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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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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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Optimization of heat treatement process for alloyed case hardenening steel
Roubalová, Jana ; Pantělejev, Libor (referee) ; Jan, Vít (advisor)
This bachelor’s thesis deals with the assessment of the influence of heat treatment on the microstructure and mechanical properties of medium alloyed steel 18CrNiMo7-6. The work contains assessment and further proposal of suitable austenitizing temperature for heat treatment. To select the optimal variants of heat treatment five different temperature modes were tested. The theoretical part describes the various methods of heat treatment, with a focus on medium alloyed steels. The practical part presents microstructure of the evaluated steel, its hardenability and hardness depending on the temperature regime of treatment.
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Mechanical properties of Al alloy prepared by SLM process
Vitásek, Ladislav ; Štěpánek, Roman (referee) ; Pantělejev, Libor (advisor)
The master's thesis deals with properties of aluminium alloys prepared by SLM process. The teoretical part of thesis is focused on decribtion of selective laser melting technology, metallurgical defects and mechanical properties of aluminium alloys processed by this technology. The experimental part of this thesis deals with selections of the SLM process parameters suitable for samples preparation in bulk. Tensile testing at room temperature was used for evaluation of basic mechanical properties. Metallographic and fractographic analyses were performed for evaluation of the microstructure and fracture mechanisms. The materials characteristics obtained on SLM samples were compared with the properties of the same materials grade produced by conventional technologies.
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Optimization of Material Plastification Process
Šeniglová, Hana ; Krpoun, Karel (referee) ; Pantělejev, Libor (advisor)
This bachelor´s thesis deal with the optimization of the process of material plastification. The purpose of the thesis is to devise feasible parameters of a injection molding machine. The goal was achieved by the „Design of Experiments“ method. The necessary measurements were taken on the sample, a filter fuel tank, which was provided by the company Robert Bosch České Budějovice. Each measurements are described in the bachelor´s thesis. The results are summarized and evaluated in the Minitab software used for optimal parameters settings of the production process.
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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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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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Microstructural stability of austenitic steels during fatigue loading
Kudelka, Martin ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
This diploma thesis studies the structure of selected austenitic stainless steels which were fatigued at room and depressed temperatures. The theoretical part is divided into three parts. The first one defines the austenitic stainless steels with accent to their chemical composition and microstructure. Second part is dedicated to deformation-induced martensite formation. The third part shows the mechanisms and stages of damage due to cyclic straining. The experimental part is focused especially on the observing of microstructural changes by methods of colour metallography and their relation to stress-strain response of material under selected conditions of fatigue loading. Series of samples of 304 and 316L steels were prepared by colour etching and their microstructures were documented using optical microscopy. Then the semi-quantitative measurements of presence and morphology of deformation-induced martensite were done and the results were discussed and correlated with fatigue damage level.
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