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The effect of temperature on the charging and discharging characteristics of lithium-ion batteries
Doleželová, Eva ; Máca, Josef (referee) ; Libich, Jiří (advisor)
This thesis deals with operation principles of lithium-ion batteries, its degradation principles, capacity fade, materials used, formats, main characteristics, development, uses and mid to high temperature behaviour. The thesis aims to study aging characteristics of commercially available lithium-ion batteries. In the practical part of the thesis, the key parameters of selected types of commercially available lithium-ion batteries were measured under normal temperature conditions. The measurement was repeated at an elevated temperature. Results were analysed and effects of different temperatures on the selected characteristics were concluded both verbally and graphically. A conclusion evaluates short-term and long-term impacts of ambient temperature on rate capability, ageing, capacity fade and longevity.
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ASSESSMENT OF REINFORCED CONCRETE STRUCTURES EXPOSED TO ELEVATED TEMPERATURES
Rozsypalová, Iva ; Kolář,, Karel (referee) ; Vítek,, Jan (referee) ; Daněk, Petr (advisor)
Doctoral thesis is focused on the assessment of concrete structures after fire exposure and extends the knowledge in view of the main aims of the research defined in the objectives of his work. Thanks to the performed fire tests of full-scale concrete specimens, material characteristics corresponding to actual fire load have been assessed for different temperature levels. Resulting from presented research, main steps of assessment procedure have been recommended for both destructive and non-destructive tests of concrete after exposure to fire. Furthermore, behaviour of FRP reinforcement at elevated temperatures have been investigated. Aiming to determine the effects of fire exposure on reinforced concrete structures, experimental program have been defined and performed, including concrete beams reinforced with either steel, or composite reinforcement with glass or carbon fibres and subjected to experimentally simulated fire load. After cooling, bending test have been executed. Above mentioned experimental program was further complemented by extensive numerical analysis. Finally, presented work provides guidelines regarding further investigations required in this field of research.
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High temperature conductivity measurements of ceramic materials
Grochal, Peter ; Kazelle, Jiří (referee) ; Novák, Vítězslav (advisor)
The aim of this work is to get acquainted with the detailed structure of yttrium-stabilized zirconia, focusing mainly on conductivity. Coating platinum electrodes by screen printing. Solution of complexity of conductivity segregation by electrode geometry. Measurement of the conductivity of macroscopic samples of ceramics by impedance spectroscopy to determine the electrical behavior of the system. Creating equivalent circuits to measured data. Detect system behavior when excited by different AC voltage and electrode geometry values.
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Fracture tests of selected specimens with special aggregates: experiments and numerical simulation
Majda, Tomáš ; Malíková, Lucie (referee) ; Keršner, Zbyněk (advisor)
The diploma thesis deals with selected fracture tests and evaluation of fracture parameters of cement-based composite. One part of the thesis deals with cement-based composite with glass spherical aggregate of a single fraction of 2 mm. After production, the beams with dimensions of 20×40×200mm exposed to temperatures in the range from 100 to 1000 °C for one hour. Using the non-destructive ultrasonic pulse method, the degree of damage caused by termal load was determined. Selected specimen with central edge notch were then tested in three-point bending and fragments after these tests were tested in compression. In the second part, attention was paid to the evaluation of fracture tests conducted on specimen from drill-cores taken from selected objects located at the former Transgas Gas Control Center in Prague. The specimen were provided with a chevron notch before being tested in three-point bending. The measured data was modified by the GTDiPS program and in the case of the glass composite the StiCrack program was used to evaluate fracture parameters.
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Influence of the Upper Die and of the Indenter Material on the Time to Rupture of Small Punch Creep Tests
Andrés, D. ; Dymáček, Petr ; Lacalle, R. ; Álvarez, J. A.
The Small Punch Creep test has proven to be a suitable technique for assessing the\nproperties of in-service components. It is a reliable, efficient and cost-effective test for predicting\nthe behaviour of the material. The aim of this paper is to analyse the influence of different factors\non the Small Punch Creep (SPC) tests. The influence of the specimen clamping has been studied,\nexperimentally and by means of finite element models on different materials. In the analysed\nconditions, it has been proven that the influence of the upper die on the tests results is generally\nrelatively insignificant, even in the absence of upper die.\nFurthermore, the use of different materials at the punch has also been analysed. In order to achieve\nthis goal, SPC tests have been carried out on two light alloys (AZ31 and AlSi9Cu3) at 473 and\n523K. Three different balls have been employed: ceramic, tungsten-carbide and steel balls. It has\nbeen proven that for the creep ductile alloy (AZ31), there is no apparent effect on the specimen\nresponse. On the other hand, for the creep brittle alloy (AlSi9Cu3), a different trend of the material\nresponse is shown, dependent on the ball used. As a result, there seems to be a significant influence\nof the friction between the punch and the specimen on the tests results, related to the material\nbehaviour.
