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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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Strength control of bicycle crank assembly
Kolenčík, Richard ; Skalka, Petr (referee) ; Burša, Jiří (advisor)
This bachelor thesis is intent on strength-deformation check of bicycle crank assembly. The first part is devoted to check safety of fatigue failure of crank bicycle, which is loaded with combination loading. The second part is devoted on safety analysis of fatigue failure in the case of pedal. Because of low safety´s coefficient is made calculation of high cyclic life of pedal. The last section is devoted to the calculation of maximum deformation of the crank assembly. The analytical calculation was performed by the software Matlab R2012b.
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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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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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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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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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Influence of Kármán vortices on the body in the air flow
Matějka, Jan ; Pochylý, František (referee) ; Skalka, Petr (advisor)
In master thesis there is main model object a 100 m high steel chimney located in the area of paper mill near the town of Świecie in Poland. In the past there was an accident with the failure of this particular construction. There is analyzed an effect of Kármán vortices on deformation – stress response of this chimney. The effect of Kármán vortices on the body in the air flow is considered to be cause of the accident in this case. In master thesis is investigated an opportunity to minimize these effects on body in the air flow (In this case the body is the above mentioned steel chimney). The negative effects termination (like for example minimalization of range of excitation frequencies or minimalization of drag forces acting on the chimney) is carried out by use of aerodynamic protection shell.
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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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Radial turbine runner design with reduced moment of inertia
Votava, Ondřej ; Skalka, Petr (referee) ; Fuis, Vladimír (advisor)
This master’s thesis deals with topological optimization of the impeller of a radial turbocharger turbine. It focuses on reducing the moment of inertia with unchanged aerodynamic properties. The optimization was carried out using CFD, thermal and structural analysis. The computational modeling was performed using the finite element analysis in ANSYS. The work proposes models of the impeller with the topological modification of the internal structure. Based on the values of moment of inertia, the stress and the strain the most suitable model was selected.
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