|
|
Prediction of static materials properties of P92 steel based on small punch test
Dymáček, Petr ; Ječmínka, M. ; Abendroth, M.
Small punch testing under constant deflection rate of P92 steel at room temperature was performed. The experimental SPT curves were used for prediction of yield and ultimate strength based on empirical formulas published in the literature and also by numerical inverse analysis with help of finite element method. Conventional tensile tests were performed for verification of the data derived from small punch testing. Good agreement was found in the case of ultimate strength. Determination of the yield strength is less accurate mainly due to significantly lower values of force at yield compared to maximum force measured by SPT. Two approaches for evaluation and determination of the force at yield limit in SPT diagram and estimation of the yield strength of the material are described in the article.
|
|
|
Embrittlement of ferritic 14%Cr ODS steel in air and in Pb/Pb-Bi coolants at elevated temperatures
Hadraba, Hynek ; Dlouhý, Ivo ; Hojná, A. ; Di Gabriele, F.
The work was focused to describing influence of long-time high-temperature exposition of the ferritic 14%Cr ODS steel to the liquid Pb and Pb-Bi metals environments. The steel was during exposition in the liquid Pb and Pb-Bi at 600°C and 550°C respectively depleted from Cr and Ti formed with Pb and Bi the surface oxide scale. In addition the isothermal ageing of the steel at 650°C caused precipitates coarsening and porosity development by dislocation annealing in the bulk of the steel. Tensile and impact bend tests reveals outstanding embrittlement of the isothermally aged ODS steel and the steel after exposition to the liquid Pb and Pb-Bi compared with the steel in as-received state.
|
|
|
The Role of Microstructure in Fracture Resistence Control of TiAl Based Intermetallics
Dlouhý, Ivo ; Haga, H. ; Chlup, Zdeněk ; Hadraba, Hynek ; Hasegawa, M. ; Fukutomi, H.
The analysis of the role of microstructure in fracture performance of TiAl intermetalics at room and elevated temperatures has been carried out. For Ti-46Al-0.7Cr-0.1Si-7Nb-0.2Ni alloy different regimes of thermal and thermal-mechanical treatment were applied enabling to control substantially microstructural parameters. Attention was paid to grain (colony) size effect, effect of lamellas thickness and morphology and, in addition, to β-phase effect. For separate treatment regimes the flexural strength and fracture toughness were evaluated in addition to microstructural parameters. Fractographic analysis enabled to evaluate fracture micromechanisms; development of shear ligament toughening was observed in almost all cases. This is the key mechanism controlling the fracture behaviour. Based on findings obtained key aspects of the effect of separate microstructural components have been discussed.
|
|
|
Effect of Microstructure Change on the Crack Formation of Heat Treated Ti-Al Intermetallic Compound
Hasegawa, H. ; Nomura, M. ; Haga, H. ; Dlouhý, Ivo ; Fukutomi, H.
Heat treatments were conducted under several conditions in order to clarify the effect of holding temperature, time and cooling rate on microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si and Ti-45Al-10V (mol%) alloys. Indentation tests were performed in order to understand the effect of beta phase precipitation on crack formation of microstructure controlled Ti-45Al-10V alloy. As for Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si alloy, phase condition on several temperatures was estimated experimentally. It is found that the cooling rate where the massive transformation occurs ranges from -300K/s to -5K/s. Furthermore, in order to obtain the fully lamellar structure, the alloy should be cooled slower than -1K/s. As regards the heat treatment on Ti-45Al-10V alloy, fully lamellar structure was formed by cooling from (alfa+gama) two phase state. However, beta precipitates were observed near the lamellar colony boundaries when the material was cooled from (beta+gama) two phase state. Though the cracks are not observed at the specimen cooled at -8x10-2K/s from (alfa+gama) two phase state, the cracks induced by Vickers indentation are observed in most of the heat treated specimens.
|
|
|
Fractural based microstructural damane evaluation in Ni-based superalloy gas turbine blades
Tarafder, M. ; Dlouhý, Ivo ; Hore, S. ; Das, S. K.
A fractal based evaluation of microstructural damage in Ni based superalloy cast IN 738 LC used in gas turbine blades is presented in the paper. Non-destructive in-situ replica method was used without damaging the blades for the evaluation of microstructure. The theoretical life of the stator blades of the gas turbine, which was exposed to temperature varying between 1060°C to 1100°C, was approximately 100,000 hours. In order to assess the suitability of the stator blades after 50% of the service life, fractal based microstructural damage evaluation has been conducted. The fractal dimensions of the in situ metallographic images can be correlated to the progressive deterioration of hardness at various locations of the blades. The extent of damage is inversely proportional to the fractal dimension. For fractal dimension below 2.4, the material can be classified as substantially damaged.
|
|
| |
|
|
Nonlinear modeling of stable crack growth
Brumek, J. ; Strnadel, B. ; Dlouhý, Ivo
This paper presents numerical study to predict crack growth rate under fatigue loading in a high pressure cylinder wall made of high strength steel. Experimental fatigue crack growth data on three point bending test samples. were applied to simulate and predict crack growth process using detailed three dimensional parametric finite elements models. The fatigue crack propagation was based on linear elastic fracture mechanics and stress intensity factor determination. Finite element model provides results of crack growth analysis optimized for the stress levels of operating pressure level. Results are plotted on a-N. Results were compared with an experimental fatigue test.
|
|
|
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.
|
|
|
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.
|
|
|
MKP studie protlačovacích zkoušek na miniaturních discích při podmínkách konstantního zatížení
Dymáček, Petr
Comparison of results of creep small punch tests (SPT) on miniaturized discs with results of their modeling by means of finite element method (FEM) is presented. Advanced heat resistant chromium steel P91 was selected for the investigations. In the numerical model, the Norton power-law and the exponential relationships were applied. Parameters of both relationships were derived from stress dependences of minimum creep rate obtained from conventional creep tests at 873 K. The FE model included contact elements taking in account the surface friction between all contact surfaces of the test setup. Various material models from elastic&creep to elastic-plastic&creep were applied in the FE model. Obtained results of the numerical analyses were compared with the experimental results. These computational results allow us to better understand the behavior of the specimen at accelerated creep rates and comprehend some of the principally important conditions of the SPT.
|
guest ::
