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Analysis of Smart Materials
Rašner, Martin ; Lošák, Petr (referee) ; Hadaš, Zdeněk (advisor)
The bachelor's thesis "Smart Materials Analysis" deals with the description of intelligent materials in the way of usability in technical practice. At first, the research of smart materials is carried out, which is further elaborated on a detailed description of shape memory materials. In order to investigate the functionality of the material and the description of its behaviour in terms of non-linear oscillation, a simplified model is proposed. The practical part deals with the application of passive damping of Nitinol. The solution is accomplished by modelling program MATLAB / Simulink.
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Ab initio calculations of the phase stability in Ni-Mn-Ga alloys
Pongrácz, Jakub ; Šesták, Petr (referee) ; Zelený, Martin (advisor)
This thesis deals with theoretical study of magnetic shape memory alloy based on Ni2MnGa with help of ab initio calculations of electronic structure within the projector augmented wave method. In particular the effect of Co- and Cu-doping is studied on total-energy profile along the tetragonal deformation path between austenite phase with cubic L21 structure and phase of nonmodulated martensite. Obtained results are used for estimation of doping influence on martensitic transformation temperature. Transformation temperature increases in the alloy doped by 3.125 at. % of copper instead of gallium whereas transformation temperature decreases in the alloy doped by 3.125 at. % of cobalt instead of nickel. If both type of doping are used the transformation temperature increases slightly because the effect of copper is stronger. Comparison of results from this work with available results obtained with help of the coherent potential approximation shows that a local lattice distortion around doping atom has negligible effect on studied properties.
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The role of material sciences in solving the problems technical accidents
Tonkovič, Miroslav ; Řičánková, Veronika (referee) ; Klakurková, Lenka (advisor)
Material sciences plays an irreplaceable role in explanation of various technical accidents. The proposed work focuses on examples of sever chosen technical accidents in which the knowledge of materials science was crucial in use and help to solve them. Description of an incident is stated to particular cases as well as results of these investigations, taking in mind the given topis of proposed work. The accidents are always described with necessary theoretical basis connected to each particular issue. Its knowledge was undoubtedly essential in solving the accident. The end of the work is a summary of the most frequent causes of technical accidents.
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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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Processing and Martensitic Transformations of NiTi-based Alloys
Kuběnová, Monika ; Kroupa, Aleš (referee) ; Zemčík, Ladislav (referee) ; Dlouhý, Antonín (advisor)
Cíle této práce jsou: (i) vyhodnocení vlivu Y2O3 kelímku na kontaminaci indukčně tavené NiTi slitiny obohacené niklem, (ii) optimalizace podmínek, při kterých jsou tavby uskutečněny a (iii) získání nových DSC a 3D AP dat o vlivu vodíkové atmosféry na martenzitickou transformaci a na strukturu NiTi slitin obohacené niklem s tvarovou pamětí. Byly provedeny následující experimenty: – Pět taveb bylo navrženo a provedeno tak, aby byla snížena maximální tavící teplota. – Pět přetaveb bylo uskutečněno při teplotě 1500 C s dobou výdrže 2, 10 a 20 minut a při teplotách 1450 C a 1550 C s 20 minutovou dobou výdrže. Experiment byl navržen tak, aby byl vyšetřen vliv tavící teploty a doby výdrže na obsah kyslíku pocházejícího z kelímku Y2O3 v tavenině. – Tepelné zpracování NiTi slitiny obohacené niklem v režimu I (žíhání) a v režimu II (kombinace žíhání se stárnutím) pod atmosférou vodíku, směsi vodíku s héliem a pod referenční atmosférou čistého hélia. Získané výsledky jsou: – Navržené tavící postupy vedou ke snížení maximální tavící teploty a to z 1800 C na 1400 C. Přesto toto velké snížení maximální tavící teploty nevedlo k významnému poklesu obsahu kyslíku. – Během přetavby uskutečněné při teplotě 1500 C s dobou výdrže 2 minuty se obsah kyslíku navýšil o trojnásobek jeho počáteční hodnoty a příliš se nelišil od obsahu kyslíku naměřeného ve slitině, která byla přetavena při stejné teplotě s dobou výdrže 10 minut. K nárustu o čtyřnásobek počáteční hodnoty obsahu kyslíku došlo u přetavby vedené na teplotě 1450 C po dobu 20 minut a hodnota obsahu kyslíku se příliš nelišila od hodnoty naměřené ve slitině přetavené při teplotě 1550 C se stejnou dobou výdrže. – S rostoucím parciálním tlakem vodíku dochází k potlačení jednokrokové martenzitické transformace. Významný pokles výšky DSC píku nastává při parciálním tlaku 100 mbar. 3D AP analýza odhalila, že nedochází k žádné lokální změně koncentrace a nebo pozic niklových a titanových atomů ve vzorku, který byl žíhán v režimu I ve vodíku. Bylo objeveno, že vodík tvoří stabilní intersticiální tuhý roztok v NiTi B2 mřížce, kde vytváří systém nanodomén s obsahem vodíku vyšší než 10 at%.
