Browsing by Author "Sobotka, Jiří"

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    Aplikace zobecněných funkcí při výpočtu tenkostěnných nosníků
    (Technická Univerzita v Liberci, 2010-01-01) Sobotka, Jiří; Hýča, Milan
    Práce se zabývá aplikacemi zobecněných funkcí k analytickému výpočtu tenkostěnných nosníků s nespojitostmi v zatížení, uložení, geometrii příčného průřezu a vlivem vložených kloubů nebo spojek. Analytické výpočty tenkostěnného nosníku s předpokládanými nespojitostmi pomocí odvozených modelů jsou velice efektivní, poněvadž není nutné dělit nosník na segmenty mezi sousedními ody nespojitosti, řešit diferenciální rovnice pro každý segment a užít podmínky spojitosti. Všechny výpočty byly provedeny pomocí symbolického programování v prostředí Maple.
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    Application possibilities of the low-temperature repairs on creep-resistance turbine components from material GX23CrMoV12-1
    (2018-01-01) Moravec, Jaromír; Nováková, Iva; Sobotka, Jiří; Kik, Tomasz
    Papers deals with the problems of repairs at new and also already loaded components of steam and gas turbines. Generally, it is about welding repairs at valve and turbine chambers, transmitters, vane carriers, tripping valve body and so on. There are both technological defects caused by casting (e.g. shrinkage cavities, misruns, porosity and cracks) and defects caused by operation (thermal-stress fatigue, incorrect method of operation, etc.). Many of the mentioned defects take effect not until the final technological method - mostly at machining. However, in this production phase it is not possible to get form the supplier new production elements due to economical and also delivery time reasons. All of that results in delay of production and penalty. As the major aim of this paper, there was to find such repairs techniques which can ensure serviceability of mentioned devices under the standard regime. In these cases is needed to use much lower tempering temperature than under the standard production, mainly because of necessity to eliminate deformation caused by heating of part that is not possible to be subsequently removed by machining.
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    Deformační analýza materiálu pomocí vysokorychlostních kamer
    (Technická Univerzita v Liberci, 2015-01-01) Špaček, Marek; Sobotka, Jiří
    Tato diplomová práce se zabývá snímáním dynamické deformace pomocí vysokorychlostních kamer v systému Aramis. V úvodu se seznámíme s cíli práce. V teoretické části je představena fotogrammetrie a její využití pro technické účely. Dále principy deformace materiálu a jejich zkoušky. V poslední části jsou představeny vysokorychlostní kamery a jejich použití. V experimentální části práce probíhá zkouška vypínáním a rázem a snímání děje vysokorychlostními kamerami. V poslední části jsou ukázány výsledky ze softwaru ARAMIS a vyhodnoceno praktické využití této metody.
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    Determination of Grain Growth Kinetics and Assessment of Welding Effect on Properties of S700MC Steel in the HAZ of Welded Joints
    (2019-06-24) Moravec, Jaromír; Nováková, Iva; Sobotka, Jiří; Neumann, Heinz
    The welding of fine-grained steels is a very specific technology because of the requirement for the heat input limit value. Applying temperature cycles results in an intense grain growth in a high-temperature heat-affected zone (HAZ). This has a significant effect on the changing of strength properties and impact values. The intensity of grain coarsening in the HAZ can be predicted based on the experimentally determined activation energy and material constant, both of which define grain growth kinetics. These quantities, together with real measured welding cycles, can be subsequently used during experiments to determine mechanical properties in a high-temperature HAZ. This paper shows a methodical procedure leading to the obtainment of the material quantities mentioned above that define the grain growth, both at fast and slow temperature cycles. These data were used to define the exposure temperature and the soaking time in a vacuum furnace to prepare test samples with grain sizes corresponding to the high-temperature HAZ of welded joints for the testing procedures. Simultaneously, by means of the thermo-mechanical simulator Gleeble 3500, testing samples were prepared which, due to a temperature gradient, created conditions comparable to those in the HAZ. The experiments were both carried out with the possibility of free sample dilatation and under a condition of zero dilation, which happens when the thermal expansion of a material is compensated by plastic deformation. It has been found that shape of the temperature cycle, maximal achieved cycle temperature, cooling rate, and, particularly, the time in which the sample is in the austenite region have significant effects on the resulting change of properties.
