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Nízkocyklová životnost v podmínkách jaderné energetiky
Sehnal, Dominik ; Kuželka, Jiří (oponent) ; Hůlka, Jiří (vedoucí práce)
Prodloužení životnosti jaderných zařízení tkví v hledání projektových rezerv. Tato práce se zabývá hodnocením nízkocyklové životnosti jaderných zařízení typu VVER a posouzením vlivu úrovně výpočtového modelu. V rámci práce jsou provedeny únavové zkoušky austenitické oceli s využitím optické metody digitální korelace obrazu, pro které je navržen a použit postup vyhodnocování. Ze získaných dat jsou kalibrovány modely plasticity s kinematickým (Chaboche) a kombinovaným zpevněním (Chaboche, Voce). Následně je určena životnost zkušebního tělesa pomocí výpočtového modelování pro různé modely materiálu. Z porovnání výsledků únavových zkoušek s výpočtem jsou stanoveny modely materiálu vhodné pro popis únavové životnosti a oblast jejich platnosti.
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Seal Plugs Design for Common-Rail System Pressure Reservoir High-Cyclic Fatigue Testing
Skrutek, Ivo ; Cupl, Zdeněk (oponent) ; Ramík, Pavel (vedoucí práce)
This diploma thesis is focused on problem with crackling of the sealing cone on the rail body during high pressure pulsation test. There are analyzed properties of currently used sealing caps for pulsation test and their influence on loading of the sealing cone. The main target is proposal of new sealing cap which creates the same or very similar loading on all components during pulsation test like high pressure pipe which is used in serial production. Next part is verification of properties of new sealing cap by high pressure pulsation test.
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Pevnostní kontrola sestavy kliky jízdního kola
Kolenčík, Richard ; Skalka, Petr (oponent) ; Burša, Jiří (vedoucí práce)
Bakalárska práca sa zaoberá pevnostno-deformačnou kontrolou zostavy kľuky bicykla. Prvá časť sa venuje kontrole bezpečnosti voči únavovému lomu kľuky bicykla, ktorá je zaťažená kombinovaným namáhaním. V druhej časti práce je prevedená bezpečnostná analýza voči únavovému lomu v prípade pedálu. Z dôvodu nízkej bezpečnosti pedálu, je vykonaný aj výpočet vysoko cyklickej životnosti. Posledná časť je venovaná určeniu maximálnej deformácie zostavy kľuky a pedálu. Samotný analytický výpočet bol vykonaný pomocou softwaru Matlab R2012b.
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Development of loading spectra and fatigue life analysis of small two-seat composite aircraft
Daňko, Matúš ; Juračka, Jaroslav (oponent) ; Augustin, Petr (vedoucí práce)
Primary goal of this thesis is to present proposed method for fatigue life evaluation applicable to light composite aircraft. The first chapter of this thesis is focused on certification specifications and requirements for fatigue life proof of structure. Significant part of this thesis is dedicated to fatigue life evaluation and guideline how to proceed in evaluation of fatigue data. Thesis also points out on possible methods of statistical fatigue data analysis and critical parts of structure in means of fatigue life. The last part of thesis is focused on design of experimental evaluation of structure including test rig and load sequence. This chapter also provides inside into possible means of introducing artificial defects into the structure.
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Cyklická plasticita a nízkocyklová únavová odolnost materiálů připravených metodou Cold Spray
Brůža, Jaromír ; Šulák, Ivo (oponent) ; Zapletal, Josef (vedoucí práce)
Diplomová práce se v teoretické části zaměřuje na technologii Cold spray a parametry ovlivňující účinnost a kvalitu depozice. Dále je zde úvod do procesu únavy materiálů. Teorie je zakončena shrnutím současných poznatků týkajících se materiálů vytvořených Cold spray technologií v oblasti únavy. V praktické části byla vytvořena objemová tělesa z materiálu EN AW7075. Z těles byly elektrojiskrově vyřezány vzorky pro tahové a únavové zkoušky. Z materiálu a prášku byly vytvořeny metalografické výbrusy pro určení porozity pomocí Archimedova zákonu, tvrdosti dle Vickerse a vyhodnocení EDS a EBSD analýzy. Z tahových zkoušek byly zjištěny základní mechanické vlastnosti a z únavových zkoušek byly stanoveny Wöhler-Basquinovy parametry spolu s křivkou životnosti. Následně došlo k fraktografické analýze lomových ploch pomocí SEM.
