Number of found documents: 971
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HYDROGEN ABSORPTION IN A-Co30Fe55B15
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2016 - English
Hydrogen solved in amorphous alloys (AAs) influences their magnetic characteristics. AAs are also perspective\nas additives that can improve hydrogen storage kinetic in certain types of ball-milled hydrogen storage\nmaterials (HSMs). Therefore, knowledge of hydrogen solubility and hydrogen sorption kinetics in AAs are of a\ngreat importance for aimed design both AAs with optimal magnetic parameters and HSMs with desired sorption\ncharacteristics. In the present paper, amorphous alloy Co30Fe55B15 (an example of the type a-TM1xTM2y Bz ;\nTM - transition metal) was investigated. Hydrogen concentration c H was measured by Sieverts method in\ntemperature interval from T = 150 °C to T = 350 °C under hydrogen pressure p up to 6 MPa. It was found that\nc H was an increasing function of p and its maximum value was typically 0.5 wt.% H2 at 350 °C and 6 MPa.\nHowever, when the alloy was preliminary hydrogen charged (PHC), the pressure dependence of total c Htot in\nthe first absorption cycle(s) is non-monotonous in dependence on PHC conditions. For the sake of comparison,\nthe same absorption characteristics were measured also in Mg2Ni intermetallic that is a common constituent\nin Mg-based HSMs. Comparing Co30Fe55B15 and Mg2Ni, it was concluded that Co30Fe55B15 shows lower\nhydrogen solubility, but much better absorption kinetics. Keywords: absorption, Co 30 Fe 55 B 15; Hydrogen; Co30Fe55B15 Available at various institutes of the ASCR
HYDROGEN ABSORPTION IN A-Co30Fe55B15

Hydrogen solved in amorphous alloys (AAs) influences their magnetic characteristics. AAs are also perspective\nas additives that can improve hydrogen storage kinetic in certain types of ball-milled ...

Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
Ústav fyziky materiálů, 2016

INFLUENCE OF LASER CUTTING AND PUNCHING ON MAGNETIC PROPERTIES\nOF ELECTRICAL STEEL M470-50A
Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrůšek, Č.; Schneeweiss, Oldřich
2016 - English
Electrical steel M470-50A belongs to the most often used materials in electrical machines. Due to this fact, it is desirable to know the magnetic parameters after processing raw sheets into the required shape. Basic parameters of mechanical, electrical, and magnetic properties of the sheets are usually obtained from the producer but the magnetic properties are changing in dependence on additional machining processes. The aim of this study is to describe changes in parameters of magnetic behavior after punching, laser and spark cutting of the original sheets. The basic information of structure was obtained by optical and scanning electron microscopy. The magnetic parameters were acquired from the measuring of magnetic hysteresis loops in dependence on saturation fields and frequencies. The results are discussed from the point of view of applied\ncutting technology with the aim to obtain the best magnetic parameters and consequently a higher efficiency of the final product. Results can be used as input parameters in simulation of the electrical machine. Keywords: magnetic properties; M470-50A steel; laser cutting; punching; spark cutting Available at various institutes of the ASCR
INFLUENCE OF LASER CUTTING AND PUNCHING ON MAGNETIC PROPERTIES\nOF ELECTRICAL STEEL M470-50A

Electrical steel M470-50A belongs to the most often used materials in electrical machines. Due to this fact, it is desirable to know the magnetic parameters after processing raw sheets into the ...

Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrůšek, Č.; Schneeweiss, Oldřich
Ústav fyziky materiálů, 2016

HYDROGENATION PROPERTIES OF BALL-MILLED Mg-Ti-C-Zr COMPOSITE
Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
2016 - English
The hydrogen storage properties of ball-milled Mg-Ti-Zr-C composite (1.8 wt.% Ti, 1.9 wt.% Zr and 0.2 wt.% C) were investigated. It has been previously shown, that the addition of Ti, Zr and C improved its storage properties. This beneficial effect of additives upon hydrogen storage properties can be explained by catalysis by the particles rich in Ti or Zr located on the surface of Mg grains. They provide effective pathways for the hydrogen diffusion into the MgH2. The morphological and microstructural characteristics were investigated by scanning electron microscopy and by X-ray diffraction. The hydrogen sorption was measured by Sieverts method using Setaram PCT-Pro device. In this paper, sorption behaviour of the composite after ball-milling and after aging on the air was compared. The ball-milled composite adsorbed 3.5 wt.% H2 within 10 min at 623 K. However, hydrogen storage capacity of the composite aged on the air for 7 months remarkably decreased: The aged composite adsorbed within 10 min only 2 wt.% H2 at 623 K and the sorption capacity decreased from 4.7 wt.% H2 to 2.1 wt.% H2. Keywords: hydrides; hydrogen storage; Mg-alloys Available at various institutes of the ASCR
HYDROGENATION PROPERTIES OF BALL-MILLED Mg-Ti-C-Zr COMPOSITE

The hydrogen storage properties of ball-milled Mg-Ti-Zr-C composite (1.8 wt.% Ti, 1.9 wt.% Zr and 0.2 wt.% C) were investigated. It has been previously shown, that the addition of Ti, Zr and C ...

Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
Ústav fyziky materiálů, 2016

Ab initio study of {101-2} twinning transition in magnesium
Káňa, Tomáš; Ostapovets, Andriy
2016 - English
Twinning is an important deformation mode in materials with the hexagonal close-packed (hcp) structures. The shear deformation combined with shuffling of atomic planes can lead to a transition between the Mg hcp structure and a twinned hcp structure. Studying such a transition by means of ab initio methods should bring more insight into the twinning mechanism in magnesium where the {1012} planes are the twinning planes. Comparison of ab initio results with those obtained using the semi-empirical embedded atom method is provided. It can help improve the fitted parameters of the embedded atom method. Keywords: Ab initio; Magnesium; Shear deformation Available at various institutes of the ASCR
Ab initio study of {101-2} twinning transition in magnesium

Twinning is an important deformation mode in materials with the hexagonal close-packed (hcp) structures. The shear deformation combined with shuffling of atomic planes can lead to a transition between ...

Káňa, Tomáš; Ostapovets, Andriy
Ústav fyziky materiálů, 2016

NUMERICAL SUPPORT FOR SPECIMEN LOADED BY BENDING AND WEDGE SPLITTING FORCES FOR MEASUREMENT OF CONCRETE PROPERTIES
Seitl, Stanislav; Liedo, R.; Holušová, T.
2016 - English
Fracture mechanical properties of silicate based materials are performed from various fracture mechanicals tests. For evaluation of parameters, the knowledge about calibration and compliance function is so important. Therefore, in contribution the compliance and calibration curves for a novel test based on combination wedge splitting test (WST) and three-point bend test (3PBT) are introduced. These selected variants exhibit significantly various stress state conditions at the crack tip, or, more generally, in the whole specimen ligament. Keywords: Stress intensity factor; T-stress, constraint; wedge splitting test; three-point bend test; compliance function; COD Available at various institutes of the ASCR
NUMERICAL SUPPORT FOR SPECIMEN LOADED BY BENDING AND WEDGE SPLITTING FORCES FOR MEASUREMENT OF CONCRETE PROPERTIES

Fracture mechanical properties of silicate based materials are performed from various fracture mechanicals tests. For evaluation of parameters, the knowledge about calibration and compliance function ...

Seitl, Stanislav; Liedo, R.; Holušová, T.
Ústav fyziky materiálů, 2016

Stress relaxation in partially pyrolysed SiOC materials
Halasová, Martina; Chlup, Zdeněk; Černý, Martin; Strachota, Adam; Dlouhý, Ivo
2015 - English
This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was not possible to evaluate it in the whole range of experimental temperatures. As experimental materials were used two types of commercialy available polysiloxane resins, pyrolysed in range from 400 to 1000°C. Keywords: polysiloxane; resin; SiOC; glass; ceramics; Vickers hardness; 3D reconstruction; indent Available at various institutes of the ASCR
Stress relaxation in partially pyrolysed SiOC materials

This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was ...

Halasová, Martina; Chlup, Zdeněk; Černý, Martin; Strachota, Adam; Dlouhý, Ivo
Ústav fyziky materiálů, 2015

Determination of mechanical properties of light alloys and composites by means of Small Punch Testing
Bártková, Denisa; Langer, J.; Dymáček, Petr; Válka, L.
2015 - English
Nowadays, in many testing areas a volume of experimental material is limited (laboratory-scaled volume, semidestructive approach). Therefore many testing techniques on miniature samples were devised. Principle of Small Punch Test (SPT) method is a penetration of small puncher through thin disc placed on a ring until the disc bursts. In dependence on loading mode it can provide information comparable to uniaxial tensile tests (UTT) and/or conventional constant load creep tests. However clarification of relations between SPT and conventional methods is difficult and empirical formulas are non-universal. The aim of this study is to i) evaluate mechanical properties of aluminium and magnesium alloys and its composites by means of SPT, ii) compare SPT results with UTT, iii) validate correlation formulas from literature, iv) propose more advanced approach to define correlation between UTT and SPT. Measurement were carried out at constant deflection rate (SPT-CDR) in two different laboratoires. Results from both laboratories were compared to evaluate the reproducibility of the method. Better results agreement was reached for the ultimate strength measurements. Yield strength results exhibited greater variance. An influence of pre-deformation of the sample on yield strength and deflection at maximum force was also identified. We can conclude, that for quantitative estimation of strength parameters we can use correlation formulas based on materials with similar composition and fracture behaviour. Keywords: Small Punch Test; Magnesium Alloys; Aluminium Alloys Thin Disc Available at various institutes of the ASCR
Determination of mechanical properties of light alloys and composites by means of Small Punch Testing

