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Highway bridge diagnostics
Křepelka, Jan ; Suza, Igor (referee) ; Cikrle, Petr (advisor)
This thesis deals with the inspection and construction-technical survey of the highway bridges D2-058..1 and D2-058..2. These structures ale located on the border with the Slovak Republic and were built in 1980. The thesis is focused on the substructure of this long overpass, because of its major failures caused by leaking water. Theoretical part contains information about construction-technical surveys of the bridges, bridges inspections and theory of ultrasound methods. That method has been used in the practical part for identification of the damage extent. Also, material property have been verified and overall condition of the substructure has been evaluated.
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Effects of Defects on Composite Structures Load Carrying Capacity: Delaminations at a Bi-Material Interface
Matěják, Vladimír ; Kotoul, Michal (referee) ; Růžička, Milan (referee) ; Juračka, Jaroslav (advisor)
Kompozitní materiály se projevují komplexním způsobem porušování, které může být dále ovlivněno přítomností různých poruch plynoucích z výrobních processů nebo se vyskytujících v průběhu života součásti. Důkladné porozmění procesů porušování a jejich okolností je nezbytné pro navrhování kompozitních konstrukcí, jenž budou bezpečnější, trvanlivější a ekonomičtější. V první části disertační práce jsou popsány způsoby porušování kompozitů a uvedeny současné matematické metody pro analýzu a výpočet únosnosti. Dále jsou zde vyjmenovány hlavní druhy vad a stručně diskutován jejich vliv na vlastnosti kompozitních materiálů. Zvláštní důraz je kladen na delaminace, společně se základními principy lomové mechaniky a jejich uplatnění při výpočtech a zkoušení kompozitů. Druhá část je zaměřena na delaminace na rozhranní dvou různých materialů. Lomová houževnatost byla experimantálně měřena ve třech typech zatížení za účelem stanovení poruchového kritéria založeného na podílu módu I a módu II. Během tohoto experimentu byla vyvinuta nová metoda měření délky trhliny pomocí digitáního zpracování obrazu a rovněž byla navržena nová definice počátku šíření trhliny. Analytické vztahy pro výpočet míry uvolnění deformační energie z naměřených dat byly rozšířeny o vliv rozdílných elastické parametrů materiálů na rozhranní. Podrobnější prozkoumání analytických vztahů a výpočet metodou konečných prvků odhalil, že podíl módu I a módu II je závislý na vzdálenosti od čela trhliny a poruchové kritérium založené na podílu smíšenosti tak nemůže být použito.
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Effective Machining Of Fiber Reinforced Composite Materials
Sedláček, Jan ; Janáč, Alexander (referee) ; Vrba, Vladimír (referee) ; Klement, Josef (referee) ; Humár, Anton (advisor)
The objectives for this dissertation are to push forward the current state of knowledge in the area of machining fiber-reinforced plastic (FRP). The most common machining operation performed on these materials is drilling owing to the need for component assembly in mechanical pieces and structures. Among the defects caused by drilling, delamination appears as to be of the most critical and may occur at both the entrance and exit plane. A number of theoretical and experimental studies have been made to create an analytical model of delamination in composite laminates. In this dissertation, the critical thrust force (force which initiates the delamination) is predicted using linear elastic fracture mechanics - assuming Mode I. Delamination is investigated by studying the evolution of feed force and torque applied by the tool on the workpiece. A four components piezoelectric dynamometer KISTLER 9272 with special PC-software is used for measuring and evaluating of torque and cutting forces, when drilling two different composite materials: carbon/epoxy laminate fabricated by hand lay-up technique and glass/polyester composite made by pultrusion. Wear mechanisms and location of the wear on the tool are also investigated (with respect to cutting material). The tool wear is measured with help of a common workshop microscope and recorded with scanning electron microscope PHILIPS XL30. Drilling experiments are performed to give complex technical information (i.e. cutting conditions, tool geometry, tool wear and so on) which enables efficient machining of composite materials. Delamination-free drilling is given special emphasis in the experiments. Methods of statistical analysis (DOE) are used to determine which factors have the most influence on delamination.
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Interlaminar fracture toughness of fiber reinforced plastics
Vodička, Vít ; Mališ, Michal (referee) ; Klement, Josef (advisor)
Cílem této diplomové práce je lépe porozumět konceptu únavového poškození damage tolerance zmapováním všech možných vlivů na lomovou houževnatost vláknového kompozitu s polymerní matricí. Toho je dosaženo provedením zkoušek za různých podmínek (např. změna parametrů měření, mód zatížení, pořadí vrstev a materiál) a monitorováním odlišností v šíření trhliny. Na základě dat získaných během těchto testů je určena lomová houževnatost. Potenciální rozdíly jsou zkonzultovány a porovnány s ostatními vzorky.
