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High strain-rate compressive testing of filling materials for inter-penetrating phase composites
Doktor, T.; Fíla, T.; Zlámal, Petr; Kytýř, Daniel; Jiroušek, O.
2019 - anglický
In this study behavior of the selected types of filling material for the inter-penetrating phase composites was tested in compressive loading mode at low and high strain-rates. Three types of the filling material were tested, (i) ordnance gelatin, (ii) low expansion polyurethane foam, and (iii) polyurethane putty. To evaluate their impact energy absorption bulk samples of the selected materials were tested in compression loading mode at strain-rates 1000 s−1 to 4000 s−1. The high strain-rate compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) which was equipped with PMMA bars to enable testing of cellular materials with low mechanical impedance. Based on the comparative measurement response to compression at both low and high strain-rates was analysed. The results show a significant strain-rate sensitivity of the ordnance gelatin and of the polyurethane putty, while strain-rate effect in the polyurethane foam was not observed.
Klíčová slova:
interpenetration phase composite; SHPB; impact protection filling materials; strain-rate sensitivity
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
High strain-rate compressive testing of filling materials for inter-penetrating phase composites
In this study behavior of the selected types of filling material for the inter-penetrating phase composites was tested in compressive loading mode at low and high strain-rates. Three types of the ...
X-ray micro-tomography characterization of voids caused by three-point bending in selected alkali-activated aluminosilicate composite
Kumpová, Ivana; Rozsypalová, I.; Keršner, Z.; Rovnaníková, P.; Vopálenský, Michal
2019 - anglický
This paper deals with the pilot characterization of a special alkali-activated aluminosilicate composite composed of waste brick powder, brick rubble and a solution of potassium water glass. Fracture tests were conducted on the specimens via three-point bending and fracture parameters were evaluated. Selected specimen was investigated using micro-tomography to supplement the results with visual information about the inner structure of this newly designed material before and after the mechanical loading. Tomographic measurements and image processing were conducted for a qualitative and quantitative assessment of changes in the internal structure with an emphasis on the calculation of porosimetric parameters and visualization of the fracture surface. Fractal dimension of fracture surface was estimated.
Klíčová slova:
alkali-activated aluminosilicate composite; fracture surface; X-ray micro-tomography; 3D porosity evaluation; fractal dimension
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
X-ray micro-tomography characterization of voids caused by three-point bending in selected alkali-activated aluminosilicate composite
This paper deals with the pilot characterization of a special alkali-activated aluminosilicate composite composed of waste brick powder, brick rubble and a solution of potassium water glass. Fracture ...
Sleva z kupní ceny za skryté vady stavby
Kratěna, Jindřich
2019 - český
Sleva z kupní ceny nemůže být rovna ceně nutných oprav, ale pouze na této ceně závisí. Discount on purchase price can not be equal to the price of necessary repairs but only depends on this price.
Klíčová slova:
purchase price; discount; necessary repairs
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Sleva z kupní ceny za skryté vady stavby
Sleva z kupní ceny nemůže být rovna ceně nutných oprav, ale pouze na této ceně závisí....
Zranitelná místa dřevěných krovů různých typů
Bláha, Jiří
2019 - český
Konstrukční rozdíly mezi krokevními a vaznicovými krovy. Přehled zranitelných míst obou typů s ohledem na dlouhodobou trvanlivost krovů. Structural differences between rafter and purlin roofs. Summary of vulnerabilities of both types with regard to long-term durability of roof trusses.
Klíčová slova:
collar and rafter roofs; purlin roofs; timber
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Zranitelná místa dřevěných krovů různých typů
Konstrukční rozdíly mezi krokevními a vaznicovými krovy. Přehled zranitelných míst obou typů s ohledem na dlouhodobou trvanlivost krovů....
Problémy s vlhkostí a zasolením historického zdiva a nově provedených omítek – budova Obecního dvora v Praze
Janotová, Dana
2019 - český
Příspěvek se zabývá průzkumem vlhkosti a zasolení historického objektu a poukazuje na důležitou metodu Stanovení hygroskopického obsahu vlhkosti, která může přispět v hodnocení zdrojů vlhkosti. The paper deals with the research of moisture and salinity of a historical object and points out the important method of determination of hygroscopic moisture content, which can contribute in the evaluation of moisture sources.
Klíčová slova:
soluble salts; hygroscopicity; moisture content; hygroscopic moisture content; moisture distribution
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Problémy s vlhkostí a zasolením historického zdiva a nově provedených omítek – budova Obecního dvora v Praze
Příspěvek se zabývá průzkumem vlhkosti a zasolení historického objektu a poukazuje na důležitou metodu Stanovení hygroskopického obsahu vlhkosti, která může přispět v hodnocení zdrojů ...
Evaluation of self-healing in concrete by means of analytical techniques
Aspiotis, K.; Sotiriadis, Konstantinos; Kumpová, Ivana; Mácová, Petra; Badogiannis, E.; Tsivilis, S.
