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Utilization of finite fracture mechanics for correction of fracture toughness measurement on samples with various notch root geometry
Dohnal, Petr ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The work deals with the use of numerical simulations and the theory of finite fracture mechanics for the analysis of conditions for the formation of a crack in a ceramic test sample with a notch (loaded by four-point bending) and possible ways of correcting the fracture toughness determined experimentally on samples with different notch root radius. For this purpose, a parametric calculation model was created to simulate the fracture toughness test by four-point bending. In the first step, the calculation of the critical force at which a crack occurs in a test specimen with a rounded notch and its subsequent unstable propagation through the remaining cross-section of the specimen was debugged. For this purpose, the finite element method (FEM) and the coupled stress-energy criterion were used. In the next step, the procedure of calculation of fracture forces was also applied to a set of experimental samples in order to compare the numerical prediction with experimentally measured values. Two methods of correction of the fracture toughness determined experimentally are also proposed in the thesis. One uses for a correction of the measured values numerical calculation using the coupled stress-energy criterion. In the second case, a correction function was derived using numerical simulation, which no longer needs an FEM calculation for its future use. Correction of the measured fracture toughness using the function proved to be better but not completely effective for the entire range of investigated notch root radii. When comparing with other correction functions found in the literature, it can be stated that the correction procedure proposed in the work provides a better agreement with the real value of the fracture toughness of the given material up to a certain value of the notch root radius.
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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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Effect of fiber direction around the hole in longfiber composite on the stress distribution
Tulis, Vojtěch ; Majer, Zdeněk (referee) ; Polzer, Stanislav (advisor)
The bachelor thesis focuses on stress distribution of longfiber composite with a hole, mainly on the influence of fiber direction on the stress distribution around such a hole. To look into the problem closely some samples of common longfiber composites have been simulated in the software environment of Ansys. These samples were analyzed on the final stress distribution – first without any change of the direction of fibers and then with different models of control. Subsequently, all the data were processed and assessed.
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Analysis of specific systems of bodies with neutral bonds
Grúz, Jan ; Hájek, Petr (referee) ; Majer, Zdeněk (advisor)
This thesis deals with analytical and graphical solution of three specific systems of bodies that are in static equilibrium. These systems of bodies contain neutral bonds. The opening part dedicates to theory and principles of solution of contact forces in bonds, which are further used for calculations and graphical solutions. The first system of bodies is a demonstrative tappet mechanism which was created for demonstration of some methods of graphical solution. The second system is inspired by lifting mechanisms in production lines. The aim is to find out the magnitude of contact forces for different positions of the lifted weight and a minimal torque of the propulsion. For solving the third system of bodies, principles of statics and hydrostatics are used. The aim is to find out the minimal magnitude of force for activating the mechanism. All systems of equations are solved in Matlab.
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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 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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Description of Stress and Strain States at Front of Inclined Cracks Loaded by Shear Modes
Roh, Marek ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The primary objective of this masters thesis is to assess the eects of the length of crack and the angle, of which is this crack inclined on the stress and strain states at its front for the test sample loaded under shear. The rst part of this thesis will analyze the individual approaches that lead to the description of the aforementioned conditions. The second part deals with the FEM model assembly, which will lead to the fracture parameters, the values of which will be compared in part three.
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Description of the residual stresses in polymer pipes
Poduška, Jan ; Majer, Zdeněk (referee) ; Hutař, Pavel (advisor)
This thesis is dealing with the issue of residual stress present in the wall of a polymer pipe and the influence on its lifetime. Experimental data obtained by the ring slitting method are evaluated and the tangential residual stress in the wall of polypropylene pipe is determined. The evaluation is carried out using a new methodology based on the curved beam theory. The method is verified using numerical simulation. 3D numerical model is used to verify the behavior of the pipe, when there are both tangential and axial residual stresses present in the pipe wall, because the presence of axial stress causes a rise in the magnitude of tangential residual stress. A correction of the tangential stress values corresponding to the pipe length is then proposed. It is shown, that the distribution of the tangential residual stress does not depend significantly on the dimensions or ma-terial of the extruded pipe and a general equation is proposed to describe the distribution. This general distribution is then involved in the calculations of the pipe lifetime that are carried out using a method based on the linear elastic fracture mechanics. A significantly lower lifetimes are obtained when taking the residual stress into account.
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Deformation, stress and safety analysis of the recumbend frame.
Verner, Jan ; Majer, Zdeněk (referee) ; Vrbka, Jan (advisor)
This work contains deformation, stress and safety analysis of recumbent bike frame from company AZUB. After introduction about history, definition of beam and beam assumptions, computational model of the frame was made fallowed the main solution. Three load states was checked - stillnes / uniform ride, deceleration and pedalling. The third one was subjected to deeper analysis. Bending problem in defined location was solved for all states. Inner stress resultans was solved as Von Misses stress, and the safet y was calculated. The fist state was compared with FEM. A program in MATLAB was made, enabeling calculation of user- selected frame geometry and loading.
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