Národní úložiště šedé literatury Nalezeno 9 záznamů.  Hledání trvalo 0.00 vteřin. 
The Role of Bi/Material Interface in Integrity of Layered Metal/Ceramic
Masini, Alessia ; Černý, Martin (oponent) ; Bermejo, Raul (oponent) ; Chlup, Zdeněk (vedoucí práce)
The present doctoral thesis summarises results of investigation focused on the characterisation of materials involved in Solid Oxide Cell technology. The main topic of investigation was the ceramic cell, also known as MEA. Particular attention was given to the role that bi-material interfaces, co-sintering effects and residual stresses play in the resulting mechanical response. The first main goal was to investigate the effects of the manufacturing process (i.e. layer by layer deposition) on the mechanical response; to enable this investigation, electrode layers were screen-printed one by one on the electrolyte support and experimental tests were performed after every layer deposition. The experimental activity started with the measurement of the elastic characteristics. Both elastic and shear moduli were measured via three different techniques at room and high temperature. Then, uniaxial and biaxial flexural strengths were determined via two loading configurations. The analysis of the elastic and fracture behaviours of the MEA revealed that the addition of layers to the electrolyte has a detrimental effect on the final mechanical response. Elastic characteristics and flexural strength of the electrolyte on the MEA level are sensibly reduced. The reasons behind the weakening effect can be ascribed to the presence and redistribution of residual stresses, changes in the crack initiation site, porosity of layers and pre-cracks formation in the electrode layers. Finally, the coefficients of thermal expansion were evaluated via dilatometry on bulk materials serving as inputs for finite elements analyses supporting experiments and results interpretation. The second most important goal was to assess the influence of operating conditions on the integrity of the MEA. Here interactions of ceramic–metal interfaces within the repetition unit operating at high temperatures and as well at both oxidative and reductive atmospheres were investigated. The elastic and fracture responses of MEA extracted from SOC stacks after several hours of service were analysed. Layer delamination and loss of mechanical strength were observed with increasing operational time. Moreover, SEM observations helped to detect significant microstructural changes of the electrodes (e.g. demixing, coarsening, elemental migration and depletion), which might be responsible for decreased electrochemical performances. All the materials presented in this work are part of SOC stacks produced and commercialised by Sunfire GmbH, which is one of the world leading companies in the field.
Estimation of mechanical parameters of thin films using finite element analysis
Tinoco Navaro, Hector Andres ; Holzer, Jakub ; Pikálek, Tomáš ; Buchta, Zdeněk ; Lazar, Josef ; Chlupová, Alice ; Kruml, Tomáš ; Hutař, Pavel
This study shows a methodology to estimate mechanical parameters of thin films by means of a bulge\ntest and a numerical approach. The methodology is based on the combination of finite element analysis with a\nclassical analytical method. Finite element modelling was conducted for monolayer (Si3N4) membranes of 2x2mm\nwith the aim to approximate both the load-deflection curves experimentally measured and the classical loaddeflection\nanalytical model. Error functions were constructed and minimized to delimit a coupled solution space\nbetween Young’s modulus and Poison’s ratio. In a traditional bulge test analysis only one of the elastic properties\ncan be determined due to that there is not unique solution in the estimations of these parameters. However, both\nelastic parameters were determined through the proposed numerical procedure which compares the deformed\nsurfaces for a specific set of optimal elastic parameters computed. Results shows that the estimated elastic\nproperties agree with corresponding values determined by other methods in the literature
Modelling mechanical properties of RNA and DNA
Dršata, Tomáš ; Lankaš, Filip (vedoucí práce) ; Banáš, Pavel (oponent) ; Schneider, Bohdan (oponent)
Strukturní a mechanické vlastnosti nukleových kyselin hrají klíčovou roli v řadě biologických procesů i v oblasti nanotechnologií. Práce předkládá výsledky několika studií zaměřených na modelování těchto vlastností. Rozsáhlé simulace atomistické molekulové dynamiky (MD) jsou použity ke studiu strukturní dynamiky nukleových kyselin a k parametrizaci modelů jejich mechaniky. Používáme dva modely, které předpokládají deformační energii ve tvaru obecné kvadratické funkce vhodně zvolených vnitřních souřadnic, a liší se v úrovní rozlišení. První model je založen na popisu konformace na úrovni jednotlivých bází, zatímco druhý, hrubší model, je vhodný k popisu tuhosti vůči globálním deformacím v ohybu a celkové torzi. Tyto modely jsou využity ke studiu mechanických vlastností A-traktů v souvislosti s tvorbou smyček a lokalizací nukleosomů, k charakterizaci spřažených deformací v torzi a prodloužení helikální DNA a RNA, a k predikci změn ve vlastnostech poškozené DNA v souvislosti s procesem rozpoznání a oprav tohoto poškození. Kromě toho je představen návrh obecného modelu alosterických efektů v DNA, který je aplikován k predikci změn ve struktuře DNA způsobených vazbou ligandů do malého žlábku a...
Large-scale micro-finite element simulation of compressive behavior of trabecular bone microstructure
Jiroušek, Ondřej ; Zlámal, Petr
Microstructural finite element analysis has become a standard technique for evaluation of mechanical properties of trabecular bone. Due to the high complexity of the trabecular bone microstructure, the FE models have a very large number of elements (about 1 million elements per cubic cm in 50 μm3 resolution). To perform FE analysis of the microstructural FE models based on micro-CT scanning of whole bone samples (e.g. vertebral bodies) it is needed to solve 107 -- 108 equations. This article deals with comparison of approaches using voxel-based microstructural FE models to calculate the overall mechanical properties of trabecular bone.
Vyšetřování elastických vlastností kompozitu akustickými metodami
Landa, Michal ; Seiner, Hanuš ; Goldmann, T. ; Pompe, V.
V souhrnné práci jsou popsány jednotlivé akustické metody vyšetřování elastických vlastností kompozitu.
Determination of elastic moduli of anisotropic solids from ultrasonic measurements
Seiner, H. ; Landa, Michal
This nondestructive, and partially noncontact method have a potential for material evalution of layered anisotropic structures.
Evaluation of anisotropic properties of composites using laser-generated ultrasound
Landa, Michal ; Blaháček, Michal ; Zídek, Jan
This nondestructive, and partially noncontact method have a potential for material evalution of layered anisotropic structures.
Evalution of anisotropic elastic properties by ultrasonic methods
Landa, Michal ; Plešek, Jiří ; Urbánek, Přemysl ; Novák, V.
Among the fundamental characteristical of solids are their elastic constants. As derivatives of the free energy, elastic constants are closely connected to thermodynamic properties of material. Extensive quantitative connection among thermodynamic properties can be made if the elastic constant are knownas function of temperatureand pressure.
Measurement of elastic constants of orthotropic C-C composite plates by resonant frequency method
Černý, Martin ; Glogar, Petr
A method was developed for determination of elastic constants of textile composite materials based on measurement of resonant frequencies of longitudinal and transversal vibrations of Timoshenko's beam.

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