2019 - anglický
In the present work, the self-healing process in concrete was evaluated using analytical techniques. For this purpose, two concrete mixes of different composition (one used as reference) were prepared with a W/B of 0.45. The self-healing process was triggered by the introduction in the concrete mix of a commercial expansive admixture (calcium sulfo-aluminate), two dicarboxylic acids, and sodium carbonate salt. After 28 days curing in water, the specimens were artificially cracked (crack width ≈ 400 μm) and then again water-cured for 40 days until self-healing occurred. The progress of self-healing was investigated with a stereo-microscope at 40, 50 and 60 days. The efficiency of the process was evaluated using micro-Raman spectroscopy and X-ray micro-computed tomography (XmCT). Significant reduction in the crack width was observed as a result of filling the crack with calcite generated during the self-healing process. In some cases, the crack was completely healed. The experimental methodology used provided new insights into the evolution of the self-healing phenomenon in concrete.
Klíčová slova:
self-healing; concrete; chemical additives; Raman spectroscopy; X-ray tomography
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Evaluation of self-healing in concrete by means of analytical techniques
In the present work, the self-healing process in concrete was evaluated using analytical techniques. For this purpose, two concrete mixes of different composition (one used as reference) were prepared ...
Lávka pro pěší Radotín - zatížení větrem dle EN 1991-1-4 a měření ve větrném tunelu
Göringer, J.; Hračov, Stanislav; Macháček, Michael
2018 - český
S ohledem na atypickou konstrukci lávky v Radotíně bylo nutno v rámci statického ověření řešit nestandardní účinky zatížení větrem, kdy EN 1991-1-4 poskytuje pro takto atypické konstrukce jen málo podpory. Zatížení větrem u takovéto konstrukce nevystupuje pouze jako náhradní statický účinek, ale zejména je nutné posoudit případné ztráty aerodynamické stability. Příspěvek předkládá postup stanovení problematiky podle EN 1991-1-4 včetně porovnání s výsledky z větrného tunelu. Due to the atypical design of the footbridge in Radotín the procedures for evaluation of the force coefficients presented in EN 1991-1-4 were experimentally verified in the wind tunnel. For the lack of the information about the structure behaviour on the edge of the aerodynamic instability the critical velocity for flutter was experimentally verified as well. The paper presents comparison of the approaches from EN 1991-1-4 with the results of the experiment.
Klíčová slova:
wind load; footbridge; wind tunnel experiments
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Lávka pro pěší Radotín - zatížení větrem dle EN 1991-1-4 a měření ve větrném tunelu
S ohledem na atypickou konstrukci lávky v Radotíně bylo nutno v rámci statického ověření řešit nestandardní účinky zatížení větrem, kdy EN 1991-1-4 poskytuje pro takto atypické konstrukce jen málo ...
Proposal for loading tests of bridges - simulation and laboratory experiments
Bayer, Jan; Urushadze, Shota; Černý, Miloš
2018 - anglický
A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient solution of piecewise linear mechanical structures were developed to assess the effects of the proposed dynamic load on a bridge model. According to the first laboratory experiments, it seems that the proposed travelling impulse load could surpass some of the shortcomings and limitations of the currently applied methods of bridge testing. The investigation is a part of a project aimed at drive-by identification of dynamic properties of bridges and further experimental and analytical research will follow.
Klíčová slova:
dynamic loading tests; transient analysis; vibrations; vehicle-bridge interaction
Dokument je dostupný na externích webových stránkách.
Proposal for loading tests of bridges - simulation and laboratory experiments
A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient ...
Strength of composite yarn under biaxial loading
Valentová, S.; Hrbek, Vladimír; Vorel, J.; Šejnoha, M.
2018 - anglický
The present paper is concerned with two types of periodic unit cell of composite yarn with different geometry but the same material properties. Their macroscopic response under tensile and compressive loading in the transverse direction and their combination are plotted in the graphs. Based on stress-strain curves the failure envelopes are constructed. A simple maximum stress criterion and linear softening law is used in the adopted progressive damage analysis to outline the softening part of stress-strain diagrams. Finally the impact of selected representative volume element is observed through the comparison of results gained for both designed periodic unit cells in the microlevel, meaning the level of yarn.
Klíčová slova:
composite yarn; periodic unit cell; strength; damage analysis; failure envelope
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Strength of composite yarn under biaxial loading
The present paper is concerned with two types of periodic unit cell of composite yarn with different geometry but the same material properties. Their macroscopic response under tensile and compressive ...
Asymmetry of the response probability density of a system with parametric random noises
Náprstek, Jiří; Fischer, Cyril
2018 - anglický
Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These parasitic processes are usually of the random character and, consequently, they exercise as parametric noises. Moreover, the input signal mostly consists of a useful signal which can be taken as composed from deterministic and random additive part. Various combinations of these noises are the origin of random and also systematic measuring errors which can have under certain circumstances a cumulative character, deteriorate the output signal quality and can lead finally to the stochastic stability loss. These effects can be theoretically described using differential systems with stochastic coefficients and stochastic right hand side considering all input and output processes to be of the Markov type.
Klíčová slova:
random vibration; signal reconstruction; parametric noise; response asymmetry
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Asymmetry of the response probability density of a system with parametric random noises
Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These ...
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