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Interaction of Creep and High Cycle Fatigue of IN 713LC Superalloy
Horník, V. ; Šmíd, Miroslav ; Hutař, Pavel ; Kunz, Ludvík ; Hrbáček, K.
The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of superalloy structures was un-affected or even slightly increased in the cases with superimposed vibrations. The reason for this behaviour was not well described up to now. Therefore, set of fatigue tests was conducted at high mean stresses level to observe this phenomenon. The mean stress was kept constant while the stress amplitudes were selected in order to measure wide range of conditions from pure creep to pure fatigue. Fractographic analysis by scanning electron microscopy (SEM) was done with the aim to identify governing damage mechanisms for particular test conditions as a preliminary evaluation of conducted tests.
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Lightweight mortars with content of alternative raw materials and resistant to adverse effects
Morkusová, Kristýna ; Jakubík, Aleš (referee) ; Bydžovský, Jiří (advisor)
This diploma thesis describes research and following development of lightweight cement mortars with alternative raw materials. Attention was focused on study of the effects of extreme influences such as high temperature (up to 1200 °C), freeze-thaw and agressive sulfur dioxide. Verification of durability of developed mortars was realized using physical and mechanical tests (density and strength), physical and chemical methods (computed tomography) and scanning electron microscopy. Assessment of durability was realized in a longer period of time (90 days).
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Study of the effect of the addition of the cellulose fibers on the selected properties of concrete
Blaha, Lukáš ; Hela, Rudolf (referee) ; Bodnárová, Lenka (advisor)
This dissertation desribes the behavior of cellulose fiber reinforced concrete. In the theoretical section one can find basic information on cellulose fiber and its methods of production and usage in concrete structures. One can find the information about the effect of high temperature on the mechanical and physical attributes of cellulose fiber reinforced concrete, and also a comparison with other fibers used in concrete based on the research done using scientific literature. Furthermore the details about particular cellulose fibers are provided. In the experimental section the formulas for CHRYSO and GREENCEL concrete are designed. The influence of the addition of various types of cellulose fibers into both liquid and solid states of concrete was researched. Tests were also done on the effect of high temperatures (600 °C and 800 °C) on the firmness and densitiy of concrete, its deformations and visual changes. Furthermore, the resistance of cellulose fibers was monitored by monitoring the development of the pH environment (from pH 4 to pH 12) with long-term deposition of different types of cellulose fibers in these environments.
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Possibilities of using X ray tomography for description of damage of temperature loaded concrete
Rozsypalová, I. ; Kumpová, Ivana ; Daněk, P. ; Šimonová, H. ; Keršner, Z.
The effect of high temperatures on concrete affects the internal structure of this composite material. The paper opens the question of the possibility of using a computed X–ray tomography to quantify the degree of damage of a concrete specimen that was drilled from the selected experimental panel loaded in a fire furnace with high temperatures at the AdMaS (Advanced Materials, Structures and Technologies) research centre at Faculty of Civil Engineering Brno University of Technology. The nominal value of the maximum temperature on the heated side of the panel was 1000 °C. Advanced workstation computer X–ray tomography TORATOM at Centre of Excellence Telč (CET) is parallel imaging of an object in two spectra of X–ray radiation, that allows to highlight differences between the material components to the full X–ray spectrum similar to the attenuation of the radiation.
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IN-SITU HIGH TEMPERATURE LOW CYCLE FATIGUE STUDY OF SURFACE TOPOGRAPHY EVOLUTION IN NICKEL SUPERALLOY
Petrenec, M. ; Polák, Jaroslav ; Šamořil, T. ; Dluhoš, J. ; Obrtlík, Karel
In-situ Low Cycle Fatigue test (LCF) at temperature 635 degrees C have been performed in Scanning Electron Microscope (SEM) equipped with Electron Backscatter Diffraction analysis (EBSD) on a small dog-bone-shaped specimen of cast Inconel 713LC superalloy. The aim of the work was to study early stage fatigue damage at high temperature by the observations of the characteristic surface relief evolution and crystallographic characterization changes by EBSD. The detail of slip bands shape was checked by FIB and AFM microscopes. The LCF test was conducted on GATAN stage with pre tilted position and constant stress amplitude of total cycle number of 20. The relief produced in the first cycle determines the other locations of the localized cyclic slip to the primary slip planes (111). The relief was modified in the next cycles but without forming additionally new slip traces in the primary system. Based on EBSD analysis before and after LCF, the orientation of two grains was changed which caused activation of second slip system. The damage mechanism evolution is closely connected with the cyclic strain localization to the persistent slip bands where the fatigue cracks were initiated.
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