Number of found documents: 967
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Fatigue damage prediction of short edge crack under various load: Direct Optimized Probabilistic Calculation
Krejsa, M.; Seitl, Stanislav; Brožovský, J.; Lehnert, P.
2017 - English
Fatigue crack propagation depends on a number and value of stress range cycles. This is a time factor in the course of reliability for the entire designed service life. Three sizes are important for the characteristics of the propagation of fatigue cracks - initial size, detectable size and acceptable size. The theoretical model of a fatigue crack progression can be based on a linear elastic fracture mechanics (uses Paris-Erdogan law). Depending on location of an initial crack, the crack may propagate in structural element (e.g. from the edge or from the surface under various load) that could be described by calibration functions. When determining the required degree of reliability, it is possible to specify the time of the first inspection of the construction which will focus on the fatigue damage. Using a conditional probability and Bayesian approach, times for subsequent inspections can be determined based on the results of the previous inspection. For probabilistic modelling of a fatigue crack progression was used the original and a new probabilistic method - the Direct Optimized Probabilistic Calculation ('DOProC'), which uses a purely numerical approach without any simulation techniques or approximation approach based on optimized numerical integration. Compared to conventional simulation techniques is characterized by greater accuracy and efficiency of the computation. Keywords: fatigue; crack propagation; calibration function Available at various institutes of the ASCR
Fatigue damage prediction of short edge crack under various load: Direct Optimized Probabilistic Calculation

Fatigue crack propagation depends on a number and value of stress range cycles. This is a time factor in the course of reliability for the entire designed service life. Three sizes are important for ...

Krejsa, M.; Seitl, Stanislav; Brožovský, J.; Lehnert, P.
Ústav fyziky materiálů, 2017

Effect of alloying and thermal processing on mechanical properties of tial alloys
Chlupová, Alice; Heczko, Milan; Obrtlík, Karel; Beran, Přemysl; Kruml, Tomáš
2017 - English
Two -based TiAl alloys with 7 at.% of Nb, alloyed with 2 at.% Mo and 0.5 at.% C, were studied. A heat treatment leading to very fine lamellar microstructure was applied on both alloys. Microstructure after the heat treatment was described and mechanical properties including fatigue behaviour were measured. The as-received material alloyed with C possesses high strength and very limited ductility, especially at RT. After application of selected heat treatment it becomes even more brittle; therefore, this process could be considered as not appropriate for this alloy. On the contrary, in the case of Mo alloyed material, both strength and ductility are improved by the heat treatment at RT and usual working temperature (~750 °C). Presence of the phase is responsible for this effect. The selected heat treatment thus can be an alternative for this alloy to other thermomechanical treatments as high temperature forging. Keywords: Fatigue; Heat treatment; Lamellar microstructure; Mechanical properties; TiAl alloys Available at various institutes of the ASCR
Effect of alloying and thermal processing on mechanical properties of tial alloys

Two -based TiAl alloys with 7 at.% of Nb, alloyed with 2 at.% Mo and 0.5 at.% C, were studied. A heat treatment leading to very fine lamellar microstructure was applied on both alloys. Microstructure ...

Chlupová, Alice; Heczko, Milan; Obrtlík, Karel; Beran, Přemysl; Kruml, Tomáš
Ústav fyziky materiálů, 2017

Theory-guided design of novel Fe-Al-based superalloys
Friák, Martin; Holec, D.; Jirásková, Yvonna; Palm, M.; Stein, F.; Janičkovič, D.; Pizúrová, Naděžda; Dymáček, Petr; Dobeš, Ferdinand; Šesták, Pavel; Fikar, Jan; Šremr, Jiří; Nechvátal, Luděk; Oweisová, S.; Homola, V.; Titov, Andrii; Slávik, Ondrej; Miháliková, Ivana; Pavlů, Jana; Buršíková, V.; Neugebauer, J.; Boutur, D.; Lapusta, Y.; Šob, Mojmír
2017 - English
Our modern industrialized society increasingly requires new structural materials\nfor high-temperature applications in automotive and energy-producing industrial\nsectors. Iron-aluminides are known to possess excellent oxidation and sulfidation\nresistance as well as sufficient strength at elevated temperatures. New Fe-Al-based\nmaterials will have to meet multiple casting, processing and operational criteria\nincluding high-temperature creep strength, oxidation resistance and room-temperature\nductility. Such desirable combination of materials properties can be achieved in multi-phase\nmulti-component superalloys with a specific type of microstructure (the matrix contains\ncoherent particles of a secondary phase - a superalloy microstructure). In order to design\nnew Fe-Al-based superalloys, we employ a state-ofthe-art theory-guided materials design\nconcept to identify suitable combinations of solutes. Keywords: superalloys; ab initio; materials design; Fe-Al Available at various institutes of the ASCR
Theory-guided design of novel Fe-Al-based superalloys

Our modern industrialized society increasingly requires new structural materials\nfor high-temperature applications in automotive and energy-producing industrial\nsectors. Iron-aluminides are known to ...

