Number of found documents: 997
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DISPLACEMENT FIELD ANALYSIS IN WEDGE SPLITTING TEST\nSPECIMEN BY ODM METHOD
Seitl, S.; Miarka, P.; Růžička, V.; Malíková, Lucie; Merta, I.
2018 - English
Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked\nstructures/specimens are investigated. The reason is that it has been shown that it can be\nhelpful and bring more accurate results when fracture processes happen in a larger\nregion around the crack tip, what can be typical for material like concrete or other\nmaterials with quasi-brittle behaviour. Various relative crack length configurations have\nbeen chosen in order to investigate the importance of the higher-order terms of the\nWilliams power expansion on the crack-tip stress field distribution in Wedge splitting\ntest specimen. The higher-order terms are calculated by means of the over-deterministic\nmethod from displacements of nodes around the crack tip obtained by a finite element\nanalysis in different radial distances from the crack tip. The effect of the constraint level\nis investigated. Although the third and higher terms of the Williams series are very often\nneglected, their influence on the opening stress values is investigated. Keywords: ODM, WST; WST; constraint; Williams series; FEM; stress intensity factor; displacement Available at various institutes of the ASCR
DISPLACEMENT FIELD ANALYSIS IN WEDGE SPLITTING TEST\nSPECIMEN BY ODM METHOD

Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked\nstructures/specimens are investigated. The reason is that it has been shown that it can be\nhelpful and bring ...

Seitl, S.; Miarka, P.; Růžička, V.; Malíková, Lucie; Merta, I.
Ústav fyziky materiálů, 2018

MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING
Švábenská, Eva; Roupcová, Pavla; Pizúrová, Naděžda; Schneeweiss, Oldřich
2018 - English
Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles taken from some car brake parts by their services. The information on structure and phase composition was obtained by X-Ray Powder Diffraction, Mossbauer Spectroscopy, scanning electron microscopy with EDX and transmission electron microscopy. The results of the wear debris analysis are compared with original brake materials components. Most of recognized particles are based mainly on iron oxides. Wear brake particles are discussed in the relation to the potential risk to the environment and human health. Keywords: Nanoparticles; wear debris; environment Available at various institutes of the ASCR
MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING

Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles ...

Švábenská, Eva; Roupcová, Pavla; Pizúrová, Naděžda; Schneeweiss, Oldřich
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

First-principles study of interface energies in Fe-Al-based superalloy nanocomposites
Miháliková, Ivana; Slávik, Anton; Friák, Martin; Všianská, Monika; Koutná, N.; Holec, David; Šob, Mojmír
2018 - English
Fe-Al-based nanocomposites with a superalloy-type of microstructure constitute a very promising class of materials. They possess a great potential as an alternative to the currently used steel grades in high temperature applications. Intermetallics-containing nanocomposites, such as those with the Fe3Al compound being one of the phases, may open a way towards future automotive and energy-conversion technologies with lower fuel consumption and reduced environmental impact. We employ quantum-mechanical calculations to analyze relations between ordering tendencies of Al atoms in the disordered Fe-18.75at.%Al phase on one hand and thermodynamic, structural and magnetic properties of Fe-Al-based nanocomposites on the other. When comparing supercells modeling disordered Fe-Al phase with different atomic distribution of atoms we find out that the supercell without 1st and 2nd nearest neighbor Al-Al pairs has a lower energy than that mimicking a perfect disorder (a special quasi-random structure, SQS). Further, coherent interfaces with (001), (110) and (1-10) crystallographic orientations between Fe3Al compound and SQS Fe-Al phase have higher energies than those exhibiting atomic distribution without 1st and 2nd nearest neighbor Al-Al pairs. Keywords: Ab initio calculations; Fe-Al based superalloys; Interface energies; Nanocomposites Available at various institutes of the ASCR
First-principles study of interface energies in Fe-Al-based superalloy nanocomposites

Fe-Al-based nanocomposites with a superalloy-type of microstructure constitute a very promising class of materials. They possess a great potential as an alternative to the currently used steel grades ...

Miháliková, Ivana; Slávik, Anton; Friák, Martin; Všianská, Monika; Koutná, N.; Holec, David; Šob, Mojmír
Ústav fyziky materiálů, 2018

Estimation of equilibrium hydrogen pressure - A new method
Čermák, Jiří; Král, Lubomír
2018 - English
A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases where the hydride phase\nis formed by nucleation and growth mechanism. The proposed method saves considerably the experimental\ntime replacing the conventional time consuming measurement of pressure-composition isotherms, the so\ncalled PCT curves. The proposed evaluation procedure is illustrated using hydrogen chemi-sorption at\ntemperatures 623 K, 573 K and 523 K in chosen hydrogen storage alloys Mg-Si-C, Mg-Li-C and Mg-Na-C. Keywords: hydrogen storage; magnesium; new method Available at various institutes of the ASCR
Estimation of equilibrium hydrogen pressure - A new method

A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases ...

