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Description of the slow crack growth in polymer materials
Trávníček, Lukáš ; Nezbedová,, Eva (referee) ; Padovec,, Zdeněk (referee) ; Hutař, Pavel (advisor)
Požadovaná životnost plastových trubek používaných v tlakových systémech je 50 let. Zároveň je však vyvíjen tlak na použití recyklovaných materiálů, které mají podstatně horší mechanické vlastnosti a samotné je pro výrobu tlakových polymerních potrubí nelze použít. Tyto dvě protichůdné podmínky jdou skloubit pomocí trubky vytvořené z více vrstev, kde pro kritické časti, kterými jsou vnější a vnitřní povrch, je použit moderní odolný materiál. Na druhou stranu pro střední vrstvu, jejíž mechanické vlastnosti nejsou tak důležité z pohledu dlouhodobé životnosti, je možno použit materiál recyklovaný. Hlavním cílem této práce je navrhnout geometrii popsaného vícevrstvého potrubí s využitím recyklovaného materiálu při zachování minimální požadované životnosti. Životnost polymerních trubek je poměrně náročné testovat za běžných provozních podmínek z časových důvodů. Je však možné ji odhadnout, neboť nejčastější mechanismus poškození je pomalé šíření trhliny. Metodika odhadu životnosti využívá parametrů lineární elastické lomové mechaniky pro popis šíření těchto trhlin. Důležitou součástí je pak simulace šíření trhliny v trubce metodou konečných prvků se zohledněním různých typů zatížení, kterým je trubka v provozu vystavena. Mezi tyto zatížení patří reziduální napětí a zatížení způsobené tíhou zeminy, dopravou nebo kameny, pokud je trubka zakopána. Pro určení reziduálního napětí byla vyvinuta metodika, která využívá kombinace experimentů a numerického modelování a která byla také použita. Případ zakopané trubky je také simulován pomocí metody konečných prvků. Část práce je věnována měření rychlosti šíření creepové trhliny pomocí CRB testů (cracked round bar) a následnému vyhodnocení experimentálních dat. Rychlost šíření creepové trhliny spolu s kombinací s výsledky numerického modelování bude použita pro stanovení odhadu životnosti vícevrstvé polymerní trubky obsahující recyklovaný materiál.
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Short fatigue crack propagation description
Trávníček, Lukáš ; Náhlík, Luboš (referee) ; Hutař, Pavel (advisor)
The presented master’s thesis deals with description of short fatigue cracks and can be divided to the several parts. In the first part, theoretical background of fatigue of materials and fracture mechanics parameters which can describe fatigue cracks is presented. Following part describes how to determine fracture mechanics parameters by finite elements method. Due to the shape of propagated fatigue crack, numerical model was established as a three-dimensional. Results obtained based on this model, was compared with literature with very good agreement. Than real shape of propagated short crack was used for description of the experimental data. It was shown, that plastic part of J-integral is suitable parameter for description of the short cracks.
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Stress and deformation analysis of railway bridge over the Morava River
Trávníček, Lukáš ; Profant, Tomáš (referee) ; Fuis, Vladimír (advisor)
This Bachelor Thesis contains stress and strain analysis of the first two parts of the railway bridge in Olomouc with an assessment of changes in the stress and strain when changing the static storage. Firstly, the theoretical basis of rod systems is presented, it is followed by the calculation of normal forces and the stress in rods for both parts separately. The calculations include the load arising from its own weight and from the weight of a train, which is represented by the load at the framework joints. Next, these two parts are connected. For this rod system a stress-strain analysis is also used. In conclusion, stress and strain is calculated for comparison by the finite element method in the program ANSYS Classic.
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Description of creep crack propagation in electrofusion sockets for polymer pipes connection
Helešicová, Petra ; Horníková, Jana (referee) ; Trávníček, Lukáš (advisor)
The presented bachelor’s thesis deals with crack propagation by the slow crack growth mechanism in electrofusion sockets used for welding of polymer pipes. The thesis can be divided into several parts. First part presents a research on the topic of polymer pipes, materials used for their production, types of failures and ways of connecting including detailed description of the process of electrofusion welding with electrofusion sockets. Next part is focused on fracture mechanics that is used for the practical part of the thesis. The theory of linear elastic fracture mechanics and its stress-intensity approach are described. Different ways of obtaining the stress intensity factor, which is the main parameter used to describe the stress distribution at the crack tip, are presented. The practical part of the thesis focuses on numerical modelling of crack propagation through an electrofusion socket wall and calculating values of stress intensity factor in dependence on the crack length. The creation of the numerical model for the crack propagation simulation is described. The direction of propagation is evaluated using MTS criterion. The whole simulation is carried out by a parametric macro created using the APDL language. The main goal of the thesis is to describe the influence of the socket geometry or joint configuration changes on the stress intensity factor values and calculated lifetimes. The stress intensity factor functions for the modified configurations are compared to the original. At the end of the thesis, lifetime estimations of the electrofusion sockets are also calculated using the stress intensity factor functions and compared.
