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Parameters of Fracture Mechanics
Oplt, Tomáš ; Ševeček, Oldřich (referee) ; Horníková, Jana (advisor)
This thesis is the descriptive summary for the most significant parameters of fracture mechanics, required to define stress field on the crack tip. The first and also the most extensive part is divided into two subparts. There are mentioned particular parameters of one-parameter fracture mechanics, firstly are considered linear elastic deformations, thereafter the elastoplastic deformations. The second, shorter part of the thesis, is aimed at multi-parameters stress field description on the crack tip, required for the calculation of constructions with the necessity to consider their geometry.
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Influence of torsional pre-strain on fracture characteristics under tensile loading
Kupka, Oldřich ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The diploma thesis is about the influence of torsional pre-strain on fracture characteristics under tensile loading of steel 11 375. Plastic strain in the cross-section of tested specimen is caused by torsional pre-strain. Plastic strain causes a different response of a material to tensile loading. A smooth tensile test specimen and tensile test specimen with a notch are examined. The research part of thesis describes tensile and torsional tests according to regular standarts. The nonlinearities considered in computational models are also described, followed by a description of material models in the software Ansys, which is used to create the computational model. Mechanisms of failure, the importance of stress triaxiality and the construction of triaxiality space are also introduced to a reader. The first experiment is about a tensile test of steel 11 375. The stress-strain curve obtained by the tensile test will be used as input in computational modelling. The aim of computational modelling is the determination of torsional pre-strain, that causes plastic strain in a tested specimen. The true stress field, true strain field and points of triaxiality space are determined by computational models. During the second experiment, tensile test specimens are torsioned according to outputs of computational models, followed by a tensile load to fracture. The main output of the experiment is fracture engineering strain. Finally, the stress-strain curves of computational models are also compared with experimental measurements.
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Elastoplastic analysis of stress and deformation and determination of fracture parameters of bodies with stress concentrators under tensile loading
Dubravec, Kristián ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The aim of this thesis is the construction of a diagram of fracture strain for high strength steel OCHN3MFA and its application for the estimation of fracture toughness of this material. The first part of the thesis contains the necessary theoretical framework for numerical modelling of tensile tests of various specimens - smooth specimen, specimen with a notch and specimen with a circumferential crack, it describes the influence of triaxiality on the fracture of bodies and the possibilities of construction of the diagram of fracture strain. Subsequently, a numerical model of these specimens is created using the finite element method (FEM). A non-linear, elastoplastic calculation is performed. Fracture is identified by means of comparing the true stress versus the strain obtained from tests with the finite element analysis results. Stress–strain states of specimens at the moment of fracture are obtained from a numerical model. A diagram of fracture strain is constructed, and it is used to estimate the fracture toughness of a cracked body. Finally, a local approach, which uses the diagram of fracture strain, and a classical approach of fracture mechanics, especially the stress intensity factor, are compared.
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Determination of stress resultants in closed frames
Horák, Richard ; Horníková, Jana (referee) ; Vaverka, Jiří (advisor)
The bachelor's thesis deals with the determination of the internal stress resultants (ISR) of planar beams with a closed centerline. The first part of the thesis presents a theoretical basis, which is then applied in the second part to solve three tasks. In the first task, the theory of symmetrical and antimetrical course of ISR is applied to reduce the degree of static indeterminacy of a symmetrical planar beam loaded by a symmetrical and antimetrical force system. In the second task the method of superposition is used to replace the general external load of the beam by symmetrical and antimetrical external loads. The task is further solved in the same way as in the case of the first task. The third task is solved by a general procedure with several options of released structures. Furthermore, the assumption enabling the solution of the stress energy due to the bending moment only is verified. At the end of the third task, the analytically determined values are compared with the values determined by the numerical method using the software ANSYS.
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Comparison of fatigue fracture criteria for torsion
Roh, Marek ; Slámečka, Karel (referee) ; Horníková, Jana (advisor)
The main goal of this bachelor thesis is to determine which criteria better suits the life prediction of the test sample loaded in the pulsating torsion. In the first part of this thesis fatigue failure will be examined, then fluctuating stresses will be characterized along with shear stress. Characteristics of the materials used will be specified in the second part. Lastly, the most appropriate criteria will be determined.
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Analysis of state of stress in press and shrink fits
Dudek, Milan ; Řehák, Kamil (referee) ; Horníková, Jana (advisor)
This thesis is focused on calculation of overlap in press fit depending on vield strength. There are used methods of analytic elasticity. The counted values are implemented into the technologic process as updated technologic specification. The practical values of overlap depend on exactness of available technology. The evaluation is done at the end of thesis (economic evaluation as well)
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Deformation and stress fields at the front of shear cracks with complicated geometry
Žák, Stanislav ; Hutař,, Pavel (referee) ; Kunz,, Jiří (referee) ; Horníková, Jana (advisor)
Tato závěrečná práce je shrnutím výzkumu smykově zatěžovaných trhlin, který proběhl v průběhu čtyř let doktorského studia jejich autora Ing. Stanislava Žáka (Středoevropský technologický institut, Vysoké učení technické v Brně). Předložená práce je zaměřena na prohloubení znalostí v oblasti pokročilé lomové mechaniky, konkrétně pro smykové zatěžování trhlin kombinované s případy geometrických odchylek trhlin od běžně používaných modelů. To mimo jiné znamená návrh nových přístupů a modelů a popis součinitelů intenzity napětí pro geometricky komplikované trhliny. První část práce je věnována shrnutí současných přístupů v lomové mechanice a dále i popisu numerických metod, použitých v dalších výpočtech. Kromě klasických přístupů se tato část textu zabývá i novějším výzkumem zaměřeným na smykové zatěžování trhlin, speciálně pro dva typy zkušebních těles – válcový vzorek s obvodovým vrubem a trhlinou zatížený prostým smykem nebo krutem a CTS těleso umožňující zatížení trhliny v módech I, II a také v jejich kombinaci I+II. Další část textu je zaměřena na konkrétní výpočty lomových parametrů při použití nových modelů s komplikovaným čelem trhliny. Teoretické řešení lomových parametrů pro oba výše zmíněné modely je porovnáno s experimentálními výsledky, získanými v navazujících projektech. U modelu válcového vzorku je popsána možnost zjednodušení budoucích modelů těles s podobným typem komplikované trhliny a současně je na něm popsán lokální vliv zubatosti čela trhliny na indukci lokálního zatížení v módu II při globálním zatížení v módu III. Tyto výsledky jsou přímo propojeny s experimentální kvantifikací únavového šíření lomu při zatížení v módu III. CTS těleso je použito k popisu vlivu drsnosti trhliny na součinitele intenzity napětí. Na tomto modelu je pozorován jak globální pokles hodnoty KII při zvyšující se drsnosti trhliny, tak i lokální změny v namáhání trhliny podél jednotlivých nerovností. Výsledky potvrzují, i pro dosud málo zkoumané smykové zatěžování, že mikrostruktura lomových ploch a čela trhliny má vliv na lomové parametry. Rozšiřují tak současné znalosti v oboru lomové mechaniky popisem geometrického stínění čela trhliny pro zátěžné módy II a III.
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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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