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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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Computational modelling and analysis of crack propagation in ceramic composites containing residual stresses
Černý, Hynek ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The diploma thesis dealt with 3D computational modelling of crack propagation in particle and layered ceramic composites. In first part of thesis, all tools for fracture mechanics implemented in software ANSYS were explored for their suitability in given topic. In the next part, crack propagation in particle composites was analysed, where extra focus was applied on influence of different stiffness and thermal expansion of all components of the composite. First, the crack propagation in homogenous material model was set up, then the effect of different stiffness of the composite components was added, and in the last stage, the effect of the residual stresses was also added. From the achieved results, it was possible to describe the influence of the previously listed factors on the energy required for crack propagation. This created model should be applicable to the model of a real composite, thanks to which it should be possible to quantify whether the composite is more resistant to crack propagation then the homogenous material. In the last part of thesis, the crack growth through layered ceramic laminates was analysed, where emphasis was again placed on the different stiffness and thermal expansion of all components of the laminate. In this part, the great advantage of the ANSYS APDL, creating of macros, were used. Using macros, a parametric model was created, which, after the input data was entered, was able to create geometry of the computational model, enter boundary conditions, create a mesh of the computational model, set up the analysis and start the simulation. The created model can be used, for example, to determine the apparent fracture toughness of laminate, thanks to which it is possible to access how much the used configuration is more suitable than the use of a homogenous material.
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Comparison of analytical and numerical solution of selected problems of compound bodies from Strength of materials II
Tichý, Marek ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The Bachelor´s thesis deals with stress-strain analysis of selected compound bodies from the subject of Elasticity and Strength II. The Wolfram Mathematica software was used for analytical calculations, and for the numerical calculations was used software called Ansys Workbench, which uses the finite element method. An overview of some compound bodies from engineering practice was compiled, and two compound bodies with different geometric variations were selected for the purpose of comparing the analytical and numerical approaches under assumptions of small and large deformations. The results of both solutions are compared in graphs and evaluated.
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Mechanical analysis of historical systems
Bilík, Pavel ; Ševeček, Oldřich (referee) ; Fuis, Vladimír (advisor)
This work thesis deals with historical machine systems from the period of antiquity and the Middle Ages. The basic concepts, quantities and phenomena related to the operation of machines are defined. Technically important inventions are described in more detail herein. In the practical part, two selected assemblies are examined, their dimensions and properties are designed. Furthermore, calculations from mechanical analysis are performed on selected systems. Numerical solutions are implemented using scripts in Matlab.
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Analysis of the three-dimensional shape of the crack in the cantilever beam
Ozimák, Eduard ; Ševeček, Oldřich (referee) ; Majer, Zdeněk (advisor)
The bachelor thesis deals with the numerical calculation of the stress intensity factor using the finite element method and the subsequent modelling of the crack face shape on a simple beam in the ANSYS Mechanical APDL computational environment. In the introductory part of the thesis, the history and beginnings of fracture mechanics are described. Then, the basic theoretical knowledge and relationships needed when working with a body containing a crack are described. This is followed by an introduction to the finite element method. In the second part of the bachelor thesis, the procedure of performing numerical calculations and modelling in the ANSYS environment is described in detail.
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Micro-cellular impact absorbers
Rakušan, Jakub ; Ševeček, Oldřich (referee) ; Skalka, Petr (advisor)
This bachelor thesis focuses on micro-cellular impact absorbers. The micro-cellular absorber converts the kinetic energy of the impacting object into the strain energy of the internal structure of the absorber. The thesis focuses on two types of absorbers, namely the absorber with internal auxetic structure and the absorber with internal non-auxetic structure. The same porosity has been kept for both internal structures for further comparison of the characteristics of both the absorbers. As part of this thesis, an impact test was simulated. In this test, objects (cylinders) of different diameters, the same length (identical to the absorber thickness), and different kinetic energy were impacted into the absorber. The finite element method (explicit solution) was used to solve this problem. The output of the study was a comparison of simulations of the impact test into auxetic and non-auxetic structures.
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