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Fatigue Properties of Stainless Austenitic Steel
Sedlák, Martin ; Němec, Karel (referee) ; Věchet, Stanislav (advisor)
Final bachelor thesis „Fatigue characteristics of anti-corrosion austenitic steels" is aimed at problematic of mechanics and fatigue properties of Chrome-Nickel austenitic steel CSN EN X2CrNiMo 18-14-3. Thesis aim is to pass judgment on influence of stress cycle asymmetry on fatigue characteristics on high cyclic loading on above mentioned steel. Design Haigh and Smith diagrams. Component of the thesis is metallographical and chemical analysis, mathematical values processing obtained from fatigue tests and also determine primary mechanical properties. Further Wohler´s curves are stated at different stress cycle asymmetry. According to mathematical values processing is designed Haigh and Smith diagrams and fatigue index is calculated. From obtained data result that medium stress of cyclic stress, has of principle influence on appreciate fatigue limit of engaged material.
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Basic Mechanism of Fatigue and Combined Fatigue/Creep Damage of Ni-based Superalloys MAR-M 247 and IN 713LC
Horník, Vít ; Kohout, Jan (referee) ; Pantělejev, Libor (referee) ; Kunz, Ludvík (advisor)
The thesis is focused on clarifying fatigue damage mechanisms and fatigue-creep damage mechanisms of MAR-M 247 and IN 713LC polycrystalline Ni-based superalloys. This thesis begins with basic information about nickel-based superalloys and their microstructure, followed by a description of fatigue and creep mechanisms and their mutual interaction. The next part contains experimentally obtained results describing the behavior of MAR-M 247 and IN 713LC superalloys under various sets of conditions. Three testing temperatures - 800, 900 and 950 °C were used for the measurement of fatigue properties under symmetrical loading cycle, because in the temperature range 800 – 950 °C, the mechanism of fatigue crack propagation of both superalloys should change from the originally crystallographic at "lower" temperatures (800 °C) to non-crystallographic at "higher" temperatures (950 °C). In addition the effect of processing technology on fatigue properties was studied on the superalloy IN 713LC. High-frequency cyclic loading (about 120 Hz) with high mean stress at elevated temperatures was applied to induce fatigue-creep interaction. The combined fatigue-creep loading was performed on the IN 713LC superalloy at 800 °C and on the MAR-M 247 superalloy at 900 °C.
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Low Cycle and High Cycle Fatigue Properties of Austempered Ductile Iron
Zapletal, Josef ; Bokůvka, Otakar (referee) ; Kunz, Ludvík (referee) ; Věchet, Stanislav (advisor)
The thesis is focused on assessment of fatigue behaviour of austempered ductile iron with nodular graphite. Optimal period of transformation was determined based on the best combination of stress and strain characteristics established by tensile test. Cyclic response and low-cycle fatigue life were studied under both stress-control and longitudinal strain-control mode at room temperature. For both modes, shapes of cyclic hardening curves are dependent on stress amplitude. Cyclic deformation curves (CDC) were fitted by power regression function. Results were compared with CDC established by multiple step test in both modes with verification of the influence of cyclic creep (high stress levels, stress-control mode). Experimental data of S-N curves are in agreement with the Manson-Coffin and the Basquin law. Fatigue and cyclic parameters were compared. Fatigue life time in high-cycle fatigue region was determined. Experimental data were fitted by suitable regression functions. Regression parameters and fatigue limit were established by means of each regression function. Experimental data in low- and high-cycle fatigue regions were used to construct S-N curve and to determine relevant parameters. Discontinuity of experimental data was not observed. Low-cycle fatigue behaviour was predicted. Approximation of tolerance bands was realized in high-cycle and both high and low cycle fatigue regions.
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Kinds of materials damage - I
Turková, Veronika ; Bryukhova, Lina (referee) ; Neterda, Zdeněk (advisor)
The material of production units it subsequently damified. The aim of this Bachelor’s Thesis is the description of way of some most frequent material defects in the process industry, the way of their judging by laboratory engines and by theoretical relations for the needed magnitude. This thesis shall show the presentation of material damages via diagram, illustrative photo and drawing. The first part of introduced thesis concerns the hyper cycling fatigue and explains basic characteristics of fatigue and cycle loading. The second part introduces the waste by high temperature flowing. The third part explains the waste by corrosion, which is the well known way of material damage.
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Fatigue Properties of Materials with Protective Thermally Deposited Layers
Matějková, Michaela ; Kovářík,, Ondřej (referee) ; Čížek, Jan (advisor)
Titanium powder was deposited into low-carbon steel specimens using three thermal spray technologies: plasma spray, cold spray (USA, Singapore) and warm spray (denoted as PS, CSU, CS-S, and WS, respectively, in further text). The aim was to determine the influence of the coatings on the fatigue lives of the specimens. The experimental work was carried out in a symmetrical cantilever-beam bending setup using a computer-controlled SF-Test loading device. Further to that, the micro-morphology of coatings structure, their respective porosity content and the fracture surfaces of both coatings and substrate materials was carried out.
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Fatigue properties of titanium alloys
Horník, Vít ; Němec, Karel (referee) ; Věchet, Stanislav (advisor)
This bachelor thesis is concerned with fatigue properties of titanium alloys. The introductory part deals with basic information about titanium, its production, distribution of titanium alloys and their heat-treating. Next part then describes basic process of fatigue loading with the focus on the high-cycle fatigue stress and its application on some titanium alloys. The final part of the thesis includes optical and fractograph pictures.
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High cycle fatigue of Ti6Al4V titanium alloy
Bártková, Denisa ; Liškutín, Petr (referee) ; Věchet, Stanislav (advisor)
The main goal of this master's thesis is an analysis of high-cycle fatigue of titanium alloy Ti- 6Al- 4V. In the first section of a theoretical part of the thesis, there are summarized current facts about production, properties and aplications of titanium alloys. The second section pursues fatigue behaviour of material. An experimental part consists of metallographic analysis, evaluation of tension and bending tests and mainly analysis of high-cycle fatigue behavior for different assymetry ratios.
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Software for an estimation of residual fatigue lifetime of mechanical parts with crack
Motyka, Jakub ; Náhlík, Luboš (referee) ; Pokorný, Pavel (advisor)
This bachelor thesis deals with the creation of software for determining the residual fatigue time of mechanical parts with a crack. In the calculation of the lifetime of fatigue-stressed parts, the existence of an initial crack is assumed. During the operating load of the part, the crack may grow up to a critical size, when a sudden fracture of the part occurs. Knowledge of the number of residual loading cycles is important for machine design and safe part-operation. The first part of this thesis deals with linear-elastic fracture mechanics which forms the theoretical basis of the calculation software. The second part is devoted to the software itself, its principles and work in user interface. The last part compares the software-acquired results with the results reached analytically.
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Structure and fatigue properties of selected titanium alloy
Prudíková, Alena ; Kohout, Jan (referee) ; Věchet, Stanislav (advisor)
Main topic of the thesis was to evaluate fatigue properties of the titanium alloy Ti-A13-V2,5, labelled by ASTM as Grade 9. Most attention was focused on fatigue behaviour of the alloy in the range of high cycle fatigue. Fatigue testing was realised to detect the fatigue properties and consequently to generate the Wöhler curve and the Haigh diagram. In addition to this, tension and bending tests were performed. Metallographic and fractographic analyses of fatigue fracture form part of the overview about material properties, which was accomplished by use of REM. Experimental part of the thesis was backed by the literature research. The first half of it contains a short summary of basic information about the titanium and its alloys, so as some chapters about the history and properties of titanium, the way of its production, classification of titanium alloys and its thermic treatment. The fatigue is thoroughly scrutinised in the second half of the background research. Here can also be found the information about the fatigue process, its stages, the fatigue life and the most significant attributes of the fatigue fracture. The last chapters of the thesis are dedicated to the alloy Ti-A13-V2,5 - being examined in the experimental part - so as to its fatigue properties. The main benefit of this thesis is the completion of the missing information concerning the fatigue behaviour of the alloy, which is – according to the literature research - generally not available.
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FATIGUE CHARACTERISTICS OF MODIFIED MAGNESIUM ALLOYS AFTER CORROSION DEGRADATION
Němcová, Aneta ; Očenášek, Vladivoj (referee) ; Hadzima, Branislav (referee) ; Pacal, Bohumil (advisor)
This doctoral thesis deals with the determination of the influence of plasma electrolytic oxidation (PEO) on fatigue behaviour of extruded AZ61 magnesium alloy in air and in the 3.5% NaCl solution. The coatings were formed in the silicate-phosphate electrolyte under pulsed current conditions at a frequency of 50 Hz. The influence of current density on coating formation was examined under current densities of 70, 130 and 200 mA cm-2 for different durations up to a maximum of 1800 s. 8 g dm-3 of KF were added to the electrolyte to study the influence of fluoride ions in plasma electrolytic oxidation. It is shown that fluoride ions inhibit localised oxidation in the initial stage of the process, associated with the secondary particles based on Al–Mn. The presence of fluoride also modified the sparking characteristics, decreased the rate of coating growth and changed the morphologies of the coatings. The influence of fluoride on the coating hardness, and the corrosion resistance of the alloy during exposure to salt spray, was negligible. Based on previous optimised PEO conditions, coatings formed under a current density of 130 mA cm-2 for 300 s in the electrolyte containing KF were chosen for fatigue testing. The high-cycle fatigue tests were carried out on cylindrical samples under a force controlled sinusoidal tension-tension cycle with asymmetry parameter R=0. The experimental data were fitted with Kohout & Věchet function. The fatigue limit of uncoated alloy in air for 107 cycles was determined at 145.4 MPa and the combination of PEO coating with chloride ions caused a reduction of ~55 %. Attention was paid to the fatigue crack initiation in different conditions of cyclic loading. The fracture surfaces underwent detailed fractography analysis including secondary crack observation on the gauge length. The contribution of Al–Mn particles were confirmed on the uncoated alloy in air and the presence of chloride ions were observed as another influential contributor to local corrosion attack. The cyclic loading caused spalling of the outer layer, and the multiple initiation was observed on PEO coated alloy, caused by cracks in the coating and stress transferring to the alloy.
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