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

HYDROGEN STORAGE PROPERTIES OF GRAPHENE OXIDE MATERIALS PREPARED BY DIFFERENT WAYS
Král, Lubomír; Čermák, Jiří; Bytesnikova, Z.
2018 - English
Graphene-based materials show unique properties. These single layered materials consist of 2D structure of carbon atoms, belong to the strongest known materials, that are very mechanically flexible, optically transparent and that are excellent electrical and thermal conductors. Recently, several studies on these types of materials have highlighted the potential of this material for hydrogen storage (HS) and raised new hopes for the development of an effective solid-state HS media. In the present paper, the structure and HS properties of graphene oxide (GO) and chemically reduced graphene oxide (rGO) produced by different procedures were studied. Hydrogen sorption characteristics of GO and rGO were measured using the Sieverts-type gas sorption analyzer PCT-Pro Setaram Instrumentation. The study of HS was carried out at temperature range from 198 K to 423 K under hydrogen pressure from 1x10(-4) to 4 MPa. \n\nFor the HS point of view, the advantage of GO or rGO compared to graphene, is the presence of multiple chemical groups that can be used for introducing modifiers and their superior spreading on the materials surface. The suitably functionalized GO or rGO materials could potentially exhibit outstanding HS properties. Keywords: Graphene oxide; hydrogen storage; adsorption; adsorption Available at various institutes of the ASCR
HYDROGEN STORAGE PROPERTIES OF GRAPHENE OXIDE MATERIALS PREPARED BY DIFFERENT WAYS

Graphene-based materials show unique properties. These single layered materials consist of 2D structure of carbon atoms, belong to the strongest known materials, that are very mechanically flexible, ...

Král, Lubomír; Čermák, Jiří; Bytesnikova, Z.
Ústav fyziky materiálů, 2018

CALIBRATION FUNCTIONS FOR EDGE CRACKS UNDER SELECTED BENDING LOADS.\n\n
Seitl, Stanislav; Miarka, Petr
2018 - English
Fatigue cracks are found during the regular structural inspections. To precisely\ndescribe/suggest of fatigue cracks propagation throughout structure and for designed\nservice life, the knowledge of calibration functions is important. The cracks usually\npropagate from the edge or the surface of the structural element. The theoretical model\nof fatigue crack propagation is based on linear fracture mechanics (Paris law). Steel\nstructural elements are subjected to various bending load (three- and four-point bending,\npure bending etc.). The calibration functions for the edge cracks are calculated for\nvarious load and appropriate polynomial function independent on the distance are\nproposed for 3PB and 4PB load. Keywords: Fracture mechanics; calibration curve; stress intensity factor; Paris-Erdogan Law; edge Available at various institutes of the ASCR
CALIBRATION FUNCTIONS FOR EDGE CRACKS UNDER SELECTED BENDING LOADS.\n\n

Fatigue cracks are found during the regular structural inspections. To precisely\ndescribe/suggest of fatigue cracks propagation throughout structure and for designed\nservice life, the knowledge of ...

Seitl, Stanislav; Miarka, Petr
Ústav fyziky materiálů, 2018

Estimation of mechanical parameters of thin films using finite element analysis
Tinoco Navaro, Hector Andres; Holzer, Jakub; Pikálek, Tomáš; Buchta, Zdeněk; Lazar, Josef; Chlupová, Alice; Kruml, Tomáš; Hutař, Pavel
2018 - English
This study shows a methodology to estimate mechanical parameters of thin films by means of a bulge\ntest and a numerical approach. The methodology is based on the combination of finite element analysis with a\nclassical analytical method. Finite element modelling was conducted for monolayer (Si3N4) membranes of 2x2mm\nwith the aim to approximate both the load-deflection curves experimentally measured and the classical loaddeflection\nanalytical model. Error functions were constructed and minimized to delimit a coupled solution space\nbetween Young’s modulus and Poison’s ratio. In a traditional bulge test analysis only one of the elastic properties\ncan be determined due to that there is not unique solution in the estimations of these parameters. However, both\nelastic parameters were determined through the proposed numerical procedure which compares the deformed\nsurfaces for a specific set of optimal elastic parameters computed. Results shows that the estimated elastic\nproperties agree with corresponding values determined by other methods in the literature Keywords: bulge test; thin film; finite element analysis; elastic properties Available at various institutes of the ASCR
Estimation of mechanical parameters of thin films using finite element analysis

This study shows a methodology to estimate mechanical parameters of thin films by means of a bulge\ntest and a numerical approach. The methodology is based on the combination of finite element ...

Tinoco Navaro, Hector Andres; Holzer, Jakub; Pikálek, Tomáš; Buchta, Zdeněk; Lazar, Josef; Chlupová, Alice; Kruml, Tomáš; Hutař, Pavel
Ústav fyziky materiálů, 2018

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

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