Institute of Theoretical and Applied Mechanics

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2019-10-19
16:35
Možnosti využití 4D výpočetní tomografie v lomových testech
Kumpová, Ivana ; Fíla, Tomáš ; Koudelka, Petr ; Rozsypalová, I. ; Keršner, Z. ; Kytýř, Daniel ; Vopálenský, Michal ; Vavřík, Daniel ; Vyhlídal, M. ; Drdácký, Miloš
Příspěvek prezentuje studium vnitřní struktury a lomových vlastností vybraných kvazikřehkých stavebních materiálů vystavených teplotním změnám a možnosti uplatnění metody kombinující ohybové lomové testy a časově závislou výpočetní tomografii (4D CT). Zkušební tělesa byla podrobena účinkům vysokých teplot a následně testována čtyřbodovým ohybem během 4D CT. Byly tak získány 3D obrazové informace v různých fázích zatížení a porušování materiálu. Rovněž bylo provedeno komparativní měření pevnosti v tlaku. Tyto výsledky jsou v dobré shodě.

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2019-08-26
09:04
Evaluation of effective properties of basalt textile reinforced ceramic matrix composites
Valentová, S. ; Hrbek, Vladimír ; Šejnoha, M.
The present paper is concerned with the analysis of a ceramic matrix composite, more specifically the plain weave textile fabric composite made of basalt fibers embedded into the pyrolyzed polysiloxane matrix. Attention is paid to the determination of effective elastic properties of the yarn via homogenization based on the Mori-Tanaka averaging scheme and the 1st order numerical homogenization method adopting a suitable representative computational model. The latter approach is then employed to simulate the response of the yarn when loaded beyond the elastic limits. The required mechanical properties of individual material phases are directly measured using nanoindentation with in-build scanning probe microscopy. Applicability of the proposed computational methodology is supported by the analysis of a unidirectional fibrous composite, representing the yarn, subjected to a macroscopically uniform strain

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2019-08-26
09:04
Using homogenization and nanoindentation for microfibril angle determination of spruce
Kucíková, L. ; Hrbek, Vladimír ; Vorel, J. ; Šejnoha, M.
This paper is concerned with the evaluation of microfibril angle of spruce. The microfibril angle is defined as an inclination of microfibrils from the longitudinal axis, the direction of lumens. It is well known and further supported by the present study that the microfibril angle has a great influence on the final mechanical properties of wood. This angle could be measured either directly using, e.g. polarisation microscopy, X-ray diffraction, infrared spectroscopy, or indirectly, as used in this study, by employing the nanoindentation measurements. Therein, the measured indentation modulus is compared with that obtained numerically using the anisotropic theory of indentation. The latter one depends on the entire stiffness matrix derived through homogenization and the searched microfibril angle. In view of the cell wall microstructure, the effective cell properties were found using the two-step micromechanical homogenization adopting both the Self-consistent and Mori-Tanaka methods.

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2019-08-26
09:04
Strength of composite yarn under biaxial loading
Valentová, S. ; Hrbek, Vladimír ; Vorel, J. ; Šejnoha, M.
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.

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2019-08-26
09:04
The effect of micro-silica on the microscopic features of the UHPC composite and its inter-facial transition zone
Hrbek, Vladimír ; Prošek, Z. ; Chylík, R. ; Vráblík, L.
The uplift of concrete overall macroscopic performance by way of alternative additives is commonly used technique. In case of ultra high performance concrete (UHPC), micro-silica is added to the mixture as a micro-filler to the structure of cement binder. As a result, the cementitious matrix macro-mechanical performance is elevated. This paper is aimed on the UHPC micro-scale enhancement by different micro-silica additive content in the mixture. More closely, the study investigate the impact of the micro-silica on the inter-facial transition zone (ITZ) between the binder matrix and basaltic aggregate.

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2019-08-26
09:04
Micro-mechanical performance of concrete used as recycled raw material in cementitious composite
Hrbek, Vladimír ; Koudelková, Veronika ; Prošek, Z. ; Tesárek, P.
The reduction of industrial pollution is recently one of main goals over all fields. In civil engineering, re-cycling of structural waste provides wide opportunity contributing this effort. This paper focus on re-use of concrete waste, which after further processing can be used in new constructions as partial supplement to the mixture. To investigate the impact of re-cycled concrete addition, it is necessary to determine mechanical and structural parameters of individual phases in the “raw” material. For this purpose, grid indentation and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM, EDX) are combined to determine properties of concrete sample.

