to cores extracted from large elements. Results are used to define toughness parameters and equivalent post-peak strengths to be used for representing the material behavior and for possible structural design. Furthermore, a parametric study considering different test variables and specimen shape is carried out in order to define a reliable test configuration. The observed modes of failure are analyzed and the stress-crack width response is evaluated. Also, a characteristic stress-crack width response is proposed for structural analysis and design. The uniaxial tension behavior is also compared with that of flexural and splitting-tension.
The shear failure is studied using the direct shear push-off test configuration, in normal and high strength concretes with and without steel fibers. The mode of failure and the stress-slip and stress-crack opening responses are analyzed. Toughness parameters and equivalent shear strengths based on the test results are defined for structural design.
In order to provide results for validating the use of steel fibers as shear reinforcement and for studying shear failure at the structural level, full-scale tests on rectangular and T-beams were performed. The load-deflection and load-crack width responses are analyzed and compared with results of plain concrete beam tests. The experimentally-obtained results are used to evaluate the applicability of existing design methods for steel fiber reinforced concrete. Furthermore, a proposal for shear design based on the shear stress versus slip relationship from the push-off shear test is presented.
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Good, Mattias. "Structural analysis of thermal interface materials and printed circuit boards in telecom units - a methodology". Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59746.
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En struktur analys på Ericssons MINILINK-6352 har utförts för att undersöka spänningar och deformationer på enheten, främst med fokus på de termiska gränskiktsmaterialen och buktningar av kretskortet. Dessa är viktiga aspekter när man överväger om enheten är termiska lämpad ur en mekanisk synvinkel, där god ytkontakt mellan de olika kropparna är avgörande för ordentlig kylning genom värmeledning. Analysen kräver tillräcklig materialdata till gränskiktsmaterialen och kretskortet för att kunna skapa lämpliga matematiska modeller. Enaxliga kompressionstester har genomförts för att karakterisera de hyperelastiska och viskoelastiska lagar för fyllda silikongummimaterial som används som termiska gränskiktsmaterial, som ibland kallas för gappad. Böjning av ett kretskort simulerades och jämfördes med ett tre--punkts böjtest för att verifiera om befintlig materialdata i beräkningsprogrammen var tillräcklig, jämförelsen visade god överensstämmelse. Kretskortet med dess komponenter, som modellerades som styva block, med gappads ovanpå som komprimeras av en platta simulerades och ett svagt område hittades. Detta område var sedan tidigare känt och har i ett senare skede eliminerats genom att tillsätta ytterligare en stödpelare. Därav visar denna studie en metod för att hitta intressanta regioner tidigt i konstruktionsfasen som lätt kan ändras för att uppfylla nödvändiga krav och undvika brister i konstruktionen. Arbetet har visat sig användbart genom att hitta detta svaga område i exempel produkten, arbetet ger även tillräckligt med information och exempeldata för att ytterligare utreda liknande produkter. Kombinationen av erfarenhet och simulering möjliggör smartare designval.A structural analysis on Ericssons MINILINK-6352 has been performed in order to investigate stresses and deformations of the unit, mainly focusing on the thermal interface materials and warpage of the printed circuit boards. These are important aspects when considering if the unit is thermally adequate from a mechanical point of view, where good surface contact between various bodies are critical for proper cooling through heat conductivity. The analysis requires sufficient materal data for the interface material and the circuit board in order to create suitable mathematical models. Uniaxial compression tests have been conducted to characterise the hyperelastic and viscoelastic constitutive laws of a filled silicone rubber material used as a thermal interface material, commonly referred to as a thermal pad. Bending of a printed circuit board was simulated and compared to a three-point bend test on the circuit board in order to verify material data already available in the computational software, which showed good agreement. The entire radio unit was mechanically analysed during its sealing process. The circuit board with attached components modelled as stiff blocks with thermal pads on top compressed by plates was simulated and a weak area was found. This area in question was already known and has in a later stage been eliminated by adding an additional supporting pillar. Hence this study shows a methodology to find regions of interest at an early design phase which can easily be altered to fulfil necessary requirements and eliminate design flaws. This work has proven useful in finding weak regions in the example product, it also provides enough information and example data to further investigate similar products. The combination of experience and simulation allows for smarter design choices.
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Guillaume, Alexandre. "Transitions de phases dans les fermions lourds sous contrainte uniaxiale". Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10060.
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Nous presentons les premiers resultats obtenus avec un dispositif experimental permettant de changer la contrainte uniaxiale continument a tres basse temperature. Le principe de l'appareil consiste a controler la pression d'helium appliquee sur un soufflet metallique connecte thermiquement a la boite de melange d'un refrigerateur a dilution. Nous etudions l'effet de la contrainte uniaxiale, appliquee selon l'axe c du compose tetragonal uru#2si#2. Nous trouvons que la temperature de transition supraconductrice t#c varie de facon parabolique en fonction de la contrainte #c avec une pente de 76 mk/kbar a #c = 0 kbar et une pente nulle a 6. 5 kbar. La temperature de transition antiferromagnetique t#n varie lineairement en fonction de la contrainte avec une pente egale a 32 mk/kbar. Nous rapportons les premieres mesures de l'evolution du gap des excitations de la phase antiferromagnetique en fonction de la contrainte uniaxiale selon l'axe c. Il decroit lineairement avec une pente de 0. 63 k/kbar. Grace aux mesures de champ critique, nous donnons la premiere estimation de la croissance de la masse effective avec la contrainte selon l'axe c, m*(6. 5 kbar) = 1. 07 m*(0 kbar). Pour le compose hexagonal upt#3, nous confirmons que la temperature de transition supraconductrice t#+#c decroit, d'abord avec une pente de 14. 71. 5 mk/kbar, pour une contrainte appliquee suivant l'axe c inferieure a 2 kbar puis decroit, avec une pente de 5. 20. 7 mk/kbar, pour des contraintes superieures. En variant de 0 a 8. 4 kbar la contrainte #a appliquee selon l'axe a, nous trouvons que la temperature t#+#c decroit regulierement avec une pente de 2. 00. 7 mk/kbar. A partir de l'evaluation du coefficient a de la loi = #0+at#2 et de la pente du second champ critique a bas champ, nous trouvons que la masse effective augmente avec la contrainte suivant l'axe c et diminue avec la contrainte suivant l'axe a:m*(#c = 6. 5 kbar) = 1. 26 m*(#c = 0 kbar) ; m*(#a = 6. 5 kbar) = 0. 86 m*(#a = 0 kbar).
