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Computational analysis of the influence of initial defects on the ceramic foam failure upon mechanical loading
Papšík, Roman ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The thesis deals with computational modelling of ceramic foams and analysis of influence of structural manufacturing defects (like broken struts, closed pores and material clumps) have on foam strength. Model of foam geometry was discretized using beam elements in order to decrease computational cost. In place where several struct join, rigid beam element was used so that the increased stiffness is better modelled. Closed walls of pores were modelled and discretised by shell elements. Influence of loading direction was analysed on foams containing no defects and then influence of amount of defects in foam on strength was further analysed. Highest strength show foams created by cells whose structs are oriented in direction of loading. These were losing strength most rapidly. Foam with structure of rhombic dodecahedral cell was least influenced by presence of closed pore defects but it also showed lowest strength even without defects. Cells with struts oriented in direction of loading experienced biggest drop in strength. Kelvin cell is a compromise. It was shown that difference in strength of strut with constant and varying cross-section is tenths of percent.
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Design of laminate handlebars for mountain bikes
Hanák, Jiří ; Ševeček, Oldřich (referee) ; Polzer, Stanislav (advisor)
This bachelor’s thesis describes design of laminate handlebars for mountain bikes. The first part describes the mechanical properties of composite materials, with the emphasis on fiber composites. The algorithm for acquiring material characteristics of fiber composite by analytical method is presented. In the next part, it is shown how to control the direction of fibers in lam-inate in the finite element calculations and its impact to resulting stresses in the material. The aim of the last part is design geometry model of laminate handlebars for mountain bikes with following stress – strain analysis by FEM and software ANSYS. The analysis is performed for static loading.
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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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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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Modelling of the randomly formed ceramic foam structure for FEM simulations
Papšík, Roman ; Navrátil, Petr (referee) ; Ševeček, Oldřich (advisor)
This bachelor thesis deals with construction of ceramic foam model with various levels of (ir)regularity for finite element simulations in Ansys. The main objective is to substitute the complex structure of the open cell foam using the beam elements, enabling to perform FE analysis on much larger volumes of foams than the realistic foam models composed of solid elements. In this work, the technique of the model creation is based on the Voronoi tessellation and enables choice of arbitrary (ir)regularity of the modelled structure. The created source codes generate the model data directly in the syntax of APDL language for FEM system Ansys. The first part of the work describes several methods of the space partitioning and methods for substitution of the real foam structure by simplified “wire” model. The second part defines the Voronoi tessellation (diagram) as a key technique for creation of the foam model and describes its algorithms. The next part of the work deals with possibilities and utilizations of various software and libraries, describes creation of the own code in mathematical software Matlab and way how to transfer the model data into the system Ansys. The last part of the work demonstrates functionality of the created model on several FEM simulations, studying response of the ceramic foam on the external mechanical loading, upon consideration of various levels of the foam structure irregularity.
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Modelling and analysis of the contact failure of ceramic materials
Machů, Zdeněk ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
This bachelor thesis deals with contact damage of ceramic materials. The purpose of this work is to create an analytical and FEM model of contact between a sphere and flat plate and subsequently use these models to analyse loading conditions that lead to crack initiation in the ceramic plate. The research part contains description of contact failures in ceramic materials with strong emphasis on Hertzian cone crack, followed by Hertzian theory of contact between two spheres and Hertzian stress field equations for flat plate. The next part of research chapters describes how contact problems are modelled in FEM software ANSYS Mechanical APDL and introduces the basics of fracture mechanics, which are necessary for the prediction of ring crack initiation. The next chapter contains information about the creation of analytical and FEM model and includes illustrative results of both models, which are then compared between these two models. The last chapter of this work deals with fracture mechanics FEM model that can simulate the ring crack initiation. This chapter also contains analysis of ideal crack position, where the crack has the best conditions for its initiation and growth. The last part of this chapter contains parametrical study where critical loading conditions are analysed in relation to radius of indentation sphere and different mechanical properties of used ceramic plate. In the final part of this work, the results of fracture mechanics FEM model are compared to experimental results of real specimens.
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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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Design of the composite rotor sleeve of a high speed rotary machine
Pavlík, Ondřej ; Ševeček, Oldřich (referee) ; Návrat, Tomáš (advisor)
The diploma thesis focuses on manufacturing carbon fiber and epoxy composite material using filament winding method. Material properties of manufactured composite are ap-proximated using analytical and numerical homogenization models. Calculated material properties are applied to design and evaluate reserve factor of retaining sleeve for high speed brushless permanent magnet synchronous motor. Margin of safety of designed rotor is evaluated using composite failure criteria. Test stand for both static and dynamic testing is designed, static test stand is manufactured and assembled. Static strength test is carried out.
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