No (1013)
Yes (4)
Number of found documents:
1017
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LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
2017 - English
The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at elevated temperatures in hostile environments. The microstructure consists mainly of the face centred cubic γ matrix and ordered γ´ strengthening precipitates (L12 crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in a symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambient air. Cyclic stress-strain curves and fatigue life curves in the representation of plastic strain amplitude vs. stress amplitude and stress amplitude vs. the number of cycles to failure, respectively, were plotted and compared with data obtained on Inconel 713LC. Special attention was paid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. 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). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation. Observations in transmission electron microscope (TEM) confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long.
Keywords:
Nickel-based superalloy; cyclic stress-strain curve; Fatigue life; fatigue crack initiation; focus ion beam
Available at various institutes of the ASCR
LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at ...
Effect of rivet holes on calibration curves for edge cracks under various loading types in steel bridge structure
Seitl, Stanislav; Miarka, Petr; Kala, Z.; Klusák, Jan
2017 - English
Attention has been paid to fatigue cracks in steel structures and bridges for a long time. In spite of efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. There is some limitation of crack sizes which are detectable on structure (from 2 up to 10 mm). Note that depending on the location of the initial crack, the crack may dominantly propagate from the edge or from the surface. The theoretical model of fatigue crack progress is based on linear elastic fracture mechanics. Steel specimens are subjected to various load types (tension, three- and four-point bending, pure bending etc.). The calibration functions for short edge cracks that are near the hole for a rivet or bolt are compared for various loads and the discrepancies are discussed.
Keywords:
edge cracks; rivet holes; fracture mechanics; calibration curves
Available at various institutes of the ASCR
Effect of rivet holes on calibration curves for edge cracks under various loading types in steel bridge structure
Attention has been paid to fatigue cracks in steel structures and bridges for a long time. In spite of efforts to eliminate the creation and propagation of fatigue cracks throughout the designed ...
Interaction of Creep and High Cycle Fatigue of IN 713LC Superalloy
Horník, V.; Šmíd, Miroslav; Hutař, Pavel; Kunz, Ludvík; Hrbáček, K.
2017 - English
The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of superalloy structures was un-affected or even slightly increased in the cases with superimposed vibrations. The reason for this behaviour was not well described up to now. Therefore, set of fatigue tests was conducted at high mean stresses level to observe this phenomenon. The mean stress was kept constant while the stress amplitudes were selected in order to measure wide range of conditions from pure creep to pure fatigue. Fractographic analysis by scanning electron microscopy (SEM) was done with the aim to identify governing damage mechanisms for particular test conditions as a preliminary evaluation of conducted tests.
Keywords:
Creep-fatigue interaction; Fractography; High temperature; IN 713LC; Superalloy
Available at various institutes of the ASCR
Interaction of Creep and High Cycle Fatigue of IN 713LC Superalloy
The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of ...
Fracture Toughness of Massively Transformed and Subsequently Heat Treated TiAl Intermetallic Compound
Sakurai, K.; Hasegawa, M.; Dlouhý, Ivo
2017 - English
The effects of massive transformation and subsequent heat treatments on the microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si (mol%) intermetallic compounds are studied. Massive transformation occurs at the center region of the specimen by cooling from alpha single phase state. At the surface side of the specimen, alpha phase has remained. Fine convoluted microstructure with alpha 2, gamma phases and lamellar structure has formed by heating at (alpha + gamma) two phase state after massive transformation. Colony size or grain size is about 25 micrometer. Fine fully lamellar structure is obtained after heat treatment of convoluted microstructure at alpha phase for 60 s. Fracture toughness seems to be increasing with the increase in lamellar colony size. However, some massively transformed specimens show lower toughness due to the formation of microdamage present in samples before the test.
Keywords:
TiAl intermetallic compound; Massive transformation; Fracture toughness
Available at various institutes of the ASCR
Fracture Toughness of Massively Transformed and Subsequently Heat Treated TiAl Intermetallic Compound
The effects of massive transformation and subsequent heat treatments on the microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si (mol%) intermetallic compounds are studied. Massive transformation occurs at ...
Basic features of aggregate-matrix-interface fracture of concrete: pilot modelling
Vyhlídal, M.; Šimonová, H.; Veselý, V.; Keršner, Z.; Klusák, Jan; Malíková, Lucie
2017 - English
In this paper, the attention is paid to investigation of the importance of the Interfacial Transition Zone (ITZ) in concrete for the global fracture behaviour. A simplified cracked geometry (consisting matrix, ITZ and aggregate) is modelled by means of the finite element method with a crack terminating at the matrix-ITZ interface. Numerical studies assuming two various ITZ thicknesses and several various ITZ elastic moduli are performed. Based on the values of the opening stress ahead of the crack tip (its average value and stress range) a few conclusions are discussed. The pilot analyses dealing with the effect of ITZ on the stress distribution should contribute to better description of toughening mechanisms in silicate-based composites.
Keywords:
Fracture behaviour; Interfacial transition zone; Matrix interfaces; Toughening mechanisms; Concrete; Fracture mechanics
Available at various institutes of the ASCR
Basic features of aggregate-matrix-interface fracture of concrete: pilot modelling
In this paper, the attention is paid to investigation of the importance of the Interfacial Transition Zone (ITZ) in concrete for the global fracture behaviour. A simplified cracked geometry ...