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Morland, Catherine. "Etude de la contrainte et de l'orientation dans les reseaux d'elastomeres diformes". Paris 6, 1987. http://www.theses.fr/1987PA066057.
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La contrainte appliquee et l'orientation sont mesurees simultanement durant une traction uniaxiale de reseaux polybutadiene et de copolymeres sbr par fluorometrie. Le modele d'anneaux glissants, qui considere que les enchevetrements forment des anneaux virtuels et mobiles entre les chaines, est utilise pour interpreter les resultats. Caracterisation de la topologie du reseau par le modele thermique de flory et erman
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Belmehdi, Yassine. "Contribution à l'identification de nouveaux indicateurs de défaillance des modules de puissance à IGBT". Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14258/document.
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L’électronique de puissance a un rôle de plus en plus grandissant dans les systèmes de transports : voitures électriques et hybrides, trains et avions. Pour ces applications, la sécurité est un point critique et par conséquent la fiabilité du système de puissance doit être optimisée. La connaissance du temps de fonctionnement avant défaillance est une donnée recherchée par les concepteurs de ces systèmes. Dans cette optique, un indicateur de défaillance précoce permettrait de prédire la défaillance des systèmes avant que celle-ci soit effective. Dans cette thèse, nous nous sommes intéressés à la caractérisation électromécanique des puces de puissance IGBT et MOSFET. L’exploitation de cette caractérisation devrait permettre, à plus long terme, de mettre en évidence un indicateur de l’état mécanique des assemblages de puissance à des fins de fiabilité prédictivePower electronics has a role increasingly growing up in transport:electric and hybrid vehicles, trains and aircraft. For these applications, security is a critical point, thus the reliability of the power assembly must be optimized. The knowledge of time to failure is very important information for the designers of these systems. Inthis context, an early failure indicator would predict system failuresbefore it becomes effective. In this thesis, we focused on the electromechanical characterization of power transistors: MOSFET and IGBT. Based on these results this electromechanical characterization should help us in the longer term, to highlight an early failure indicator of the power assembly
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Giannotta, Jean-Claude. "Comportement mecanique et evolution structurale de cuivres de haute purete dans le domaine dynamique". Paris, ENMP, 1986. http://www.theses.fr/1986ENMP0029.
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Caracteristiques du comportement mecanique dans du cuivre soumis a des essais de traction uniaxiale ou lamine dans le domaine dynamique. Analyse de la ductilite. Etude par microscopie electronique de la microstructure, notamment de la structure des dislocations apres laminage. Analyse de la texture. Comparaison avec l'etat quasistatique
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Al-Nasser, Amin Eyad. "Characterization of Sheet Materials for Stamping and Finite Element Simulation of Sheet Hydroforming". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243953225.
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Noudem, Jacques Guillaume. "Texturation des céramiques supraconductrices Bi-Pb-Sr-Ca-Cu-O par combinaison des effets du champ magnétique et de la contrainte uniaxiale à haute température". Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10169.
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Les ceramiques supraconductrices des composes bi-(pb)-sr-ca-cu-o ont une capacite de transport de courant electrique a 77 k faible qui est due a la presence des porosites et a la desorientation des feuillets. Pour obtenir des densites de courant critique de transport elevees dans ces materiaux, il est necessaire de les densifier et d'induire une orientation cristallographique preferentielle. Un procede permettant de texturer par effet combine du champ magnetique et de la contrainte uniaxiale a haute temperature a ete mis au point. Le dispositif experimental permet d'appliquer une pression uniaxiale de 60 mpa sous un champ magnetique de 8 t jusqu'a une temperature de 1100c. Les echantillons elabores sont obtenus a partir des precurseurs industriels (hoechst) de la phase bi:2223. La technique de texturation par solidification sous champ magnetique s'est averee tres efficace pour obtenir des echantillons massifs polycristallins bi-(pb)-sr-ca-cu-o orientes avec l'axe-c des cristallites parallele au champ magnetique applique. Les densites de courant critiques (jc) obtenues par ce procede sont de 1450 a/cm#2 pour une densite de 5. 1 g/cm#3 (82% de la densite theorique). La texturation par fluage sous contrainte uniaxiale, a permis d'obtenir des ceramiques denses ( 6 g/cm#3), homogenes ayant des densites de courant critiques de 2500 a/cm#2. Les rubans ag/bi:2223 fournis par alcatel alsthom ont aussi ete textures avec succes par le procede de pressage a chaud. La combinaison du champ magnetique et de la contrainte uniaxiale permet d'ameliorer la texture et la densite des echantillons qui par ailleurs sont tres homogenes et possedent une bonne tenue mecanique. Les densites de courant critique de transport a 77 k atteignent 3800 a/cm#2 suivant les plans (a,b) et 1100 a/cm#2 suivant l'axe-c. Par ailleurs, nous avons mis en evidence la possibilite d'utiliser ces ceramiques texturees dans le domaine de l'electrotechnique pour limiter le courant
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Renversade, Loïc. "Analyse expérimentale et numérique de la plasticité à l’échelle des grains individuels dans un polycristal d’aluminium déformé en traction uniaxiale". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEM019/document.
