Number of found documents: 969
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HYDROGEN SORPTION BEHAVIOR OF CHOSEN BINARY MAGNESIUM-CONTAINING INTERMETALLICS
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2018 - 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 ...

Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
Ústav fyziky materiálů, 2018

LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
2018 - 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 ...

Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
Ústav fyziky materiálů, 2018

Characterization of Mo-B-C nanostructured coating microstructure by means of AEM and GDOES
Buršík, Jiří; Svoboda, Milan; Švábenská, Eva; Buršíková, V.; Souček, P.; Zábranský, L.; Vašina, P.
2017 - English
A Mo-B-C nanostructured coating was prepared on WC-Co hard-metal substrate by magnetron sputtering. The details of microstructure of deposited thin layer as well as elements redistribution caused by subsequent annealing at 1000°C were studied by several experimental techniquec. Keywords: coating; nanostructure; analytical electron microscopy Available at various institutes of the ASCR
Characterization of Mo-B-C nanostructured coating microstructure by means of AEM and GDOES

A Mo-B-C nanostructured coating was prepared on WC-Co hard-metal substrate by magnetron sputtering. The details of microstructure of deposited thin layer as well as elements redistribution caused by ...

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

Evaluation of thin discontinuities in planar conducting materials using the diffraction of electromagnetic field
Savin, A.; Nový, F.; Fintová, Stanislava; Steigmann, R.
2017 - English
The current stage of nondestructive evaluation techniques imposes the development of new electromagnetic (EM) methods that are based on high spatial resolution and increased sensitivity. In order to achieve high performance, the work frequencies must be either radifrequencies or microwaves. At these frequencies, at the dielectric/conductor interface, plasmon polaritons can appear, propagating between conductive regions as evanescent waves. In order to use the evanescent wave that can appear even if the slits width is much smaller that the wavwelength of incident EM wave, a sensor with metamaterial (MM) is used. The study of the EM field diffraction against the edge of long thin discontinuity placed under the inspected surface of a conductive plate has been performed using the geometrical optics principles. This type of sensor having the reception coils shielded by a conductive screen with a circular aperture placed in the front of reception coil of emission reception sensor has been developed and 'transported' information for obtaining of magnified image of the conductive structures inspected. This work presents a sensor, using MM conical Swiss roll type that allows the propagation of evanescent waves and the electromagnetic images are magnified. The test method can be successfully applied in a variety of applications of maxim importance such as defect/damage detection in materials used in automotive and aviation technologies. Applying this testing method, spatial resolution can be improved. Keywords: Electromagnetic fields; Electromagnetic wave reflection; Electromagnetic waves; Geometrical optics; Image resolution; Nondestructive examination; Testing Available at various institutes of the ASCR
Evaluation of thin discontinuities in planar conducting materials using the diffraction of electromagnetic field

The current stage of nondestructive evaluation techniques imposes the development of new electromagnetic (EM) methods that are based on high spatial resolution and increased sensitivity. In order to ...

Savin, A.; Nový, F.; Fintová, Stanislava; Steigmann, R.
Ústav fyziky materiálů, 2017

Crack initiation in austenitic stainless steel sanicro 25 subjected to thermomechanical fatigue
Petráš, Roman; Škorík, Viktor; Polák, Jaroslav
2017 - English
Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the specimens. Mechanical response was recorded and fatigue lives were obtained. Scanning electron microscopy combined with FIB technique was used to study the mechanism of crack initiation in in-phase and in out-of-phase thermomechanical cycling. Different mechanisms of the crack initiation were found in these two types of loading. During in-phase loading fatigue cracks start in grain boundaries by cracking of the oxide. Cracks grew preferentially along grain boundaries which resulted in rapid crack initiation and low fatigue life. In out-of-phase loading multiple cracks perpendicular to the stress axis developed only after sufficiently thick oxide layer was formed and cracked in low temperature loading half-cycle. The cracks in oxide allowed localized repeated oxidation and finally also cracking. The cracks grow transgranularly and result in longer fatigue life. Keywords: Damage mechanism; FIB cutting; Localized oxidation-cracking; Sanicro 25 steel; Thermomechanical fatigue Available at various institutes of the ASCR
Crack initiation in austenitic stainless steel sanicro 25 subjected to thermomechanical fatigue

Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the ...

Petráš, Roman; Škorík, Viktor; Polák, Jaroslav
Ústav fyziky materiálů, 2017

Lifetime Assessment of Particulate Ceramic Composite with Residual Stresses
Náhlík, Luboš; Majer, Zdeněk; Štegnerová, Kateřina; Hutař, Pavel
2017 - English
A micro-crack propagation in particulate ceramic based composite was studied using finite element method (FEM). Subcritical crack growth (SCG) was numerically simulated under complex load conditions (mechanical loading and loading by internal residual stresses). The effect of residual stresses on the crack propagation was studied. Two-dimensional computational model of particulate ceramic composite with material properties corresponding to low temperature co-fired ceramics (LTCC) was developed. The results indicate that the presence of residual stresses significantly reduces values of stress intensity factor in the vicinity of composite surface and the direction of residual stresses around the particles contributes to the micro-crack deflection from the particles. The time to failure of the composite under mechanical loading was determined. Results obtained contribute to a better understanding of the role of residual stresses during micro-crack propagation in ceramic particulate composites. Keywords: ceramic particulate composite; sub-critical crack growth; residual stresses Available at various institutes of the ASCR
Lifetime Assessment of Particulate Ceramic Composite with Residual Stresses

A micro-crack propagation in particulate ceramic based composite was studied using finite element method (FEM). Subcritical crack growth (SCG) was numerically simulated under complex load conditions ...

