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Stress state aspects of quasi-brittle fracture
Sobek, Jakub ; Němeček,, Jiří (referee) ; Keršner, Zbyněk (referee) ; Klusák,, Jan (referee) ; Veselý, Václav (advisor)
The presented dissertation thesis is focused, as the title suggests, on the analysis of stress state aspects of quasi-brittle fracture. That means the fracture of composite materials with cement matrix (such as concrete, mortar, plaster, etc.), ceramics and other composites. Used methods are based on the theory of multi-parameter linear elastic fracture mechanics, which highlights the importance of considering of several initial terms of Williams power series, approximating the stress and displacement fields in a cracked body, within conducted fracture analyses. Determination of values of coefficients of terms of this series, recalculated into the shape functions serving in most of the conducted stress state analyses, is performed via the so called over-deterministic method. Another tool for the problem solving is nonlinear fracture mechanics, represented primarily by the cohesive crack model, namely the crack band model implemented in the used ATENA software. For the backward reconstruction of stress field in the cracked bodies the application ReFraPro is used. The analytical part deals with various aspects of wedge-splitting test – from the boundary conditions, though various possibilities of nodal selection (required as input variables for the over-deterministic method) up to the advanced (automated) analysis of numerical model. Special chapter includes atypical test specimens designed for adjusting of various levels of constraint of stress and deformation at the propagating crack tip. The study of this geometry and also the subsequent detail analysis reveals important information for real experiments. Backward reconstruction of stress field presents analysis on suitable possibilities of nodal selections as inputs into the procedure of approximation of the crack tip fields and answers the question of the necessity of application of the multi-parameter linear elastic fracture mechanics for certain fracture analyses of specimens from quasi-brittle materials. The th
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Tools for threading and their use
Veselý, Václav ; Polzer, Aleš (referee) ; Sliwková, Petra (advisor)
The bachelor’s thesis Tools for threading and their use deals with issues connected to tools, the materials used and their usage in the field of mechanical engineering. Individual parts of the thesis cover types of tools for threading, methods of threading and materials suitable for tap making. Further, the range of monolithic milling taps in the producers’ supply is also analysed.
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Biological pretreatment sewages water
Veselý, Václav ; Beňo, Zdeněk (referee) ; Pěček, Jan (advisor)
Bachelor's thesis deals with waste water purification at the stage of pre-inflow of water into the biological waste water treatment plants. It is divided into two parts, a theoretical and calculation. The theoretical part deals about sewage water and the method of biological treatment. Design proposal is part of the activation tank for quantity EO.
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Analysis of fracture of quasibrittle materials using numerical modelling and acoustic/electromagnetic emission
Vodák, Ondřej ; Vořechovský, Miroslav (referee) ; Veselý, Václav (advisor)
This master thesis gives overview of non-destructive tests of concrete and provides detailed information concerning the acoustic and electromagnetic emission during monitoring of concrete failure. Conducted loading tests of plain concrete specimens are described in the thesis together with the performed numerical simulations of these tests in the software ATENA. The simulation results of concrete failure are analysed in detail and compared with the experimental results recording failure processes with the help of acoustic and electromagnetic emission. The majority of simulation results in software ATENA 3D show good agreement with the recorded data.
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Initiation of stable crack propagation of selected building composites
Majtánová, Romana Viktória ; Veselý, Václav (referee) ; Keršner, Zbyněk (advisor)
The purpose of my bachelor’s thesis is study of the effects of fibres in normal-weight concrete and light-weight concrete. Specimens were prepared from concrete with polypropylene fibres FORTA FERRO of three different lengths – 19, 38 and 54 mm – and also reference concrete (without fibres) was prepared. This thesis contains gradual evaluation of fracture tests on specimens from mentioned materials. The used fracture test was a three–point bending fracture test on beams with a central notch. From the measured load–deflection in the middle of span and load–crack mouth opening displacement diagrams were determined values of modulus of elasticity, unstable fracture toughness, initiation part of fracture toughness and also load level for beginning of stable crack propagation composites. For determination was used „double–K“ fracture model. For illustration is described evaluation using the effective crack model.
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Analysis of stress state and failure in test specimens used for determination of fracture-mechanical parameters of quasi-brittle materials
Holušová, Táňa ; Seitl,, Stanislav (referee) ; Veselý, Václav (advisor)
The thesis is focused on a test on determination of the fracture-mechanical parameters of quasi-brittle materials, especially concrete. What is referred to as the wedge-splitting test is considered, for which a variety of shapes of notched specimen can be used. This work is exclusively focused on the cylinder-shaped specimen of diameter 150 mm and breadth of 100 mm. The test is performed virtually using Atena 2D FEM software. Progress of failure is observed during loading of the specimen for various notch lengths. The amount of energy released for the development the failure outside of the tested cross-sectional area (weakened by the notch) is quantified and the size of the fracture process zone is investigated. The described analysis is performed for several material sets witch differ in cohesive properties of the quasi-brittle material expressed via the so-called characteristic length. Suitable proportions of the test specimen are sought, in order to avoid the failure and thus also the energy dissipation outside of the specimen ligament area during the experimental tests, which shall lead to more accurate estimates of fracture-mechanical parameters of the tested material.
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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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Bidirectional pneumatic stepper motor
Veselý, Václav ; Pavlík, Jan (referee) ; Kolíbal, Zdeněk (advisor)
The diploma thesis Bidirectional pneumatic stepper motor concentrates on a step shaft rotation in the presented scheme of a kinematic mechanism. The introductory research part of the diploma thesis lists various types of pneumatic components and the analysis of elements in pneumatic circuits is provided. The following section of the thesis concentrates on designing a new scheme of a pneumatic stepper and construction of a functional mock-up. The final part of the diploma thesis offers a summary and final evaluation of the design and offers subsequent alterations for its further usage.
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Design of highway tunnel Polana
Kaderka, Jan ; Ebermann,, Tomáš (referee) ; Veselý, Václav (advisor)
The subject topic of this thesis is to establish a suitable technique of tunnel construction using New Austrian Tunnelling Method with the help of mathematical modeling. Based on the mathematical modelling output the dimensioning primary moulding model was executed.
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Fracture process zone and energy dissipation during fracture of quassi-brittle materials
Klon, Jiří ; Seitl, Stanislav (referee) ; Veselý, Václav (advisor)
The work is focused on the comparison of selected fracture properties of quasi-brittle materials, particularly concrete, determined from results from tests on specimens of different sizes and notch lengths. The first part deals with the study of selected plasticity (failure) criteria and their testing within the mathematical package (MathCAD) for their later intended implementation in a program for estimation of the size and shape of the fracture process zone. Next part is devoted to numerical simulations of three-point bending test of notched beams. These simulations were performed using the ATENA FEM software. Results of the simulations are evaluated using fracture models; this thesis presents values of fracture parameters quantifying the amount of energy dissipated in the fracture process zone.
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