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    Determination of the temperature influence on the change of Young’s modulus
    (TANGER Ltd., 2019-01-01) Sobotka, Jiří; Solfronk, Pavel; Koreček, David
    Materials commonly used in various branches of the engineering industries are very often tested under basic conditions. This is due not only to the frequent effort to determine e.g. mechanical properties of the tested material just under reference conditions but also to the assumption that some material characteristics remain constant over the entire range of material loading conditions. In this paper, the change of Young's modulus in dependence on temperature is studied. Stainless steel was selected as the test material. To determine the required Young's modulus of elasticity, a static tensile test was performed on a testing machine equipped with a split tube furnace which allowed the desired loading temperature to be adjusted (generally from RT to about 1,400 °C). The force channel was thus detected by means of a load cell (using bridge strain-gauge circuit) clamped in a testing machine. Specimen extension was simultaneously monitored using the external Mercury contact-less optical system, where the actual distance between two monitored points was measured. The entire system thus functioned as a "virtual" strain-gauge delivering the necessary specimen extension channel. From these measured characteristics, the corresponding Young´s modulus of elasticity was finally calculated as a function of temperature. The resulting temperature influence on the values of Young´s modulus change not only gives a better insight into the deformation behaviour of the tested material in the elastic deformation area, but can be also used in the numerical simulations of deformation processes.
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    Heat Input Influence on the Fatigue Life of Welds from Steel S460MC
    (MDPI, 2020-01-01) Moravec, Jaromír; Sobotka, Jiří; Solfronk, Pavel; Thakral, Robin
    Fine-grained steels belong to the progressive materials, which are increasingly used in the production of welded structures subjected to both static and dynamic loads. These are unalloyed or microalloyed steels hardened mainly by the grain-boundary strengthening mechanism. Such steels require specific welding procedures, especially in terms of the heat input value. At present, there are studies of the welding influence on the change of thermomechanically processed steels’ mechanical properties, however mainly under static loading. The paper is therefore focused on the assessment of the welding effect under dynamic loading of welded joints. In the experimental part was determined the influence of five different heat input values on the change of weld fatigue life. As a result, there is both determination of five S-N curves for the double-sided fillet welds from the thermomechanically processed fine-grained steel S460MC and the quantification of the main influences reducing the fatigue life of the joint.
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    Hodnocení mechanických vlastností nových vysokopevnostních materiálů
    (Technická Univerzita v Liberci, 2008-01-01) Sobotka, Jiří
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    Měření mezního stavu deformace při zkoušce rozšiřování otvoru pomocí optického systému ARAMIS
    (Technická Univerzita v Liberci, 2013-01-01) Knížek, Jiří; Sobotka, Jiří
    Tato bakalářská práce je zaměřena na zjišťování velikosti přetvoření.V okolí otvoru při zkoušce rozšiřováním otvoru, která byla vyhodnocena pomocí manuálního měření a optického systému ARAMIS. V teoretické části bakalářské práce je popsána tvářitelnost plechů a jejich hodnocení. Dále jsou popsány základy fotogrammetrie a optické měřící systémy pracující na tomto principu. V experimentální části je popsáno měření zkoušky rozšiřováním otvoru a zjišťování velikosti přetvoření. Hlavním cílem této bakalářské práce bylo porovnání výsledků obou způsobu měření.
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    Modifikace vyhodnocování diagramů mezních přetvoření pro vysokopevnostní materiály pomocí sledování rozložení přetvoření podél měřeného vzorku.
    (Technická Univerzita v Liberci, 2010-01-01) Wasserbauer, Ondřej; Sobotka, Jiří
    Diploma deals with describing deformation behavior of TWIP steel (Twinning Induced Plasticity). This is a new type of high-strength material. Deformation mechanism of TWIP steel ? twinning - provide a unique mechanical properties. That predisposes this steel as one of the main structural materials in the applications for car-bodies design. During the experiment (stretching test of shaped samples with cut-out circular segments of constant radius by semispherical punch) was carried out measurements to obtain construction points of final limit curves. The results of the experiment were also used to extend the evaluation method for final limit diagrams of high-strength materials. On the basis of them was designed new 2D diagram with coordinates m?-SFLC. During measurement was used optical contact less system ARAMIS. The results serve as a basis for further testing of TWIP steel, as well as a starting point about improving the modified evaluation method of the final limit diagrams.
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    Prediction of foaming process in the production of aluminium foams
    (J. E. Purkyne University in Usti nad Labem, 2019-01-01) Nová, Iva; Sobotka, Jiří; Fraňa, Karel; Solfronk, Pavel; Koreček, David; Nováková, Iva
    The paper deals with the physical-chemical effects of a blowing agent on production the cellular metal systems (in this case aluminium foams). Based on the isothermal concertation and pressure curves for the H-Ti system and by using the maximum gas volume obtained from equation of state, there was applied the blowing agent to 1 kg of AlSi12 aluminium alloy. Moreover, using relation to determine aluminium foam relative density (ρREL) from alloy AlSi12, there was done prediction to determine density of 1 kg metal foam from AlSi12 alloy at different blowing agent contents from 0.1 up to 1.5 wt% of titanium hydride TiH2. These isothermal calculations were compared with the density of aluminium foal from alloy AlSi12, which was produced by an industrial process. Basic mechanical properties were subsequently measured on the produced foam samples.
