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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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Comparison of mechanical properties of bolts with various surface treatment and upon consideration of their operation on the safety limit
Krško, Peter ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
This bachelor thesis deals with issues of critical bolt joints tightening on the safety limit. The aim of this work is to find the optimal surface treatment of the bolt for reliable application in industrial vacuum pumps and to clarify its stress-strain behaviour upon using various surface treatments and different surface lubrication. Next part consists of finding the maximum torque values causing a fracture in bolts of the vacuum pumps. For this purpose, on one hand, the analytical model of the bolt joint is used and, on the other hand, the experimental observations on the real bolt joint are utilized. The outputs of both approaches are then compared to each other and, on their basis, the most suitable surface treatment of the bolt joint for the given industrial pump is recommended in order to achieve the maximum possible safety against torque applied to the bolt when assembling the device.
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Determination of the mechanical properties of the multilayer structure materials with utilization of the sonic resonance method and modal FE analysis
Fodor, Ján ; Lošák, Petr (referee) ; Ševeček, Oldřich (advisor)
Thesis deals with determination of layerwise mechanical properties of composite ceramics by indirect method, namely Youngs modulus. Based on literature review, it was found that a method to determine elastic properties of one or more components of multi layered composites based on experimental modal analysis and finite element modal analysis, or analytical approach exists. Method based on FE modal analysis was applied to ceramic laminate, where it was attempt to determine youngs modulus of one component. Beyond that, it was attempt to determine Youngs moduli of both components using first two bending resonant frequencies. Results were unsatisfying. Sensitivity analysis showed that layers with unknown Youngs modulus were overly sensitive to small changes in input parameters due to their small relative thickness with respect to thickness of laminate and due to location in laminate. Based on this conclusion, recommendations were made with respect to suitable geometry of test specimens.
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Numerical simulation of failure of ceramic foams upon mechanical loading
Hanák, Jiří ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
The master’s thesis deals with a numerical simulation of failure of ceramic foams with open-cell structure and with understanding of conditions required for the failure of the structure under various mechanical loading conditions. To this purpose, the so-called stress-energy coupled criterion was utilized. The motivation for this thesis was to create a model able of the most accurate prediction of the ceramic foam strength in comparison with experimental observations. First part of the thesis is focused on the theoretical background required for solving the problem. More specifically there are mentioned methods of the foam material modelling, Linear Elastic Fracture Mechanic (LEFM) and coupled stress-energy criterion used for definition of the crack initiation. In the second part of the thesis, numerical Finite Element Analyses (FEA) whose main purpose was to determine critical conditions necessary for the initiation of strut failure within the foam structure, were performed. These pieces of knowledge were then used for creation of the numerical simulation algorithm of the mechanical test of foam material with regular cell pattern. Outputs of numerical simulations were at the end of this work compared with experimental results (of the compression test) made on the real Al_2 O_3 foams prepared by 3D printing technology and provided by the Institute of Physics of Materials Czech Academy of Science. It can be concluded that a good agreement between results of both approaches was reached and the prediction of the ceramic foam mechanical strength using the developed model is in the meanwhile the most accurate estimation from recently published approaches.
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Problem of the crack terminating at the bimaterial interface
Svoboda, Miroslav ; Ševeček, Oldřich (referee) ; Profant, Tomáš (advisor)
The objective of this diploma thesis is the stress-strain analysis of the crack terminating at the orthotropic bi-material interface suggested as the plane problem of the linear fracture mechanics. The first part is engaged in basic relations of the linear fracture mechanics. The second part is focused on the singularity exponent evaluation for the crack impinging and generally inclined with respect to the bi-material interface. It follows the determination of the generalized stress intensity factors applying the analytical-numerical approach represented by the finite element analysis. The last part of this work is focused on the testing of algorithms applied to the specific crack and bi-material interface configurations. A conclusion discusses the influence of the bi-material mechanical properties and the angel of the crack inclination to the obtained numerical results.
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Multi-material topology optimization of the vibrating beam
Kordula, Tomáš ; Ševeček, Oldřich (referee) ; Lošák, Petr (advisor)
The master‘s thesis deals with optimization of continuum consisting of one or more different materials loaded statically or dynamically. The thesis aims on minimum compliance design and maximum eigen frequency design. For solution of each problem situation are written computational programmes in Python language itself and also as combination with commercial software ANSYS APDL.