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Ce travail vise à améliorer la compréhension de la déformation locale des matériaux polycristallins. Pour cela, les comportements des grains individuels d'un polycristal d'aluminium déformé plastiquement sont étudiés par une approche couplant expériences in situ en synchrotron et simulation par élément finis.Dans l'expérience, la microstructure initiale est cartographiée par tomographie en contraste de diffraction (DCT). L'éprouvette est déformée en traction uniaxiale et 466 grains sont suivis par microscopie 3D par diffraction des rayons X (3DXRD) jusqu'à une déformation de 4.5%. De nouvelles méthodes d'analyse originales donnent accès aux orientations, déformations élastiques et contraintes, en moyenne par grain, et permettent de déterminer les distributions d'orientations intragranulaires à partir des données 3DXRD.Dans la simulation, la microstructure réelle (DCT) est modélisée par une partition de Laguerre, maillée finement et soumise au chargement expérimental. Les champs mécaniques et les champs d'orientations résultants peuvent être comparés aux données expérimentales.La comparaison entre expérience et simulation révèle un accord au premier ordre. Les rotations expérimentales montrent une forte variabilité associée à l'interaction intergranulaire et bien reproduite dans la simulation. Les distributions d'orientations ont des directions d'étalement privilégiées perpendiculaires à la direction de traction, ce qui est relié aux mécanismes de déformation du matériau. Les contraintes montrent un bon accord, dans la limite de la précision de mesure. Ces données, très riches, fournissent des pistes d'amélioration pour les modèles de plasticité cristallineThis work aims to improve our understanding of the local deformation of polycrystalline materials. To this end, in situ synchrotron experiments and finite element simulations are coupled to study the individual grain responses in an aluminium polycrystal during plastic deformation.In the experiment, the initial microstructure is mapped by Diffraction Contrast Tomography (DCT). The specimen is deformed in uniaxial tension and 466 grains are followed by 3D X-Ray Diffraction (3DXRD) up to 4.5% plastic strain. New original analysis methods provide the grain average orientations, elastic strains and stresses, and allow determining the intra-grain orientation distributions from the 3DXRD measurements.In the simulation, the real microstructure (DCT) is modeled by a Laguerre tessellation, finely meshed and submitted to the experimental loading. The resulting mechanical and orientation fields can be compared to the experimental data.The comparison reveals a first-order agreement between experiment and simulation. The experimental rotations exhibit a high variability, associated to grain interaction and well reproduced in the simulation. The orientation distributions exhibit preferential spread directions perpendicular to the tensile direction, which can be related to the deformation mechanisms. Lastly, the stresses are found to be in agreement within the measurement accuracies. Such a rich dataset provides routes to improve crystal plasticity models
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Král, Petr. "Verifikace nelineárních materiálových modelů betonu". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227601.
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Diploma thesis is focused on the description of the parameters of nonlinear material models of concrete, which are implemented in a computational system LS-DYNA, interacting with performance of nonlinear test calculations in system LS-DYNA on selected problems, which are formed mainly by simulations of tests of mechanical and physical properties of concrete in uniaxial compressive and tensile on cylinders with applying different boundary conditions and by simulation of bending slab, with subsequent comparison of some results of test calculations with results of the experiment. The thesis includes creation of appropriate geometric models of selected problems, meshing of these geometric models, description of parameters and application of nonlinear material models of concrete on selected problems, application of loads and boundary conditions on selected problems and performance of nonlinear calculations in a computational system LS-DYNA. Evaluation of results is made on the basis of stress-strain diagrams and load-displacement diagrams based on nonlinear calculations taking into account strain rate effects and on the basis of hysteresis curves based on nonlinear calculations in case of application of cyclic loading on selected problems. Verification of nonlinear material models of concrete is made on the basis of comparison of some results of test calculations with results obtained from the experiment.
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Jakel, Roland. "Grundlagen der Elasto-Plastizität in Creo Simulate - Theorie und Anwendung". Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-87141.
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Der Vortrag beschreibt die Grundlagen der Elasto-Plastizität sowie die softwaretechnische Anwendung mit dem FEM-Programm Creo Simulate bzw. Pro/MECHANICA von PTC. Der erste Teil des Vortrages beschreibt die Charakteristika plastischen Verhaltens, unterschiedliche plastische Materialgesetze, Fließkriterien bei mehrachsiger Beanspruchung und unterschiedliche Verfestigungsmodelle. Im zweiten Vortragsteil werden Möglichkeiten und Grenzen der Berechnung elasto-plastischer Probleme mit der Software dargestellt sowie Anwendungstipps gegeben. Im dritten Vortragsteil schließlich werden verschiedene Beispiele vorgestellt, davon besonders ausführlich das Verhalten einer einachsigen elasto-plastischen Zugprobe vor und nach dem Eintreten der EinschnürdehnungThis presentation describes the basics of elasto-plasticity and its application with the finite element software Creo Simulate (formerly Pro/MECHANICA) from PTC. The first part describes the characteristics of plastic behavior, different plastic material laws, yield criteria for multiaxial stress states and different hardening models. In the second part, the opportunities and limitations of analyzing elasto-plastic problems with the FEM-code are described and user information is provided. The last part finally presents different examples. Deeply treated is the behavior of a uniaxial tensile test specimen before and after elongation with necking appears
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Baumgarten, Lars. "Gesteinsmechanische Versuche und petrophysikalische Untersuchungen – Laborergebnisse und numerische Simulationen". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-202612.
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Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen.
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Yi-Wei, Chang. "Uniaxial Stress-Strain Behavior of MWCNT-Reinforced Epoxy-Matrix Composites". 2005. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0009-0112200611361168.
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Chang, Yi-Wei, i 張益瑋. "Uniaxial Stress-Strain Behavior of MWCNT-Reinforced Epoxy-Matrix Composites". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/28358134028948908663.
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碩士元智大學
機械工程學系
94
Due to its excellent stiffness and strength, the carbon nanotube (CNT) is considered as an ideal candidate for reinforcement in composites. In the present work, the epoxy resin is used as the matrix whereas multi-walled carbon nanotubes (MWCNTs) with various diameters are used as the reinforcement. The composite is subjected to uniaxial tension and the effects of CNT weight fraction and CNT diameter on the mechanical properties of the composite are studied. The experiment results show that the Young modulus of 5 wt% CNT/epoxy composites with a CNT diameter D < 20 nm and D = 40 ~ 60 nm is 4.56 GPa and 4.36 GPa, and the tensile strength is 52.89 MPa and 46.80 MPa, respectively, whereas the Young modulus and the tensile strength of the pure epoxy is 2.83 GPa and 25.67 MPa, respectively. Micromechanics models are developed to predict the Young modulus of CNT-reinforced composites. The predicted Young moduli are benchmarked with the experimental data of MWCNT-reinforced epoxy-matrix composites.
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Lin, You-Lun, i 林佑倫. "A Three-Dimensional Equivalent Uniaxial Strain and Stress Constitutive Model". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/85x5ek.
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碩士國立中央大學
土木工程學系
105
This research presents a three-dimensional constitutive model of material based on the concept of equivalent uniaxial strain in order to decouple Poisson’s effect in multiaxial loading condition. The equivalent uniaxial strain is a fictitious material index which is invented to compute the parameters such as material stiffness modulus and Poisson’s ratio. The characteristics of uniaxial stress-strain model which defined by the ultimate strength parameters are obtain from material failure surface and the ultimate strength parameters varies with current stress or strain state. This research contains not only concrete material but also rock material and metal material, exerted by monotonic loading, proportional loading non-proportional loading and cyclic loading. A hypothesis of kinematic cap model is proposed to reflect the influence of the non-proportional loading path. Further, a hypothesis of softening model is applied on concrete and rock material not only to simulate post-peak branch behavior but to reflect the transition between brittle softening and ductile softening under different confining pressure. In concrete material established closed Menetrey-Willam (CMW) failure model which combined with Menetrey-Willam meridian and the cap model in concrete material and replaced Menetrey-Willam meridian with Drucker-Prager criterion in rock material. Saenz stress-strain model is applied and adjusted by the ultimate strength parameters from material failure model to reflect the latest stress or strain condition in both concrete and rock material. von-Mises criterion is applied to build material failure model for metal material as well. Correlation studies with available experimental tests are presented to valid the performance of proposed three d constitutive of materials.
