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Numerical analysis of visco-elastic material models
Michálková, Veronika ; Lang, Rostislav (referee) ; Trcala, Miroslav (advisor)
The serviceability of concrete structures is a multiphysical problem where viscoelasticity is interrelated with plasticity or damage, among other things. This work focuses on the analysis and testing of an isotropic viscoelastic material model based on a generalized Kelvin chain. The Kelvin chain is described in detail for 1D strain and then its application to multi-axial 2D plane strain is shown. In this paper, a total of 3 studies are carried out using the Kelvin chain. The first study concerns the analysis of the Kelvin chain with damage on several benchmark refinement problems. The second study compares the results of the Kelvin chain including damage with an experiment on a three-point beam bending problem. The third study concerns the analysis of the Kelvin chain with damage on a stress relaxation problem in a loaded concrete beam and compares the results with the ANSYS calculation and experimental measurements. The aim is to analyze the effect of the parameter on the time-dependent behavior of the concrete and also the effect of the number of time increments N on the result.
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Residual Service Lifetime of Furnaces in Petrochemical Industry
Horsák, Libor ; Vincour, Dušan (referee) ; Lukavský, Jiří (referee) ; Vejvoda, Stanislav (advisor)
The objectives of this work is residual lifetime of heaters in petrochemical industry. There is no comprehensive publication about this theme. This paper lists and describes the most of main phenomena that has to be taken into account in the process of determination of residual lifetime. This paper focuses on creep damage of a real heater based on deformation measurement. It describes some heater failures that could cause unplanned operation interruption however, appropriate intervention made possible safe heater operation until planned heater shutdown. No compact method is given how to determine heater residual lifetime, but a direction is given how a complex method of residual lifetime assessment of refinery heaters could be created.
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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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Design of concrete structures with FRP reinforcement
Januš, Ondřej ; Girgle, František (referee) ; Štěpánek, Petr (advisor)
The diploma thesis presents design of construction with FRP reinforcement. Including design process of cross-section with FRP reinforcement exposed to bending moment and shear force at ultimate limite state according to given standards and guidelines. Long term physical and mechanical properties of FRPs are taking into account. There are also compared load capacities of cross-section exposed to combination of bending moment and axial force, which were designed according to mentioned standards. In another part of diploma thesis there is a design of construction (precast gatehouse) with FRP reinforcement and steel reinforcement with ordinary and lightweight concerete.
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Influence of Air Entrainment and Curing on Development of Elastic Modulus of Concrete
Bartulíková, Radka ; Kucharczyková, Barbara (referee) ; Kocáb, Dalibor (advisor)
Master's thesis deals with influence of various factors on the concrete compressive strength and modulus of elasticity. This work concentrates mainly on the influence of early curing and air entrainment of concrete. One part of this work is the evaluation of laboratory measurement, which was carried out on cubes of standard and norm prisms. The development of elastic moduli was monitored in time to 730 days of age with respect to air entrainment and curing conditions. The second part of the experiment deals with a comparison of theoretical creep curves depending on the value of the modulus of elasticity based on different standards. Again, the air entrainment effect and influence of initial conditions are reflected.
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Design and evaluation of process equipment damaged by degradation mechanisms
Cablková, Zuzana ; Naď, Martin (referee) ; Lošák, Pavel (advisor)
This bachelor thesis is aimed at the evaluation of selected degradation mechanisms which occurs in process equipment. The assessment is undoubtedly important in terms of safety and prediction of residual life. This issue is demonstrated by two mechanisms described in this thesis. A phenomenon called creep is the first of these mechanisms and appears in environments with elevated temperature. The theoretical part of the thesis covers the basic principles of the creep mechanism and its effect on the material. A marginal but not negligible problem is the occurrence of this damage in welded joints. Many standards deal with the prediction and assessment of creep. Part of this thesis is the mapping and to some extent a comparison of several selected procedures. The second degradation mechanism is related to the presence of aggressive compounds such as sulfide. This can lead to hydrogen embrittlement, blisters, and many other damages. As with creep, an overview of standards devoted to the design, evaluation, or maintenance of equipment used in this way is created for these mechanisms. The content of the practical part of this thesis is the calculation of the evaluation of such a device by using the procedures of the API 579-1 standard.
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Relationship between Structure and Properties of cast Ni-alloys
Smékalová, Jana ; Hutařová, Simona (referee) ; Podrábský, Tomáš (advisor)
Nickel superalloys are developed for conditions which request the corrosion resistance, the heat-resisting and the creep-resisting material. They are used for components of air turbine motors and internal combustion turbines. The efficiency of these mechanisms is elevated with increasing combustion temperature so their development is accentuated. This thesis is concerned with a relationship between a structure and properties of nickel superalloys Inconel 713LC and Inconel 738LC in this thesis.
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The effect of boiler tube bundle fouling on its service life
Volná, Kateřina ; Ing. Zdeněk JŮZA, Ph.D., MBA (referee) ; Naď, Martin (advisor)
Fouling of tube bundles in boilers on the flue gas side affects not only the service life, but also the boiler heat output and increases maintenance and operating costs. Therefore, it is necessary to minimize or completely eliminate this process. This thesis focuses on comparison of the service life and the heat output of the tube bundles with and without deposit in the coal fired boiler. Simulations of flue gas flow in area of tube bundles with and without deposit are performed using ANSYS Fluent software, which shows that the surface of tube bundles with deposit is much less heated than the surface without deposit. The thermal loads of tubes obtained by the CFD analysis are applied to the model, which is created in the program ANSYS Mechanical, where the calculation of the temperature field in the cross section of the pipe is realized. The effect of fouling on creep life and heat output is then evaluated based on simulation results. The results show that fouling increases creep life, but significantly reduces heat output of heavily fouled tubes. Hence the flue gas flows at a higher temperature to the rest of the tube bundle, and the service life of those tubes will therefore probably decrease.
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Design of the circle concrete tank
Šimek, Ondřej ; Chalabala, Jiří (referee) ; Klusáček, Ladislav (advisor)
The diploma‘s thesis deals with the design and assessment of prestressed cocrete tank of biogas station at ultimate limit state and also at serviceability limit state, according to ČSN EN 1992-1-1: Design of concrete structures. Specifically, the design of wall of the tank and foundation slab. The text part contains general information on the desing of the structure, static idealization of the structure, type of load and method for calculation of inner forces. Attachments contain drawing documentation and structural analysis, which completes the text part and solves in detail said structure.
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