Number of found documents: 997
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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 ...

Malíková, Lucie; Seitl, Stanislav
Ústav fyziky materiálů, 2017

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 ...

Vyhlídal, M.; Šimonová, H.; Veselý, V.; Keršner, Z.; Klusák, Jan; Malíková, Lucie
Ústav fyziky materiálů, 2017

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 ...

Seitl, Stanislav; Miarka, Petr; Kala, Z.; Klusák, Jan
Ústav fyziky materiálů, 2017

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 ...

Horník, V.; Šmíd, Miroslav; Hutař, Pavel; Kunz, Ludvík; Hrbáček, K.
Ústav fyziky materiálů, 2017

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 ...

Sakurai, K.; Hasegawa, M.; Dlouhý, Ivo
Ústav fyziky materiálů, 2017

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 ...

Holzer, Jakub; Pikálek, Tomáš; Buchta, Zdeněk; Lazar, Josef; Tinoco, H.A.; Chlupová, Alice; Kruml, Tomáš
Ústav fyziky materiálů, 2017

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 ...

Krepl, Ondřej; Klusák, Jan
Ústav fyziky materiálů, 2017

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 ...

Dymáček, Petr; Dobeš, Ferdinand; Kloc, Luboš
Ústav fyziky materiálů, 2017

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 ...

Pokorný, Pavel; Hutař, Pavel; Náhlík, Luboš
Ústav fyziky materiálů, 2017

3D Model of Crack Propagation in Particulate Ceramic Composite Containing Residual Stresses
Štegnerová, Kateřina; Majer, Zdeněk; Hutař, Pavel; Náhlík, Luboš
2017 - English
A crack propagation and fracture behaviour of particulate ceramic composite were investigated. Influence of 3D shape of particles on the crack propagation was studied together with influence of the presence of residual stresses, which are developed inside the composite during manufacturing process. Finite element (FE) method was used for numerical simulation of propagating crack in the composite. Basic numerical models of low-temperature co-fired ceramics (LTCC) with alumina particles homogenously dispersed in the glass matrix were developed. Volume fraction of alumina phase was 20vol.%, which is typical amount for LTCC. The results show that existence of residual stresses retards the crack propagating under conditions of sub-critical crack growth (SCG). Presented results contribute to a better understanding of the role of residual stresses in particulate ceramic composites. Keywords: ceramic particulate composite; sub-critical crack growth; residual stresses Available at various institutes of the ASCR
3D Model of Crack Propagation in Particulate Ceramic Composite Containing Residual Stresses

A crack propagation and fracture behaviour of particulate ceramic composite were investigated. Influence of 3D shape of particles on the crack propagation was studied together with influence of the ...

Štegnerová, Kateřina; Majer, Zdeněk; Hutař, Pavel; Náhlík, Luboš
Ústav fyziky materiálů, 2017

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