Friák, Martin; Holec, D.; Jirásková, Yvonna; Palm, M.; Stein, F.; Janičkovič, D.; Pizúrová, Naděžda; Dymáček, Petr; Dobeš, Ferdinand; Šesták, Pavel; Fikar, Jan; Šremr, Jiří; Nechvátal, Luděk; Oweisová, S.; Homola, V.; Titov, Andrii; Slávik, Ondrej; Miháliková, Ivana; Pavlů, Jana; Buršíková, V.; Neugebauer, J.; Boutur, D.; Lapusta, Y.; Šob, Mojmír
Ústav fyziky materiálů, 2017

Crack Resistance Characterization in TiAl Intermetallics with Enhanced Toughness
Dlouhý, Ivo; Stratil, Luděk; Fukutomi, H.; Hasegawa, M.
2017 - English
The paper is focused on the analysis of the role of lamellar microstructure in fracture performance of model TiAl intermetallic compound. Coarse lamellar colonies and, at the same time, fine lamellar morphology were prepared by compressive deformation at 1553 K (region of stable alpha phase in TiAl equilibrium diagram) followed by controlled cooling to 1473 K (region of alpha+gamma phase) with delay on this temperature and then cooling down. The fracture toughness was evaluated by means of chevron notch technique. In addition, because of enhanced toughness, crack resistance curves were obtained by load - unload technique of pre-racked beams, namely in two directions of crack propagation relative to lamellar structure. Extensive development of shear ligament toughening mechanism was observed in fracture surfaces leading to quite good fracture toughness thanks to the heat treatment applied. Keywords: Titanium aluminides; Intermetallics; Fracture micromechanisms; Shear ligament toughening; Fracture toughness; Crack resistance Available at various institutes of the ASCR
Crack Resistance Characterization in TiAl Intermetallics with Enhanced Toughness

The paper is focused on the analysis of the role of lamellar microstructure in fracture performance of model TiAl intermetallic compound. Coarse lamellar colonies and, at the same time, fine lamellar ...

Dlouhý, Ivo; Stratil, Luděk; Fukutomi, H.; Hasegawa, M.
Ústav fyziky materiálů, 2017

Effect of residual stresses on the fatigue lifetime of railway axle
Hutař, Pavel; Pokorný, Pavel; Poduška, Jan; Fajkoš, R.; Náhlík, Luboš
2017 - English
The operation of railway axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals which should reveal potential fatigue cracks in railway axle. The detection of cracks is of a probabilistic nature, therefore their detection is not ensured in all cases. For the safe operation of trains, an existence of potential initial crack should be considered on the axle surface and residual fatigue lifetime should be conservatively determined for this case. Reliable procedure of residual fatigue lifetime estimation should take into account real axle geometry, material characteristics and loading of the railway axle. This paper shows methodology for determination of residual fatigue lifetime (RFL) based on the fracture mechanics approach, taking into account real spectrum of the loading cycles, existence of press-fitted wheels and surface residual stresses given by the thermo-mechanical surface treatment of the railway axle. It is demonstrated that the effect of the residual stresses is significant and should not be neglected in the numerical estimation of residual fatigue lifetime of the axle. Keywords: Railway axle; residual fatigue lifetime; residual stresses; inspection intervals; numerical simulation Available at various institutes of the ASCR
Effect of residual stresses on the fatigue lifetime of railway axle

The operation of railway axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals ...

Hutař, Pavel; Pokorný, Pavel; Poduška, Jan; Fajkoš, R.; Náhlík, Luboš
Ústav fyziky materiálů, 2017

Method of Threshold Stress Determination for a Local Approach to Cleavage Fracture
Kotrechko, S.; Gryshchenko, V.; Kozák, Vladislav; Dlouhý, Ivo
2017 - English
The contribution is focused on a new methodology description for determination of threshold stress sigma th, as the third parameter in Beremin local approach to cleavage fracture that is using three-parameter Weibull statistics. Nature of the methodology lies in tensile testing of rounded notched specimens at liquid nitrogen temperature and corresponding calculations. Reactor pressure vessel steel was chosen as an example for the illustration. Keywords: Cleavage; Fracture; Local approach; Threshold stress Available at various institutes of the ASCR
Method of Threshold Stress Determination for a Local Approach to Cleavage Fracture

The contribution is focused on a new methodology description for determination of threshold stress sigma th, as the third parameter in Beremin local approach to cleavage fracture that is using ...

Kotrechko, S.; Gryshchenko, V.; Kozák, Vladislav; Dlouhý, Ivo
Ústav fyziky materiálů, 2017

Creep damage tolerance factor lambda of selected creep-resistant steels
Sklenička, Václav; Kuchařová, Květa; Dvořák, Jiří; Kvapilová, Marie; Král, Petr
2017 - English
The creep damage tolerance factor lambda as an important outcome of the continuum damage mechanics approach has been used to asses the creep fracture mode and the susceptibility of material to localized cracking at strain concentrations. In this work, using sets of our earlier published creep data of three advanced ferritic creep-resistant steels (T23 low alloy steel, P91 and P92 chromium steels) are analysed in terms of the creep damage tolerance factor lambda. It was found that the value of the creep damage factor lambda is not constant and depends on the creep loading conditions. The data analysis is followed by fractographic investigations, which is used to identify the creep fracture mode(s) experimentally. Keywords: creep; creep damage tolerance factor lambda; fracture mode; creep fracture plasticity Available at various institutes of the ASCR
Creep damage tolerance factor lambda of selected creep-resistant steels

The creep damage tolerance factor lambda as an important outcome of the continuum damage mechanics approach has been used to asses the creep fracture mode and the susceptibility of material to ...

