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Field measurement of natural electromagnetic emissions near the active tectonic and mass-movement fractures in caves
Trčka, T. ; Macků, R. ; Koktavý, P. ; Škarvada, P. ; Baroň, I. ; Stemberk, Josef
Laboratory tests on a wide range of solid materials shoved that the electromagnetic emission (EME) signals are generated during the samples mechanical stress. EME anomalies have been observed also under natural conditions in association to fracture processes, tectonic loading, stress redistribution and crack propagation prior to earthquake or in relation to deep-seated gravitational mass movements. This paper describes a first prototype of the Emission data logger, which was specially developed for the continual EME monitoring in field conditions. Our equipment has been installed and tested in Obir Caves (Austria) at an active tectonic fault. The pilot long-term EME measurement results from this location are also presented in this paper.
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Analysis of the force loading of the end mills with PCD considering their sharpening
Trčka, Tomáš ; Kalivoda, Milan (referee) ; Polzer, Aleš (advisor)
Measurement of the force loading is a significant type of measurement in mechanical engineering applied to analyse important aspects in the machining process. In addition to the determination of specific material constants, it is possible to analyse, for example, various machining strategies, geometries of tools or the degree of wear of the cutting edges of cutting tools. This master’s thesis deals especially with the last two mentioned aspects which are subjects of an experiment on end mills with PCD inserts sharpened by a different technology. In the introductory part the cutting forces are theoretically analysed along with their measurement possibilities and the technology of the production of the mills including their sharpening – WEDM and EDM-G. One chapter is concerned with the milling of plastic materials, as PVC was the material used for the workpiece during the experiment. The first experimental part is devoted to the analysis of sharpened tools followed by the measurement of forces using the piezoelectric dynamometer and the subsequent analysis of the influence of the different tool geometry. The last conducted experiment monitors how the overall cutting forces of individual end mills sharpened by different technology changed over specific milling time slots.
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Time lapse tomography of fracture progress in silicate-based composite subjected to the loading a combination with acoustic emission scanning
Kumpová, Ivana ; Kytýř, Daniel ; Fíla, Tomáš ; Veselý, V. ; Trčka, T. ; Vopálenský, Michal ; Vavřík, Daniel
The initiation and propagation of a fracture in quasi-brittle materials (such as silicatebased composite) is an increasingly discussed topic for which various methods of research have been developed/applied. As the quasi-brittle silicate-based composite compounds are very non-homogenous, the mechanism of the crack initiation and propagation can be very different even for samples with the\nidentical geometry. One possible approach to study the fracture mechanism in quasi-brittle materials is to use several different experimental techniques in a single experiment and perform detail analysis to identify generally valid fracture process phenomena. In this work, a simultaneous monitoring of fracture\nprocess zone formation and propagation by three different methods is presented and discussed. A three point bending test was performed on a notched silicate composite specimen. During the loading process, a highly accurate force displacement dependence was recorded accompanied with X-ray radiography,\nX-ray computed tomogra-phy and acoustic emission scanning.
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Application of Electromagnetic and Acoustic Emission for the Diagnostics of Advanced Composite Materials
Trčka, Tomáš ; Chobola, Zdeněk (referee) ; Lokajíček,, Tomáš (referee) ; Koktavý, Pavel (advisor)
The subject of this dissertation is a theoretical and experimental study of electromagnetic and acoustic emission generated in the course of crack formation in solid dielectric materials. Theoretical part of this work is focused on the electromagnetic emission method, because it is related to a number of unsolved problems in the field of generated emission signals measurement, as well as in the field of the correct interpretation of obtained experimental data. Consequently, issues of emission signals detection by capacitance sensors and the transformation of crack primary parameters on the measured variables within the proposed transfer system have been dealt with. The results in this area were an extension of application range of the electromagnetic emission method on composite materials (especially on fiber reinforced polymer composites), identification and evaluation of the most significant emission sources in investigated composites and developing a methodology for evaluating of the crack primary parameters based on the measured emission signals waveforms in time and frequency domain. The experimental part of this dissertation was focused on a complex methodology for emission signals (including data from additional sensors) continual recording, processing and evaluation and for monitoring the response of stressed material to an applied mechanical load in real-time. Partial results from different research areas were also implemented into this methodology. This included the detection of emission signals, design and implementation of the appropriate measuring apparatus, analysis of measured signals in the time and frequency domain and advanced methods for processing and evaluation of measured data.
