|
Modeling of shape-memory alloys on the mesoscopic level
Benešová, Barbora
This contribution presents some recent results on modeling of phase transformation in the pseudo-elastic regime within the framework of continuum mechanics. We recall an efficient concept for quasi-static evolution of microstructure in the isothermal rate-independent case. We then concentrate on simulation results obtained by the presented model, performed on a single-crystal prismatic NiTi-specimen. Algorithmic details, i.e. energy-estimates-based optimization, are also given.
|
|
Stress-free and stress-assisted aging of NiTi shape memory alloys
Dlouhý, Antonín ; Bojda, Ondřej ; Fiala, J.
The present work investigates coherent Ni4Ti3 precipitates in a Ti-50,7at%Ni shape memory alloy after different thermo-mechanical treatments. The study is based on the quantitative TEM (transmission electron microscopy) image analysis using the ACC (Adaptive Contrast Control) programme. The attention is given to a number, size and volume fraction of individual crystallographic variants of the Ni4Ti3 precipitates. Preliminary results suggest that, after common heat treatments, the precipitation of Ni4Ti3 particles is inhomogeneous not only as far as the density of particles in the original B2 grains is concerned but also with respect to the distribution of the crystallographic particle variants. The possible influence of the heterogeneous Ni4Ti3 precipitation on the characteristics of the martensitic transformations B2-R-B19’ is discussed.
|
|
Analysis and modification of thin layers using ion beams
Jonner, Jakub ; Lörinčík, Jan (referee) ; Bábor, Petr (advisor)
This diploma thesis deals with analysis and modification of thin layers using ion beams. The first part of this diploma thesis deals with phenomena accompanying ion beam bombardment of solid matter. The second part of this diploma thesis is concerned with Secondary Ion Mass Spectroscopy (SIMS) and Low Energy Ion Scattering (LAIS). This work convey some basic information about these two techniques and it also deals with some benefits result in their connection into parallel depth profiling mode (such as better depth resolution of the LEIS profile, quantification of the SIMS). These benefits are demonstrated on MoSi film measurement. Within the framework of this thesis a new UHV manipulator was designed. This new UHV manipulator is equipped with precise stepper UHV motor and since the proportions are smaller, the manipulation with a sample in a space limited UHV chamber is much more comfortable and more precise. The third part of this diploma thesis deals with ion-beam induced transformation of epitaxially grown Fe films with thickness of 22 monolayer (ML) and 44 ML on Cu(100) single crystal at room temperature. Metastable Fe films of 22 ML thickness were prepared in CO pressure and 44 ML Fe films were prepared by co-evaporation of Fe with Fe64Ni36 (invar). Structural changes are analyzed by scanning tunneling microscopy and low-energy electron diffraction. The aim of this thesis is to discuss the influence of the sputtering parameters such as ion dose and ion energy on the nucleation of bcc nanocrystals, their growth, final shape and size. The influence of different Ni concentration on stability of 44 ML thick Fe films is also discussed.
|
|
Design of telescope
Hudáková, Kristína ; Paliatka, Peter (referee) ; Sládek, Josef (advisor)
The diploma thesis deals with a design solution of an astronomical mirror telescope, also called Newton reflector on the Dobson Altazimuth mount. The design focuses on the determination of appropriate optic parameters and mounting parameters, on the new styling and shape solution with an emphasis on technical, operational, ergonomic and aesthetic requirements. The main benefit of the design is the simplicity of compilation and decompilation of entire device, intuitive control and safe usage and shape compactness of the whole appliance. I designed the device in the light of the fact that it is used mainly in complete darkness, and the colour solution corresponds to the fact.
|
|
Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System
Čapek, David
Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System Abstract of the Ph.D. thesis \s David Capek It has been shown, that the thermal effects are very important in the dynamics of small Solar System bodies. A phenomenon which is known as the Yarkovsky effect is able to secularly change the semimajor axis of an orbit, while the YORP effect affects the rotation state of a body. The Yarkovsky effect and the YORP effect were previously calculated with many constraining assumptions like spherical shapes of asteroids, circular orbits, small variations of the surface temperature, principal axis rotation, constant thermal parameters, etc. We developed a sophisticated numerical model of the Yarkovsky/YORP effect without such simplifications. With this model, we have been able to describe the shape, the orbit, the rotation and the thermal behaviour of an asteroid in a very precise way. The YORP effect was studied on a sample of artificially generated shapes, roughly resembling Main Belt asteroids, and also on several shapes of real asteroids. The depen- dence of YORP on the obliquity and the thermal parameters of the surface were studied (Vokrouhlicky and Capek, 2002; Capek and Vokrouhlicky, 2004). A wide variety of pos- sible YORP evolution paths of the spin state was found. The possibility of...
