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Problems of the crack near the bimaterial interface
Svoboda, Miroslav ; Klusák, Jan (referee) ; Profant, Tomáš (advisor)
Subject of this work is resolving problems of linear crack mechanics, description of stress and deformations in the vicinity of the top of the concentrator with plane elasticity theory in orthotropy materials. First part is engaged in basic relations in crack mechanics. Second part is engaged in numeric-analytic algorithm for determination of stress singularity of crack perpendicular to interface of two materials. Third part is focused on testing algorithm on specific configuration of material and tension of crack in bimaterial interface. In the conclusion, numeric results and impact of mechanic qualities of materials with crack perpendicular to their interface are evaluated.
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Optimization of heavy steel castings manufacture
Jankůj, Josef ; Martínek, Ludvík (referee) ; Šenberger, Jaroslav (advisor)
The work deals with the occurrence of cracks and fissures in the massive steel castings produced in the ŽĎAS a.s. foundry which create in castings through the elimination of the extension. The influence on the final deoxidation on the creation of fissures and cracks is researched at the experimental samples. The beginning of the work is about teoretical analysis of these defects. Next it is described the place of the collection of these samples their chemical composition and cracks identification. After that it is evaluated the appearance of various defects in connection with modificatory and deoxidation additive, observation of experimental material with the microscope and the results of mechanical tests. The conclusion of the work belongs to sum up the individual results and proposal of optimal procedure.
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Procedure of residual fatigue lifetime assesment of railway axle
Scholz, David ; Seitl, Stanislav (referee) ; Náhlík, Luboš (advisor)
The goal of the bachelor's thesis is to present options to calculate residual life of a railway axle from more sophisticated points of view. These methods are requested by railway operators to ensure higher safety of train traffic. The main issue is the perspective of fracture mechanic, considering railway axle as a component with an initial crack or other defect. The theoretical part deals with basic definitions of fracture mechanics and processes describing crack propagation, using conception of stress intensity factor, which is the most used nowadays. Following part also describes a fatique life estimation process in real. This process is demon-strated using an example after that.
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Elastic Analysis of Crack Stability under Shear Loading Modes
Žák, Stanislav ; Profant, Tomáš (referee) ; Horníková, Jana (advisor)
The main goal of this thesis is to create a numerical simulation of a real experiment for specifying the ultimate state of spread of fatigue crack in pure shear stress modes and to deal with results of simulations for different specimen geometries. The simulations emulate real conditions of the experiment within the frame of linear elastic fracture mechanics. The first part of this work discusses a number of approaches to describe the stability and behaviour of cracks. The second part of this thesis deals with several possibilities of calculating crack characteristics employing ANSYS software. The third and most comprehensive part of the thesis describes the experiment which served as the template for the calculations. In addition, the setup of the simulations and the post-processing of the results for different crack parameters are discussed.
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Mechanical fracture parameters of concrete after exposure to high temperatures
Bejček, Michal ; Keršner, Zbyněk (referee) ; Šimonová, Hana (advisor)
The diploma thesis is focused on the evaluation of mechanical fracture parameters of concrete after exposure to high temperatures. In the introductory theoretical part general principles of fracture mechanics with the concentration on a linear elastic fracture mechanics and non-linear fracture models for the concrete are summarized. The meaning of the three-point bending fracture test used for determination of fracture parameters is also explained. Further the influence of high temperatures on the partial components of concrete and general modeling of temperature loading is described. The practical part is concerned with the evaluation of fire experiments on the concrete panels including numerical simulations using GiD and ATENA software. The evaluation of data obtained from the three-point bending test carried out on specimens with initial stress concentrator taken from concrete panels is a main part of the diploma thesis. The values of modulus of elasticity, effective fracture toughness, work of fracture and fracture energy are determined from the measured F–d and F–CMOD diagrams after their proper corrections in the GTDiPS application. The evaluation of the selected mechanical fracture parameters was performed by StiCrack software using effective crack model and work of fracture method and DKFM_BUT software using the double-K fracture model. Finally, the attention is paid to the analysis of the obtained data.
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Numerical simulation of crack propagation in ceramic composites in 3D
Svoboda, Josef ; Horníková, Jana (referee) ; Majer, Zdeněk (advisor)
The strength of materials such as glass and ceramics can be influenced by the environment (stress corrosion). Under applied stress defects (cracks) can grow sub-critically below fracture toughness K_Ic. The aim of this work was to develop a three-dimensional finite-element model to analyze the subcritical crack growth behavior of ceramic-based particulate composites. The maximum tangential stress criterion (MTS) was used to predict the direction of the crack propagation in the framework of linear elastic fracture mechanics. The modeled material was a Low Temperature Co-fired Ceramics (LTCC), containing alumina particles embedded in a glass matrix. The main aim of this work was to develop a 3D model describing the crack growth. Conclusions from this work can contribute to a better understanding of subcritical crack propagation in particle composites.
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An aplication of the boundary element method to the problem of the crack in the vicinity of the bi-material interface
Sedláček, Stanislav ; Vrbka, Jan (referee) ; Profant, Tomáš (advisor)
There are many shape and other changes in the engineering constructions. These changes cause the concentration of the stress. There is a higher probability of the crack initiation in the vicinity of these stress concentrators. The problems of the crack can be solved nowadays only with help of sufficient numeric tools. The Boundary Element Method is one of the many numerical tools which offer the solution of some problems of the mechanics. The goal of this diploma thesis is to formulate boundary element method for the plane problem of the linear elasticity for izotropic material with different types of the stress concentrators.
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Residual fatigue lifetime of model railway axle
Netopil, Vladimír ; Majer, Zdeněk (referee) ; Náhlík, Luboš (advisor)
The aim of this diploma thesis is to estimate the residual fatigue lifetime of the model train axle. Primarily, the thesis is focused on determination of the stress intesity factor, the main variable for estimation of the residual fatigue lifetime. At first, the theoretical approaches of estimation of the residual fatigue lifetime are listed and then the residual fatigue lifetime of the model train axle is estimated.
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Diagnostic and Reconstruction Design of Brick Building in Medlice
Košárek, Jan ; Cikrle, Petr (referee) ; Kocáb, Dalibor (advisor)
Master’s thesis deals with diagnostics and reconstruction of neo-gothic chapel in Medlice. Summary of appropriate testing methods for this chapel is compiled. Visual examination of whole structure have been performed by diagnostics. Masonry element strength was found out at specimens which had were taken out from structure (drill cores and whole bricks). Masonry elements also was tested by Schmidt hammer LB. Mortar was tested by Kucera’s drill. Masonry strength required for static calculation was computed from achieved values. After examination of all structure defects have been designed reconstruction by post-tensioning.
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