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Design of thermal system for accurate temperature stabilization using Peltier thermoelectric modules
Motl, Jakub ; Trčka, Tomáš (referee) ; Macků, Robert (advisor)
This master’s thesis describes design procedure of a heat-regulating system to stabilize its temperature using a Peltier module. The implementation uses eight-bit microcontroller ATmega16 made by company ATMEL for the local and remote control system. The temperature sensors communicate with the microcontroller by serial SPI interface. To display user data, it has a DEM16217SYH type character LCD display with HD44780 control circuit. To collect data from the cooling areas of Peltier module, accurate ADT7320 temperature sensors are used, made by company Analog Devices. The Control of the Peltier module happens in two points of the electrode system and a bistable hysteresis software regulator is used. The first part summarizes the theory, which concerns with the design. Next part concerned with issues of the Peltier module, overview of temperature sensors, description of the microcontroller, the display unit and the used regulator. Last part describes the hardware and software implementation.
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Turbocodes and their application in telecommunication systems
Trčka, Tomáš ; Křivánek, Vítězslav (referee) ; Němec, Karel (advisor)
This Diploma thesis deals with Turbo code problems. The Turbo codes belong to the group of error correction codes, sometimes referred to as forward error correcting (FEC) codes or channel codes. This thesis can be thematically divided into two basic parts. The first part describes turbo code encoder and decoder block diagram with the illustration of two most frequently used iterative decoding algorithms (SOVA and MAP). The end of this part contains best known turbo codes, which are used in present communication systems. The second part pursues simulation results for the turbo codes using Binary Phase Shift Keying (BPSK) over Additive White Gaussian Noise (AWGN) channels. These simulations were created in the MATLAB/SIMULINK computer program. It will be shown here, that there exist many different parameters, greatly affecting turbo codes performance. Some of these parameters are: number of decoding iterations used, the input data frame length, generating polynoms and RSC encoders constraint lengths, properly designed interleaving block, decoding algorithm used, etc.
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Hardness measurement of metal materials
Trčka, Tomáš ; Kandus, Bohumil (referee) ; Podaný, Kamil (advisor)
The hardness is the mechanical property of each metal material that affects his behaviour. There are many methods of measurement. Each method has its advantages, shortcomings and possibilities of use. The best known tests are according to Brinell, Vickers and Rockwell. The newer methods with portable hardness tester are UCI, TIV and the dynamic method by Leeb. The tests are carried out by mechanical pressure load using the impact body (indenter) of the harder material than the test material. The experimental measurement was executed on the three types of cutting inserts with different nominal hardness made from cemented carbides using the Vickers method with the load of 10 kp and 30 kp. The highest value of hardness was measured on the cutting insert SMG02 - 1988 HV10.
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Surface examination of ultra-sharp cold field-emission cathode
Knápek, A. ; Brüstlová, J. ; Trčka, T. ; Klampár, M. ; Mikmeková, Šárka
An experimental cold field-emission cathode, based on metal-oxide-insulator structure has been analyzed by several non-destructive evaluation methods in order to describe the material properties and electrical behaviour of the sample. Owing to the fact that the tip of the cathode reaches nanoscopic-scale, several different evaluation methods have been incorporated. Firstly, the scanning electron microscopy (SEM), along with the electron dispersive spectroscopy (EDS) was performed to describe general proportions of the shape and the abundance of elements present in the surface layer. Secondly, the scanning low-energy electron microscopy (SLEEM) was applied in order to visualize the crystalline microstructure of the cathode surface. Finally, the epoxy coating covering the cathode tip was characterised using the dielectric relaxation spectroscopy (DRS) method.
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