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Porušování jemnozrnného cementového kompozitu v blízkosti rozhraní plniva a matrice
Vyhlídal, Michal ; Kabele,, Petr (referee) ; Profant, Tomáš (referee) ; Keršner, Zbyněk (advisor)
The Interfacial Transition Zone (ITZ) between the aggregate grain/reinforcement bar and the matrix is considered to be the weakest element in cementitious composites and is, according to some authors, directly responsible for the nonlinear (more precisely, quasi-brittle) behavior of the composites. The aim of this work is verification of the generally accepted paradigm of the weakest element by means of fracture experiments and corresponding numerical simulations. In the experimental part, in addition to traditional fracture tests, modern methods of 3D scanning, scanning electron microscopy, chemical analysis using an electron microprobe and nanoindentation were used. In the numerical part, models based on generalized linear elastic fracture mechanics as well as modern models intended for the simulation of cement composites, namely crack band model with smeared cracks and the Microplane model, were used. Based on the results, the numerical part was complemented by the Cohesive Zone Material model simulating the behavior of the interface. All results are discussed and put into context with already published work. The main conclusion of the work is that the properties of the ITZ do not have such an influence on the behavior of cement composites as the adhesion between the inclusion and the ITZ, i.e. the matrix.
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On the stress distribution near the tip of a sharp notch
Ostratický, Jakub ; Hrstka, Miroslav (referee) ; Profant, Tomáš (advisor)
The notch is a stress concentrator from the point of view of elasticity theory and the knowledge of the description of this stress in the vicinity of its tip is necessary for the correct functionality of a wide range of mechanical components and products. The stress at the tip of the notch is singular and it is technically impossible to prevent the initiation of cracks in its vicinity. However, it is known from fracture mechanics that the initiation and propagation of cracks is not influenced by the magnitude of the stress at their tips, but its intensity characterized by the so-called stress intensity factor. In the case of a notch, it is a generalized stress intensity factor or simply the amplitudes of the singular parts of the stress filed. These coefficients cannot be determined directly from the results of widely used numerical methods such as FEM, but it is necessary to use linear fracture mechanics methods based on the asymptotic solution of the equilibrium equations in elasticity. The presented work deals with the case of a symmetric sharp notch in an isotropic material under the mode I or II loadings. The stress singularity and the related stress intensity factor at the notch tip are analysed and evaluated. The derived asymptotic solution is compared with the results obtained from the FEM analysis.
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Analysis of stress field in the vicinity of fatigue crack in IPE made from stainless steel
Juhászová, Tereza ; Malíková, Lucie (referee) ; Seitl, Stanislav (advisor)
The master thesis is focused on analysis of stress field in the vicinity of stress concentration of stainless steel IPE beam loaded in tree point bending. Theoretical part includes introduction to fracture mechanics with basic terms, principles and variables used to describe fatigue behaviour of material. It concludes teoretical grounds of fracture tests which are future focus of the thesis, methodes used by numerical softwares and methodes used to obtain numerical results. Practical part includes comparision between two and three dimensional numerical models in three point bending, IPE model with different crack front shapes and plastic zone size. Numerical modelling was processed in Ansys Mechanical APDL. Thesis also involves results of experimental testing evaluated using numerical model.
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Application of generalized linear elastic fracture mechanics on estimation of crack propagation origin from sharp V-notch
Štegnerová, Kateřina ; Máša, Bohuslav (referee) ; Náhlík, Luboš (advisor)
The master thesis is focused on estimation of crack propagation origin from sharp V-notch. Stress distribution around the tip of the V-notch is described on the base of generalized linear elastic fracture mechanics. The change of the stress singularity exponent caused by geometry of the V-notch and the vertex singularity is taken into account. The first part of the work is devoted to the estimation of the stress singularity exponent of the V-notch either from stress distribution around the tip of the V-notch or by using analytical solution. Formerly derived stability criteria are applied in the second part of the work. The origin of the crack propagation is estimated for several experimental specimens. The aim of this thesis is to compare the available experimentally observed data with results obtained using those criteria based on the application of generalized linear elastic fracture mechanics developer at the Institute of Physics of Materials Academy of Sciences of the Czech Republic. The finite element code Ansys and mathematical software Matlab were used for the necessary calculations.