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Influence of lamine thickness on bifurcation appearance in ceramic laminate
Sorokina, Kristina ; Ševeček, Oldřich (referee) ; Hadraba, Hynek (advisor)
Z důvodu rozdílných koeficientů délkové teplotní roztažnosti jednotlivých vrstev vzniká ve vrstvách keramického vrstevnatého kompozitního materiálů reziduální napětí. V průběhu chladnutí vrstevnatého kompozitu ze slinovací teploty jednotlivé vrstvy smršťují různými rychlostmi v závislosti na velikosti koeficientu délkové teplotní roztažnosti. Jestliže jsou tyto vrstvy spolu pevně spojeny vzniká v jednotlivých vrstvách různě velké trvalé zbytkové napětí. Velikost residuálního napětí je dána objemovým podílem obou složek v kompozitu. Tato práce byla zaměřena na přípravu a popis 7-mi a 9-ti vrstevných keramických laminátů složených ze střídajících se vrstev dvou rozdílných materiálů. Keramické lamináty byly připraveny pomocí metody suspenzního lití a elektroforetické depozice. U připravených laminátu byl sledován vznik tzv. hranových trhlin (edge cracks) ve vrstvách obsahujících tlaková zbytková pnutí. Výsledky pozorování přítomnosti hranových trhlin pro různou konfiguraci velikosti zbytkových napětí a tloušťky vrstev byly srovnány s teoretickou předpovědí vytvořenou pomocí parametrického 2D modelu. Vliv vzniklých hranových trhlin na průběh lomu byl studován pomocí 3D rekonstrukce lomového povrchu po ohybové zkoušce připravených vrstevnatých kompozitů.
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Computational analysis of the electro-mechanical characteristics of ferroelectric/dielectric composite material
Vítek, Tomáš ; Marcián, Petr (referee) ; Ševeček, Oldřich (advisor)
This diploma thesis deals with the computational modeling of ceramic ferroelectric/dielectric particle composites. The literature review section explains the principle of the piezoelectric phenomenon, describes the quantities defining the piezoelectric behaviour of materials, and provides characteristics of commonly used piezoelectric materials, including the mentioned ferroelectric/dielectric composites. The computational part of the thesis begins with the homogenization of particle composites consisting of a ferroelectric matrix and dielectric particles. Available analytical models for determining the effective electromechanical properties of the composite are tested, and parametric finite element models of the particle composite are assembled using Ansys Mechanical APDL software. The algorithm for creating these models is described, and the procedure for computing the relevant effective properties of the composite based on the obtained results is explained. Subsequently, the results obtained from the analytical and finite element models are compared, and the usability of the chosen analytical models is assessed based on the composite parameters. Sensitivity analyses are then performed using the assembled finite element models to evaluate how specific geometric and material parameters affect the effective electromechanical properties of the composite. These properties predicted by the finite element method are compared to the provided experimental results in the next part of the thesis. A computational analysis of residual stresses induced in the composite during sintering follows, and the output of this analysis provides recommendations for the manufacturing of these composites, aiming to reduce residual stresses and, thus, the risk of crack formation. Finally, various designs of ferroelectric/dielectric composites that can be manufactured using 3D printing are proposed and analysed, with the presented results serving as a basis for future research.
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Analysis fitness machine with respect to frictional force and the rolling resistance
Pospíšilová, Kateřina ; Ševeček, Oldřich (referee) ; Majer, Zdeněk (advisor)
The bachelor's thesis deals with the solution of a system of bodies with NNTP bonds, i.e. pas-sive effects are included in the solution of the examples. The first part describes the theoretical foundations of statics, bonds and types of passive effects. Next, kinematic analysis, relaxation of bodies, static analysis and compilation of static balance equations are explained. This know-ledge is then applied to a specific example. In one example, three tasks are solved using the Matlab program. The template for the calculations was a real weight training machine, on which an experiment was subsequently performed to verify the calculated results. In the se-cond part of the work, it is mentioned what the finite element method is and what it is used for. Finally, a deformation analysis is performed in the Ansys program.
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Strain-stress analysis of membrane shells and influence of their fixing on origination of local bending moments
Méheš, Libor ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
The bachelor's thesis deals with a stress-strain analysis of spherical and toroidal membrane shells. Both of these tasks are modeled based on real water towers. A literature review is conducted on the field of membrane shell theory, the utilization of shells, and their design. Parametric computational models were created for the purpose of analysis, both analytical in Matlab and numerical based on the finite element method in Ansys Workbench. These solution approaches and their results are properly compared and evaluated in the thesis. Special attention is paid to the possibilities of shell support with respect to maximum safety factor. The main outcome of the thesis is the design of the most suitable support system depending on the connection position, along with the creation of parametric models required for this analysis.
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