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Yen, Yu-Cheng, i 顏昱丞. "Equivalent Uniaxial Strain And Stress Material Constitutive Model Under Dynamic Loading". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/jyt44t.
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碩士國立中央大學
土木工程學系
107
This research presents a dynamic three-dimensional constitutive model of material equivalent uniaxial strain and stress. The purpose is to study the behavior of concrete materials under dynamic loading, because most of the structures in daily life are subject to dynamic loading such as earthquakes, impacts and explosions. This research uses the equivalent uniaxial strain concept proposed by Darwin & Pecknold to separate the Poisson's ratio of multi-axial forces. The equivalent uniaxial strain is a fictitious material index which is invented to compute the parameters such as material stiffness modulus and Poisson’s ratio. This research proposes a dynamic material failure model, which combines the three-parameter failure criterion proposed by Menetrey and Willam with the cap model proposed by Balan et al. to form the Close-Menetrey-Willam model. The dynamic failure model is expanded by the DIF (Dynamic Increase Factor). The dynamic failure model under different strain rate loading states is established, and the stress state at different moments on the dynamic material failure model to define the ultimate strength parameters at the current moment. Using the uniaxial stress-strain model proposed by Saenz, this formula only needs to define the ultimate strength parameters to describe the hardened and softened sections in concrete behavior. It is quite simple and convenient to use in numerical simulation. This study proposes a concrete deterioration model. The combination of the concrete deterioration strength formula proposed by Du Jian-min and the Close-Menetrey-Willam model, establishes a deterioration model with different damage levels, defines the ultimate strength parameters of deterioration model. The numerical examples in this study verify the high strain rate, low strain rate loading of concrete, low strain rate loading of ice, the low strain rate loading of ice at different temperatures and concrete deterioration.
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WU, JIAN-HONG, i 吳建宏. "THE STUDY ON FAILURE CHARACTERISTIC OF MU-SHAN SANDSTONE UNDER UNIAXIAL STRESS". Thesis, 1998. http://ndltd.ncl.edu.tw/handle/25612553555492248281.
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Hung, Pei Heng, i 洪培恒. "A Method to Apply Uniaxial Stress on Silicon Substrate at High Temperatures". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/55157011718544499917.
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碩士長庚大學
電子工程學系
100
In this study, the effect of strain on USJs was studied. A method was developed to apply uniaxial stress on silicon substrate at high temperatures for ultra-shallow junctions (USJs). Polished (001) Si wafers with a thickness of 50 μm were cleaved along (110) directions into strips with a dimension of 18 mm × 3 mm. Stress was applied by bending and inserting the strips into slots in a u-shape quartz tray. After furnace process was finished, the sample curvature was measured. The stress on the sample was released then cut into small square pieces for Hall measurement. The influence of stress on was studied. Solid phase epitaxial regrowth (SPER). The specimens were prepared by Ge preamorphization implantation (PAI) and coimplantation with carbon and phosphorous. The samples with PAI were bending and annealed to cause SPER. Tensile stress increases the sheet concentration, but decreases the mobility. This leads to a higher sheet resistance. The experiment for deactivation annealing was performed with phosphorus USJ samples which had been activated by laser annealing. The samples were bended and annealed at low temperature for deactivation. Carrier concentration increases and the mobility decrease due to tensile stress. The trend of sheet concentration and mobility was both observed in SPER and deactivation experiments.
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chien, Hsu-Wei, i 徐維謙. "Flow stress characteristics of magnesium alloy AZ31B-O thin sheet during Uniaxial tension". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/71067225130531681143.
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碩士中華大學
機械工程學系碩士班
97
The magnesium alloy has been used in Aerospace industry in 30’ due to its distinguish feature of light weight with high specific stiffness. However, the high cost of refining limited its application. In recent years, the electronic industry has gradually increased the usage of the Mg alloys for 3C products. Many electronic products, such as cell phone and notebook, use a great quantity of Mg alloys as the case materials. The Mg alloys can also play as the substitutional materials for ferroalloys and Al alloys, revealing the increasing needs of the Mg alloy. The main purpose of this paper is to explore the flow behavior of AZ31B-O Mg alloy thin sheet under uniaxial tension at different temperatures and strain rates. The values of strain hardening exponent n, strain rate sensitivity exponent m, and strength coefficient k based on the approximation of the Backofen formula were calculated form the stress-strain curves obtained from the tensile test results. Quantitative analysis was performed to investigate the effects of temperatures and strain rates on the mechanical properties and deformation characteristics of AZ31B Mg alloy. Experimental results showed that the 0° samples exhibited the largest elongation to failure for testing at temperatures of room temperature and 250°C. While the largest elongations to failure were observed in the 45° samples for testing at the temperatures of 300°C, 370°C and 420°C, the maximum tensile strengths were found in the 90° specimens. Under all test conditions, The maximum elongation to failure of 270% was obtained in the 45° sample for testing at a strain rate of 4×10-3 s-1 and at a temperature 420°C. The characteristics of the stress-strain cures at elevated temperatures are different from that of at room temperature. The stress-strain curves with serrations were found at elevated temperatures. Theses results were resulted from dynamic recrystallization during deforming the alloy at elevated temperatures. Dynamic recrystallization would cause softening effect resulting in the decrease in the flow stress and the rate of work-hardening. The softening effect would increase elongation to failure, necking in the test sample could be apparently observed for AZ31B Mg alloy tested at elevated temperatures. Calculated flow stress based on the Backofen formula was quite consistent with the tensile test results at room temperature. Since softening effect was not taken into account in this analysis, the calculated results at elevated temperatures only consisted with the experimental data before necking took place.
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Jiratatprasot, Pornchai. "Mechanical properties and stress-strain behavior of high performance concrete under uniaxial compression". Thesis, 2002. http://library1.njit.edu/etd/fromwebvoyage.cfm?id=njit-etd2002-005.