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Crack Propagation in Railway Wheel under Operating Conditions
Navrátil, Petr ; Schmidová, Eva (referee) ; Fuis, Vladimír (referee) ; Janíček, Přemysl (advisor)
This doctoral thesis was written under supervision of my supervisor Prof. Ing. Přemysl Janicek, DrSc. and under supervision of my specialist supervisor Ing. Petr Skalka, Ph.D. The thesis deals with the influence of various operating conditions on crack behaviour in in a wheel rim and/or tire. The dissertation topic was motivated by cooperation with Pardubice University, Faculty of Jan Perner. The first part of the thesis presents a literature search, which provides a current state-of-art in the field of contact loading, crack propagation behaviour under mixed-mode and thermal field generated during braking. The next part of thesis deals with the solution of the given problem and the obtained results are presented. Specifically, crack behaviour under various operating conditions including the crack growth rate is simulated. Also, an influence of thermal field on crack is investigated. The linear elastic fracture mechanics approach is considered to treat the above mentioned problems. Last part of thesis summarizes the obtained results which are discussed in a broader context.
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Using Salome Meca computing environment to solve problems of solid mechanics
Ptáček, Tomáš ; Vaculka, Miroslav (referee) ; Vosynek, Petr (advisor)
Given bachelors thesis deals with solutions of basic tasks of body mechanics with usage of the finite element method (FEM). An open-source software Salome Meca with Code_Aster solver is used there. Basic formulas of strength of materials on which is FEM based are introduces in the beginning. Then is presented software Salome Meca with its solver Code_Aster. Followed by own solution of tasks, which contain structural analysis and series of examples for solving the fracture mechanics. Numerical solutions from Salome Meca are compared with analytical solutions, if some exist, and with solutions from commercial software Ansys Workbench.
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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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A study of the stress field near the stress concentrator at the bi-material interface
Krepl, Ondřej ; Klusák, Jan (referee) ; Profant, Tomáš (advisor)
The aim of this work is the solution of problems of the stress distribution near bimaterial notch tip or eventually the crack impinging orthogonaly the bimaterial interface, determination of stress singularity exponent. The first part is concerned with basics of linear elastic fracture mechanics, i.e. Irwin's concept of stress intensity factor. The second part is devoted to description of anisotropic materials by complex potencial theory. The final part is focused on calculation of eigenvalues of both isotropic and anisotropic materials and application of LES formalism on the calculation of stress singularities of the bimaterial ortotropic notch or the crack impinging orthogonaly the bimaterial interface.
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Crack path calculation using linear elastic fracture mechanics
Bónová, Kateřina ; Malíková, Lucie (referee) ; Eliáš, Jan (advisor)
This diploma thesis deals with the different possible calculations of crack path. Specifically, it focuses on criteria based on maximum tangential stress, minimal strain energy density, crack tip displacement, and local symmetry. These criteria are used for calculations in ANSYS software to estimate possible crack paths on four simple structures. The thesis also contains the codes created in ANSYS. Using these, the crack trajectory of a given structure can be calculated by any of the four criteria described.
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Numerical support for wedge splitting test on non-traditional geometry
Juhászová, Tereza ; Malíková, Lucie (referee) ; Seitl, Stanislav (advisor)
Bachelor thesis is focused on numerical support of wedge splitting test with non-traditional geometry. Numerical analysis takes place in program Ansys, defining behavior of models with modified entry parameters. Attention is focused on values of parameters characteristic for fracture mechanics; stress intensity factor and T-stress and functions describing their relationship to length of crack, evaluation of which is graphically illustrated.
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