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Determination of optimum sintering schedule of oxide ceramics
Průdek, Miloš ; Hadraba, Hynek (referee) ; Maca, Karel (advisor)
The sintering of cubic ZrO2 (stabilized with 8mol% Y2O3) by Single-Step sintering was studied in this bacherol‘s thesis. Two types of commercial powders with different particle size of 80nm and 140nm were used. It was studied whether the grain size of the sample sintered for shorter time at higher density is higher or smaller than after sintering for longer time at lower temperature. It was found taht for cubic zirconia the sintering for a longer time at lower temperature is advantageous from the point of view of decreasing the grain size fo cintered ceramics.
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Bioactive ceramic foams – processing, properties testing and applications
Motyka, Jan ; Hadraba, Hynek (referee) ; Řehořek, Lukáš (advisor)
Porous materials for tissue engineering are novel group of materials. They provide some unique properties, namely bioactivity, biodegradability and osteoconductivity. Ceramics porous structure for bone substitutes have considerable potential for applications in medical surgery. But they have poor mechanical properties. Hence they are used for low bearing applications. Those are the reasons for extensive investigation of these materials, mainly in the last few years. Lots of production procedures exist, which leads to production of foams with various shapes and properties.
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Dynamic Tensile Test – Material Parameters Determination
Sismilich, Vladimír ; Hadraba, Hynek (referee) ; Severa, Martin (advisor)
The purpose of the work is to summarise todays existing methods of testing materials at high strain rates and techniques of evaluation acquired experimental data. There are shown the most important dynamic materials characteristics, by which is able to describe material behaviour at high strain rates. Dynamic tensile test on Eurofer’97 steel at loading rate 1m/s was conducted experimental data were analysed and evaluated. In the evaluation The most important strain and stress properties of this steel were determined.
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Ageing evaluation of the heterogeneous weld joint based on instrumented indentation
Dlouhý, Ivo ; Hadraba, Hynek ; Stodola, M. ; Čupera, Pavel
Hardness measurement analyses are presented in the report being focused on base materials of heterogeneous weld joint and its simulated ageing. The change of the instrumented indentation/hardness data is analysed across the weld joint from low carbon steel to highly alloyed weld metal. Methodology for parameter computing of the material characteristics is also described based on data of instrumented indentation tests. The raw data have been supplied also to be available for further development of the methodology.
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Aging assessment of heterogeneous weld on the basis of instrumented indentation
Dlouhý, Ivo ; Hadraba, Hynek ; Stodola, M. ; Čupera, Pavel ; Al Khaddour, Samer
Sets of data for development of computing procedures of tensile loading curves from indentation curves have been summarised. The data obtained have been supplied also in digital form (tables) representing indentation curves for different loads by ball indentation technique and, in addition, tensile loading curves of the same microstructures obtained at room temperature. The paper focuses interest on the effect of simulated ageing on fracture behaviour of sub weld deposit regions, and, in addition, empirical analyses of indentation curves obtained from the interface between 22K low carbon steel and weld deposit.
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The Gurson-Tvergaard-Needleman model calibration from sub-size test specimens by size corresponding to the half of Charpy specimen
Stratil, Luděk ; Šiška, Filip ; Hadraba, Hynek ; Dlouhý, Ivo
The paper deals with a utilization of miniaturized tensile specimens for purposes of local approach application from limited amount of test material. The motivation for application of those miniaturized specimens is the utilization of volume of test material corresponding to the half of Charpy specimen. The tensile testing of miniaturized specimens was conducted at room temperature in ductile regime of the Eurofer97 steel followed by detailed fractography and quantitative analysis of micromechanism of damage. The parameters of Gurson-Tvergaard-Needleman micromechanical model of ductile fracture were calibrated. Except for the slight differences in strength and deformation characteristics no other differences between two sizes of tensile specimens were found. The calibrated sets of parameters of GTN model using the same element size were very similar. The application of different calibrated sets of GTN model parameters for simulation of damage in cracked specimen (R-curve) is sensitive to the element size and needs its calibration.
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A calibration of Gurson-Tvergaard- Needleman micromechanical model of ductile fracture
Stratil, Luděk ; Hadraba, Hynek ; Šiška, Filip ; Dlouhý, Ivo
Fracture mechanics characteristics of ductile fracture often depend on geometry and size of specimens. A micromechanical modelling of material damage proposes a tool for treatment of geometry and size effects in fracture mechanics. Application of micromechanical model for certain materiál requires a calibration of model‘s parameters. This contribution presents the calibration procedure of Gurson-Tvergaard-Needleman model of ductile fracture for Eurofer97 steel. The identification of ductile damage of the steel and its tensile properties at various level of stress triaxiality by testing smooth and notched bars were determined in the previous study. The calibration procedure was performed by hybrid method as a combination of FEA simulations of tensile tests and fractography analyses. The Gurson-Tvergaard-Needleman model performance is greatly influenced by true stress-true strain curve of the material.
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Study of ductile damage mechanism for Eurofer97 steel
Stratil, Luděk ; Hadraba, Hynek ; Dlouhý, Ivo
The contribution deals with the investigation of ductile damage mechanisms acting in the EUROFER97 steel. For evaluation of material response to various levels of the stress triaxiality the tests on smooth and notched tensile bars were performed. The broken tensile specimens were fractographically and metallographically analyzed and also a quantitative study of mirco-void initiation and nucleation was performed. The more serve conditions of the stress triaxiality in the notched specimens increase the strength characteristics and lower their fracture strain. The nucleation of the voids by decohesion mechanism and gradual void’s growth form substantial part of damage process of the material, finally rapid void coalescence takes place. The higher stress triaxiality promotes growth of voids and on restricts void’s nucleation.
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