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Hardenning of polymeric composites by nanotubes
Kuběna, Martin ; Zajíčková, Lenka (referee) ; Pantělejev, Libor (advisor)
This diploma thesis focuses on the influence of carbon nanotubes (CNTs) on the mechanical properties of a composite material with polyurethane (PU) matrix. The material was supplied in the form of thin films with thickness from 0.2 mm to 1.2 mm. The theoretical part of this thesis describes the production technology, properties and applications of composite materials PU/CNTs, and also deals with preparation technology and properties of both components of this composite material separately. The theoretical part also describes the principle of tensile testing of polymer materials. The experimental part of the thesis was primarily focused on comparing the tensile properties of a composite material PU/CNTs with tensile properties of pure PU. At first, tensile properties of pure PU were investigated, while the influence of various factors like strain rate, specimen thickness, heat treatment and aging was examined. In adition, stress relaxation tests and tests with strain rate jumps were performed on pure PU specimens. Then composite PU/CNTs was tested in tension and the results were compared with the results of tensile tests of pure PU. Composite material PU/CNTs was prepared with various concentrations, so it was possible to determine the effect of CNTs content on the tensile properties of the composite. The last part of this thesis deals with tensile tests of PU composite material with functionalized carbon nanotubes (PU/FCNTs), where the influence of surface modification (functionalization) of CNTs on the tensile properties composites was investigated. It was shown that the effect of both CNT and FCNT on mechanical properties of the composite is not significant. This conclusion was discussed on basis of the works of other authors, which do not unambiguously proved the positive effect of CNT or FCNT on mechanical properties of composites with polymer matrix.
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Low cycle fatigue of pseudoelastic NiTi alloy
Kaňová, Monika ; Hutař, Pavel (referee) ; Pantělejev, Libor (advisor)
This work is focused on study of mechanical properties of NiTi alloy which shows pseudoelastic and shape memory behaviour. Functional and structural fatigue of the material is examined. The main aim of this work was to perform and to evaluate a series of fatigue tests. The material was supplied in the form of wire which was gripped in the machine using special grips. In the first part of the experiment, tensile tests are evaluated and the reproducibility of measurements is demonstrated. Then, a series of cyclic tests was performed. Results were analysed together with previous measurements. One part of discussion concerned changes of the hysteresis loops during cycling and their dependence on strain rate. The fatigue life curves were plotted. It was found that these curves have non-standard shapes. The reasons for this are explained in the work.
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Fatigue properties of AZ61 magnesium alloy
Provazníková, Andrea ; Juliš, Martin (referee) ; Pantělejev, Libor (advisor)
This master’s thesis is dealing with low-fatigue behavior of magnesium alloy AZ61, prepared via squeeze casting method. The main aim of this work was to obtain the basic mechanical properties as well as the low cycle fatigue data. Additional metallographical evaluation of microstructure and fractographical analysis after fatigue tests was made.
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Analysis of Strain - induced Variations of Phase Composition of the TRIP Steel using EBSD Method
Pešina, Zbyněk ; Pantělejev, Libor (referee) ; Man, Ondřej (advisor)
The diploma thesis deals with phase composition measurement of the TRIP steel, using EBSD method. The steel was delivered as thermo-mechanically treated via two different routes. The phase composition of the steel was examined during gradual plastic deformation in the range 0 to10.99%. One route of thermo-mechanical treatment exhibited good agreement with the literature in terms of measured fraction of the retained austenite (15.6%) as well as its decrease during the deformation (to 8.9% at the maximum imposed strain). The samples of the second route did not show any agreement in either of the parameters spoken.
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Kinetics of Short - crack Growth in Superduplex Steel
Bártová, Lenka ; Pantělejev, Libor (referee) ; Polák, Jaroslav (advisor)
The fatigue life and the kinetics of short crack growth in specimen of austenitic-ferritic duplex steel cycled with constant stress amplitude and different mean stresses is studied. Fatigue life was determined on smooth cylindrical specimens. Strain amplitude and mean strain were recorded. Short crack growth was studied in cylindrical specimens with a shallow notch. Cyclic straining was interrupted and crack length was measured using an optical microscope mounted on the testing machine. Crack length and crack growth rates were evaluated. The effect of the mean stress on the rate of short cracks and fatigue life were discussed.
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Fatigue Properties of Ultra-fine Grain Copper Produced by ECAP Method
Navrátilová, Lucie ; Němec, Karel (referee) ; Pantělejev, Libor (advisor)
This diploma thesis describes properties of ultra-fine grain Cu prepared via ECAP procedure. The influence of fatigue loading with positive mean stress on S-N curve (i.e. fatigue life), cyclic plastic behaviour and grain size was investigated. It was found that tensile mean stress leads to shorter lifetime in comparison with fatigue loading with zero mean stress. During main part of the lifetime, significant hardening of UFG Cu was observed. There is no distinct effect on microstructural orientation and stability.
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Failure analysis of the space shuttle Columbia
Neduchal, Ondřej ; Man, Ondřej (referee) ; Pantělejev, Libor (advisor)
Bachelor´s thesis is focused on the analysis of the space shuttle Columbia accident. Text firstly generally discusses materials used in aviation and cosmonautic, specifically composite materials. These are discussed firstly in general and then is the thesis focused on their strength and dynamic properties. Second half of the thesis describes the course of the last flight of the space shuttle Columbia and its subsequent demise. Emphasis is placed on the cause of the accident in which plays a crucial influence the material on the surface of the wing.
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Assessment of probable causes of corrosion damage of a mould made of cast iron
Sobola, Petr ; Pantělejev, Libor (referee) ; Man, Ondřej (advisor)
Bachelor’s thesis deals with solution of problems on glass moulds, which were exposed to the corrosion medium for up to two days causing their damage. The thesis contains theoretical analysis of the problem, layout for the corrosion experiment and its execution. Based on the experiment a conclusion was pronounced that the extent of damage which was observed was not able to be created by corrosion of initial surface without any previous defect.
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