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Influence of notches under cyclic high-frequency fatigue loading
Kozáková, Kamila ; Ševeček, Oldřich (referee) ; Klusák, Jan (advisor)
The diploma thesis deals with the evaluation of the lifetimes of smooth and notched specimens. The comparison of their lifetimes is focused on the case of high-frequency cyclic loading in the area of high-cycle and gigacycle fatigue of materials. The theory of critical distances is used to evaluate and recalculate the life curves of the notched specimens. The effect of the notch is quantified using the Line method. The critical length parameter is determined so that the life curve of the notched specimens corresponds to the curve measured on smooth specimens. The result is the dependence of the critical length parameter on the number of cycles to fracture. Knowledge of critical length parameters can be used to determine the lifetime of notched specimens as well as real notched components using the results of fatigue tests of smooth specimens.
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Determination of the elastic characteristics of highly-porous materials by means of the impulse excitation technique
Kollmann, Marek ; Lošák, Petr (referee) ; Ševeček, Oldřich (advisor)
The bachelor thesis dealt with the application of pulse excitation technique (IET) to determine the elastic characteristics of highly-porous materials. The first part explained the principle of this method together with the arguments for use outside the conditions given by the standard. In the next part, a model of foam structure with open porosity based on Kelvin cell was created in ANSYS software. The influence of porosity and cell size on its elastic characteristics was determined on the model. It was showed to agree with the theory according to Gibson and Ashby. The result of the work was the evaluation of the possibility of using IET to determine these characteristics, these results were then compared with the experimental values. It turned out that the IET provides the correct information about the stiffness of the model.
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Modelling and analysis of auxetic materials response on the mechanical loading
Vítek, Tomáš ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
This bachelor’s thesis is focused on auxetic materials, especially on their response on the mechanical loading. Historical development, significant mechanical properties, different ways of modelling and possible practical applications of these materials are described in the research part of the thesis. The computational part deals with the detailed analysis of selected auxetic structures in order to evaluate their elastic properties depending on different geometric parameters and also on the magnitude of applied deformation. Computational modelling is primarily performed using the software ANSYS Mechanical APDL based on the finite element method (FEM). This method is briefly explained in one chapter. In the following part of the thesis the process of creating a parametric model and reducing the whole structure to a minimum geometry size (a part of a basic unit) is described. A detailed explanation of generating the mesh and setting appropriate boundary conditions is also included together with the results evaluation. Elastic properties obtained by numerical simulations are then compared to available analytical model. Dependencies of elastic properties are presented for a wide range of values of selected geometric parameters and applied deformations of the structure considering small and large deformation regimes. An influence of these parameters on a structure response during the mechanical loading is discussed based on these dependencies. At the end of the thesis the values of elastic properties computed using a finite element method are confronted to the experimental data available in the literature and the validity of the computational model is considered based on this comparison.
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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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Proposal of topology of piezoceramic composite sensor
Dostal, Vojtěch ; Ševeček, Oldřich (referee) ; Majer, Zdeněk (advisor)
This master thesis deals with design and numerical modelling of piezoceramic sensor, which is placed on a rail, in order to generate electrical energy, which can be used for wireless monitoring of railway traffic and to monitor the condition of the railway. The thesis is divided into three parts. Theoretically background of piezoelectric energy harvesting is described in first part, where some previous application of piezoelectric generator in railway area are shown. In the second part, parametric analysis of numerical model is performed, which directly leads to finding best location on a rail, where piezoelectric generator should be placed. For this analysis the homogenized model of MFC sensor was used. Results of the numerical model were then compared with the results of the conducted experiment. The third part presented own design of piezoceramic sensor, which is placed onto most suitable location on a rail. Results from numerical analysis shown eligibility of using piezoceramic sensor to monitor the railway traffic.
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Computational simulation of the compression test of the open cell metal foam
Homola, Václav ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
The thesis presents computational simulation of compression test of a nickel foam and the 3D reconstruction of micro-CT images was utilized to generate the foam’s model of geometry. Explicit FEM is used to simulate compression test using software tool LS-DYNA and the stress–deformation curve is obtained together with deformed model’s mesh used for subsequent analysis. Sensitivity analyses were performed to configure the model and ensure best fit with values obtained during real-life experiment. The ANSYS Classic environment was then used to simulate tensile test of the foam compressed to various thicknesses. The tensile moduli in three mutually perpendicular directions of nickel foam were computed and the results were compared to experimental values as well. The results of tensile test simulation revealed considerable anisotropy of the foam’s elastic behavior. It can be said that the measured experimental data correspond very well with the elastic properties obtained from simulation up to certain level of compression. Analysis of the relationship between the element size and tensile moduli showed a significant difference between fine and coarse mesh. The optimal level of discretization and the overall model configuration ensuring high level of accuracy is proposed in this thesis.
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Verification of operation of piezoelectric composite strain sensor
Kubiš, Juraj ; Ševeček, Oldřich (referee) ; Hadaš, Zdeněk (advisor)
The bachelor thesis deals with the use of piezoelectric elements as sensing elements in engineering practice. The work can be divided into three main parts. The first part describes the actual use of these elements in practice, either as sensing elements or as a source for energy harvesting. This section contains the selection of components for a given experiment, the creation of a model using FEM and the measurement process of the experiment. The third part is the evaluation of the obtained results and subsequent comparison with the obtained values from strain gauges and other sensors.
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Computational tool for a stress-strain analysis of the mechanically loaded circular and annular plate
Dohnal, Jakub ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The bachelor's thesis primarily deals with the creation of a computational tool for stress-strain analysis of rotationally symmetric circular and intercircular plates. The commercial software MATLAB and its component APP DESIGNER were used for this purpose. The program uses analytical relationships of general solid mechanics to solve differential equations for several types of plates and loads. Part of the bachelor thesis is also a parametric study comparing the outputs of analytical and numerical model based on the finite element method, aimed at identifying the practical application of the analytical solution and its accuracy for a particular case of the plate.
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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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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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