Number of found documents: 967
Published from to

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

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

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

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

Microstructural Study and Analysis of Hard Zinc
Luptáková, Natália; Pešlová, F.; Stodola, P.; Stodola, J.
2015 - English
The presented work is focused on the character and morphology of the input material for the production of metallic zinc which is used in the production of ZnO through indirect pyrometallurgical processes. The input material is the key parameter in the production of high-quality zinc oxide. For the prediction of a complex production process when problematic situation may occur, the systematic analysis of the input zinc raw materials is needed. Undesirable phases in the feedstock can be identified through profound recognition of the source material and the nature of its microstructure. Chemical composition of zinc metal and zinc additives helps to detect the phases occurring in the matrix. Undesirable phases in the feedstock can form hard and brittle compounds. If these compounds diffuse into the lining during thermal processes, they become the cause of stress in metallurgical ceramics. From the microstructure viewpoint, the heterogeneity of the grain size, various morphology of intermediate phases, their layout, arrangement, etc. can be expected. The results obtained by analysis are used to minimize waste-zinc slag and to eliminate the conditions which enable the formation of the undesired product, thereby increasing the productivity of the zinc oxide production. Moreover, another important knowledge could be used for modernization and effective the process of industrial production of ZnO in practical application in military technologies. Keywords: zinc; zinc oxide; pyrometallurgical process; metallurgy; structural phase; intermediate phase; residual elements Available at various institutes of the ASCR
Microstructural Study and Analysis of Hard Zinc

The presented work is focused on the character and morphology of the input material for the production of metallic zinc which is used in the production of ZnO through indirect pyrometallurgical ...

Luptáková, Natália; Pešlová, F.; Stodola, P.; Stodola, J.
Ústav fyziky materiálů, 2015

The effect of σ-phase formation on long-term durability of SUPER 304H steel
Horváth, J.; Král, Petr; Janovec, J.; Sklenička, Václav
2015 - English
This work presents results of the analysis of phases formed in a SUPER 304H steel during a medium-term static isothermal ageing (675 degrees C/15000 h). The investigations of the precipitates were especially focused on the occurrence of sigma-phase because its formation leads to the serious embrittlement. \nThe evaluation and distribution of brittle sigma-phase were determined on macroscopic level by using light microscopy/colour etching. The microstructure was also investigated on microscopic level by scanning electron microscopes Tescan Lyra 3 and JEOL JSM 5410 equipped by electron backscatter diffraction unit and by transmission electron microscope Jeol 2100F. This work also investigates the effect of sigma-phase formation on the impact strength of an aged state of SUPER 304H steel. For comparison reasons the microstructure and the mechanical properties of the initial as-received) state were also investigated. It was found that the formation of brittle sigma-phase in the aged and therefore degraded microstructure led to the significant decrease of the impact strength. The influence of brittle sigma-phase on long-term durability of the degraded steel regarding its insufficient impact strength is discussed. Keywords: austenitic steel; medium-term ageing; SUPER 304H; sigma-phase; impact strength Available at various institutes of the ASCR
The effect of σ-phase formation on long-term durability of SUPER 304H steel

This work presents results of the analysis of phases formed in a SUPER 304H steel during a medium-term static isothermal ageing (675 degrees C/15000 h). The investigations of the precipitates were ...

Horváth, J.; Král, Petr; Janovec, J.; Sklenička, Václav
Ústav fyziky materiálů, 2015

The Changes in Structure of Steel P91 after Short Annealings
Král, Lubomír; Čermák, Jiří; Král, Petr
2015 - English
Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray spectroscopy (EDS) and electron diffraction in transmission microscopy (TEM). Only Nb-rich particles were found in the studied samples austenitized at 1423 °C for 20h and water cooled. After tempering at 673 °C for 2 h, the formation mainly M3C type carbides and after tempering at 873 °C for 2 h, the formation of M7C3 and M23C6 was observed. These structure changes play an important role for stability and also carbon diffusion. Keywords: P91; carbides; carbon; precipitation Available at various institutes of the ASCR
The Changes in Structure of Steel P91 after Short Annealings

Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray ...

Král, Lubomír; Čermák, Jiří; Král, Petr
Ústav fyziky materiálů, 2015

About project

NRGL provides central access to information on grey literature produced in the Czech Republic in the fields of science, research and education. You can find more information about grey literature and NRGL at service web

Send your suggestions and comments to nusl@techlib.cz

Provider

http://www.techlib.cz

Facebook

Other bases