Number of found documents: 1101
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Optimization of acquisition parameters in radiography and tomography
Vopálenský, Michal; Vavřík, Daniel; Kumpová, Ivana
2017 - English
Contrast in radiographic images is one of the most important parameters both in radiography and tomography. This paper investigates the possibility of adjusting the radiographic parameters, in particular the accelerating voltage of the X-ray tube, in order to maximize the difference in the detected intensity in response to the change in the thickness of the investigated object. Simplified model is used that allows finding the optimal operating point for the given material and thickness without an apriory knowledge about the X-ray spectra, detector response and the material composition. It is shown that in case of small changes of thickness, the optimum is met when the detected intensity behind the object of certain thickness is at approx. 37 % of the full range (i.e., of the value that would be measured under the same conditions in the absence of the object). In spite of simplifications made, the theoretical model shows a very good correspondence with the experimental data. A brief consideration is made on the case of a general difference in thicknesses. Keywords: X-ray computed tomography; X-ray radiography; X-ray optimization; image processing; contrast Fulltext is available at external website.
Optimization of acquisition parameters in radiography and tomography

Contrast in radiographic images is one of the most important parameters both in radiography and tomography. This paper investigates the possibility of adjusting the radiographic parameters, in ...

Vopálenský, Michal; Vavřík, Daniel; Kumpová, Ivana
Ústav teoretické a aplikované mechaniky, 2017

Early stage microstructure development of cement paste modified by crystalline admixture
Hrbek, V.; Petráňová, Veronika; Němeček, J.
2017 - English
This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on reference specimens consisting of pure cement. Samples of pure CA and cement modified by 1% of CA with the same w/c ratio were examined and compared in this paper. By investigation of these materials on the micro-scale, it is possible to identify the development of the microstructure of each and determine the impact of the modification. For this purpose, backscattered electrons microscopy (BSE) with energy-dispersive X-ray spectroscopy (EDX) was used for phase analysis as well as instrumental nano-indentation to obtain micro-mechanical properties. Presented results show the evolution of mechanical properties and microstructure in time and the impact of the crystalline admixture on modified cement. Keywords: cement; crystalline admixture; microstructure; nanoindentation; phase; SEM Available at various institutes of the ASCR
Early stage microstructure development of cement paste modified by crystalline admixture

This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on ...

Hrbek, V.; Petráňová, Veronika; Němeček, J.
Ústav teoretické a aplikované mechaniky, 2017

Investigation of Strouhal number of ice-accreted bridge cables at moderate flow turbulence
Górski, P.; Tatara, M.; Pospíšil, Stanislav; Kuznetsov, Sergeii
2017 - English
This paper is concerned with the investigation of the Strouhal number (St) for a stationary iced cable model of cable-supported bridges using wind tunnel tests with respect to three principal angles of wind attack. The investigations were carried out in the Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in Telč. The St values were determined at the flow turbulence intensity of the order of 12%, within the range of the Reynolds number from 2.4·10^4 to 12.9·10^4, based on the dominant vortex shedding frequencies measured in the wake of the model. The obtained experimental St values of the iced cable of a cable-supported bridge will allow to determine the critical wind velocity as well as will be helpful for prediction of the cable response due to the vortex excitation phenomenon at moderate flow turbulence condition. Keywords: Strouhal number; climatic wind tunnel; vortex excitation phenomenon; cable-supported bridge Available at various institutes of the ASCR
Investigation of Strouhal number of ice-accreted bridge cables at moderate flow turbulence

This paper is concerned with the investigation of the Strouhal number (St) for a stationary iced cable model of cable-supported bridges using wind tunnel tests with respect to three principal angles ...