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Lee, Chih-Haw, i 李志浩. "Studies on Electrical Properties and Terahertz Absorption Spectrum of p-Ge under uniaxial stress". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/33967337599391835205.
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碩士國立交通大學
電子工程系所
97
In this study, we measured the I-V and absorption characteristics of strained Ge:Ga samples at cryogenic temperature (10 K). As the stress increases along the [100] and [110] direction, the breakdown voltage increases to a maximum around 0.5-1 kBar and then decreases. The absorption spectra show that the energy differences between the ground states and the excited states also increase to a maximum then decrease in the same stress region. According to these results, we can propose a mechanism to explain the stress dependence of breakdown voltage. Our experiment is in agreement with the theoretical predictions.
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Chia-JungHsu i 許嘉容. "Numerical analysis on the uniaxial compression stress-strain curves of hollow sphere foams between rigid plates". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/tqm8tq.
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碩士國立成功大學
土木工程學系
105
Lightweight foam is a special kind of material with high porosity, good thermal insulation and excellent energy absorption. Foam has been widely used in lightweight structural engineering. However, due to the limitation in manufacturing, there are a variety of microstructural defects in commercially-available foams, thus reducing their engineering properties. In practice, hollow sphere foams are employed to replace the traditional foams with some microstructural defects resulting from production process. Because of the regularly-stacking microstructure of hollow sphere foams, their physical and engineering properties can be predicted more accurately. In the study, the difference in the uniaxial compressive stress-strain curves between the single-sized and dual-sized hollow sphere foams with the same relative density is discussed in detail. The commercially available finite element software ABAQUS is utilized here to conduct a series of numerical analyses. The stress-strain curves of hollow sphere foams between two rigid plates under uniaxial compression are obtained numerically. In running numerical analysis, a prescribed displacement is imposed on the rigid plates, the corresponding stresses on hollow sphere foams are calculated numerically. Furthermore, the resulting stress-strain curves of hollow sphere foams are presented and then compared to evaluate the effects of relative density and cell geometry. Numerical results show that the Young's modulus, yield strength and strain energy of dual-sized hollow sphere foams are consistently larger than those of single-sized hollow sphere foams with the same relative density.
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Ching-YaoChang i 詹晴堯. "Temperature Dependence of Electrical Characteristic on the Uniaxial Tensile Strained CMOSFETs by Using Stress Memorization Technique (SMT)". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/05511007046809980601.
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Hutcherson, Shawn Curtis. "Analysis of a database of uniaxial geogrid pullout resistance results". 2012. http://hdl.handle.net/2152/20050.
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Being able to extrapolate interaction values from a database of pullout resistance testing results may possibly help with narrowing down the most suitable reinforcement/fill material combinations for a Mechanically Stabilized Earth wall, thereby reducing the number of tests needed for a design and maximizing the efficiency of the system.
The objectives of this thesis include the following: collect and organize a broad collection of data in a way that can assist in preliminary selection of interaction properties for uniaxial geogrids; analyze the collection of data for trends related to geogrid polymer type; analyze the collection of data for trends related to the presence of fines in the fill material; compare the collected data to previous studies on the effects of geogrid specimen length on pullout performance; and compare the collected data to previous studies on the effect of geogrid rib thickness to mean particle size ratio on normalized bearing stress and CI values.
The data from 101 pullout tests are presented in tabular and graphic form so that the coefficient of interaction may be interpolated for many geogrid/fill material combinations. The effect of polymer type (PET vs HDPE) was shown to have little effect on how a geogrid performs in a fill material. In one case, the two polymer types exhibit differing trends within the same fill material. The presence of fines (>12% by weight) in the fill material results in a significant decrease in the coefficient of interaction when compared to clean granular fills. The effects of geogrid embedment length have significant effects on the results of geogrid pullout tests. Samples with shorter lengths were shown to carry a greater load per unit area than longer samples. Normalized bearing stress is shown to be heavily influenced by the geogrid transverse rib thickness to mean particle size ratio (B/D50). For a particular fill material, normalized bearing stress decreases linearly with increasing B/D50. For a particular geogrid, normalized bearing stress is shown to have a bi-linear behavior with increasing B/D50. Initially, normalized bearing stress increases with increasing B/D50. After reaching a peak, normalized bearing stress begins to decrease with increasing B/D50.text
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Ghosh, Shreenanda. "Manipulation of time reversal symmetry breaking superconductivity in Sr₂RuO₄ by uniaxial pressure". 2021. https://tud.qucosa.de/id/qucosa%3A76124.
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Unconventional superconductivity continues to be one of the most striking chapters in condensed matter physics, by posing challenges to our theoretical understanding
of its origin. During the last three decades a large number of unconventional superconductors with exotic properties have been found arising great interest, such
as the heavy fermion systems, high Tc cuprates as well as the Iron based superconductors etc. Sr2RuO4, the material I have studied, can be considered as an
exemplary case in this regard. In spite of more than two decades of comprehensive research, Sr2RuO4 remains one of the most compelling superconductors till date.
Various experimental results give evidence that the superconductivity of Sr2RuO4 is chiral: including measurements of the Kerr effect, sound velocities, critical currents
across junctions, and muon spin relaxation(μSR), the experimental technique at the heart of this dissertation. Recent NMR Knight shift measurements suggests that
the pairing is most likely spin-singlet, and in the tetragonal lattice of Sr2RuO4, the combination of singlet pairing and chirality compels consideration of an seemingly
unlikely order parameter: dxz ± idyz. It is unlikely because it comes along with a horizontal line node at kz = 0, whereas Sr2RuO4 has a very low c-axis conductivity.
And that makes the question whether or not the superconductivity of Sr2RuO4 is chiral, of great importance. This calls for an unique scenario in regard to our
understanding of unconventional superconductivity, as the presence of chirality in Sr2RuO4 might imply a new form of pairing, which is yet to be firmly determined.