Sklenička, Václav; Kuchařová, Květa; Dvořák, Jiří; Kvapilová, Marie; Král, Petr
Ústav fyziky materiálů, 2017

Characterization of Ta-B-C nanostructured hard coatings
Buršík, Jiří; Buršíková, V.; Souček, P.; Zábranský, L.; Vašina, P.
2017 - English
Microstructure and mechanical properties of Ta-B-C nanocrystalline layers prepared by magnetron sputtering were studied. DC magnetron sputtering was used to prepare thin layers on rotated substrates. Various deposition parameters were tested. Microstructure of layers was studied by means of scanning and transmission electron microscopy on thin lamellar cross sections prepared using a focussed ion beam. Both undisturbed layers and the volume under relatively large indentation prints (load of 1 N) were observed. The microstructure observations were correlated with mechanical properties characterized by means of nanoindentation experiments in both the static and the dynamic loading regime. Elastic modulus, indentation hardness and fracture resistance of prepared nanostructured coatings were evaluated and discussed. Keywords: coating; nanostructure; analytical electron microscopy Available at various institutes of the ASCR
Characterization of Ta-B-C nanostructured hard coatings

Microstructure and mechanical properties of Ta-B-C nanocrystalline layers prepared by magnetron sputtering were studied. DC magnetron sputtering was used to prepare thin layers on rotated substrates. ...

Buršík, Jiří; Buršíková, V.; Souček, P.; Zábranský, L.; Vašina, P.
Ústav fyziky materiálů, 2017

Subsized Specimens for Fracture Resistance Characterisation Including Transferability Issues
Dlouhý, Ivo; Stratil, Luděk; Šiška, Filip
2017 - English
The contribution is focused on characterization of methods enabling to apply small/subsized specimens for fracture resistance characterization. The applied methods are divided into transition region and upper shelf region. The approaches used in the upper shelf region represent at the same time methods applicable for ductile materials without transition. Relating to subsized samples two basic approaches are applicable: (i) miniaturized samples based on common standard ones and (ii) specific specimens/methods, e.g. small punch test etc. The results described in the paper belong to the first group. For interpretation of data generated under low constraint conditions toughness scaling models and master curve approached are commented. In ductile region, either the sample used generate valid toughness characteristics, or, if not, there is no way how to correct measured data except damage quantification through micromechanical models. Keywords: Fracture toughness; Crack resistance curve; Transferability; Crack tip constraint; Subsized specimen Available at various institutes of the ASCR
Subsized Specimens for Fracture Resistance Characterisation Including Transferability Issues

The contribution is focused on characterization of methods enabling to apply small/subsized specimens for fracture resistance characterization. The applied methods are divided into transition region ...

Dlouhý, Ivo; Stratil, Luděk; Šiška, Filip
Ústav fyziky materiálů, 2017

Fracture-mechanics behaviour of ceramic foam with macroscopic stress concentrator upon the tensile test
Ševeček, O.; Majer, Z.; Bertolla, Luca; Chlup, Zdeněk; Kotoul, M.
2017 - English
The work investigates an influence of the macroscopic stress concentrator inside the ceramic open cell foam structure on the fracture-mechanics response of the foam upon the tensile test. As the concentrator, the central crack/rectangular notch was taken into account. The influence of the crack/notch length and width on the stress concentration ahead the concentrator tip was assessed using the simplified FE beam element based model with irregular cells simulating the real ceramic foam structure. Average principal stresses calculated on set of struts ahead the crack/notch tip were compared with average stresses in the intact structure. It was found that the ratio of these stresses increases linearly with the crack length. The stress concentration ratio is slightly lower in case of thick rectangular notch than in case of a thin crack. Furthermore, the failure load leading to complete fracture of the studied specimens, subjected to the tensile loading, were calculated using the same model. It is shown that the difference factor between the critical fracture force in case of structure without concentrator and with concentrator is very close to the concentration factor calculated from the average stresses on particular struts in the region in front of the concentrator tip.\n Keywords: Fracture-mechanics; ceramic foam; tensile test Available at various institutes of the ASCR
Fracture-mechanics behaviour of ceramic foam with macroscopic stress concentrator upon the tensile test

The work investigates an influence of the macroscopic stress concentrator inside the ceramic open cell foam structure on the fracture-mechanics response of the foam upon the tensile test. As the ...

Ševeček, O.; Majer, Z.; Bertolla, Luca; Chlup, Zdeněk; Kotoul, M.
Ústav fyziky materiálů, 2017

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