Development of the bulge test equipment for measuring mechanical properties of thin films
Holzer, Jakub; Pikálek, Tomáš; Buchta, Zdeněk; Lazar, Josef; Tinoco, H.A.; Chlupová, Alice; Kruml, Tomáš
2017 - English
The bulge test apparatus designed for the measurement of mechanical material properties of thin films was constructed and tested. The principle of the test is to apply pressure on a free-standing membrane, to measure the membrane shape and to analyse the results. Commercially available silicon nitride (Si3N4) thin films were used for the testing. It is shown that interferometric set-up designed and assembled for the apparatus enables precise determination of 3D shape of the whole membrane, which allows more precise determination of materials parameters compared to measurement of the height of the center of the membrane only. Fit of an analytical formula gives values of Young modulus and residual stress with very good agreement with the literature data. Moreover, FEM model of the bulged membrane was developed. The main aim of the effort is to enable measurement of plastic properties of a thin film of interest, that will be deposited on the Si3N4 membrane with known properties and bulge test will be performed on the bilayer specimen. Subsequently, the material properties of the thin film will be obtained using FEM analysis.
Keywords:
thin films; bulge test; mechanical properties
Available at various institutes of the ASCR
Development of the bulge test equipment for measuring mechanical properties of thin films
The bulge test apparatus designed for the measurement of mechanical material properties of thin films was constructed and tested. The principle of the test is to apply pressure on a free-standing ...
CHANGES IN ELECTRICAL STEEL SHEETS INDUCED BY HEAT TREATMENT
Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrušek, C.; Schneeweiss, Oldřich
2017 - English
Surface coating of electrical steel sheets is very important due to minimizing eddy current losses in electrical machines. The quality of coating can differ according to the composition. The coating layer has limited heat stability and after crossing of the guaranteed temperature it can be significantly degraded and its insulation properties may change importantly. The aim of this study is to describe changes in parameters of magnetic behavior of the non-oriented Si electrical steel sheet due to degradation of the coating by annealing in air. The parameters were acquired from the measuring of magnetic hysteresis loops on two types of samples with different excitation. The basic information on structure was obtained by optical microscopy. Acquired data are compared between samples with the damaged coating layer by annealing and the original coating layer. The results are discussed from the point of view of the possibility of using sheets with damaged insulation in electrical machines.
Keywords:
advantages; coatings; Surface coating; magnetic properties; annealing; degradation
Available at various institutes of the ASCR
CHANGES IN ELECTRICAL STEEL SHEETS INDUCED BY HEAT TREATMENT
Surface coating of electrical steel sheets is very important due to minimizing eddy current losses in electrical machines. The quality of coating can differ according to the composition. The coating ...
Multi-parameter based stress distribution in vicinity of sharp material inclusion tip
Krepl, Ondřej; Klusák, Jan
2017 - English
General Singular Stress Concentrators (GSSCs) which exhibit singular stress concentration are often responsible for crack initiation and thus failure of the component. The GSSC of the type of bonded bi-material junction occurs in a variety of technical applications including but not limited to sharp material inclusions, silicate based composites and electronic components. The GSSC cannot be assessed by means of standard fracture mechanics. Approaches of generalized fracture mechanics require precise description of stress distribution near the stress concentration points. In order to determine the stress field accurately, the paper incorporates the multi-parameter based description.
Keywords:
Bi-material junction; General singular stress concentrator; Generalized fracture mechanics; Muskhelishvili plane elasticity; Sharp material inclusion
Available at various institutes of the ASCR
Multi-parameter based stress distribution in vicinity of sharp material inclusion tip
General Singular Stress Concentrators (GSSCs) which exhibit singular stress concentration are often responsible for crack initiation and thus failure of the component. The GSSC of the type of bonded ...
Determination of Mechanical Properties of Metallic Materials from Very Small Volumes by Means of Small Punch Test
Dymáček, Petr; Dobeš, Ferdinand; Kloc, Luboš
2017 - English
The paper summarizes capabilities of the small punch tests on miniature disc specimens\nfrom metallic materials. Results obtained by small punch tests can be correlated with mechanical\nproperties determined by conventional or other miniature tests. Three basic types of small punch test\nsetup: i) static/fracture, ii) creep and iii) stress relaxation are described and the basic quantities that\ncan be obtained are shown. Relations for an assessment of conventional mechanical properties from\nquantities obtained by small punch test are presented.
Keywords:
small punch test; uniaxial test; creep; stress relaxation
Available at various institutes of the ASCR
Determination of Mechanical Properties of Metallic Materials from Very Small Volumes by Means of Small Punch Test
The paper summarizes capabilities of the small punch tests on miniature disc specimens\nfrom metallic materials. Results obtained by small punch tests can be correlated with mechanical\nproperties ...
Influence of Extension of Load Spectrum on Estimation of Residual\nFatigue Lifetime of Railway Axle
Pokorný, Pavel; Hutař, Pavel; Náhlík, Luboš
2017 - English
Railway axles are subjected to cyclic amplitude loading which can lead to fatigue failure.\nFor safe operation of railway axles a damage tolerance approach taking into account a possible\ndefect in railway axle is often required. Because of different operation regimes of trains (fast/slow\nride, ride on straight track, on curved track, over switches etc.) the load amplitude of axle is not\nconstant. The variability of load is defined by a load spectrum, which is determined experimentally\nby measuring of load in service conditions. Even though the load spectrum is measured on several\nhundreds or thousands of operation kilometres, the railway axles are in operation much longer time\n(often tens of years). Therefore, some load amplitudes higher than ones measured in the test can\noccur during a long-term axle service. The contribution presented deals with the effect of extension\nof load spectrum by rare high load amplitudes, which can occur during long-term operation, on\nresidual fatigue lifetime of railway axles.
Keywords:
railway axle; fatigue crack; load spectrum; overload
Available at various institutes of the ASCR
Influence of Extension of Load Spectrum on Estimation of Residual\nFatigue Lifetime of Railway Axle
Railway axles are subjected to cyclic amplitude loading which can lead to fatigue failure.\nFor safe operation of railway axles a damage tolerance approach taking into account a possible\ndefect in ...
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