Chiral superconductors break time reversal symmetry by definition, and in general time-reversal-symmetry breaking (TRSB) superconductivity indicates complex two component order parameters. Probing Sr2RuO4 under uniaxial pressure offers the possibility to lift the degeneracy between such components. However, despite strenuous efforts, a splitting of the superconducting and TRSB transitions under uniaxial pressure has not been observed so far. In this thesis, I report muon spin relaxation measurements on Sr2RuO4 samples, placed under uniaxial stress. The relatively large sample size suitable for μSR demanded for a customized uniaxial pressure cell in order to perform our experiments. It has been a technically challenging task to have a fully fledged uniaxial pressure cell with stringent requirements, that is suitable for time restricted facility experiments like μSR. The technical advancement has been documented thoroughly in this thesis. Using the dedicated uniaxial pressure cell, we observed the much awaited stress induced splitting between the onset temperatures of superconductivity and time reversal symmetry breaking, consistent with the qualitative expectations for a chiral order parameter in Sr2RuO4. In addition to that, we report the appearance of a bulk magnetic order in Sr2RuO4 under higher uniaxial stress for the first time, above the critical pressure at which a Lifshitz transition is known to occur. The signal in the state appearing at high stress qualitatively differs from that in the TRSB
state in unstressed Sr2RuO4, which provides evidence that the enhanced muon spin relaxation at lower stresses is not a consequence of conventional magnetism. As
a whole, our results strongly support the idea of two-component superconducting order parameter in Sr2RuO4, that breaks time-reversal symmetry.
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LU, YU-YING, i 陸昱縈. "Investigation into Electrical Characteristics of Uniaxial Tensile Strained nMOSFETs by Using Stress Memorization Technique with Different SiN Film Thickness". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/85496588211706000434.
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碩士正修科技大學
電子工程研究所
101
In this dissertation, the electrical characteristics of uniaxial tensile strained nMOSFETs were investigated, including DC characteristics and low-frequency (1/f ) noise. The strained nMOSFETs were fabricated by using stress memorization technique (SMT) with different thickness of tensile SiN film. Through series DC measurements, it found that SMT process-induced stress is truly transmitted from the deposited SiN layer, resulting in improved drive current stemming from enhanced carrier mobility. For 1/f noise measurement, as devices have more tensile stress, the decrease in 1/f noise can be observed. These results indicated the intrinsic benefit of uniaxial stained nMOSFETs. Consequently, based on these experimental results, optimal thickness of SiN film was also demonstrated.
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Chia-ChiehHung i 洪佳杰. "Uniaxial Ratcheting of Sn/3.5Ag Solder Induced by Cyclic Shear Strain with Constant Tensile Stress–Investigation by Endochronic Cyclic Plasticity". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/23331969364055991341.
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Hartig, Jens. "Numerical investigations on the uniaxial tensile behaviour of Textile Reinforced Concrete". Doctoral thesis, 2010. https://tud.qucosa.de/id/qucosa%3A25532.
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In the present work, the load-bearing behaviour of Textile Reinforced Concrete (TRC), which is a composite of a fine-grained concrete matrix and a reinforcement of high-performance fibres processed to textiles, exposed to uniaxial tensile loading was investigated based on numerical simulations. The investigations are focussed on reinforcement of multi-filament yarns of alkali-resistant glass. When embedded in concrete, these yarns are not entirely penetrated with cementitious matrix, which leads associated with the heterogeneity of the concrete and the yarns to a complex load-bearing and failure behaviour of the composite. The main objective of the work was the theoretical investigation of effects in the load-bearing behaviour of TRC, which cannot be explained solely by available experimental results. Therefore, a model was developed, which can describe the tensile behaviour of TRC in different experimental test setups with a unified approach.
Neglecting effects resulting from Poisson’s effect, a one-dimensional model implemented within the framework of the Finite Element Method was established. Nevertheless, the model takes also transverse effects into account by a subdivision of the reinforcement yarns into so-called segments. The model incorporates two types of finite elements: bar and bond elements. In longitudinal direction, the bar elements are arranged in series to represent the load-bearing behaviour of matrix or reinforcement. In transverse direction these bar element chains are connected with bond elements. The model gains most of its complexity from non-linearities arising from the constitutive relations, e. g., limited tensile strength of concrete and reinforcement, tension softening of the concrete, waviness of the reinforcement and non-linear bond laws. Besides a deterministic description of the material behaviour, also a stochastic formulation based on a random field approach was introduced in the model. The model has a number of advantageous features, which are provided in this combination only in a few of the existing models concerning TRC. It provides stress distributions in the reinforcement and the concrete as well as properties of concrete crack development like crack spacing and crack widths, which are in some of the existing models input parameters and not a result of the simulations. Moreover, the successive failure of the reinforcement can be studied with the model. The model was applied to three types of tests, the filament pull-out test, the yarn pull-out test and tensile tests with multiple concrete cracking.