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Description of creep crack propagation in electrofusion sockets for polymer pipes connection
Helešicová, Petra ; Horníková, Jana (referee) ; Trávníček, Lukáš (advisor)
The presented bachelor’s thesis deals with crack propagation by the slow crack growth mechanism in electrofusion sockets used for welding of polymer pipes. The thesis can be divided into several parts. First part presents a research on the topic of polymer pipes, materials used for their production, types of failures and ways of connecting including detailed description of the process of electrofusion welding with electrofusion sockets. Next part is focused on fracture mechanics that is used for the practical part of the thesis. The theory of linear elastic fracture mechanics and its stress-intensity approach are described. Different ways of obtaining the stress intensity factor, which is the main parameter used to describe the stress distribution at the crack tip, are presented. The practical part of the thesis focuses on numerical modelling of crack propagation through an electrofusion socket wall and calculating values of stress intensity factor in dependence on the crack length. The creation of the numerical model for the crack propagation simulation is described. The direction of propagation is evaluated using MTS criterion. The whole simulation is carried out by a parametric macro created using the APDL language. The main goal of the thesis is to describe the influence of the socket geometry or joint configuration changes on the stress intensity factor values and calculated lifetimes. The stress intensity factor functions for the modified configurations are compared to the original. At the end of the thesis, lifetime estimations of the electrofusion sockets are also calculated using the stress intensity factor functions and compared.
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Short fatigue crack propagation description
Trávníček, Lukáš ; Náhlík, Luboš (referee) ; Hutař, Pavel (advisor)
The presented master’s thesis deals with description of short fatigue cracks and can be divided to the several parts. In the first part, theoretical background of fatigue of materials and fracture mechanics parameters which can describe fatigue cracks is presented. Following part describes how to determine fracture mechanics parameters by finite elements method. Due to the shape of propagated fatigue crack, numerical model was established as a three-dimensional. Results obtained based on this model, was compared with literature with very good agreement. Than real shape of propagated short crack was used for description of the experimental data. It was shown, that plastic part of J-integral is suitable parameter for description of the short cracks.
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Zhodnocení vývoje populace daňka evropského na území bývalé obory Nové Zámky
Trávníček, Lukáš
The aims of this diploma thesis are to evaluate development of the fallow deer population, his trophy quality, evaluate the impact of wildlife on vegetation and propose an amendment in the game management. The materials needed for this thesis were obtained from a literature, the statements about game management, trophies shows, and by my own field research. In this work, we can find a brief description of the basic game census methods, the description of the fallow deer, principles of breeding and parts of the legislation related to this topic. The work includes a description of the area and also my own results of the thesis by analysis of available data, including attachments.
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Stress and deformation analysis of railway bridge over the Morava River
Trávníček, Lukáš ; Profant, Tomáš (referee) ; Fuis, Vladimír (advisor)
This Bachelor Thesis contains stress and strain analysis of the first two parts of the railway bridge in Olomouc with an assessment of changes in the stress and strain when changing the static storage. Firstly, the theoretical basis of rod systems is presented, it is followed by the calculation of normal forces and the stress in rods for both parts separately. The calculations include the load arising from its own weight and from the weight of a train, which is represented by the load at the framework joints. Next, these two parts are connected. For this rod system a stress-strain analysis is also used. In conclusion, stress and strain is calculated for comparison by the finite element method in the program ANSYS Classic.
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Using of VBA language in statistical analysis
Trávníček, Lukáš ; Řezanková, Hana (advisor) ; Vrabec, Michal (referee)
The main thesis aim is to introduce possibilities of MS Excel in data analysis and to point out to some strengths and weaknesses of MS Excel in data processing. I pay attention to tools which MS Excel contains by default as well as to statistical products which are not normally part of MS Excel. These products can be run in MS Excel environment as statistical add-ins for MS Excel. In the first case I focus on MS Excel tools as statistical functions, graphic analysis and statistical methods, in the other case on statistical products as XLStatistics, Analyse it, WinSTAT. In connection with the first mentioned statistical product I show some examples how to analyze and work with real data samples in product XLStatistics. The aim of this part is to show other way how to analyze data then in the others products or MS Excel itself. At the end of my thesis I programmed my own product Regxcel with the help of VBA language as the main contribution of my entire work. Product Regxcel provides solution in regression analysis for the six most common types of regression function. The main aim of this part is to point out to other possibility how to analyze data and solve some problems which users can face in regression analysis in MS Excel. I also try to show VBA language as big help in data processing in MS Excel. At the very end I presented all possibilities of Regxcel on real data sample. The product itself is part of attached CD
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