Number of found documents: 968
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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

Prediction of the Traction Separation Law of Ceramics Using Iterative Finite Element Modelling
Kozák, Vladislav; Chlup, Zdeněk; Padělek, P.; Dlouhý, Ivo
2017 - English
Specific silicon nitride ceramics, the influence of the grain size and orientation on the bridging mechanisms was found. In ceramic matrix composites, crack-bridging mechanisms can provide substantial toughness enhancement coupled with the same and/or increased strength. The prediction of the crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated. From a number of damage concepts the cohesive models seem to be especially attractive for the practical applications. Within the standard finite element package Abaqus a new finite element has been developed; it is written via the UEL (user’s element) procedure. Its shape can be modified according to the experimental data for the set of ceramics and composites. The element seems to be very stable from the numerical point a view. The shape of the traction separation law for four experimental materials is estimated via the iterative procedure based on the FEM modeling and experimentally determined displacement in indentation experiments, J-R curve is predicted and stability of the bridging law is tested. Keywords: cohesive zone model; Si3N4 composite; finite element user’s procedure Available at various institutes of the ASCR
Prediction of the Traction Separation Law of Ceramics Using Iterative Finite Element Modelling

Specific silicon nitride ceramics, the influence of the grain size and orientation on the bridging mechanisms was found. In ceramic matrix composites, crack-bridging mechanisms can provide substantial ...

Kozák, Vladislav; Chlup, Zdeněk; Padělek, P.; Dlouhý, Ivo
Ústav fyziky materiálů, 2017

LCF behaviour of 301LN steel: coarse-grained vs. UFG-bimodal structure
Man, Jiří; Chlupová, Alice; Kuběna, Ivo; Kruml, Tomáš; Man, O.; Järvenpää, A.; Karjalainen, L. P.; Polák, Jaroslav
2017 - English
Low-cycle fatigue (LCF) behaviour of metastable austenitic 301LN steel with different grain sizes – coarse-grained (14 µm) and UFG (1.4 µm) with a grain bimodality – produced by reversion annealing (RA) was investigated. Symmetrical push-pull LCF tests were conducted on flat sheet specimens at room temperature with constant strain rate of 2×10–3 s–1 and constant total strain amplitude ranging from 0.4% to 0.8%. After completion of fatigue tests a ferritescope was adopted for quantitative assessment of volume fraction of deformation induced martensite (DIM). Microstructural changes, distribution and morphology of DIM in the volume of material were characterized at different scales by colour etching, TEM and EBSD techniques. Experimental data on microstructural changes are confronted with the stress-strain response and with the chemical heterogeneity present in the material. Keywords: low cycle fatigue; 301LN austenitic stainless steel; UFG microstructure; reversion annealing; deformation induced martensite Available at various institutes of the ASCR
LCF behaviour of 301LN steel: coarse-grained vs. UFG-bimodal structure

Low-cycle fatigue (LCF) behaviour of metastable austenitic 301LN steel with different grain sizes – coarse-grained (14 µm) and UFG (1.4 µm) with a grain bimodality – produced by reversion annealing ...

Man, Jiří; Chlupová, Alice; Kuběna, Ivo; Kruml, Tomáš; Man, O.; Järvenpää, A.; Karjalainen, L. P.; Polák, Jaroslav
Ústav fyziky materiálů, 2017

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 ...

Andrés, D.; Dymáček, Petr; Lacalle, R.; Álvarez, J. A.
Ústav fyziky materiálů, 2017

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 ...

Šulák, Ivo; Obrtlík, Karel
Ústav fyziky materiálů, 2017

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

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

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

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