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    Production of porous aluminium using sodium chloride
    (J. E. Purkyne University in Usti nad Labem, 2020-01-07) Fraňa, Karel; Nová, Iva; Sobotka, Jiří; Solfronk, Pavel; Koreček, David; Nováková, Iva
    Our workplace, Technical University of Liberec, is currently engaged in research and production of cellular metal systems. Basically, cellular metal systems are materials with lower density. It is a research in the field of mechanical engineering that is focused on the development of new materials. In general, many methods have been developed for the p oduction of cellular metal systems, e.g. by BANHART [2] or ASHBY [4]. At their production, the direct gassing of molten metals (mostly aluminium ones) or gassing by the powder agents (e.g. specially formulated aluminium powders) are mostly used. Depending on the manufacturing method, a cellular system with open or closed cells can be obtained. The most commonly used metal is aluminium and its alloys. We are currently focusing on the production of porous aluminium by using sodium chloride. Sodium chloride occupies regular sites in the aluminium material and thus contributes to the aluminium porosity. After solidification of the aluminium, sodium chloride is dissolved in water. Sodium chloride is relatively inert to the aluminium and together with it, has a favourable density (2160 kg·m-3) compared to the aluminium density (2700 kg·m-3). The values of these physical quantities were observed on the produced aluminium test specimens having O 60 × 10 mm: relative density of porous system ρREL; porosity of metal system P; amount of solid phase system volume fraction VPM; density of porous metal system ρPM and porous material Young's modulus of elasticity EPM.
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    Research of the temperature influence on the change of titanium alloy mechanical properties by means of the optical contact-less analysis
    (TANGER Ltd., 2019-01-01) Koreček, David; Solfronk, Pavel; Sobotka, Jiří
    Today, more and more accent is in the automotive, aerospace and energy industries put on the use of materials with the specific utilize properties such as high strength and at the same time sufficient ductility to enable the production of given part. In addition to these key forming features, low weight and, last but not least, good corrosion resistance are also important. In view of the above requirements, titanium alloys appear to be a progressive construction material for the most demanding applications in a wide range of engineering production. This paper deals with the change of mechanical properties of titanium alloy with the trade name Grade 5 (Ti-CP 6Al-4V). The change of mechanical properties is evaluated by means of a static tensile test carried out in an insulated temperature chamber with resistance heating. The tests are carried out in the selected temperature interval, which should sufficiently represent changes in mechanical properties depending on temperature. Scanning and evaluation of the test deformation characteristics is performed by using an advanced contact-less optical deformation analysis method, which operates on the principles of the photogrammetry. Lab NET software and Mercury software are used for this purpose. The results of the measurements are dependencies of the titanium alloy mechanical properties on temperature within the selected temperature interval. Furthermore, the resulting temperature dependence of mechanical properties can be used as input material characteristics into the numerical simulation environment of the material forming process.
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    Rizika vzniku domácího násilí
    (Technická Univerzita v Liberci, 2008-01-01) Sobotka, Jiří; Michalová, Zdeňka
    The bachelor work was focused on conditions of the formation of the private violence, its situation and the important factors whose comes before. These results were achieved by comparing the information from the literature, the statistical reports, model of the risk factors and the own author experience. The theory part includes the account some concepts and forms of the private violence, motives of behaviour, sorts, conditions and reasons of the birth aggression and aggressiveness. There are processed the statistical data of victims and offenders but also the legislative changes in this section with the resulting data after the introduction of the deportation. Further there are described the various models of potential factors contributing to the home violence, the mental disorder and some "triggers (starter power) of this. The practical part was focused on the characteristics of the risk persons and situations which could minister to detecting of the private violence and next aid to the endangered persons.
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    Rizika vzniku domácího násilí
    (2008-01-01) Sobotka, Jiří
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    Testy mechanických vlastností vrstveného materiálu
    (Technická Univerzita v Liberci, 2016-01-01) Šulc, Marek; Sobotka, Jiří
    Tato bakalářská práce se zaměřuje na mechanické zkoušky vrstvených materiálů. V teoretické části jsou popsány základní mechanické vlasnosti materiálů, rozdělení materiálů pro stavbu karosérií automobilů a vrstvených materiálů. Experimentální část se zabývá statickou zkouškou tahem vrstveného materiálu ve formě plochých zkušebních tyčí v závislosti na teplotě.
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    Využití fotogrammetrie pro digitalizaci tažných nástrojů v rámci numerických simulací plošného tváření
    (Technická Univerzita v Liberci, 2015-01-01) Flodrman, Jiří; Sobotka, Jiří
    Tato práce se zabývá možnostmi využití fotogrammetrie pro simulace procesů tváření při výrobě karosářských dílů. Je zde popsán proces získávání dat a také jejich možné využití pro numerické simulace. Jedná se především o skenování funkčních ploch lisovacího nářadí, získávání materiálových dat a provedení deformační analýzy pomocí optických měření. Byla vytvořena simulace s použitím dat používaných v předvýrobní etapě a druhá simulace s použitím dat získaných pomocí laserového měření. Na závěr byl využit systém ARGUS, který umožňuje měřit deformace materiálu a verifikaci výsledků simulací.
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