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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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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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Mathematical and computational modeling of shape-memory alloys
Benešová, Barbora ; Roubíček, Tomáš (advisor) ; Krejčí, Pavel (referee) ; Stefanelli, Ulisse (referee)
This dissertation thesis is concerned with developing a mesoscopic model for sin- gle crystalline shape-memory alloys including thermo-dynamically consistent thermo- mechanical coupling - here the term "mesoscopic" refers to the ability of the model to capture fine spatial oscillations of the deformation gradient by means of gradient Young measures. Existence of solutions to the devised model is proved in a "phase-field-like approach" by a scale transition from a microscopic model that features a term related to the interfacial energy; this scale transition from a physically relevant model justifies the mesoscopic relaxation. Further, existence of solutions is also proved by backward- Euler time discretization which forms a conceptual numerical algorithm. Based on this conceptual algorithm a computer implementation of the model has been developed and further optimized in the rate-independent isothermal setting; some calculations using this implementation are also presented. Finally, refinements s of the analysis in the convex case as well as a limit of the phase-field-like approach in this case are exposed, too.
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Investigation of Functional Properties of Thin NiTi Filaments for Applications in Smart Structures and Hybrid Textiles
Pilch, Jan ; Pokluda, Jaroslav (advisor)
PhD thesis focuses the field of textile application of modern functional materials, namely metallic shape memory alloys with unique thermomechanical properties deriving from martensitic transformation in solid state. Particularly, it deals with the development of a nonconventional thermomechanical treatment of thin NiTi filaments via Joule heating by electric current and related basic research involving thermomechanical testing and modeling of functional properties of the filaments, investigation of martensitic transformations and deformation processes in NiTi and investigation of the fast recovery and recrystallization processes in metals heated by short pulses of controlled electric power. The method was developed and called FTMT-EC. In contrast to conventional heat treatment of metallic filaments in environmental furnaces, this method allows for precise control of the raise of the filament temperature and filament stress during the fast heating (rate ~50 000 °C/s). As a consequence, it is possible to precisely control the progress of the fast recovery and recrystallization processes in heat treated filaments. In this way it is possible to prepare filaments with desired nanostructured microstructure and related functional properties. A prototype equipment for application of the method for heat treatment of continuous SMA filaments during respooling in textile processing was designed and built. Comparing to the conventional heat treatment of SMA filaments in tubular environmental furnaces, this approach is faster, saves energy and allows for preparation of filaments with special functional properties. International patent application was filed on the method. It is currently utilized in the research and development of smart textiles for medical applications.
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Investigation of Functional Properties of Thin NiTi Filaments for Applications in Smart Structures and Hybrid Textiles
Pilch, Jan ; Dlouhý, Antonín (referee) ; Heczko,, Oleg (referee) ; Pokluda, Jaroslav (advisor)
PhD thesis focuses the field of textile application of modern functional materials, namely metallic shape memory alloys with unique thermomechanical properties deriving from martensitic transformation in solid state. Particularly, it deals with the development of a nonconventional thermomechanical treatment of thin NiTi filaments via Joule heating by electric current and related basic research involving thermomechanical testing and modeling of functional properties of the filaments, investigation of martensitic transformations and deformation processes in NiTi and investigation of the fast recovery and recrystallization processes in metals heated by short pulses of controlled electric power. The method was developed and called FTMT-EC. In contrast to conventional heat treatment of metallic filaments in environmental furnaces, this method allows for precise control of the raise of the filament temperature and filament stress during the fast heating (rate ~50 000 °C/s). As a consequence, it is possible to precisely control the progress of the fast recovery and recrystallization processes in heat treated filaments. In this way it is possible to prepare filaments with desired nanostructured microstructure and related functional properties. A prototype equipment for application of the method for heat treatment of continuous SMA filaments during respooling in textile processing was designed and built. Comparing to the conventional heat treatment of SMA filaments in tubular environmental furnaces, this approach is faster, saves energy and allows for preparation of filaments with special functional properties. International patent application was filed on the method. It is currently utilized in the research and development of smart textiles for medical applications.
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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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