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Complete series of lanthanide oxalates: Structure and properties
Uríková, Daniela Veronika ; Tyrpekl, Václav (advisor) ; Hynek, Jan (referee)
Metal oxalates are salts of very low solubility allowing an easy precipitation of metal ions from the acidic aqueous solutions into crystalline material. Due to this property, oxalates have an important role in the technology of lanthanides and actinides. It is namely the separation of actinides from the spent nuclear fuel that is its industrial application of interest. 4f-lanthanides are often used as 5f-actinides surrogates when optimizing or modelling the precipitation process. A synthetic route for homogeneous precipitation of oxalates based on the thermal decomposition of oxamic acid was developed by our research team. The present work deals with further investigation into the structure and morphology of simple lanthanide oxalates. The synthesis products, developed microcrystals, were studied by means of solid-state analysis (optical microscopy, single crystal X-ray diffraction, X-ray powder diffraction, TGA, SEM, AFM). Among the known, the previously not-specified structures of Er2(C2O4)3∙6H2O and Yb2(C2O4)3∙6H2O were obtained and refined. According to our observations, the synthesized oxalates form two isostructural series: decahydrates and hexahydrates. Structurally, both types of Ln oxalates form 2D frameworks that are stacked together in one direction and connected by hydrogen bonds to...
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Synthesis and properties of zinc hydroxide and zinc oxide nanosheets
Hynek, Jan ; Lang, Kamil (advisor) ; Kovanda, František (referee)
1 Abstract The structure of layered zinc hydroxide intercalated with dodecyl sulfate (LZH-DS) anions was studied in detail. LZH-DS was prepared by direct precipitation in water and formed different phases. The following phases of LZH-DS were prepared - "extended" phase (ex) by direct precipitation in water, "shrunk" (s) and "super-shrunk" (ss) phases via treatment of LZH-DS(ex) phase in methanol. The studies of the thermal behavior of LZH-DS(ex) revealed interstratification of intercalated DS anions. It is the first example of interstratification in layered hydroxides that are intercalated with long aliphatic alkyl chain anions. The experimental results were used for molecular dynamic modelling of the structures. Nanometric thin films were prepared by dip-coating and inkjet printing of ZnO nanosheets on glass plates. The side-by-side alignment of the ZnO nanosheets on the substrate resulted in thin, transparent, oriented ZnO surfaces with the high-energy {001} facets exposed. The method of nanosheet deposition affected the film morphology; the dip-coated films were smooth and nonporous, while the inkjet-printed films were rough and had a surface area in the range of approximately 100-160 m2 g-1 . The first-order rate constants for the photocatalytic degradation of 4-chlorophenol on the nanosheet-based films...
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Highway bridge diagnostics
Křepelka, Jan ; Suza, Igor (referee) ; Cikrle, Petr (advisor)
This thesis deals with the inspection and construction-technical survey of the highway bridges D2-058..1 and D2-058..2. These structures ale located on the border with the Slovak Republic and were built in 1980. The thesis is focused on the substructure of this long overpass, because of its major failures caused by leaking water. Theoretical part contains information about construction-technical surveys of the bridges, bridges inspections and theory of ultrasound methods. That method has been used in the practical part for identification of the damage extent. Also, material property have been verified and overall condition of the substructure has been evaluated.
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Layered Transition Metal Hydroxides: Delamination and Properties
Hyklová, Barbora ; Lang, Kamil (advisor) ; Zima, Vítězslav (referee) ; Bujdák, Juraj (referee)
Charles University Faculty of Science Study programme: Inorganic Chemistry Mgr. Barbora Hyklová Layered Transition Metal Hydroxides: Delamination and Properties Extended abstract Supervisor: Ing. Kamil Lang CSc., DSc. Supervisor-Consultant: RNDr. Jan Demel PhD. Prague, 2017 Layered transition-metal hydroxides have attracted increasing attention as promising active electrode materials for electrochemical energy storage and conversion device due to facile preparation and modification, good tunability, high capacitance capability, fast reversible redox reactions, and cost effectiveness. Many reported hierarchical architectures based on nickel and cobalt hydroxides are composed of bulky nanoplatelet-like aggregates; however, the nanomorphology and behavior of the separated hydroxide nanosheets is much less known. Figure 1. Scheme of layered nickel or cobalt hydroxide delamination and subsequent restacking on conductive HOPG support. In this respect, the dissertation thesis reports characterization and electrochemical performance of nickel, nickel-cobalt, and cobalt hydroxide nanosheets, synthesized by an economical and environmentally friendly method based on delamination of corresponding layered hydroxides in water (Figure 1). For this purpose, lactate and nitrate layered hydroxides were prepared by two...
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Hierarchical Problems with Evolutionary Equilibrium Constraints
Adam, Lukáš ; Outrata, Jiří (advisor) ; Lachout, Petr (referee) ; Hoheisel, Tim (referee)
Title: Hierarchical Problems with Evolutionary Equilibrium Constraints Author: Lukáš Adam Supervisor: Prof. Jiří Outrata Abstract: In the presented thesis, we are interested in hierarchical models with evolutionary equilibrium constraints. Such models arise naturally when a time-dependent problem is to be controlled or if parameters in such a model are to be identified. We intend to discretize the problem and solve it on the basis of the so-called implicit programming approach. This technique requires knowledge of a generalized derivative of the solution mapping which assigns the state variable to the control variable/parameter. The computation of this generalized derivative amounts equivalently to the computation of (limiting) normal cone to the graph of the solution mapping. In the first part we summarize known techniques for computation of the normal cone to the set which can be represented as a finite union of convex polyhedra. Then we propose a new approach based on the so-called normally admissible stratification and simplify the obtained formulas for the case of time-dependent problems. The theoretical results are then applied first to deriving a criterion for the sensitivity analysis of the solution mapping and then to the solution of two practically motivated problems. The first one concerns optimal...
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