The results of the simulations regarding the filament pull-out tests showed good correspondence with experimental data. Parametric studies were performed to investigate the influence of geometrical properties in these tests like embedding and free lengths of the filament as well as bond properties between filament and matrix. The presented results of simulations of yarn pull-out tests demonstrated the applicability of the model to this type of test. It has been shown that a relatively fine subdivision of the reinforcement is necessary to represent the successive failure of the reinforcement yarns appropriately. The presented results showed that the model can provide the distribution of failure positions in the reinforcement and the degradation development of yarns during loading. One of the main objectives of the work was to investigate effects concerning the tensile material behaviour of TRC, which could not be explained, hitherto, based solely on experimental results. Hence, a large number of parametric studies was performed concerning tensile tests with multiple concrete cracking, which reflect the tensile behaviour of TRC as occurring in practice. The results of the simulations showed that the model is able to reproduce the typical tripartite stress-strain response of TRC consisting of the uncracked state, the state of multiple matrix cracking and the post-cracking state as known from experimental investigations. The best agreement between simulated and experimental results was achieved considering scatter in the material properties of concrete as well as concrete tension softening and reinforcement waviness.Die vorliegende Arbeit beschäftigt sich mit Untersuchungen zum einaxialen Zugtragverhalten von Textilbeton. Textilbeton ist ein Verbundwerkstoff bestehend aus einer Matrix aus Feinbeton und einer Bewehrung aus Multifilamentgarnen aus Hochleistungsfasern, welche zu textilen Strukturen verarbeitet sind. Die Untersuchungen konzentrieren sich auf Bewehrungen aus alkali-resistentem Glas. Das Tragverhalten des Verbundwerkstoffs ist komplex, was aus der Heterogenität der Matrix und der Garne sowie der unvollständigen Durchdringung der Garne mit Matrix resultiert. Das Hauptziel der Arbeit ist die theoretische Untersuchung von Effekten und Mechanismen innerhalb des Lastabtragverhaltens von Textilbeton, welche nicht vollständig anhand verfügbarer experimenteller Ergebnisse erklärt werden können. Das entsprechende Modell zur Beschreibung des Zugtragverhaltens von Textilbeton soll verschiedene experimentelle Versuchstypen mit einem einheitlichen Modell abbilden können. Unter Vernachlässigung von Querdehneffekten wurde ein eindimensionales Modell entwickelt und im Rahmen der Finite-Elemente-Methode numerisch implementiert. Es werden jedoch auch Lastabtragmechanismen in Querrichtung durch eine Unterteilung der Bewehrungsgarne in sogenannte Segmente berücksichtigt. Das Modell enthält zwei Typen von finiten Elementen: Stabelemente und Verbundelemente. In Längsrichtung werden Stabelemente kettenförmig angeordnet, um das Tragverhalten von Matrix und Bewehrung abzubilden. In Querrichtung sind die Stabelementketten mit Verbundelementen gekoppelt. Das Modell erhält seine Komplexität hauptsächlich aus Nichtlinearitäten in der Materialbeschreibung, z.B. durch begrenzte Zugfestigkeiten von Matrix und Bewehrung, Zugentfestigung der Matrix, Welligkeit der Bewehrung und nichtlineare Verbundgesetze. Neben einer deterministischen Beschreibung des Materialverhaltens beinhaltet das Modell auch eine stochastische Beschreibung auf Grundlage eines Zufallsfeldansatzes. Mit dem Modell können Spannungsverteilungen im Verbundwerkstoff und Eigenschaften der Betonrissentwicklung, z.B. in Form von Rissbreiten und Rissabständen untersucht werden, was in dieser Kombination nur mit wenigen der existierenden Modelle für Textilbeton möglich ist. In vielen der vorhandenen Modelle sind diese Eigenschaften Eingangsgrößen für die Berechnungen und keine Ergebnisse. Darüber hinaus kann anhand des Modells auch das sukzessive Versagen der Bewehrungsgarne studiert werden. Das Modell wurde auf drei verschiedene Versuchstypen angewendet: den Filamentauszugversuch, den Garnauszugversuch und Dehnkörperversuche. Die Berechnungsergebnisse zu den Filamentauszugversuchen zeigten eine gute Übereinstimmung mit experimentellen Resultaten. Zudem wurden Parameterstudien durchgeführt, um Einflüsse aus Geometrieeigenschaften wie der eingebetteten und freien Filamentlänge sowie Materialeigenschaften wie dem Verbund zwischen Matrix und Filament zu untersuchen. Die Berechnungsergebnisse zum Garnauszugversuch demonstrierten die Anwendbarkeit des Modells auf diesen Versuchstyp. Es wurde gezeigt, dass für eine realitätsnahe Abbildung des Versagensverhaltens der Bewehrungsgarne eine relativ feine Auflösung der Bewehrung notwendig ist. Die Berechnungen lieferten die Verteilung von Versagenspositionen in der Bewehrung und die Entwicklung der Degradation der Garne im Belastungsverlauf. Ein Hauptziel der Arbeit war die Untersuchung von Effekten im Zugtragverhalten von Textilbeton, die bisher nicht durch experimentelle Untersuchungen erklärt werden konnten. Daher wurde eine Vielzahl von Parameterstudien zu Dehnkörpern mit mehrfacher Matrixrissbildung, welche das Zugtragverhalten von Textilbeton ähnlich praktischen Anwendungen abbilden, durchgeführt. Die Berechnungsergebnisse zeigten, dass der experimentell beobachtete dreigeteilte Verlauf der Spannungs-Dehnungs-Beziehung von Textilbeton bestehend aus dem ungerissenen Zustand, dem Zustand der Matrixrissbildung und dem Zustand der abgeschlossenen Rissbildung vom Modell wiedergegeben wird. Die beste Übereinstimmung zwischen berechneten und experimentellen Ergebnissen ergab sich unter Einbeziehung von Streuungen in den Materialeigenschaften der Matrix, der Zugentfestigung der Matrix und der Welligkeit der Bewehrung.
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Bochmann, Jakob. "Carbonbeton unter einaxialer Druckbeanspruchung". 2019. https://tud.qucosa.de/id/qucosa%3A35075.
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Die Forschung an Carbonbeton konzentrierte sich bisher überwiegend auf die Untersuchung des Tragverhaltens unter Zugbeanspruchung und die Entwicklung entsprechender Bemessungsmodelle für grundlegende Belastungsarten. Zur vollständigen und detaillierten Klärung des Tragverhaltens von Carbonbetonkonstruktionen ist es jedoch notwendig, das Verhalten unter Druckbeanspruchung zu kennen, da erste Erkenntnisse reduzierte Druckfestigkeiten vermuten lassen.
In der Dissertation werden erste systematische Untersuchungen zum Tragverhalten von Carbonbeton unter einaxialer Druckbeanspruchung durchgeführt. Ein optimierter Versuchsaufbau erlaubte es, eine Vielzahl von Einflussparametern, wie z. B. die Textilgeometrie, Garnstärke, Tränkung oder die Ausrichtung der Gelege, zu untersuchen. Die Auswertung des umfangreichen Versuchsprogrammes erfolgte hauptsächlich an Hand der aufgenommenen Spannungs-Dehnungs-Beziehungen in Längs- und Querrichtung und den Bruchbildern. Ergänzend zu den Versuchen wurden nummerische Untersuchungen hinsichtlich der Spannungsverteilungen im Probekörper durchgeführt.
