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Influence of a Free Surface and Gradient Change of Material Properties on a Crack Behaviour
Ševčík, Martin ; Kohout, Jan (referee) ; Klusák, Jan (referee) ; Náhlík, Luboš (advisor)
This thesis was written under the supervision of Assoc. Prof. Luboš Náhlík, Ph.D. and Assoc. Prof. Pavel Hutař, Ph.D. The topic of this thesis is the study of a free surface effect and gradient change of material properties on a crack behavior. The common theme of the work is a fracture mechanics description of a crack behavior near a material nonhomogeneity. Here, the material nonhomogeneity can be understood either as a boundary of a body (interface between body and surrounding) or as a continuous change of material properties. The thesis is introduced by a review part where the state-of-the-art of the concerned topic is described. This part presents several stress state descriptions in the vicinity of some general singular stress concentrators, particularly a crack and a V-notch. The influence of the free surface on a fatigue crack front shape is discussed here. The review part follows with the fracture mechanics description of the graded materials. The problem formulation and the main aims of the thesis are stated in the following chapter. The core of this work is the fracture mechanical description of a crack propagating near the material nonhomogeneity. The thesis focuses on a stress field description near the free surface of the body where a change in a type of the singular stress field occurs. Methods used in generalized fracture mechanics are applied here to describe the stress field near the free surface. The difference between crack behavior in thin-walled and thick-walled structures is shown and supplied by relevant examples. Methods and procedures used are later utilized for estimation of a crack behavior in graded structures. The thesis is concluded by the discussion of obtained results in appropriate context.
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Evaluation of fracture test of selected core-drilled cylindrical specimen
Halfar, Petr ; Sobek, Jakub (referee) ; Keršner, Zbyněk (advisor)
The diploma thesis deals with effective crack model for a cylinder specimen with an chevron-shaped notch, loaded by a three-point bending. The first part of the thesis is theoretical and the it describes the use of fracture mechanics for quasi-brittle materials – concrete and rocks. Furthermore there is described the linear elastic fracture mechanics and founding the geometry function for a different geometries of fracture tests. The second part describes the FEM program, which was used to calculate the fracture parameters, that were used to determine the length of the effective crack and how the program was tested before it was used. The last part describe calculations of fracture toughness by using the effective crack model on selected rock and concrete specimens.
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Basic features of aggregate-matrix-interface fracture of selected building composites
Vyhlídal, Michal ; Seitl, Stanislav (referee) ; Keršner, Zbyněk (advisor)
The aim of this work is to analyze the behavior of cement composite, depending on the features of ITZ. The first part of the thesis is theoretical and deals with the origin and features of ITZ, defines the basic relationships and concepts of continuum mechanics and linear elastic fracture mechanics and presents crack tips posibilities in the three-phase composite, including their short characterization. The second part is practical and describes creation of numerical model in the ANSYS software, presentation of partial results and compare of them. The result of this work is a comparison of the mean values of stress and amplitude of stress depending on the features of ITZ.
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Short fatigue crack propagation description
Trávníček, Lukáš ; Náhlík, Luboš (referee) ; Hutař, Pavel (advisor)
The presented master’s thesis deals with description of short fatigue cracks and can be divided to the several parts. In the first part, theoretical background of fatigue of materials and fracture mechanics parameters which can describe fatigue cracks is presented. Following part describes how to determine fracture mechanics parameters by finite elements method. Due to the shape of propagated fatigue crack, numerical model was established as a three-dimensional. Results obtained based on this model, was compared with literature with very good agreement. Than real shape of propagated short crack was used for description of the experimental data. It was shown, that plastic part of J-integral is suitable parameter for description of the short cracks.
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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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Crack in prismatic bars
Meňhert, Samuel ; Hrstka, Miroslav (referee) ; Profant, Tomáš (advisor)
This thesis deals with summarization of information about fracture mechanics mainly with methods which estimate stress intensity factors. They play an important role in determination of behavior of cracks in engineering process. The main goal of this thesis will be familiarization with Kienzler hypothesis which deals with strain energy release rate and internal effects in a point of disrupted cross section and comparison with classic K-concept, when the stress intensity factors are determined by infinite series.
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Analysis of crack propagation using J-integral
Bónová, Kateřina ; Květoň, Josef (referee) ; Eliáš, Jan (advisor)
The bachelor thesis is focused on importance and application of J-integral in crack propagation analysis. J-integral is a method of fracture mechanics used to determine the strain energy release rate. In other words it provides the amount of energy available for crack propagation in elastic and elasto-plastic materials. The thesis presents derivations of relations between J-integral, crack driving force and stress intensity factor. The most important contribution of this thesis is detailed analytical calculation of the J-integral on simple structures. The results are verified by numerical models in ANSYS.
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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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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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