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

Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe
Král, Petr; Sklenička, Václav; Kuchařová, Květa; Svobodová, M.; Kvapilová, Marie; Dvořák, Jiří
2017 - English
The microstructure and creep behaviour of the welded joints of P92 steel pipe were\ninvestigated in order to determine the influence of orbital heat welding technology on the creep\nresistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded\njoints were performed at 873 K using different stresses. The microstructure of tested specimens was\ninvestigated by scanning electron microscope Tescan equipped with an electron-back scatter\ndiffraction. The creep results showed that the creep fracture strain of the welded joints decreases\nwith decreasing value of applied stress. Microstructure investigation showed that fracture behaviour\nof welded joints is influenced by an enhanced cavity formation at grain boundaries in the heataffected\nzone causing lower fracture ductility. Keywords: P92 steel; welding; creep damage; creep fracture; microstructure Available at various institutes of the ASCR
Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe

The microstructure and creep behaviour of the welded joints of P92 steel pipe were\ninvestigated in order to determine the influence of orbital heat welding technology on the creep\nresistance. Creep ...

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

Influence of surface morphology on fatigue behavior of metastable austenitic stainless steel AISI 347 at ambient temperature and 300°C
Smaga, M.; Skorupski, R.; Mayer, P.; Kirsch, B.; Aurich, J. C.; Raid, I.; Seewig, J.; Man, Jiří; Eifler, D.; Beck, T.
2017 - English
The effect of surface modification by cryogenic turning on fatigue behavior of metastable austenitic stainless steel AISI 347 was investigated in stress-controlled fatigue tests at ambient temperature (AT) and 300 °C in air. Five different surface morphologies were manufactured by the variation of turning parameters. Surface and near surface morphology were comprehensively characterized by various experimental techniques. The experimental data on the cyclic deformation behavior, stress-strain response and fatigue life for all surface morphologies are reported. Keywords: metastable austenitic stainless steel; cryogenic turning; fatigue; surface morphology; martensite Available at various institutes of the ASCR
Influence of surface morphology on fatigue behavior of metastable austenitic stainless steel AISI 347 at ambient temperature and 300°C

The effect of surface modification by cryogenic turning on fatigue behavior of metastable austenitic stainless steel AISI 347 was investigated in stress-controlled fatigue tests at ambient temperature ...

Smaga, M.; Skorupski, R.; Mayer, P.; Kirsch, B.; Aurich, J. C.; Raid, I.; Seewig, J.; Man, Jiří; Eifler, D.; Beck, T.
Ústav fyziky materiálů, 2017

Detekce plasticity v tenkých hliníkových vrstvách pomocí bulge testu
Holzer, Jakub; Pikálek, Tomáš; Buchta, Zdeněk; Lazar, Josef; Tinoco, H.A.; Chlupová, Alice; Náhlík, Luboš; Sobota, Jaroslav; Fořt, Tomáš; Kruml, Tomáš
2017 - English
The Bulge test proved to be a useful tool for measuring elastic properties of thin films and\nfree standing membranes, particularly Young’s modulus and residual stress. The basic principle\nof bulge test is application of differential pressure on one side of the a membrane, measurement of\nthe shape of bulged surface as a function of pressure, in this case via laser interferometer, and\nevaluation of a pressure-deflection relationship. In this study, bilayer membrane consisting of a\nsilicon nitride supporting layer and an aluminium layer deposited by means of magnetron\nsputtering is subjected to the bulge test. The results clearly show signs of a non-linear behavior\nthat is caused by plastic deformation in the aluminium layer. Finite element analysis is being\ndeveloped to describe this behavior because analytical model using deflection of central point and\npressure relation falls apart in case of non-linearity. Keywords: Bulge test; thin films; mechanical test Available at various institutes of the ASCR
Detekce plasticity v tenkých hliníkových vrstvách pomocí bulge testu

The Bulge test proved to be a useful tool for measuring elastic properties of thin films and\nfree standing membranes, particularly Young’s modulus and residual stress. The basic principle\nof bulge ...

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

Effect of the load eccentricity on fracture behaviour of cementitious materials subjected to the modified compact tension test
Seitl, Stanislav; Ríos, J. D.; Cifuentes, H.; Veselý, V.
2017 - English
Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or possibly other relevant fracture models. Our contribution is focused on a set of experimental tests which are used to study the fracture behaviour on notched dog-bone-shaped specimens made of cementitious materials. These specimens are subjected to modified compact tension (ModCT) test under a specific range of eccentricity of the tensile load. This type of test generates a stress state in the specimen ligament which combines a direct tension with a defined level of bending due to eccentricity of the tensile load. Several values of relative notch length are also considered. While the crack propagates, a variety of stress states, resulting in variations in the crack-tip stress and deformation constraint, appears in the ligament zone because of the changes in the eccentricity of the applied load, which influences the fracture behaviour of the investigated specimens. The K-calibration, T-stress, CMOD and COD curves for ModCT specimens are introduced and variations of these curves with varying load eccentricity are discussed. Keywords: constraint; fracture; load accentricity Available at various institutes of the ASCR
Effect of the load eccentricity on fracture behaviour of cementitious materials subjected to the modified compact tension test

Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or ...

Seitl, Stanislav; Ríos, J. D.; Cifuentes, H.; Veselý, V.
Ústav fyziky materiálů, 2017

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