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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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Simulation of ultrasonic wave in the composite aircraft structures
Cimrhanzl, Jan ; Koštial, Rostislav (referee) ; Šplíchal, Jan (advisor)
V této diplomové práci jsou popsané SHM metody používané v letectví a dále jsou udělány MKP simulace šíření ultrazvoukových vln v celokompozitním tenkostěnném materiálu používaném u leteckých konstrukcí. Pro simulaci byla zvolena SHM metoda nazývaná pitch-catch. Simulace byla provedena na dvou různých kompozitových materiálech a každý z nich byl testován třemí různými konfiguracemi s trhlinou a jednou konfigurací bez trhliny. Jako prepocessor byl použit MSC.Patran a jako post processory byli použity MSC.Nastran a MSC.Dytran, jejichž výsledky byli na závěr porovnány. Simulace prokázali, že rychlost šíření a amplituda vln šířících se v simulovaném panelu je trhlinami ovlivněna. Při konfiguracích s trhlinami rychlost šíření i amplituda vln byli menší, než v případě bez trhliny. Jako vhodnější post processor při MKP simulacích se ukázal MSC.Nastran, jehož výsledky byli přesnější a zárověň bylo i snažší správně odečítat hodnoty dat z grafů pro podrobnější pozorování šíření vln.
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Influence of thermal shocks on fatigue of pressure equipment components
Umlauf, Martin ; Vincour, Dušan (referee) ; Létal, Tomáš (advisor)
This thesis examines influence of thermal shock on fatigue of pressure equipment components. The paper relates to project of IMI CCI Brno, which is a leading manufacturer of valves for the energy and process industries. Analysis concerns the impact of thermal shock concentrating on high pressure part of the steam valve. And proposal for a new valve geometry that reduces machining operations and reduce financial costs of production. First part of the thesis presents a basic review of fatigue damage components concerning mechanical loading and thermal – mechanical loading. Second part of the study creates FEM model of the valve. FEM model simulate temperature field and stress during thermal shock. Influence of thermal shock to fatigue damage was computed on basis of stress tensor obtained from FEM simulation under Chapter 18 of the standard EN 13445-3. Existing valve geometry was verified and the new geometry was proposed that simplified and reduce financial costs of production.
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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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Simulation of ultrasonic wave in the composite aircraft structures
Cimrhanzl, Jan ; Koštial, Rostislav (referee) ; Šplíchal, Jan (advisor)
V této diplomové práci jsou popsané SHM metody používané v letectví a dále jsou udělány MKP simulace šíření ultrazvoukových vln v celokompozitním tenkostěnném materiálu používaném u leteckých konstrukcí. Pro simulaci byla zvolena SHM metoda nazývaná pitch-catch. Simulace byla provedena na dvou různých kompozitových materiálech a každý z nich byl testován třemí různými konfiguracemi s trhlinou a jednou konfigurací bez trhliny. Jako prepocessor byl použit MSC.Patran a jako post processory byli použity MSC.Nastran a MSC.Dytran, jejichž výsledky byli na závěr porovnány. Simulace prokázali, že rychlost šíření a amplituda vln šířících se v simulovaném panelu je trhlinami ovlivněna. Při konfiguracích s trhlinami rychlost šíření i amplituda vln byli menší, než v případě bez trhliny. Jako vhodnější post processor při MKP simulacích se ukázal MSC.Nastran, jehož výsledky byli přesnější a zárověň bylo i snažší správně odečítat hodnoty dat z grafů pro podrobnější pozorování šíření vln.
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Influence of thermal shocks on fatigue of pressure equipment components
Umlauf, Martin ; Vincour, Dušan (referee) ; Létal, Tomáš (advisor)
This thesis examines influence of thermal shock on fatigue of pressure equipment components. The paper relates to project of IMI CCI Brno, which is a leading manufacturer of valves for the energy and process industries. Analysis concerns the impact of thermal shock concentrating on high pressure part of the steam valve. And proposal for a new valve geometry that reduces machining operations and reduce financial costs of production. First part of the thesis presents a basic review of fatigue damage components concerning mechanical loading and thermal – mechanical loading. Second part of the study creates FEM model of the valve. FEM model simulate temperature field and stress during thermal shock. Influence of thermal shock to fatigue damage was computed on basis of stress tensor obtained from FEM simulation under Chapter 18 of the standard EN 13445-3. Existing valve geometry was verified and the new geometry was proposed that simplified and reduce financial costs of production.
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The Simulation of impact test on R7T steel
Severa, Martin
Charpy impact is dynamic experiment that we detect material behaviour under high loading rates. Charpy impact test is used as method for brittle farcture characterization. In this work material model based on Johnson – Cook equations was used for prediction of the dynamic behaviour of the experimental material. Comparison of numerical solution and data obtained in experimental test is presented.
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Piezokeramický generátor pro syntetizovaný proud
Dančová, P. ; Vít, T. ; Trávníček, Zdeněk
Synthetic jets are jets of fluid which are generated by periodic pulzations of fluid. The pulsation generator can work on principle of loudspeaker, piston, pieocrystal or the other equipment. In our experiments, the actuator works on piezoceramic transducer (PTC). The paper shows results of vibrometry principle and results of FEM simulations.
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