Browsing by Author "Švec, Martin"
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- ItemExperiments and Numerical Simulations of the Annealing Temperature Influence on the Residual Stresses Level in S700MC Steel Welded Elements(MDPI, 2020) Kik, Tomasz; Moravec, Jaromír; Švec, MartinThe article presents the results of research on the influence of temperature and time changes of the annealing process on the values and distribution of stresses in the simulated heat-affected zone of S700MC steel welded joints. For this purpose, tests were carried out on a thermal cycle simulator, as well as heating the prepared samples in accordance with the recorded welding thermal cycles, and then annealing at temperatures from 200 to 550 °C. The stresses values in the tested samples before and after the annealing process were measured by using X-ray diffraction (XRD). The performed tests were verified with the results of numerical analyses using the finite element method (FEM) performed in the VisualWeld (SYSWELD) environment as, on the one hand, the verification of the obtained results, and, on the other hand, the source of data for the development of a methodology for conducting analyses of heat treatment processes of S700MC steel welded structures. Also presented are three examples of numerical analyses for Gas Metal Arc (GMAW), laser and hybrid welding and then the annealing process of the obtained joints at selected temperatures. The main purpose of the work was to broaden the knowledge on the influence of annealing parameters on the values and distribution of stresses in welded joints, but also to signal the possibility of using modern software in engineering practice.
- 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.
- ItemProblém agresivity a šikany na SŠ(Technická Univerzita v Liberci, 2010) Švec, Martin; Futschiková, IvonaThe bachelor work deals with the expressions of aggressivity and bullying among youngpeople. It investigates the influence of mass mediums to the development and increasing ofaggressivity of young people. It deals with modern sorts of bullying too, that appear moreoften and more frequently and they are connected with the fast development of newtechnologies in communication.In the practical part of the work there has been investigated the impact of influence ofmass mediums and new modern technologies in communication to the social relationschipsand discipline in the selected sample of the secondary pupils, that it is the subject of theinvestigation.
- ItemProblém agresivity a šikany na středních školáchŠvec, Martin
- ItemRecycling of sisal fiber reinforced polypropylene and polylactic acid composites: Thermo-mechanical properties, morphology, and water absorption behavior(2019) Ngaowthong, Chakaphan; Borůvka, Martin; Běhálek, Luboš; Lenfeld, Petr; Švec, Martin; Dangtungee, Rapeephun; Siengchin, Suchart; Rangappa, Sanjay Mavinkere; Parameswaranpillai, JyotishkumarThe effect of recycling on the thermo-mechanical and water absorption behavior of polypropylene (PP)/sisal fiber and polylactic acid (PLA)/sisal fiber composites were studied. The PP-based non-biodegradable composites and PLA-based biodegradable composites were recycled for four times. The effect of recycling was determined by examining the morphology, thermo-mechanical properties, and water absorption behavior and the obtained results were compared. The results showed that the incorporation of sisal fibers in the PP and PLA matrix enhances the tensile modulus and percentage crystallinity of the composites. The tensile strength and modulus of the sisal fiber reinforced PP composites were not affected with recycling. Even though the tensile properties of PLA and PLA/sisal fiber reinforced composites are superior to PP and PP/sisal fiber composites, the PLA-based composites show a dramatic decrease in tensile strength and modulus after the first recycling due to the degradation of the polymer. The thermal stability of the PP/sisal fiber composites was not affected by the repeated recycling process. On the other hand, the PLA-based composites with higher sisal fiber content show a bit lower thermal stability after recycling. The PP-based composites show fluctuations in percentage crystallinity with recycling. On the other hand, a remarkable increase in percentage crystallinity for PLA and PLA-based composites was observed with increasing recycling times. Water diffusion study divulges that the diffusion of water into the polymer composites was reduced with recycling, irrespective of the polymer matrix.
- ItemSouvislosti mezi strukturou a vysokoteplotními mechanickými vlastnostmi aluminidů železa s příměsí niobu, uhlíku a chrómu(Technická Univerzita v Liberci, 2012) Švec, Martin; Hanus, PavelThis work for my diploma deals with the research into the connections between structure and high-temperature mechanical properties of Fe3Al iron aluminides with the addition of niobium, carbon and chromium. The iron aluminides are very promising materials for structural applications with many advantages (eg. excellent oxidation and sulfidation resistance, relatively high tensile strength at room temperature and lower density than stainless steel), but there are some problems in their properties, for eg. limited ductility at room temperature or a sharp drop in strength above 600°C, prevent their expansion. Research conducted within this thesis aims to verify the influence of some alloying elements on high-temperature mechanical properties. The effect of niobium, carbon and chromium on improving the high-temperature strength was studied. It was verified that the effect of subsequent heat treatment of alloys on the structure and high-temperature mechanical properties too. The yield stress for the individual states of alloys was studied at temperatures ranging from 200-800°C.
- ItemStruktura a vysokoteplotní mechanické vlastnosti aluminidů železa s karbidotvornými příměsemi niobem a zirkoniem(Technická Univerzita v Liberci, ) Švec, Martin
- ItemStruktura a vysokoteplotní mechanické vlastnosti aluminidů železa s karbidotvornými příměsemi niobem a zirkoniem(Technická Univerzita v Liberci, 2016) Švec, MartinThe dissertation deals with a study of structure and high-temperature mechanical properties of Fe3Al-type iron aluminides doped by carbide forming elements (Zr, Nb) and carbon. The influence of mutual Zr/C (event. Nb/C) ratio on type and amount of emerging secondary phases (Laves phase and carbides) were studied. The influence, which have these phases on high-temperature mechanical properties, was studied. It was also verified the influence of heat treatment and heat-mechanical treatment of alloys on phase structure and high-temperature mechanical properties. The structure of investigated materials was studied by light optical microscopy and scanning electron microscopy. The phase composition was verified by EDX, RTG diffraction and EBSD. Yield strength for individual types of alloys was measured in compression in temperature range 600 800°C. For alloys with niobium addition there was also measured (except yield strength in compression) yield strength in tension in the same temperature range, creep resistance and coefficient of thermal expansion in temperature range 400 1200°C.
- ItemVýzkum porózity kovových soustav v práškové metalurgii metodami nedestruktivního testování(Technická Univerzita v Liberci, 2009) Švec, Martin; Skrbek, BřetislavThis bachelor work deals with the research of porosity and thickness of a cake up bronze layer on the bearing pans with an assistance of a nondestructive proofing. The work evaluates suitability and reliability of the used nondestructive methods for the exposure of an extent of porosity.