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Memory Materials
Josiek, Robert ; Šesták, Petr (referee) ; Molliková, Eva (advisor)
Currently, shape memory materials are very popular, especially intermetallic compounds NiTi. This alloy is very stable and corrosion resistant, but its production is very difficult because of the high reactivity of titanium. Shape memory effect in this material is dependent on many parameters, such as chemical composition or heat treatment. This bachelor’s thesis explains one-way and two-way memory effect. Another one phenomenon associated with the martensitic transformation, superelasticity, is mentioned, too. The applications of these materials are described in separate chapter of this bachelor’s thesis.
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Influence of Fe substitutions on tranformation temperatures in Ni2MnGa alloys
Drastichová, Kristýna ; Klicpera, Milan (advisor) ; Prchal, Jiří (referee)
In this bachelor thesis we are interested in studying the properties of Ni2MnGa alloy and their development with the other element substitution, for example with iron. Overally, we were studying five samples with four different compositions described by the formula Ni50Mn 25Ga25-xFex where the concentration of iron was in the interval . Consequently we performed on the prepared single crystals an extensive characterization by the methods of x-ray and electron diffraction, differential scanning calorimetry and dilatometry. Special emphasis was devoted to measuring the magnetization with vibrational magnetometer. The obtained data enabled us to confirm the quality of the prepared single crystals and to observe a development of Ni2MnGa properties, especially the temperatures of the phase transformations.
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Magnetic shape memory alloys: Effects of doping with Cu and Fe
Kancko, Andrej ; Colman, Ross Harvey (advisor) ; Uhlířová, Klára (referee)
In this thesis, the focus is set on studying the properties of Ni-Mn-Ga magnetic shape memory (MSM) alloys, ferromagnetic Heusler compounds, codoped with Fe and Cu. Codoping Ni-Mn-Ga MSM alloys with Fe and Cu had previously been studied due to a synergy in increasing the martensitic transformation temperature - a key parameter for practical applications of the magnetic shape memory effect. We present the preparation process of five Ni-Mn-Ga-Fe-Cu single crystals using the optical floating zone method, as well as the analysis of their composition, crystal structure and magnetic properties, performed following the growth. The results obtained from our single crystals were finally compared with the data from the previously studied polycrystalline Ni-Mn-Ga-Fe-Cu alloys, showing similar trends in increasing the martensitic transformation temperature, the Curie temperature and the saturation magnetisation.
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Application of the spectral method to the simulation of the phase-field model for martensitic transformation
Sejková, Klára ; Tůma, Karel (advisor) ; Kružík, Martin (referee)
For some alloys martensitic transformation is responsible for the so-called shape memory effect and pseudoelasticity. These properties are used in a wide range of industry applications. Each of these materials is transformed to the shape it was manufactured in when heated to its critical temperature (austenite phase) no matter how seriously it was deformed at lower temperatures (martensite phase). Looking at the microstructure, one can observe significant change of crystalographic lattice depending on temperature and deformation. This the- sis focuses on modelling the evolution of microstructure during deformation for materials in the martensite phase. In this case, the creation of multiple variants of martensite is observed, divided by interfaces where a part of energy is stored. This behaviour can be described by the phase-field model. The numerical im- plementation of this model using the standard finite element method requires large computational costs. The aim of this thesis is to implement this model in MATLAB using a spectral method based on the fast Fourier transform, which is suitable for solving problems on a periodic domain. It is interesting to com- pare the computation using spectral method on a conventional PC with the computation written in FEniCS computed on a cluster. However, the...
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Study of martensitic tranformation in Co doped NiMnGa films by optical and magnetooptical methods
Nowak, Lukáš ; Veis, Martin (advisor) ; Hamrle, Jaroslav (referee)
Martenzitic transformation is responsible for multiferroic behaviour of mag- netic shape memory effect. However, the origin of the transformation is not yet fully understood. Magnetic shape memory materials in general offer broad spectrum of possible applications. NiMnGa is the prototype compound of these materials. Particular changes in the electronic structure are the origin of marten- zitic transformation which is the key to magnetic shape memory effect. There- fore, the optical and magneto-optical methods are the ideal tools for its analysis. Studied samples were prepared using magnetron sputtering on MgO substrate. Measurements of the Kerr effect at polar configuration and normal light in- cidence were done using rotating analyzer method. Experimental results, in- cluding spectral ellipsometry and temperature dependent measurements, were compared with theoretical models and then discussed. 1
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