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Complex evaluation of brittleness of selected building composites
Machačová, Denisa ; Veselý, Václav (referee) ; Keršner, Zbyněk (advisor)
Specified topic of the thesis is a multilevel evaluation of brittleness of selected building composites. The work deals with the opinions of fracture parameters of test specimens of lightweight and ordinary concrete. Specimens further differed fibres content in concrete mixtures, their type and length. The work is divided into two parts, theoretical and practical. The theoretical part conceives composite materials and introduction to fracture mechanics. The practical part describes the different steps for fracture-mechanical parameters evaluation using StiCrack and Excel Visual Basic software. The main part of the work is to evaluate the brittleness of different test specimens, taking into account the type of concrete mix and type of fibres.
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Fracture Analysis of Cube- and Cylinder-shaped WST Specimens Made of Cementitious Composites with Various Characteristic Length
Řoutil, L. ; Veselý, V. ; Seitl, Stanislav
The paper is focused on finding reasonable proportions for both cube-shaped and cylinder-shaped silicate-based composite specimens subjected to wedge-splitting tests. The analysis is conducted using finite element method code with an implemented cohesive crack model. The aspect of the material's brittleness, related to the heterogeneity of the material and described by what is termed as the characteristic length of quasi-brittle material, is accented. The results yield some recommendations for the determination of parameters of nonlinear fracture models for cementitious composites by means of wedge splitting tests of laboratory specimens of the two standard shapes.
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Complex evaluation of brittleness of selected building composites
Machačová, Denisa ; Veselý, Václav (referee) ; Keršner, Zbyněk (advisor)
Specified topic of the thesis is a multilevel evaluation of brittleness of selected building composites. The work deals with the opinions of fracture parameters of test specimens of lightweight and ordinary concrete. Specimens further differed fibres content in concrete mixtures, their type and length. The work is divided into two parts, theoretical and practical. The theoretical part conceives composite materials and introduction to fracture mechanics. The practical part describes the different steps for fracture-mechanical parameters evaluation using StiCrack and Excel Visual Basic software. The main part of the work is to evaluate the brittleness of different test specimens, taking into account the type of concrete mix and type of fibres.
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Prediction of Fracture Toughness Transition from Tensile Test Parameters Applying Artificial Neural Networks
Dlouhý, Ivo ; Hadraba, Hynek ; Chlup, Zdeněk ; Kozák, Vladislav ; Šmida, T.
Reference temperature localizing the fracture toughness temperature diagram on temperature axis was predicted based on tensile test data. Regularization artificial neural network (ANN) was adjusted to solve the interrelation of these properties. For analyses, 29 data sets from low-alloy steels were applied. The fracture toughness transition dependence was quantified by means of master curve concept enabling to represent it using one parameter - reference temperature. Different strength and deformation characteristics from standard tensile specimens and notched specimens, instrumented ball indentation test etc. have been applied. A very promising correlation of predicted and experimentally determined values of reference temperature was found.
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Microstructure and impact response of high-chromium ODS steels
Hadraba, Hynek ; Fournier, B. ; Stratil, Luděk ; Dlouhý, Ivo
A new class of ODS steels alloyed by Cr and W is developed as a high temperature structural material for prospective power sources, the fission reactors of IV generation and the fusion reactors. The aim of the work was to investigate the influence of microstructure on the fracture properties of ODS (9-18)Cr-W-Ti-Y2O3 steels. It was found that the increasing in the Cr and W content brought to the steels strength at elevated temperatures and increased upper shelf energy level and shifted transition region towards lower temperatures. The increase in the yttria content led to the decreasing the upper shelf energy and shifted the TDBTT towards higher temperatures. The impact energy of rolled ODS sheet depended strongly on the fracture plane orientation regarding to the rolling direction. The splitting edges profile changed according to the sample orientation and thus the energy portion consumed for the shearing was changed.
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Lomové chování oceli EUROFER´97 po tepelném stárnutí
Hadraba, Hynek ; Dlouhý, Ivo
Eurofer´97 steel is candidate structural material for in-vessel components of proposed fusion reactors. The use of the steel is limited up to a temperature about 550 °C. On the other hand the efficiency enhancement of the fusion reactors to the level suitable for energy production is predetermined by an increase of temperature in reactor. The long term exposition of the steel at high temperatures leads to microstructural changes. The aim of the work was to investigate the influence of short and long term thermal ageing on fracture properties of Eurofer´97 steel. Short term thermal ageing of the steel was simulated by step-cooling treatment and long term thermal ageing was simulated by isothermal annealing treatment at 550 °C/5000 h. No evident changes in impact properties have been registered comparing the properties of the steel in as-received state and in state after step-cooling. Outstanding embrittlement of the thermally aged steel was observed after long term isothermal ageing.
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Lomové chování RAFM oceli Eurofer´97 po tepelném stárnutí
Hadraba, Hynek ; Dlouhý, Ivo
Eurofer´97 steel is candidate structural material for in-vessel components of proposed fusion reactors. The use of the steel is limited up to a temperature about 550 °C. The aim of the work was to investigate the influence of short and long term thermal ageing on fracture properties of Eurofer´97 steel. Short term thermal ageing of the steel was simulated by step-cooling treatment and long term thermal ageing was simulated by isothermal annealing. No evident changes in impact properties have been registered comparing the properties of the steel in as-received state and in state after step-cooling. Outstanding embrittlement of the thermally aged steel was observed after long term isothermal ageing. Risk of grain boundary weakening by phosphorus segregation is very low while the carbide coarsening could led to outstanding embrittlement of the Eurofer´97 steel.
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