Górski, P.; Tatara, M.; Pospíšil, Stanislav; Kuznetsov, Sergeii
Ústav teoretické a aplikované mechaniky, 2017

Measurements of dynamic wind pressures on gable roofs – comparison with ČSN EN 1991-1-4
Pospíšil, Stanislav; Macháček, Michael; Hračov, Stanislav; Kuznetsov, Sergeii; Trush, Arsenii
2017 - English
The contribution is dealing with the wind tunnel measurements of dynamic pressures on the canopy roofs. It compares experimentally determined pressure coefficients Cp with the values in ČSN EN 1991-1-4 and former code ČSN 73 0035 as well. The pressures are expressed by the dynamic values. Thus, the averaged values are presented together with the fluctuating part, which significantly contributes to the overall loading. The measurement is carried out at two roof models, two basic directions, and two turbulence intensities. Keywords: wind tunnel experiments; dynamic pressures on roofs; wind loads; wind load codes; gable roof; atmospheric boundary layer Available at various institutes of the ASCR
Measurements of dynamic wind pressures on gable roofs – comparison with ČSN EN 1991-1-4

The contribution is dealing with the wind tunnel measurements of dynamic pressures on the canopy roofs. It compares experimentally determined pressure coefficients Cp with the values in ČSN EN ...

Pospíšil, Stanislav; Macháček, Michael; Hračov, Stanislav; Kuznetsov, Sergeii; Trush, Arsenii
Ústav teoretické a aplikované mechaniky, 2017

The Cloak Bridge in Český Krumlov – measuring of mechanical properties
Kloiber, Michal; Sebera, V.; Hrivnák, Jaroslav; Tippner, J.; Kunecký, Jiří
2017 - English
Timber bridges are often exposed to harsh conditions of the environment. The exposure of the timber structure often leads to its deterioration. Standard test procedures to determine typical properties of wood cannot be used as there is the requirement of the minimum interference with the structure. Several non-destructive testing (NDT) methods for the determination of timber condition have been developed and are used. However, the results of NDT can be used to predict mechanical properties of timber elements only to a limited degree. Semi-destructive testing (SDT) methods are a compromise. In the paper a functional model of a device that allows for the measurement of conventional strength and modulus of deformation of timber in compression parallel to the grain is presented. The device is inserted to a bored hole and pushes the jaws apart with a small test jack loading the bore walls. This paper presents possible use of the device for surveys of timber bridges. Keywords: model of device; mechanical properties Available at various institutes of the ASCR
The Cloak Bridge in Český Krumlov – measuring of mechanical properties

Timber bridges are often exposed to harsh conditions of the environment. The exposure of the timber structure often leads to its deterioration. Standard test procedures to determine typical properties ...

Kloiber, Michal; Sebera, V.; Hrivnák, Jaroslav; Tippner, J.; Kunecký, Jiří
Ústav teoretické a aplikované mechaniky, 2017

Chemický a mikroskopický rozbor vnější omítky, Petschkova vila, V sadech 2, Praha 6
Slížková, Zuzana; Viani, Alberto; Koudelková, Veronika; Frankeová, Dita; Hauková, Petra
2017 - Czech
Cílem práce bylo provedení analýzy malty z Petschkovy vily, byly navrženy analýzy XRD a SEM-EDX, jejichž výsledkem je charakterizace kameniva a pojiva malt. Pomocí analýz bylo určeno, že se jedná o sádrovou omítku s nátěrem. The aim of this work was to analyze mortar from Petschek villa, XRD and SEM-EDX analyzes have been proposed, which results in the characterization of aggregate and mortar binders. The analyses proved gypsum plaster with surface paint. Keywords: chemical composition; survey; material characterization; binder; aggregate Available at various institutes of the ASCR
Chemický a mikroskopický rozbor vnější omítky, Petschkova vila, V sadech 2, Praha 6

Cílem práce bylo provedení analýzy malty z Petschkovy vily, byly navrženy analýzy XRD a SEM-EDX, jejichž výsledkem je charakterizace kameniva a pojiva malt. Pomocí analýz bylo určeno, že se jedná o ...

Slížková, Zuzana; Viani, Alberto; Koudelková, Veronika; Frankeová, Dita; Hauková, Petra
Ústav teoretické a aplikované mechaniky, 2017

Chemické a mineralogické analýzy vzorků omítek ze SH Krakovec
Slížková, Zuzana; Frankeová, Dita; Hauková, Petra; Viani, Alberto
2017 - Czech
Pomocí mikroskopické analýzy, termické analýzy a XRD bylo určeno, že oba analyzované vzorky malty jsou malty vápenné s příměsí jílových minerálů. Obsažený písek v maltě je křemenný, jsou přítomna také zrna živců a slídy, struktura obou malt je odlišná. With using microscopic analysis, thermal analysis, and XRD, it was determined that both analyzed mortar samples are lime mortars with admixtures of clay minerals. The contained sand in the mortar is quartz, there are also grains of feldspar and mica, the structure of the two mortars is different. Keywords: chemical composition; survey; material characterization; binder; aggregate Available at various institutes of the ASCR
Chemické a mineralogické analýzy vzorků omítek ze SH Krakovec

Pomocí mikroskopické analýzy, termické analýzy a XRD bylo určeno, že oba analyzované vzorky malty jsou malty vápenné s příměsí jílových minerálů. Obsažený písek v maltě je křemenný, jsou přítomna také ...

