Use of laser-TIG hybrid technology for welding of different materials used in power engineering

Práce se zabývá analýzou vlivu procesních parametrů předehřevu pomocí elektrického oblouku z TIG hořáku během laserového svařování na vlastnosti svaru korozivzdorné martenzitické oceli a uhlíkové oceli s vyšší pevností. V této práci byl zhotoven experiment, při němž se svařily plechy o tloušťce 3 mm z ocelí X12Cr13 a S355. Svařovalo se postupně laserem, pak laserem s TIG předehřevem a naposled laserem s předehřátím materiálu indukčním ohřevem. Při využití TIG předehřevu se měnil svařovací proud nastavený na zdroji. Zhotovené svary se následně vyhodnotily na základě makrostruktury, mikrostruktury a zkoušce tvrdosti podle Vickerse.Thesis is focused on analyzing the influence of preheating process parameters using electric arc from TIG torch during laser welding on weld properties of stainless steel and carbon steel with higher strength. In this thesis experiment was done in which metal sheets 3 mm thick from X12Cr13 and S355 steels were welded. Welding was done first with using only laser, then laser with TIG preheating and lastly laser with preheated material by induction heater. When TIG preheating was used than set welding current was changed on the power source. The welds were subsequently evaluated based on macrostructure, microstructure and Vickers hardness test.

Radio Telemetry for RC Aircrafts

Diplomová práce je zaměřena na problematiku měření telemetrických údajů RC modelu letadla během letu. Zapojení je schopno měřit přetížení, výšku, pozici, tlak a rychlost letu a následně tato data uložit na paměťové médium. Cílem diplomové práce bylo navrhnout funkční desku, obslužný firmware a jednoduchý program na PC pro vyhodnocení naměřených dat. Zapojení obsahuje pět základních částí. Je to mikrokontrolér pro řízení celého zapojení, akcelerometr, slouží pro snímání přetížení, barometr měří výšku a tlak. Poslední je GPS modul, který sleduje pozici a rychlost letu. Údaje jsou ukládány na microSD kartu. Vyhodnocení probíhá pomocí programu vytvořeného v Matlabu s jednoduchým uživatelským rozhráním.Master‘s thesis is focused on problematic about state of RC plane model during the flight. Device is able to measure overload, height, position, pressure and velocity of the flight and store this measurement data to memory medium. The main aim of the master‘s thesis was to design a functional board, firmware for device and design simple program for evaluating of measured data. Involvement consists of five basic parts. First part is microcontroller, which processes measurement data and communicate with others parts. Next is accelerometer. Accelerometer is used for scanning overload of the plane. Barometer is used for measurement of height and pressure. For measuring position and velocity is used GPS module. Last part is memory medium. MicroSD is used as memory medium for storing measurement data. Evaluation of measured data is realized as simple program with base graphical user interface. Program was created in Matlab.

Pile Wall Solution of Blanka Tunnel Portal Pit in Prague

Import 07/02/2011Předmětem této diplomové práce je zajištění stavební portálové jámy pro tunel Městského okruhu v Praze ,,Blanka“ Jedná se o přístupovou jámu Myslbekova. Při výběru technologie zajištění je kladen důraz na nejefektivnější řešení. Realizované statické řešení je modelováno metodou konečných prvků. Výpočet je porovnáván se skutečně naměřenými veličinami na konstrukci. První část této práce je popisuje projekt zajištění stavební jámy, druhá část porovnává vypočtené veličiny s naměřeními. Dále hodnotí poznatky z výstavby.The aim of this diploma thesis was the shoring structures of tunnel´s portal pit. This tunnel is belong to Prague urban ring called „Blanka“. This thesis was concerned especially the Myslbekova pit. The selection of technologies was limited by the claim to find the most effective solving for security of the Myslbekova portal pit. There was used the FEM for simulation of realized solving in this portal pit. The results obtained by this method were compared with actual values significances on construction. The first part is based on describing the security project of the trench foundation pit. Next part of this thesis bring information about confrontation the rated values significances and values significances measured in site. Finally, I was appended some own notices from bulding-up of Myslbekova portal pit.Prezenční224 - Katedra geotechniky a podzemního stavitelstvídobř

Returns on investment in reducing heat loss of the house

Bakalářská práce se zabývá možnostmi snížení tepelných ztrát zvoleného rodinného domu. Součástí práce je výpočet tepelné ztráty před realizací rekonstrukce podle ČSN EN 12381. Hlavní částí této práce je zhodnocení navržených tepelně-izolačních opatření na základě návratnosti investic.Bachelor thesis is engaged with possibilities of heat loss reduction in the selected family house. Part of this thesis is calculation of heat losses before reconstruction according to ČSN EN 12381. The main part of this work is the evaluation of proposed heat insulation measures based on the returns of investments.

On the connection between mode II and mode III effective thresholds in metals

Closure-free long cracks under the remote mode III loading grow in a more complicated way than those under the remote mode II. For bcc metals, a coplanar in-plane spreading of tongues driven by the local mode II loading components at crack-front asperities prevails while twisting of crack-front segments to mode I, often leading to factory-roof morphology, is typical for other materials. In bcc metals, therefore, the formulation of a quantitative relationship connecting effective thresholds in modes II and III demands to calculate the local mode II components of stress intensity factors at typical asperities of a crack front loaded in the remote mode III. Therefore, a numerical model of a serrated crack front was created and the results were compared with experimentally determined ratio of mode II and III effective thresholds for the ARMCO iron. Although the calculated crack-front roughness needs an experimental verification, the preliminary results indicate that the model can provide a quantitative explanation of the experimentally observed ratio of mode II and mode III effective thresholds in bcc metals

