No (1019)
Yes (4)
Number of found documents:
1023
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to
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 ...
HYDROGENATION OF CHOSEN MgMXN INTERMETALLICS (X=Al, Ga, In, Si, Sn)
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2017 - English
Hydrogen sorption in chosen intermetallics MgmXn (Mg17Al12 , Mg2Ga, mixture of beta-Mg-In phases, Mg2Si and Mg2Sn) formed by magnesium and elements from the 13 th (X: Al, Ga, In) and 14 th (X: Si, Sn) groups was studied between the room temperature and T = 350 °C. Hydrogen pressure p varied from 10-3 MPa to 6 MPa.\nHydrogen solubility in alpha phase (solid solution of hydrogen in MgmXn before the hydride phase was nucleated) was close to hydrogen solubility in pure Mg. Concentration cH of hydrogen solved in Mg m X n depended linearly on pressure p , dependence of cH on temperature T was relatively weak. MgH2 was the main hydrogen storage phase in all the compounds MgmXn . Nucleation of MgH2 at 350 °C was observed at pressure above approximately 1 MPa in Mg17Al12 and above 2 Ma in other compounds. Maximum values of c H in hydride-containing compounds MgmXn detected at T = 350 °C depended on the stability of MgmXn .
Keywords:
Hydrogen; hydrogen storage; Mg alloys; hydrogen solubility; MgH2
Available at various institutes of the ASCR
HYDROGENATION OF CHOSEN MgMXN INTERMETALLICS (X=Al, Ga, In, Si, Sn)
Hydrogen sorption in chosen intermetallics MgmXn (Mg17Al12 , Mg2Ga, mixture of beta-Mg-In phases, Mg2Si and Mg2Sn) formed by magnesium and elements from the 13 th (X: Al, Ga, In) and 14 th (X: Si, Sn) ...
HYDROGEN SORPTION BEHAVIOR OF CHOSEN BINARY MAGNESIUM-CONTAINING INTERMETALLICS
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2017 - English
Hydrogen absorption in chosen binary Mg-X (X-Al, Ga, In, Si and Sn) intermetallics was studied. These compounds are prospective as additives in other Mg-based hydrogen storage materials. From this point of view it is desirable to know the hydrogen solubility in Mg-X and their resistivity against hydride formation. The present study was carried out at temperatures up to 623 K.
Keywords:
Hydrogen storage; magnesium alloys; Mg-based intermetallics
Available at various institutes of the ASCR
HYDROGEN SORPTION BEHAVIOR OF CHOSEN BINARY MAGNESIUM-CONTAINING INTERMETALLICS
Hydrogen absorption in chosen binary Mg-X (X-Al, Ga, In, Si and Sn) intermetallics was studied. These compounds are prospective as additives in other Mg-based hydrogen storage materials. From this ...
Influence of the Upper Die and of the Indenter Material on the Time to Rupture of Small Punch Creep Tests
Andrés, D.; Dymáček, Petr; Lacalle, R.; Álvarez, J. A.
2017 - English
The Small Punch Creep test has proven to be a suitable technique for assessing the\nproperties of in-service components. It is a reliable, efficient and cost-effective test for predicting\nthe behaviour of the material. The aim of this paper is to analyse the influence of different factors\non the Small Punch Creep (SPC) tests. The influence of the specimen clamping has been studied,\nexperimentally and by means of finite element models on different materials. In the analysed\nconditions, it has been proven that the influence of the upper die on the tests results is generally\nrelatively insignificant, even in the absence of upper die.\nFurthermore, the use of different materials at the punch has also been analysed. In order to achieve\nthis goal, SPC tests have been carried out on two light alloys (AZ31 and AlSi9Cu3) at 473 and\n523K. Three different balls have been employed: ceramic, tungsten-carbide and steel balls. It has\nbeen proven that for the creep ductile alloy (AZ31), there is no apparent effect on the specimen\nresponse. On the other hand, for the creep brittle alloy (AlSi9Cu3), a different trend of the material\nresponse is shown, dependent on the ball used. As a result, there seems to be a significant influence\nof the friction between the punch and the specimen on the tests results, related to the material\nbehaviour.
Keywords:
small punch test; creep; high temperature; light alloys
Available at various institutes of the ASCR
Influence of the Upper Die and of the Indenter Material on the Time to Rupture of Small Punch Creep Tests
The Small Punch Creep test has proven to be a suitable technique for assessing the\nproperties of in-service components. It is a reliable, efficient and cost-effective test for predicting\nthe ...
Fatigue Crack Initiation in Nickel-Based Superalloy MAR-M247 at High Temperature
Šulák, Ivo; Obrtlík, Karel
2017 - English
The present work is focused on the study of crack initiation during low cycle fatigue (LCF) loading of the second generation nickel-based superalloy MAR-M247 treated with hot isostatic pressing. LCF tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 800 °C in air atmosphere. Selected specimens were electrolytically polished to facilitate surface relief observations. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). The microstructure of the material is characterised by coarse dendritic grains with numerous carbides and small casting defects. The average grain size was 2.1 ± 0.3 mm. Fractographic analysis revealed the fatigue crack initiation sites and their relation to the casting defects and material microstructure. Casting defects, carbide inclusions and interdendritic areas were found to be important crack nucleation sites. Specimens’ surface observations revealed the formation of pronounced surface relief with short worm-like markings. Fatigue crack initiation in these places is documented and discussed.
Keywords:
Fatigue crack initiation; Focus ion beam; MAR-M247; Surface relief
Available at various institutes of the ASCR
Fatigue Crack Initiation in Nickel-Based Superalloy MAR-M247 at High Temperature
The present work is focused on the study of crack initiation during low cycle fatigue (LCF) loading of the second generation nickel-based superalloy MAR-M247 treated with hot isostatic pressing. LCF ...
Application of the Williams expansion near a bi-material interface
Malíková, Lucie; Seitl, Stanislav
2017 - English
A simplified model of a crack approaching a bi-material interface is modelled by means of the finite element method in order to investigate the significance of the higher-order terms of the Williams expansion for the proper approximation of the opening crack-tip stress near the bi-material interface. The discussion on results is presented and the importance of the higher-order terms proved.
Keywords:
Bi - material interface; Crack - tip stress distribution; Finite elements; Over - deterministic methods; Williams expansion
Available at various institutes of the ASCR
Application of the Williams expansion near a bi-material interface
A simplified model of a crack approaching a bi-material interface is modelled by means of the finite element method in order to investigate the significance of the higher-order terms of the Williams ...
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 ...
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. ...
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 ...
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 ...
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