Slížková, Zuzana; Frankeová, Dita; Hauková, Petra; Viani, Alberto
Ústav teoretické a aplikované mechaniky, 2017

Chemical and microstructural characterization of the render, sampled from the Garden wall of the US Embassy in Prague 1
Slížková, Zuzana; Frankeová, Dita; Viani, Alberto; Hauková, Petra; Koudelková, Veronika; Svoboda, Milan
2017 - English
The aim of the work was to analyze the mortar taken from the Garden wall (US Embassy, Prague 1). Analyzes were performed for the binder and filler characterization and the sample was also dissolved in HCl to determine the mixing ratio. Keywords: survey; material characterization; chemical composition; binder and aggregate characterization Available at various institutes of the ASCR
Chemical and microstructural characterization of the render, sampled from the Garden wall of the US Embassy in Prague 1

The aim of the work was to analyze the mortar taken from the Garden wall (US Embassy, Prague 1). Analyzes were performed for the binder and filler characterization and the sample was also dissolved in ...

Slížková, Zuzana; Frankeová, Dita; Viani, Alberto; Hauková, Petra; Koudelková, Veronika; Svoboda, Milan
Ústav teoretické a aplikované mechaniky, 2017

Microscopic features of cement paste modified by fine perlite
Hrbek, V.; Koudelková, Veronika; Padevět, P.; Šašek, Petr
2017 - English
The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight aggregate enhancing the insulating performance of concrete. This paper focuses on integration of fine perlite into the cement matrix and possible replacement of the cement binder in the composition of the material. The macromechanical performance of the modified paste is tested on specimens with 5, 10, 15 and 20% fine perlite substitution and pure cement sample. To distinguish the effect of the perlite on the microstructural level, pure cement material and specimen containing 10% of fine perlite are investigated by the electron microscopy. Furthermore, the mechanical properties of individual phases are examined and compared on same samples by instrumented indentation. The presented results enabled estimation of fine perlite impact on the macro and microscopic performance of the material.. Keywords: perlite; SEM; nanoindentation; mechanical properties Available at various institutes of the ASCR
Microscopic features of cement paste modified by fine perlite

The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight ...

Hrbek, V.; Koudelková, Veronika; Padevět, P.; Šašek, Petr
Ústav teoretické a aplikované mechaniky, 2017

Semi-automated assessment of micromechanical properties of the metal foams on the cell-wall level
Krčmářová, Nela; Šleichrt, J.; Doktor, T.; Kytýř, Daniel; Jiroušek, O.
2017 - English
Metal foams are innovative porous material used for wide range of application such as deformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict mechanical properties of the metal foam is necessary to precisely describe elasto–plastic properties of the foam on cell–wall level. Indentation with low load is suitable tool for this purpose. In this paper custom designed instrumented microindentation device was used for measurement of cell-wall characteristics of two different aluminium foams (ALPORAS and ALCORAS). To demonstrate the possibility of automated statistical estimation of measured characteristics the device had been enhanced by semi-automatic indent positioning and evaluation procedures based on user-defined grid. Vickers hardness was measured on two samples made from ALPORAS aluminium foam and one sample from ALCORAS aluminium foam. Average Vickers hardness of ALPORAS foam was 24.465 HV1.019 and average Vickers hardness of ALCORAS was 36.585 HV1.019.. Keywords: metal foam; Vickers hardness; cell-wall; indentation under low loads Available at various institutes of the ASCR
Semi-automated assessment of micromechanical properties of the metal foams on the cell-wall level

Metal foams are innovative porous material used for wide range of application such as deformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict ...

Krčmářová, Nela; Šleichrt, J.; Doktor, T.; Kytýř, Daniel; Jiroušek, O.
Ústav teoretické a aplikované mechaniky, 2017

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