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Influence of the residual stresses on the contact failure of ceramic laminates
German, Roman ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The presence of the compressive or tensile thermal residual stresses in layers of a ceramic laminate induced due to different volume change of each layer´s material during the cooling from the sintering temperature can considerably affect resistivity of ceramics against contact damage. Within this work 2D parametric FEM models were created, in order to study the effect of the surface layer thickness, residual stress values and indenting body dimension on the initiation and propagation of the cone crack in the surface layer of the laminate. For the analysis of the critical conditions for the crack initiation, the coupled stress-energy criterion was used and for the determination of the direction of crack propagation we used the maximum tangential stress criterion. The results show that compressive thermal stresses in the surface layer increase the critical force for the crack initiation, shorten the crack distance from the contact area and shorten the occurred crack itself. Moreover, the compressive stresses enlarge the angle of the crack declination during the propagation process which cause an earlier crack arrest. The tensile thermal stresses have exactly the opposite effect. Results of simulations were compared to experimental results but due to lack of available measurements, the verification is partially limited.
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Topology optimization of the rocker in the shoe making machine
Gargulák, Jiří ; Ševeček, Oldřich (referee) ; Lošák, Petr (advisor)
Topology optimization, SIMP, LSM, Ansys, experiment, data processing, analysis, model
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Parameters of Fracture Mechanics
Oplt, Tomáš ; Ševeček, Oldřich (referee) ; Horníková, Jana (advisor)
This thesis is the descriptive summary for the most significant parameters of fracture mechanics, required to define stress field on the crack tip. The first and also the most extensive part is divided into two subparts. There are mentioned particular parameters of one-parameter fracture mechanics, firstly are considered linear elastic deformations, thereafter the elastoplastic deformations. The second, shorter part of the thesis, is aimed at multi-parameters stress field description on the crack tip, required for the calculation of constructions with the necessity to consider their geometry.
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Computational analysis of auxetic structures application potential in impact absorbers
Dohnal, Jakub ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
Master thesis deals with the analysis of the application potential of auxetic materials in the field of shock absorption (absorption of impact energy). Due to their cellular structure and specific geometry, these materials are characterized by a negative Poisson’s ratio, which means that they are able to reduce their transverse dimension under compressive stress in the longitudinal direction. The aim of this work is to use this interesting property for the absorption of kinetic energy. After the introduction, devoted to the theoretical basis and research in the field of auxetic structures, a numerical FEM model is described in detail. The task of the model is to study the mechanical response of auxetic and conventional cellular structure to an impact loading. An explicit solver in the commercial software LS-DYNA is used to numerically simulate fast processes. The results of the analyses are used to compare auxetic and conventional structures and quantify the differences in their ability to dampen the kinetic energy of the impact effectively and gently. It also serves to demonstrate the influence of individual geometric or material parameters on impact attenuation. At the end of the work, numerical simulations are confronted with available experiments in order to verify the informative value of computational models and to point out the application potential of auxetic structures in the discussion. There are also partial recommendations for their design so that they best serve the intended purpose.
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Linear elastic fracture mechanics and its application on study of composed materials
Dohnalík, Petr ; Ševeček, Oldřich (referee) ; Máša, Bohuslav (advisor)
The main objective of this bachelor thesis is the introduction to computational methods of fracture parameters of the crack, which terminates at the bi-material interface. The preface of the work deals with composites, where possible crack can grow in materials with different elastic properties. In this part advantages of composite materials are closely described and usual structure arrangements of the components are presented. The next part of this work is focused on the linear elastic fracture mechanics and available concepts for assessment of the body with presence of the crack in the homogenous material are described. These concepts are based on analytical expressions and, also, on numerical methods. This problem is furthermore extended in the next chapter by case, when the crack terminates perpendicularly to the bi-material interface. Here are given procedures, which can provide information about the further crack behaviour. In practical part all presented procedures have been used in order to evaluate the crack parameters in the homogenous material and for the crack terminating at bi-material interface. Necessary calculations were performed using the finite element method implemented in the commercial system ANSYS. Calculated results were compared and closely discussed in the conclusion.
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Statická analýza trojkolky
Gural, Artur ; Ševeček, Oldřich (referee) ; Fuis, Vladimír (advisor)
This thesis summarize knowlidge necessary for solving problems of statics with resistant effects. Thesis defines all important terms and explains mechanics of this kind of object interaction. The practical part deals with creating application, which should be able to solve this kind of task acording to principles, which students of statics at FME are learned. There are shown in the text several problems, which are solved using created program. These should present studied problematics. Thesis and program are intended to deepen knowledge of solving statics problems.