Nowadays, in many testing areas a volume of experimental material is limited (laboratory-scaled volume, semidestructive approach). Therefore many testing techniques on miniature samples were devised. ...

Bártková, Denisa; Langer, J.; Dymáček, Petr; Válka, L.
Ústav fyziky materiálů, 2015

Stress analysis of modified compact tension specimens: K-calibration curves
Seitl, Stanislav; Viszlay, V.
2015 - English
Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, J-R curves etc. [20]. The modified compact tension (MCT) specimen for cement based composites has to be prepared due to negligible concentration around the holes for tenons. An accurate determination of fracture parameters requires the use of a valid calibration curves, there for in this contribution the stress analysis near the crack tip and calibration curve for modified compact tension test are introduced. The calibration curve is introduced for diameter 150 mm (the specimen could be easy made from the specimen for compression test) and includes all theoretical imperfections that results from preparation of the MCT specimens. Keywords: Modified compact tension specimen; stress intensity factor; concrete; FEM Available at various institutes of the ASCR
Stress analysis of modified compact tension specimens: K-calibration curves

Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, ...

Seitl, Stanislav; Viszlay, V.
Ústav fyziky materiálů, 2015

Compressive creep testing of MoSi2-SiC nanocomposites
Luptáková, Natália; Ballóková, B.; Dymáček, Petr
2015 - English
The aim of this study is to investigate the creep resistance of molybdenum disilicide (MoSi2-SiC) based composites with different types of embedded particles. The materials were prepared via powder metallurgy using high temperature controlled reaction sintering (CRS). The creep experiments were performed in uniaxial compression at constant stress in the temperature range from 1273 K (1000 °C) to 1473 K (1200 °C) for applied stress from 50 to 100 MPa. Creep was tested by stepwise loading: in each step, the load was changed to a new value after steady state creep rate had been established. The applied stress dependences of the creep rate at different temperatures were analyzed in terms of stress exponent (n) and activation energy (Q). Possible rate-controlling mechanisms were suggested. Keywords: MoSi2-SiC; creep test; compressive creep; stress exponent; activation energy Available at various institutes of the ASCR
Compressive creep testing of MoSi2-SiC nanocomposites

The aim of this study is to investigate the creep resistance of molybdenum disilicide (MoSi2-SiC) based composites with different types of embedded particles. The materials were prepared via powder ...

Luptáková, Natália; Ballóková, B.; Dymáček, Petr
Ústav fyziky materiálů, 2015

Book of Abstracts: 17th International Conference on the Strength of Materials
Dlouhý, Antonín; Kunz, Ludvík
2015 - English
The Book of Abstracts covers twelve exciting scientific topics addressed by the International Conference on the Strength of Materials 17 (ICSMA 17). Eight excellent plenary speakers were selected based on the discussion and vote within the International Committee of ICSMA. The topics include not only traditional areas like cyclic or high temperature deformation and scale-bridging modeling but also still growing subjects of nano-micro scale experiments and the strength of biological systems. Moreover, the Local Organizing Committee, in cooperation with the Department of Materials Physics, Charles University in Prague, has decided to highlight the 80th anniversary of Prof. Pavel Lukáč, a brilliant international teacher and scientist. The thirteenth topic of the ICSMA 17 is thus dedicated to honour his contribution to materials research. Altogether, the Book presents 376 abstracts evenly distributed among the individual research areas that entered the scope of the conference. Keywords: Materials; Strength; Plasticity; Dislocations Available at various institutes of the ASCR
Book of Abstracts: 17th International Conference on the Strength of Materials

The Book of Abstracts covers twelve exciting scientific topics addressed by the International Conference on the Strength of Materials 17 (ICSMA 17). Eight excellent plenary speakers were selected ...

Dlouhý, Antonín; Kunz, Ludvík
Ústav fyziky materiálů, 2015

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