|
|
The electrical discharge machining in production of shaped moulds
Kalenda, Jan ; Prokop, Jaroslav (referee) ; Osička, Karel (advisor)
In this diploma thesis is theoretically written about the production of shaped cavities using electroerosive sinking. The possibilities of usage and the production of electrodes for own usage likewise development of technology, tools and machines for electroerosive machining. The quality of machined surface and surface layer using own process of electroerosive sinking of shaped cavities are as well mentioned in this project.
|
|
Modulated ultrasonic water jet cutting – optimization of the liquid wave guide shape
Veselý, Radek ; Foldyna, Josef (referee) ; Habán, Vladimír (advisor)
High speed water jets have un-substitutable place in unconventional technologies in the machining of materials. Indeed its larger spreading is limited above all by its really high purchase price and also high costs of the operation. Certain possibility is represented by high-speed pulsating jets, which don’t put such a high pretension on arrangement of generating the pressure during the comparable operation. Probably the most effective method of the generating of pulsating water jets is ultrasonic modulation. This work could benefit to understanding spreading of pressure impulses between ultrasonic generator and output nozzle. Pulsating is solved by the numerical calculation using transfer matrix method.
|
| |
|
Walter Scott's historical novel in anglo-american context and in Czech translations
Mohrová, Hana ; Mánek, Bohuslav (referee) ; Kalivodová, Eva (advisor)
The dissertation deals with the reception of new and world-acclaimed genre of Walter Scott's historical novel and its forms in specific cultures. The theoretical part of this dissertation is focused on comparing the reception of Scott's prose in the original Anglo-Scottish context, in North American cultural context with special emphasis on the context of the American South, and in Czech context. The researching of the two English speaking cultural contexts proves our hypothesis claiming that every single cultural context shapes its own interpretation. Such cultural interpretation in the non-English speaking context materialises in the form of translations. Each chapter on the reception in given cultures deals with the unprecedented success of the new genre of historical novel as established by Walter Scott. When describing the reception the dissertation uses period reviews and criticisms, and monographs dealing with Scott's reputation. In comparison with the Czech reception, which manifests itself as nationally conscious only allusively (in cultural responses, in the choice of novels to be translated, in their texts and paratexts), the reception in North America manifests itself as the transformation of the influence of Scott's works on original literature and also in cultural attitudes and social life....
|
|
Fracture Toughness of Composite with Al-matrix and Carbon Fibres
Michalička, Jan ; Klement, Josef (referee) ; Molliková, Eva (advisor)
Abstract The objective of this study was a values evaluation of fracture toughness of fiber-metal laminates (FML) compounded from carbon fibers in epoxy matrix and aluminium plates of lay-up 6/5. Samples with unidirectional and bidirectional orientation were tested experimentally. In the case of unidirectionally oriented samples an effect of moisture absorption to epoxy matrix on the values of fracture toughness was reviewed. A fracture toughness calculation was realized by COD method firstly. A bigger pop-ins in F – COD diagram as critical moments for "delta"c evaluation were considered; it was determined by 5% tangential line. It was found out, that results of this measurement weren’t in agreement with plane deformation condition and for this the results couldn’t be rated as fracture toughness "delta"Ic. A method of J integral for fracture toughness evaluation was used consequently. A test of elastic compliance changes before J integral calculation by all of samples was performed. Beginning of stable grow of crack was determined by this method. A critical forces Fc from beginnings were established, which were used for calculation of Jc. A functional dependence of elastic compliance on crack opening had specific waved shape before its linear (up to exponential) grow. It was observed in all cases. The critical forces Fc from the end of “wave” preceding the continual grow of compliance were determined. Equations stated in standards for J integral calculation were used, which are for metal materials normally used. Despite this was found out all of results of Jc were in good agreement with plane deformation condition and could be rated as fracture toughness JIc. In this study were found out these pieces of knowledge about fracture toughness of FML CARE: Unidirectional CARE had fracture toughness JIc about 76 kJ/m^2 and the same type but with bigger amount of absorbed moisture had JIc about 4 % higher. In this case negative moisture influences on CARE weren’t found. Bidirectional CARE had fracture toughness JIc about 31 kJ/m^2; it was about 65 % less then in the case of unidirectional CARE
|
guest ::
