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Probabilistic discrete model of concrete fracturing
Kaděrová, Jana ; Lehký, David (referee) ; Konečný,, Petr (referee) ; Eliáš, Jan (advisor)
The thesis presents results of a numerical study on the performance of 3D discrete meso–scale lattice–particle model of concrete. The existing model was extended by introducing the spatial variability of chosen material parameter in form of random field. An experimental data from bending tests on notched and unnotched beams was exploited for the identification of model parameters as well as for the subsequent validation of its performance. With the basic and the extended randomized version of the model, numerical simulations were calculated so that the influence of the rate of fluctuation of the random field (governed by the correlation length) could be observed. The final part of the thesis describes the region in the beam active during the test in which the most of the fracture energy is released in terms of its size and shape. This region defines the strength of the whole member and as shown in the thesis, it does not have a constant size but it is influenced by the geometrical setup and the correlation length of the random field.
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The role of material sciences in solving the problems technical accidents
Tonkovič, Miroslav ; Řičánková, Veronika (referee) ; Klakurková, Lenka (advisor)
Material sciences plays an irreplaceable role in explanation of various technical accidents. The proposed work focuses on examples of sever chosen technical accidents in which the knowledge of materials science was crucial in use and help to solve them. Description of an incident is stated to particular cases as well as results of these investigations, taking in mind the given topis of proposed work. The accidents are always described with necessary theoretical basis connected to each particular issue. Its knowledge was undoubtedly essential in solving the accident. The end of the work is a summary of the most frequent causes of technical accidents.
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Evaluation failures of masonry buildings
Kopecký, Martin ; Stehlík, Michal (referee) ; Cikrle, Petr (advisor)
This bachelor’s thesis deals with an evaluation of defects of masonry buildings. The theoretical part gives a sorting of defects of masonry buildings according to various criteria including types of cracks, defects of brick walls and columns and systems of cracks in masonry buildings with their causes. The pictures with examples of the defects are enclosed. The practical part gives the documentation of a typical failure. This documentation is about uneven subsiding of two different parts of the church of St. James in Brno. The experimental part describes the failure in building „C“ which is the part of the area of Masaryk university, Faculty of Arts. This experimental part is based on the measuring of the deformations. The results of the measuring and photos are included.
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Mutual interaction of multiple cracks growing in the particulate composite with brittle matrix under conditions of sub-critical crack growth
Slávik, Ondrej ; Ševeček, Oldřich (referee) ; Majer, Zdeněk (advisor)
In the first part of the submitted diploma thesis, the knowledge in the sphere of the fracture mechanics, related to the practice part of this thesis are summarized. In that the 2D parametrical numerical model of the particle composite with multiple cracks was created, using the finite elements method. Thanks to this model it is possible to find specific configurations which are showing the existance of multiple mutual interactions between these cracks, just by simple manipulation of the input data. In the calculations the influence of the residual stresses was considered which are formed during production of the material. The effect of the subcritical crack growth was taken into account as well in this thesis.
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Advanced evaluation of fracture tests of selected rock specimens
Kubeš, Pavel ; Veselý, Václav (referee) ; Keršner, Zbyněk (advisor)
This bachelor's thesis deals with the advanced evaluation of fracture tests of selected rock (sandstone) specimens. The first part describes several fracture models/methods, fracture-mechanical parameters, process and configuration of the tests, used specimens and the procedure of data processing using the program GTDiPS. The second part contains neatly sorted evaluation of load-displacement diagrams. The results of the work are calculated fracture-mechanical parameters of various sandstones and their mutual comparison.
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Fatigue crack front shape estimation
Zouhar, Petr ; Klusák, Jan (referee) ; Hutař, Pavel (advisor)
The presented master’s thesis deals with fatigue crack front shape estimation. The aim of this thesis is to create an iterative process leading to the real fatigue crack front shape. Thesis is solved using finite element method. The work is divided into two logical parts. The first part of the thesis describes the basic concepts of linear elastic fracture mechanic (LEFM), methods used for estimation of stress intensity factor and stress singularity exponent. The first part further describes some phenomenon’s accompanying the mechanism of fatigue crack growth as for example crack tip curving and crack closure. In the second part of the thesis there is studied an affect of the free surface on the fracture parameters, especially the affected distance from the free surface is determined. Based on the assumption of a constant stress intensity factor and stress singularity exponent along the crack front, an iterative process leading to fatigue crack front shape is presented. The accuracy of the result is discussed by comparing of obtained crack front shapes with experimental data at the end of the thesis.
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Models of plastic zone on the crack front
Surovec, Jindřich ; Žák, Stanislav (referee) ; Horníková, Jana (advisor)
This bachelor thesis is about analytical determination of plastic zone shape at the crack tip using Von Mises and max yield criterions. Next goal is obtain characterictic parameters of kinked crack. Theoretical part clarifies some basic concepts needed to understand the analytical models, then follows the analytical solution itself.
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Classification and evaluation of rail wear
Nohel, Rostislav ; Frýza, Josef (referee) ; Galas, Radovan (advisor)
This bachelor’s thesis is focused on the wear of rails. In this thesis, the reader will be firstly introduced to the fundamentals such as nomenclature of wheel and rail, adhesion, adhesion coefficient, contact area, slip, traction characteristic and wear. Subsequently, the fundamental types of material wear (adhesive, abrasive and fatigue) will be explained, which occur in the wheel-rail contact. In the next part, the individual rail defects are analysed with respect to locations. The output of the bachelor’s thesis is overview and description of the most common rail defects which are usually caused by fatigue wear.
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On the Problems of LEFM of Composite Materials
Kopp, Dalibor ; Profant, Tomáš (referee) ; Klusák,, Jan (advisor)
The objects of this bachelor thesis is to familiarize oneself with the basics of linear elastic fracture mechanics (LEFM) of homogeneous materials and to specify these problems for composite materials. The work is divided into three parts. The first part is aimed at the basics of LEFM. The second part is concerned with generalization of LEFM. The third part is oriented to the numerical application of the studied problems to notches composed of two orthotropic materials.
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