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Microstructure and hardness of TiB2
Halasová, Martina ; Bača, L. ; Šajgalík, P. ; Chlup, Zdeněk ; Dlouhý, Ivo
MICROSTRUCTURE AND HARDNESS OF TIB2 TiB2 in its pure form is extremely hard material with high melting point. This behaviour predetermines it to be used as e.g. nozzles, armour or wear parts. It is also very brittle and the effort is to decrease brittleness trough addition of various dopants. This contribution deals with the TiB2 dopped with Ta and Ni in various ratio. For observing the microstructure was used SEM and Vickers hardness was calculated by measuring the diagonals of indents. For comparison the values obtained by machine were shown in graph, too.
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Qantum-mechanical study of structural stability of Ni4N allotropes
Hemzalová, P. ; Friák, Martin ; Šob, Mojmír ; Neugebauer, J.
Parameter-free density functional theory (DFT) calculations of Ni4N in eight crystallographic phases were performed using the pseudopotential approach implemented in the VASP code; the exchange-correlation energy was evaluated within the generalized gradient approximation (GGA). In agreement with experiments, the cubic structure with Pearson symbol cP5, space group Pm-3m (221), has been found to be the most stable. It is also the only thermodynamically stable structure at T=0 K with respect to decomposition into elemental Ni crystal and N2 gas phase. We determine structural, thermodynamic, electronic, magnetic and elastic properties of all eight Ni4N allotropes studied. The thermodynamic stability and bulk modulus is found to be anti-correlated. For the cubic allotropes, we predict a complete set of single-crystalline elastic constants, directional dependence of the single-crystalline Young modulus and homogenized polycrystalline elastic moduli.
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Study of Influence of Segregated Impurities on Magnetism of Grain Boundaries and Free Surfaces in FCC Nickel and Cobalt
Všianská, Monika ; Vémolová, H. ; Šob, Mojmír
We present an ab initio study of segregation of 12 nonmagnetic sp impurities (Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb and Te) at the Sigma5(210) grain boundary (GB) and (210) free surface (FS) in ferromagnetic fcc nickel and cobalt. We analyze their effect on structure, magnetic and mechanical properties. We determine the preferred segregation sites of the impurity atoms, their segregation enthalpies and strengthening/embrittling energies with their decomposition into the chemical and mechanical components. In this contribution, we focused on the influence of segregated impurities on the magnetic moments of neighbouring atoms, the changes in the density of states and why the magnetically dead layers may be present in nickel but not in the cobalt.
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Push Out Test: Numerical Study of the Influence of Concrete Part Width on Load Test
Holušová, Táňa ; Klusák, Jan ; Seitl, Stanislav
The concrete and steel are often performed by mechanical connectors, which are resistant against shear load. These connectors can be subjected to adverse effect, which is high concentration level of tension in connectors or their tendency to corrosion. By using bonded joint such as an epoxy layer gritted by granulates it is possible to avoid these negative effects. The aim of the contribution is to show the influence of the various concrete block widths on values of the maximum load. The modelling was performed by 2D software ATENA (Červenka Consulting)
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Influence of residual stresses in ceramic laminates on the crack propagation
Máša, Bohuslav ; Zouhar, Michal ; Náhlík, Luboš
Příspěvek je zaměřen na lomové chování vrstevnatých keramických kompozitů – Al2O3/ZrO2. Byly uvažovány rozdílné tloušťky vrstev. Reziduální napětí získané v průběhu slinovacího procesu bylo zjištěno a předepsáno v modelech. Byly předpokládány podmínky k nasazení lineární elastické lomové mechaniky. Složky napětí a přetvoření v blízkosti kořene trhliny byly získány numerickým modelováním metodou konečných prvků implementovanou v komerčním software Ansys. K určení součinitele intenzity napětí byly použity analytické vztahy. Článek může přispět k lepšímu porozumění propagace trhliny mezi jednotlivými vrstvami.
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Study of ductile damage mechanism for Eurofer97 steel
Stratil, Luděk ; Hadraba, Hynek ; Dlouhý, Ivo
The contribution deals with the investigation of ductile damage mechanisms acting in the EUROFER97 steel. For evaluation of material response to various levels of the stress triaxiality the tests on smooth and notched tensile bars were performed. The broken tensile specimens were fractographically and metallographically analyzed and also a quantitative study of mirco-void initiation and nucleation was performed. The more serve conditions of the stress triaxiality in the notched specimens increase the strength characteristics and lower their fracture strain. The nucleation of the voids by decohesion mechanism and gradual void’s growth form substantial part of damage process of the material, finally rapid void coalescence takes place. The higher stress triaxiality promotes growth of voids and on restricts void’s nucleation.
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