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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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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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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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Realization of hybrid integrated circuits leads for high-temperature applications
Valíček, Jan ; Jankovský, Jaroslav (referee) ; Řezníček, Michal (advisor)
Bachelor thesis deals with realization possibilities of hybrid integrated circuit terminals for high temperature applications. It describes the realization method of direct mounting of terminals, this method of fixation using the conductive paste for the thick film technology. It also describes the selection of suitable materials and the temperature profile in the reflow and muffle furnace and follow removal of terminal oxides. Furthermore, a method for testing of terminals thermal resistance was realized. In conclusion, the method shows increased mechanical strength with the using of dielectric paste.
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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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Study of the properties of fillers to the composites requiring high temperature resistance
Vovesný, Václav ; Gross,, Tomáš (referee) ; Bydžovský, Jiří (advisor)
The diploma thesis is focused on the behaviour of natural and synthetic aggregates and their behaviour in polymer – cement composites, while being exposed to high temperature. The processes, happening in aggregates and mortar under the thermal load, were described in the theoretical part of the thesis same as the testing of heat effects on the aggregates and mortar. Further, the influence of high temperature on each component of concrete was described, followed by the suggestion of the appropriate components for concrete exposed to high temperature. Various aggregates were tested in the experimental part of the thesis. The basic physical and mechanical properties of aggregates were examined same as their mineralogical composition with using XRD, DTA and SEM methods. At the mortar, the influence of high temperature on the concrete density, compressive strength and tensile strength was defined. The gained knowledge was evaluated in the final part of the thesis
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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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Conceptual design of a gear tester for space applications
Florián, Vojtěch ; Černohlávek, Mikuláš (referee) ; Košťál, David (advisor)
This bachelor thesis deals with the creation of a conceptual design of gears tester for space applications. The tester must simulate space conditions and test whether the gear can operate in those conditions. It is more important to test the wheel material than its geometry. The work is divided into theoretical and practical part. In the theoretical part, a search of current knowledge of the issue is created. The second part describes several conceptual designs of testers and their models. Subsequently, a concept that can most faithfully simulate real conditions in low orbit is selected and described in detail. The final design of this concept will facilitate the testing of gears and minimize their failure rate during operation.
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The specimen size effect on R-curve and on crack tip blunting
Mrňa, Tomáš ; Konopík,, Pavel (referee) ; Stratil, Luděk (advisor)
The thesis deals with the determination of fracture toughness using compact tension (CT) test specimens at elevated and high temperatures. The experimental material steel P91 designated for application at temperatures 550650°C was used. The fracture toughness in the ductile fracture region of the steel was characterized by the R curve, which characterises the resistance against crack propagation depending on the crack length. The effect of temperature on the R curve at range 23600°C was evaluated. Next the specimen size effect using three sizes of CT specimens at 23°C and the effect of loading rate (2, 0,2 a 0,02 mm/min) at 600°C was examined. The results showed that the temperature has distinct effect on the R-curve, which yields minimal values at 400°C. Only the smallest test specimen size with thickness 6.25mm showed the specimen size effect giving about 10% lower values of toughness comparing to larger specimens. The effect of loading rate was clearly distinguishable. The values of toughness varied about 20% of the toughness value comparing individual loading rate.
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Design of synchronous reluctance motor with permanent magnets
Knebl, Ladislav ; Huzlík, Rostislav (referee) ; Ondrůšek, Čestmír (advisor)
V dnešní době je kladen vysoký nárok na účinnost elektrických zařízení a to jak ze strany provozovatele, tak i legislativy. Nejlepší účinnosti dosahují synchronní motory s permanentními magnety umístěnými na povrchu rotoru (SMPM), se kterými lze i u malých motorů dosáhnout účinnosti nad 90%. Nicméně tyto motory jsou z důvodů použití magnetů ze vzácných zemin, např. NdFeB, drahé a jsou schopny provozu pouze s frekvenčním měničem. Z cenových důvodů jsou hledány levnější alternativy k SMPM motorům. Jedním z typů motorů, kterým lze SMPM nahradit je synchronní reluktanční motor s permanentními magnety (PMASR). Tento motor je cenově výhodnější, protože používá menší množství magnetů, při zachování podobných, mnohdy i lepších vlastností, nicméně neodpadá potřeba použití frekvenčního měniče. Navíc je zde možnost použití levnějších feritových magnetů a tím ještě výrazněji snížit cenu motoru. V této práci bude PMASR topologie popsána důkladněji včetně elektromagnetického návrhu metodou konečných prvků. Bude provedena i mechanická analýza zvoleného optimálního modelu. Výsledky dosažené metodou konečných prvků budou následně porovnány s analytickým modelem. Z navrženého modelu bude vyroben prototyp a naměřené výsledky budou porovnány s výpočty.
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