An overstoichiometric Nd–Fe–B hard magnetic material

A commercial Nd-rich Nd–Fe–B-based hard magnetic material was studied. The obtained results were compared before and after recording of the thermomagnetic curve up to 800 °C. The curve itself showed clearly besides Curie points of the Nd2Fe14B phase and α-Fe also another critical temperature. Mössbauer spectroscopic (MS) phase analysis and X-ray diffraction analysis (XRD) showed in addition to the commonly known phases Nd2Fe14B and NdFe4B4 also some paramagnetic and ferromagnetic iron atoms (MS) and Fe17Nd2 intermetallics (XRD). During the exerted thermal treatment, the content of the Nd2Fe14B and NdFe4B4 phases remained almost unchanged, while iron atoms from remnant minor phases built a separate α-Fe phase. The XRD pattern also showed the presence of some minor Nd phase. The results of Squid magnetic measurements suggest a nanocrystalline decoupled structure of the Nd-rich alloy in the optimized magnetic state. Measurement of the magnetization loop showed, in spite of small changes in the phase composition, that magnetic properties of the quality material deteriorated during the thermal treatment

Thermal stability and mechanism of thermally induced crystallization of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy

Investigation of thermal stability of the alloy revealed stepwise crystallization process, manifested by two distinct complex exothermic peaks in differential scanning calorimetry curves. Kinetic parameters of individual crystallization steps were found using the Kissinger and Vyazovkin methods. Structural characterization of thermally treated samples showed formation of different iron-based phases including α-Fe(Si), Fe2B, Fe16Nb6Si7 and Fe2Si and some metastable intermediary species. Morphology characterization of the surface and cross-section of the thermally treated samples showed granulated structure composed of several different phases and indicated occurrence of impingement effects during crystal growth. Value of estimated lifetime suggested very high stability against crystallization at room temperature and abrupt decrease of lifetime with temperature increase

Hibdridni Nd-Fe-B/barijum-ferit magnetni materijali sa epoksi matricom

Lately, there has been great attention paid to the research of bonded hybrid composites with improved dynamic mechanical capacities capable of replacing bonded Nd-Fe-B magnetic materials, by using cheaper (ferrite) materials instead of the Nd-Fe-B powder while retaining the satisfying values of the maximum magnetic energy. The objective of this study is to assess how different contents of Nd-Fe-B and/or barium ferrite particles can affect morphological, dynamic mechanical and magnetic properties of bonded composite materials. The interactions between employed magnetic powders and the interactions between magnetic powders and polymer binder are considered. For the examination of the magnetic behaviour, a vibrating sample magnetometer (VSM) is used. Different shapes and sizes of the obtained hysteresis loops are used for comparison and prediction of the polymer bonded materials properties. The homogeneous distribution of the magnetic particles in the polymer matrix is validated using scanning electron microscopy (SEM). The elastic and damping behavior examined by dynamic mechanical analysis (DMA) show improved properties for hybrid composite materials.Istraživački trend u oblasti polimerom vezanih (bonded) Nd-Fe-B magnetnih materijala se reflektuje kroz razvoj bonded hibridnih kompozita sa poboljšanim dinamičko-mehaničkim svojstvima i primetno nižoj ceni zbog zamene skupe Nd- Fe-B legure jeftinijim magnetnim materijalima (ferit) uz postizanje zadovoljavajućih vrednosti maksimalne magnetne energije. Cilj ovog rada je da ukaže i predvidi uticaj različitog sadržaja Nd-Fe-B i/ili barijum feritnih čestica na morfološka, dinamičko mehanička i magnetna svojstava bonded magneta. Posmatrane su i analizirane interakcije između magnetnih prahova, kao i interakcije između magnetnih prahova i polimernog veziva i njihov uticaj na finalna svojstva bonded magneta. Za ispitivanje magnetnog ponašanja korišćen je vibraconi magnetometar (VSM). Različite veličine i oblici dobijenih histerezisnih krivih su poređeni i korišćeni za predviđanje svojstava ispitivanih kompozitnih materijala. Homogena raspodela magnetnih čestica u polimernoj matrici je potvrđena korišćenjem skenirajućeg elektronskog mikroskopa (SEM). Elastična svojstva i svojstvo prigušenja oscilacija ispitivano je korišćenjem dinamičko mehaničke analize (DMA) koja ukazuje na poboljšana svojstva kod hibridnih kompozita

Relationship between serum bilirubin and uric acid to oxidative stress markers in Italian and Czech populations

Summary Recently, a South-to-North oxidative stress marker gradient has been reported; consistent with known differences in the incidence of coronary heart disease between southern and northern European countries. The aim of the present study was to compare the plasma concentrations of 7-oxocholesterol (7OxCH) and 7β-hydroxycholesterol (7BCH) with systemic antioxidants in healthy Italian and Czech subjects. The study was performed in healthy subjects of Italian (n=131) and Czech (n=84) origins. In all subjects routine biochemistry work-ups were performed; additionally, plasma oxysterols and the peroxyl radicals scavenging activity (PERSA) of the sera were determined. Close relationship of serum bilirubin and uric acid to markers of oxidative stress was observed in both examined populations. Compared to the Czechs, the Italian population showed higher plasma concentrations of both oxysterols (7OxCH: 3.6 vs. 6.0 ng/ml, p −6 ; 7BCH: 5.3 vs. 8.6 ng/ml, p −6 ), lower PERSA (p −6 ), and lower serum concentrations of bilirubin and uric acid (p −6 in both cases). The dietary patterns of the Italian population did not match the Mediterranean style, but was more similar to the Continental type of diet, presumably due to non-adherence to a Mediterranean diet