Browsing by Author "Koreček, David"
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- ItemDetermination of the temperature influence on the change of Young’s modulus(TANGER Ltd., 2019) Sobotka, Jiří; Solfronk, Pavel; Koreček, DavidMaterials 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.
- ItemInfluence of the welding process on the change of mechanical properties in the HAZ of welds at alloy AW 6005 and possibilities of their renewal by heat treatment(J. E. Purkyne University in Usti nad Labem, 2019) Nováková, Iva; Moravec, Jaromír; Švec, Martin; Kik, Tomáš; Koreček, DavidThis paper deals with monitoring the influence of welding on the mechanical properties degradation in HAZ of welds at aluminium alloy AW 6005 and also with assessing the possibility of utilization the heat treatment to minimize these effects. Workpieces from alloy AW 6005 are mostly supplied in aged state. After application of the temperature cycles during welding, there is a very intensive decrease of the mechanical properties in HAZ. The mechanical properties of the weld metal, HAZ and parent material were evaluated by means of the Vickers hardness. Moreover, influence of annealing and artificial aging on the final mechanical properties of the parent material was also evaluated. Based on the results, there were chosen the relevant heat treatment parameters, which were subsequently applied in order to recover the mechanical properties of welds in the HAZ.
- ItemPrediction of foaming process in the production of aluminium foams(J. E. Purkyne University in Usti nad Labem, 2019) Nová, Iva; Sobotka, Jiří; Fraňa, Karel; Solfronk, Pavel; Koreček, David; Nováková, IvaThe 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.
- ItemProduction 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, IvaOur 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.
- ItemResearch of the temperature influence on the change of titanium alloy mechanical properties by means of the optical contact-less analysis(TANGER Ltd., 2019) Koreček, David; Solfronk, Pavel; Sobotka, JiříToday, 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.
- ItemVliv střižné mezery na rozložení tvrdosti v okolí střižné hrany(Technická Univerzita v Liberci, 2014) Koreček, David; Solfronk, PavelTato bakalářská práce se zabývá vlivem velikosti střižné mezery na rozložení tvrdosti v okolí střižné hrany. Cílem práce je připravit metalografické vzorky pro různé střižné mezery a v jednotlivých pásmech střihu změřit mikrotvrdost a následně vyhodnotit závislost tvrdosti na velikosti střižné mezery.
- ItemVyužití pokročilých výpočetních modelů pro predikci odpružení výliskůKoreček, David; Solfronk Pavel, doc. Ing. Ph.D. :55399Disertační práce "Využití pokročilých výpočetních modelů pro predikci odpružení výlisků" se zabývá možnostmi matematického modelování přechodu materiálu do plastického stavu a následného deformačního chování v oblasti rozvinutých plastických deformací a nakonec korektní predikcí odpružení materiálu. V rámci řešení práce je kladen důraz na testování nových typů materiálů se specifickými užitnými vlastnostmi s možností aplikace těchto materiálů v automobilovém, leteckém a energetickém průmyslu. Cílem práce je stanovení vhodné metodiky získávání a vyhodnocování potřebných materiálových dat nutných pro definici pokročilých MKP modelů s jejich následnou implementací do softwaru umožňujícího numerické simulace procesu plošného tváření plechů. Prováděné experimenty a numerické simulace procesu tváření jsou cíleně zaměřeny především na verifikaci výpočetních materiálových modelů v kombinaci se sledováním vlivu vybraných technologických a procesních parametrů na průběh deformace, a po odeznění zatěžujících silových účinků, i následného odpružení materiálu. Provedené numerické výpočty procesu deformace a odpružení materiálu jsou zde porovnány s výsledky reálného procesu zhotovení výlisku z plechu. V závěru disertační práce je hodnocen význam a vliv zvolených materiálových výpočetních modelů a vybraných parametrů s ohledem na průběh deformace a následného odpružení materiálu.
- ItemZjištění vhodného materiálového modelu pro numerickou simulaci tažení výlisku plechu ze slitiny titanu(Technická Univerzita v Liberci, 2016) Koreček, David; Solfronk, PavelTato diplomová práce se zabývá zjištěním vhodného materiálového modelu slitiny titanu, který se použije pro numerickou simulaci tažení výlisku z plechu. Pro numerickou simulaci se použijí modely Hill 48 a Vegter. Oba modely jsou ve variantě s izotropním nebo kinematickým zpevněním materiálu. Pro definici těchto modelů se provede řada materiálových zkoušek. Dále se provede experiment zhotovení výlisku z plechu, který bude v závěru porovnán s numerickou simulací.