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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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Prediction of Fracture Toughness Temperature Diagram from Tensile Test Parmaeters
Dlouhý, Ivo ; Hadraba, Hynek ; Šmida, T. ; Babjak, J.
Reference temperature of fracture toughness temperature diagram has been predicted based on tensile test data. Neuron analysis was applied to solve these properties correlation. For fracture toughness determination three-point bend specimens have been applied, the reference temperature being calculated applying multi-temperature method. Different strength and deformation properties have been evaluated from standard tensile specimens focusing on data from localised deformation during specimen necking. Totally 29 data sets from low alloy steels have been generated for the analysis. Good correlation of predicted and experimentally determined values has been found. Further analysis with higher number of data sets is needed to increase the accuracy of predicted values and decrease the number of input data.
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Fraktální anisotropie a heterogenita lomových ploch oceli
Strnadel, B. ; Dlouhý, Ivo
The change in the fractal dimension of the fracture surface demonstrates a wavy character and dispersion depending on the microstructural state of the tested steel. The results of the fractal analysis in the crack growth direction and across the entire crack front were used as the basis for a reconstruction of the geometry of the fracture surface. The competing effects of transgranular and intergranular brittle fracture may lead to increased roughness of the fracture surface and its fractal dimension.
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Reference temperature prediction from tensile test parameters
Šmida, T. ; Babjak, J. ; Dlouhý, Ivo
Reference temperature of fracture toughness temperature diagram has been predicted based on tensile test data. Neuron analysis was applied to solve these properties correlation. For fracture toughness determination three-point bend specimens have been applied, the reference temperature being calculated applying multi-temperature method. Different strength and deformation properties have been evaluated from standard tensile specimens focusing on data from localised deformation during specimen necking. Totally 29 data sets from low alloy steels have been generated for the analysis. Good correlation of predicted and experimentally determined values has been found. Further analysis with higher number of data sets is needed to increase the accuracy of predicted values and decrease the number of input data.
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Search of local maximum of function, algorithm "postup06"
Byczanski, Petr
Local maximum of differentiable function is found by sequential change of argument. In the neighbourhood of each proceed point is function approximated with only 2 elements of Taylor expansion. The change of argument is primary bounded by keeping certain level accuracy of approximation.
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Transgranular and intergranular failure competition as a manifestation of steel degradation
Dlouhý, Ivo ; Hadraba, Hynek ; Strnadel, B.
Main purpose of the work was to quantify causes and characteristics that control the intergranular fracture initiation and occurrence of this fracture micromechanism in competition with cleavage one. A CrNi steel of commercial quality and the same steel with increased content of impurity elements, Sn and Sb, was used. Step cooling treatment was applied in order to induce intergranular embrittlement and brittle fracture initiation in both steel melts. For fracture toughness determination standard bend specimen and pre-cracked Charpy type specimens both tested in three point bending were applied. Relation of cleavage fracture stress and critical stress for intergranular failure has been followed showing capability of this parameter for quantification of the transgranular/intergranular fracture. In order to characterise the quantitative morphological differences in fracture surfaces fractal analysis was applied.
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Použití lokálního přístupu při řešení transferability lomově mechanických parametrů
Dlouhý, Ivo ; Hadraba, Hynek ; Jurášek, L.
In some applications the pre-cracked Charpy specimens (PC) can be, after meeting the validity conditions applied for specification of fracture toughness characteristics corresponding to standard specimens. Typically this is the case of pearlitic steel R7T (used for railway wheelset production) with Lüders’ flow and higher strength properties. It has been found that there is a gap in fracture toughness data of PC specimens between the 60 and 90 MPam1/2 due to plastic hinge in net section of PC specimens. The distribution of maximum principal stress ahead of the crack tip in PC specimen loaded into fully plastic regime was found to be identical with that of reference stress-strain field in plane-strain SSY condition. 3D FEM simulations also shown that there is no constraint loss in PC specimens.
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