Als Ergebnis der Arbeit konnte das Tragverhalten von Carbonbeton unter einaxialer Druckbeanspruchung ergründet werden. Grundlegend wurde ein anisotropes Verhalten von Carbonbeton unter Druck festgestellt. Die beobachteten Druckfestigkeiten waren dabei stark von der Ausrichtung der Gelege zur Druckbeanspruchung und vom vorhandenen Bewehrungsgrad abhängig. Basierend auf diesen Feststellungen werden zwei verschiedene Bemessungsmodelle zur Beschreibung der Druckfestigkeitsreduktion vorgeschlagen.:1 Einleitung
1.1 Problemstellung
1.2 Zielstellung
1.3 Aufbau
2 Stand des Wissens
2.1 Durchführung einaxialer Druckversuche
2.1.1 Allgemein
2.1.2 Probekörpergröße
2.1.3 Probekörperform
2.1.4 Toleranzen bei Druckversuchen
2.1.5 Lasteinleitung
2.2 Textilbeton
2.2.1 Allgemein
2.2.2 Betonmatrix
2.2.3 Textile Bewehrung
2.2.4 Herstellung
2.2.5 Tragverhalten von Textilbeton unter Zugbeanspruchung
2.2.6 Tragverhalten unter Querzugbeanspruchung
2.2.7 Tragverhalten von Textilbeton unter Druckbeanspruchung
2.2.8 Verbundverhalten von Textilbeton
2.3 Tragverhalten von Beton unter Druck - Heterogenität
2.3.1 Allgemein
2.3.2 Normalbeton
2.3.3 Leichtbeton
2.3.4 Faserbeton
2.3.5 Beton mit Einlagen
2.3.6 Gerissener Stahlbeton - zweiaxiale Belastung
2.4 Vergleichsmodell - Anisotropes Gestein unter Druckbeanspruchung
2.4.1 Schulter-Typ Gesteinsmodelle
2.4.2 U-Typ Gesteinsmodelle
2.5 Zusammenfassung
3 Experimentelle Methodik
3.1 Materialien
3.1.1 Betone
3.1.2 Textilien
3.2 Probekörper
3.2.1 Probekörpergeometrie
3.2.2 Herstellung
3.2.3 Qualitätskontrolle
3.3 Versuchsstand
3.3.1 Vorbetrachtungen
3.3.2 Prüfapparatur
3.3.3 Messtechnik
3.3.4 Versuchsdurchführung
3.4 Versuchsprogramm
3.5 Auswertung
4 Versuchsergebnisse und Tragverhalten unter einaxialer Druckbelastung
4.1 Referenzserie
4.2 Unbewehrte laminierte Versuche
4.2.1 Tragverhalten in Längsrichtung
4.2.2 Tragverhalten in Querrichtung
4.2.3 Bruchbilder
4.2.4 Charakteristische Punkte
4.2.5 Elastizitätsmodul
4.3 Bewehrte laminierte Versuche
4.3.1 Tragverhalten in Längsrichtung
4.3.2 Tragverhalten in Querrichtung
4.3.3 Versagenstypen
4.3.4 Charakteristische Punkte
4.3.5 Elastizitätsmodul
4.4 Bewehrte gegossene Versuche
4.4.1 Tragverhalten in Längsrichtung
4.4.2 Tragverhalten in Querrichtung
4.4.3 Versagenstypen
4.4.4 Charakteristische Punkte
4.4.5 Elastizitätsmodul
4.5 Zusammenfassung zum Tragverhalten
5 Numerische Untersuchungen
5.1 Modell
5.1.1 Materialmodell - Beton
5.1.2 Materialmodell - EP
5.1.3 Modellbildung
5.2 Untersuchungsergebnisse
5.2.1 Referenzserie
5.2.2 Bewehrte Serien - Öffnungen
5.2.3 Bewehrte Serien - gefüllte Öffnungen
5.3 Erkenntnisse zum Tragverhalten
6 Einflussparameter auf die Druckfestigkeit von Carbonbeton
6.1 Bezugssystem der Auswertung
6.2 Herstellung
6.2.1 Ein2uss des Handlaminierverfahrens
6.2.2 Ein2uss des Gießverfahrens
6.3 Lagenabstand
6.3.1 Bewehrte laminierte Serien
6.3.2 Bewehrte gegossene Serien
6.4 Maschenweite
6.4.1 Bewehrte laminierte Serien
6.4.2 Bewehrte gegossene Serien
6.5 Garnstärke
6.6 Effektiver Flächenanteil kA,eff
6.7 Anordnung
6.7.1 Versetzte Anordnung der Textilebenen
6.7.2 Verdrehte Anordnung in der Textilebene
6.8 Tränkung
6.9 Festigkeit
6.10 Zusammenfassung der Hauptein2ussparameter
7 Berechnungsmodell und Bemessungsvorschlag
7.1 Allgemein
7.2 Berechnungsmodell für Festigkeiten
7.2.1 Allgemein
7.2.2 Herleitung
7.2.3 Kritik
7.3 Vorschlag für Bemessungsmodell
7.3.1 Allgemein
7.3.2 Herleitung
7.3.3 Kritik
8 Zusammenfassung und Ausblick
8.1 Zusammenfassung
8.2 Ausblick
Literaturverzeichnis
A1 Verwendete Textilien
A2 Erläuterung zur Auswertung der Einzelversuche
A3 Zusammenstellung der untersuchten Serien
A4 Ergebnisse der numerischen Berechnungen
A5 Untersuchte Gesteinsmodellen
48
Ng, Evelyn. "Strengthening Mechanisms in Microtruss Metals". Thesis, 2012. http://hdl.handle.net/1807/34825.
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Microtrusses are hybrid materials composed of a three-dimensional array of struts capable of efficiently transmitting an externally applied load. The strut connectivity of microtrusses enables them to behave in a stretch-dominated fashion, allowing higher specific strength and stiffness values to be reached than conventional metal foams. While much attention has been given to the optimization of microtruss architectures, little attention has been given to the strengthening mechanisms inside the materials that make up this architecture. This thesis examines strengthening mechanisms in aluminum alloy and copper alloy microtruss systems with and without a reinforcing structural coating. C11000 microtrusses were stretch-bend fabricated for the first time; varying internal truss angles were selected in order to study the accumulating effects of plastic deformation and it was found that the mechanical performance was significantly enhanced in the presence of work hardening with the peak strength increasing by a factor of three. The C11000 microtrusses could also be significantly reinforced with sleeves of electrodeposited nanocrystalline Ni-53wt%Fe. It was found that the strength increase from work hardening and electrodeposition were additive over the range of structures considered. The AA2024 system allowed the contribution of work hardening, precipitation hardening, and hard anodizing to be considered as interacting strengthening mechanisms. Because of the lower formability of AA2024 compared to C11000, several different perforation geometries in the starting sheet were considered in order to more effectively distribute the plastic strain during stretch-bend fabrication. A T8 condition was selected over a T6 condition because it was shown that the plastic deformation induced during the final step was sufficient to enhance precipitation kinetics allowing higher strengths to be reached, while at the same time eliminating one annealing treatment. When hard anodizing treatments were conducted on O-temper and T8 temper AA2024 truss cores, the strength increase was different for different architectures, but was nearly the same for the two parent material tempers. Finally, the question of how much microtruss strengthening can be obtained for a given amount of parent metal strengthening was addressed by examining the interaction of material and geometric parameters in a model system.
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Baumgarten, Lars. "Gesteinsmechanische Versuche und petrophysikalische Untersuchungen – Laborergebnisse und numerische Simulationen". Doctoral thesis, 2015. https://tubaf.qucosa.de/id/qucosa%3A23031.
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Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen.