|
|
Mechanical properties Al-alloy EN AW 7020 at increase temperatures
Slouka, Marek ; Kohout, Jan (referee) ; Věchet, Stanislav (advisor)
The master’s thesis deals with high strength aluminium alloys AlZn4Mg (EN AW 7020). This alloy is used for high strength, low density, a good corrosion resistant and a good weldability in protective atmospheres. At first this thesis is described to aluminium alloys, ways of manufacturing and history. Next this thesis mainly deals with wrought aluminium alloys, heat treatment this alloys and alloys Al-Zn-Mg. Tensile tests were made of alloys EN AW 7020 at room temperature and increased temperature. Next this alloy was made of fatigue test and metallographic analysis. The model was construct. This model describe to behaviour alloy at increased temperature and this model was compared with measure values. This thesis describe to behaviour of study alloy at room temperature and increased temperature.
|
|
|
The Influence of the Isothermal Transformation Dwell on the Structure and Mechanical Properties of ADI
Falta, Petr ; Kohout, Jan (referee) ; Věchet, Stanislav (advisor)
The thesis ,,The Influence of Transformation dwell on the Structure and Mechanical Properties of ADI´´ deals with problems of optimal properties of the unalloyed nodular cast iron, which are obtained by the heat treatment. The heat treatment consists of austenitization and then rapidly quenching to the transformation temperature, isothermal transformation and water cooling in the end. The aim of the thesis is focused on estimating the influence of isothermal transformation on the content of stabilized austenite, static mechanical properties and on the fatigue properties in high-cycle fatigue region for selected samples. The theoretical part of this work analyses the production of the nodular cast iron and its possibilities of the heat treatment, final technological and mechanical properties. Furthermore, it examines the conditions of austempering (temperature and time of isothermal dwell), which has a fundamental influence on mechanical properties of ADI. Problems of fatigue properties are described at the end of this part. The experimental part contains a chemical composition of studied samples and their metallographic analysis. Among others the basic mechanical static properties were determined as well as the Wöhler curves including values of fatigue limits for ten on seventh cycles. Wöhler curves were obtained by a mathematical processing using data reached by fatigue tests.
|
|
|
The Analysis of Databases Suitable for IoT Environment
Kohout, Petr ; Vrána, Roman (referee) ; Kořenek, Jan (advisor)
In recent years, the volume of data stored in applications of all types has increased. As the volume of data grows, the demands on databases increase. The classic relational databases are no longer suitable. Therefore, it is switching to new, non-relational storage (called NoSQL). During this work, NoSQL databases focusing on processing large data volumes were analyzed and compared for their performance and system requirements. In addition, requirements for new sensor data storage for IoTCloud project were specified. Driver for database Cassandra was implemented and integrated into the IoTCLoud project.
|
|
|
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.
|
|
|
Haigh diagram of selected spring steel
Zejdová, Lucie ; Kohout, Jan (referee) ; Věchet, Stanislav (advisor)
This master’s thesis focuses on the fatigue properties of spring steel 54SiCrV6. The theoretical part deals with the properties and use of spring steel and metal response to cyclic loading. The main aim of this work was to obtain the basic mechanical properties as well as the hight cycle fatigue data. Additional metallographical evaluation of microstructure.
|
|
|
Nanocomposites with a metal matrix
Chlupová, Monika ; Kohout, Jan (referee) ; Zapletal, Josef (advisor)
This baechelor thesis is focused on metal matrix nanocomposites (MMNCs), whose research has started recently. In the first part of this thesis are generally defined composite materials, the larger part is dedicated to metal matrix composites (MMCs), on which are described the strengthening mechanisms that are also applied to MMNCs. The second part of the thesis is focused specifically on MMNCs. The concept of MMNCs and their distribution is defined first, followed by a definition of the reinforcement that can be used for the production of MMNCs. There are also described the posibilities for the production of these reinforcing phases, and their influence on the structural and mechanical properties of the final MMNCs. This section is followed by a description of possible processes of MMNCs production with their advantages and limitations. The last part outlines how research and development of these materials should be carried out in order to be commercially produced and used in the future.
|
|
|
Fracture Behaviour of Steels and Their Welds for Power Industry
Al Khaddour, Samer ; Kohout, Jan (referee) ; Válka, Libor (referee) ; Dlouhý, Ivo (advisor)
Práce byla zaměřena na ověření platnosti koncepce master křivky pro hodnocení heterogenních svarových spojů, resp. teplotně stárnutých svarů. Současně bylo cílem disertace vyvinout kvantitativní model pro predikci referenční teploty lokalizující tranzitní oblast na teplotní ose za použití dat získaných z tahové zkoušky, a to za použití metody umělých neuronových sítí. Studie je současně zaměřena na heterogenní svarový spoj připravený tavným svařováním. Je zacílena na hodnocení lomového chování v tranzitní oblasti nejméně odolné části svaru, tj. tepelně ovlivněné zóny ferritické oceli v blízkosti zóny natavení s vysokolegovaným materiálem. Pro predikci referenční teploty master křivky je použita zmíněná metoda neuronových sítí, a to za použití dat z tahových zkoušek a měření tvrdosti. Predikovaná referenční teplota byla ověřována na základě výsledku experimentálních měření. Vytvoření modelu za použití neuronových sítí vyžaduje dostatečné množství dat a není vždy snadno tuto podmínku splnit. V případě sledovaného problému to znamenalo použití dat z dostatečně věrohodných zdrojů (skupiny Křehký lom ÚFM AVČR) a se známou metalurgickou historií. Smysl práce je tak možno spatřovat ve vývoji modelu neuronové sítě, která bude dostatečně přesně predikovat referenční teplotu. Celkově byla pro tyto účely použita data z 29 nízkolegovaných ocelí. Pro účely vývoje byly použity kromě hladkých zkušebních tyčí, rovněž tahové zkoušky s obvodovým vrubem testované při kritické teplotě křehkosti (mez makroplastických deformací) a při teplotě pokojové. Při tvorbě modelu byla postupně v různých kombinacích využita všechna data z uvedených zkoušek. Studie ukázala, že referenční teplota charakterizující tranzitní chování lomové houževnatosti oceli s převažující feritickou strukturou je jedinečným parametrem predikovatelným na základě vybraných charakteristik tahových zkoušek.
|
|
|
Influence of a Free Surface and Gradient Change of Material Properties on a Crack Behaviour
Ševčík, Martin ; Kohout, Jan (referee) ; Klusák, Jan (referee) ; Náhlík, Luboš (advisor)
This thesis was written under the supervision of Assoc. Prof. Luboš Náhlík, Ph.D. and Assoc. Prof. Pavel Hutař, Ph.D. The topic of this thesis is the study of a free surface effect and gradient change of material properties on a crack behavior. The common theme of the work is a fracture mechanics description of a crack behavior near a material nonhomogeneity. Here, the material nonhomogeneity can be understood either as a boundary of a body (interface between body and surrounding) or as a continuous change of material properties. The thesis is introduced by a review part where the state-of-the-art of the concerned topic is described. This part presents several stress state descriptions in the vicinity of some general singular stress concentrators, particularly a crack and a V-notch. The influence of the free surface on a fatigue crack front shape is discussed here. The review part follows with the fracture mechanics description of the graded materials. The problem formulation and the main aims of the thesis are stated in the following chapter. The core of this work is the fracture mechanical description of a crack propagating near the material nonhomogeneity. The thesis focuses on a stress field description near the free surface of the body where a change in a type of the singular stress field occurs. Methods used in generalized fracture mechanics are applied here to describe the stress field near the free surface. The difference between crack behavior in thin-walled and thick-walled structures is shown and supplied by relevant examples. Methods and procedures used are later utilized for estimation of a crack behavior in graded structures. The thesis is concluded by the discussion of obtained results in appropriate context.
|
|
|
Biocompatible titanium alloys and theirs application
Hofírek, Michal ; Kohout, Jan (referee) ; Věchet, Stanislav (advisor)
This thesis presents use of titanium alloys in medical applications in form of literature research. In first part the basic properties of titanium as element are discussed as well as its behavior in alloys. Next part focuses on proper explanation of term biocompatibility and sums up specific requirements for alloys used in orthopaedic applications. These properties are shown on alloy Ti-6Al-4V ELI and other selected titanium based alloys which are currently being developed.
|
|
|
Microscopic Observations of Active Mass Structures of the Negative Electrode of a Lead-Acid Battery
Zimáková, Jana ; Dostál, Zdeněk (referee) ; Kohout,, Jan (referee) ; Bača, Petr (advisor)
This doctoral dissertation deals with the study of the effect of additives on the properties of the negative electrode of a lead-acid battery. The work focuses on the investigation of the additive/base material interface for the negative electrode (so-called active mass) using atomic force microscopy (AFM). A lead sheet was used as the base material, on which the given additive was applied. The effects of carbon, TiO2, glass fibers and Indulin AT were specifically investigated. The negative electrode was cycled by a potentiostat in a defined manner and the morphology of the electrode surface was continuously scanned by AFM. This created a time sequence of images on which events on the surface of the electrode during its charging/discharging were captured. These records serve to better understand the effect of additives on the resulting properties of constructed lead-acid cells, specifically on the ability to form or dissolve PbSO4 crystals, which are formed during cell discharge and are responsible for the decrease in total capacity - gradual surface sulfation.
|
guest ::
RSS feed.