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Vliv výpočtového modelu dynamiky klikového mechanismu na zatížení bloku motoru
Charvát, Adam ; Dlugoš, Jozef (oponent) ; Drápal, Lubomír (vedoucí práce)
Tato práce zkoumá vliv výpočtového modelu dynamiky klikového mechanismu na zatížení bloku motoru v oblasti hlavních ložisek v závislosti na úrovni diskretizace použitých těles. Jsou srovnány čtyři varianty výpočtového modelu klikového mechanismu v prostředí Multi-Body System softwaru SIMDRIVE 3D z hlediska zatížení hlavních ložisek. Na základě získaných zatížení je provedena pevnostní analýza bloku sériového motoru 1,5 MPI řady EA211 výrobce ŠKODA AUTO včetně vlivu předpětí při montáži hlavy válců a ložiskových vík. K vyhodnocení je proveden výpočet únavové životnosti a výsledné součinitele bezpečnosti v oblasti konstrukčních zápichů na spodní straně bloku motoru jsou porovnány.
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Fatigue resistance and mechanisms of the fatigue damage in materials for high temperatures
Petráš, Roman ; Kohout,, Jan (oponent) ; Weidner, Anja (oponent) ; Polák, Jaroslav (vedoucí práce)
Superaustenitic stainless 22Cr25NiWCoCu steel designed for high temperature applications in power generation industry was investigated in terms of low cycle fatigue at room and elevated temperature. Individual specimens were subjected to different loading procedures in order to study the material response along with the mechanism of fatigue damage. Cyclic hardening/softening curves, Coffin-Manson and cyclic stress-strain curves were evaluated. Life-time behavior for various types of loading procedures was discussed with respect to the effective damage mechanisms developed under specific loading conditions. Standard isothermal low cycle fatigue tests at room and elevated temperature were conducted. Hysteresis loops recorded during cycling were analyzed by means of generalized statistical theory of hysteresis loop. The probability density distribution function of the internal critical stresses and its evolution during cycling straining was derived for different strain amplitudes. Evolution of the surface relief along with the internal dislocation arrangement for both temperatures was assessed in relation to the development of the probability density function of internal critical stresses. Surface relief evolution using SEM equipped with FIB revealed the early fatigue crack formation. Cyclic loading at room temperature resulted in the localization of the cyclic plastic strain into persistent slip bands and formation of surface persistent slip marking consisting of extrusions and intrusions. Deepening of an intrusion leads to the initiation of the fatigue crack from the tip of the deepest intrusion. Distinctive mechanism of the early crack formation was found in test at elevated temperature where the effect of environment is crucial. Rapid oxidation of the grain boundaries and subsequent cracking of the oxidized grain boundaries represent effective mechanisms of the nucleation of I-stage fatigue crack. Additional 10 minute tensile dwells implemented into the loading cycle led to the internal damage evolution. To reveal internal damage the longitudinal cross-sections parallel to the stress axis of the tested specimen were produced. The crack paths and their relation to the grain and twin boundaries were studied using electron back-scattered diffraction (EBSD) technique. The influence of dwells introduced in the loading cycle on fatigue life is assessed in relation to the evolution of the surface relief and internal damage. Specimens were also exposed to more complex loading procedures where the load along with the temperature varies with time simultaneously. In-phase and out-of-phase type thermomechanical fatigue (TMF) tests with or without dwells were conducted. Rapid cyclic hardening was observed in all tests regardless of the strain amplitude applied while tendency to saturation was found primarily in out-of-phase loading with/without dwells. Investigation of the surface relief by means of SEM along with FIB cutting revealed the preferential oxidization and cracking of the grain boundaries perpendicular to the loading axis. Dwells implemented in maximum tension resulted in the enlargement of the plastic strain amplitude and to the additional creep damage in the form of internal cracks. Intergranular crack propagation was observed for in-phase cycling with/without dwells. Damage evolution in out-of-phase cycling was found to be principally similar for straining with and without dwell.