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Computational modelling of the layered piezoelectric composites and analysis of their electro-mechanical response upon harmonic vibrations
Machů, Zdeněk ; Profant, Tomáš (referee) ; Ševeček, Oldřich (advisor)
V současnosti je velmi aktuálním tématem generování elektrické energie z alternativních zdrojů, zejména z vibrací. Zařízení, která přeměňují mechanickou energii na elektrickou, využívají často ke své činnosti piezoelektrický jev. Pro optimální nastavení takového elektromechanického měniče pro danou aplikaci je třeba mít k dispozici výpočtový model, který bude schopný postihnout všechny klíčové aspekty jeho provozu. Tato práce se tedy zabývá vytvořením takovéhoto nástroje, který je schopen komplexně popsat elektromechanickou odezvu studovaného piezoelektrického měniče energie v podobě vetknutého, vícevrstvého keramického nosníku s piezoelektrickými vrstvami. Uvažovaná vícevrstvá konstrukce je během své činnosti vystavena kinematickému buzení a je rovněž zatížena tepelnou zbytkovou napjatostí vznikající při její výrobě. Vytvořený výpočtový model využívá klasickou laminátovou teorii k určení statické elektromechanické odezvy dané konstrukce. Elektromechanická odezva při kmitání uvažované konstrukce v ustáleném stavu je získána s využitím Hamiltonova variačního principu a teorie kmitání prutů. Vytvořený výpočtový model je dále schopen odhadnout zdánlivou lomovou houževnatost dané vícevrstvé konstrukce pomocí metody váhových funkcí. Výstupy vytvořeného výpočtového modelu jsou ověřeny s využitím numerických simulací na bázi MKP a dostupných experimentálních výsledků. V diplomové práci je následně vytvořený výpočtový model aplikován při hledání optimálního rozložení jednotlivých vrstev konkrétního vícevrstvého nosníku s cílem maximalizovat jeho elektrický výkon a odolnost vůči šíření povrchových trhlin, resp. vzniku křehkého lomu. Tohoto cíle je dosaženo pomocí vhodného rozložení tepelných zbytkových napětí v jednotlivých vrstvách uvažované konstrukce (řízeného použitými materiály a tloušťkami jednotlivých vrstev).
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Methods for topology optimization of mechanically loaded structures and their application on trusses
Pánek, Ondřej ; Lošák, Petr (referee) ; Ševeček, Oldřich (advisor)
This bachelor thesis deals with a topology optimization of truss structures. In the first part of this thesis an overview of individual methods of the structural optimization and brief description of their principle based on recherche of available literature is given. The second part of the thesis deals with an application of selected methods to the topology optimization of truss structures, employing the computational codes programmed in the MATLAB software. In the first step, a code for computation of stresses in individual trusses and displacements in nodes of the truss structure by the finite element method was programmed. This code was later used in individual topology optimization codes for computation of parameters mentioned above. Selected topology optimization methods and their computational codes were then used for optimization of two model tasks – bridge and cantilever beam subjected to isolated forces, in order to reduce their weight while maintaining safety to the limit states of elasticity and buckling stability. At the end of the thesis, gained results were compared to results available in literature (nevertheless optimized as a continuum structure) and it can be concluded, that both these results are in a very good agreement.
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Design of optimal parameters of multilayer ceramic protective coating for high temperature applications
Dohnalík, Petr ; Hrstka, Miroslav (referee) ; Ševeček, Oldřich (advisor)
The main objective of this work was to design a suitable composition of a protective coatings, made of several different layers of specific materials - with respect to residual stress, induced due to a mismatch in thermal expansion coefficients of each layer. Protective coating in this work means both the thermal and the environmental barrier. These coatings protect components against high temperatures and harsh environment. In this work, necessary theoretical background in the field of the thermal and environmental barrier coatings is introduced. There are mentioned some basic design approaches, commonly used materials and processing methods for the coating structure. The literature review gives an overview of modeling of such coated structures, in particular it is devoted to the thermal barrier coatings deposited by air plasma spray process. The next chapter closely describes classical laminate theory used for calculation of residual stresses in the coating. One of the assumptions of this theory is homogenous temperature field through the coating’s thickness. However, in this work was revealed a way to extend the classical lamination theory of such cases, in which the temperatures vary along the thickness of the coating. In the practical part, the analytical model was used for designing suitable properties of some coatings, which were consists of two, three and four layers. The calculations were performed both for constant temperature and for the temperature gradient. All results obtained from analytical approach were verified by numerical calculations.
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