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Fatigue evaluation methods for pressure equipment utilising numerical analysis results
Boleloucký, Václav ; Lošák, Pavel (oponent) ; Létal, Tomáš (vedoucí práce)
This thesis deals with the fatigue assessment of a pressure vessel structural detail. This is an area of stress concentration, thus significant influence on fatigue is expected. The thesis is divided into theoretical and practical parts. In the theoretical part, methods of the stress evaluation in the vicinity of welds are described. The subsequent finite element analysis of the inspected area based on these methods is carried out in Ansys Workbench. Final evaluation of fatigue is done according to the recent draft amendment to Clause 18 of EN 13445--3. The obtained results and methods used are discussed in the conclusion.
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Short Crack Growth in Materials for High Temperature Applications
Mazánová, Veronika ; Obrtlík, Karel (oponent) ; Krupp, habil Ulrich (oponent) ; Polák, Jaroslav (vedoucí práce)
: Advanced highly-alloyed austenitic stainless steel Sanicro 25 based on Fe-Ni-Cr matrix was studied under the conditions of low cycle fatigue at room temperature and at elevated temperature of 700 °C. Several state-of-the-art experimental techniques were used to investigate the mutual effects of alloy composition, microstructural changes and deformation mechanisms, which determine the overall damage resistance of the material. The main effort has been focused on the fatigue crack initiation and the short crack growth, two stages which play an essential role in the resulting fatigue life of the material in the service. • The internal deformation mechanisms were correlated with the evolution of the surface relief in the form of persistent slip markings. It was found that the high planar character of the dislocation slip causes the high cyclic plastic strain localization into the persistent slip bands and thus the early Stage I crack nucleation associated with the presence of the persistent slip markings in all studied samples. The twin boundary cracking was found to be related to the presence of the persistent slip marking along the surface trace of twin boundary as well. • The intergranular crack initiation was observed only rarely at high strain amplitude loading. It was found to be related to the presence of the persistent slip markings at the grain boundary. Owing to high number of local incompatibilities at the grain boundary caused by the shape of the persistent slip markings the grain boundary cracks under the external tensile loading. • The crack growth mechanisms of natural short cracks were studied on the samples subjected both to low and high strain amplitude cycling. The role of microstructure was analysed using experimental techniques and discussed. • The crack growth rates of the longest cracks were measured on the samples with a shallow notch. The results were analysed using the fracture mechanics approaches based both on amplitude of KI and of J-integral as well as on the plastic strain amplitude. All approaches were discussed in the relation to the Manson-Coffin fatigue life curve. The simple power law of the short crack growth based on the plastic strain amplitude shows very good correlation to the fatigue life law. • In the case of cycling at elevated temperature the role of oxidation was studied. The brittle cracking of the oxidized grain boundaries was found to play a major role in the early stages of crack nucleation. Later the crack growth path changes to be preferentially transgranular. The crack growth path is very similar to that studied in room temperature cycling.
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Low cycle fatigue behaviour and fatigue crack initiation in MAR-M247 at 700 °c
Šulák, Ivo ; Obrtlík, Karel ; Hrbáček, K.
The second generation nickel-based superalloy MAR-M247 offersa satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that arerequired for application at elevated temperatures in hostile environments. The microstructure consists mainly oftheface centred cubic γ matrix and ordered γ ́ strengthening precipitates (L12crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambientair. Cyclic stress-strain curvesand fatigue life curves in the representation ofplastic strain amplitude vs. stress amplitude andstress amplitude vs. the number of cycles to failure, respectively,were plotted and compared with data obtained on Inconel 713LC. Special attention waspaid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation.Observations in transmission electron microscope (TEM)confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long.
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