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2019-07-25
09:14
Výzkumná zpráva. Experimentální studie vlivu ošetření vápenné omítky na její mechanické vlastnosti
Slížková, Zuzana
Byly zjištěny chemicko-fyzikální vlastnosti historické vápenné omítky vyžadující zpevnění a provedeny zkoušky zpevnění ethylsilikátem a nanovápennou disperzí. Nejvyššího zpevnění bylo dosaženo dvojnásobným ošetřením omítky prostředkem na bázi ethylsilikátu s koncentrací SiO2 300 g/l. Z důvodu požadovaných hydrofilních vlastností omítky bylo doporučeno finální ošetření omítky nanovápenným prostředkem, např. CaLosil IP 15 nebo CaLoSiL E 25.
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2019-06-11
07:51
In-situ compression test of artificial bone foams in controlled environment using X-Ray micro-computed tomography
Glinz, J. ; Kytýř, Daniel ; Fíla, Tomáš ; Šleichrt, Jan ; Schrempf, A. ; Fürst, D. ; Kastner, J. ; Senck, S.
X-RayMicro-computed tomography (XCT) has already become a standard method for investigations of bone and bone replacement materials in medical research. For an in-depth characterization of histomorphometric features, digital volume data acquired by XCT can be processed and visualized three dimensionally to determine parameters such as bone volume fraction, cortical thickness and porosity. In this study, we investigated specimens of artificial bone foams, developed by the research group for surgical simulators at the UAS Linz, which are used to mimic the haptic feedback of physiologic and pathologic bone for more realistic surgery training. Similar specimen of artificial bone foam in a dry state have already been characterized precisely in [1]. However, since physiological bone typically is in a wet state, the main purpose of this study was the investigation of the influence of environmental conditions on artificial bone foams of varying composition. Thus, specimens with two kinds of mineral filler material as well as different amounts of foaming agent were prepared and tested in an in-situ loading stage developed by the ITAM CAS. In this stage, specimens can be immersed in liquid and tested under temperature-controlled conditions. Consequently, a total amount of 12 specimens was subjected to compression loading; half of them immersed in water at 36.5◦C and half in dry condition. Results showed that there is no significant influence of liquid immersion to the compression outcome. However, foams with less amount of foaming agent appeared to have smaller pores resulting in higher compression strength. Different types of mineral filler material also showed no significant influence on compression strength. Furthermore, a time-lapse in-situ investigation with XCT scans in-between the load steps was performed for one specimen immersed in water to investigate behavior during load. Despite of the open porous morphology of the foam, water immersed only partially into the foam, leaving pores closer to the center unfilled. Concluding, the usage of the artificial bone foams investigated is despite their physiologically wet condition also valid in a dry state since environmental differences are nonessential for their mechanical properties.

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2019-06-11
07:51
Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
Trush, Arsenii ; Pospíšil, Stanislav ; Kuznetsov, Sergeii
A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of the last century. At the moment is an actual issue is the reconstruction and determination of residual life of these structures. Guyed masts and particularly guy ropes have significant dimensions and comparatively low mass and damping with high flexibility. Therefore, aerodynamic and aeroelastic loads, such as vortex induced vibrations, galloping, wind gusts, etc., are key for them. As a tensile construction elements (guy ropes) for guyed masts the traditional open wire spiral strand cables are used. This type of cable has a characteristic helical surface roughness pattern that can act as vortex suppressor, high fatigue endurance, although somewhat lower corrosion resistance comparing to modern locked coil cables with non-circular shaped wires of outer layer and cables with protective polymer coatings. At the same time, on numerous bridges with the above-mentioned modern cable types the fatigue damage to wires in anchorage zones and destruction of protective coatings was detected. Present paper provides results of wind tunnel testing of three models of helical strake cable in order to evaluate separately impact of lay angle and surface roughness factors and reference smooth cylinder model in flow with grid generated turbulence of different intensities. The reduction of the lock-in range of helical strand cables comparing to reference smooth model was observed whereby the greatest impact was an increase of lay angle.

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2019-06-11
07:51
Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading
Martino, F. ; Vinařský, V. ; Šleichrt, Jan ; Kytýř, Daniel
To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. Polydimethylsiloxane (PDMS) based material Sylgard 184 is used for construction of microfluidic organ on chip devices for cell culture due to ease of device preparation, bonding, and possibility of surface functionalization. However it has stiffness orders of magnitude out of physiological range. Therefore we adapted recently published protocol [1] aiming to prepare substrates which offer stiffness in physiological range 5−100 kPa using various mixtures of Sylgard 527 and Sylagard 184. The inhouse developed loading device with the loading capacity of 3 kN with 1 μm position tracking accuracy and sub-micron position sensitivity was employed for this experimental campaign. The experiments were controlled by the proprietary LinuxCNC software running on the real-time kernel [2]. All batches of the samples were subjected to monotonic compression loading. During the displacement driven experiment with loading rate 10 μm · s−1 the samples with diameter 12.00 ± 0.05mm and height 14 − 16mm were compressed to minimally 50% deformation. Because of high differences in the samples stiffness various load cells with nominal capacity 50N, 10N, and 1N was used for the most reliable force logging. Material properties for all batches were derived from a set of tests under dry and simulated physiological conditions. The results are represented in the form of stress-strain curves calculated from the acquired force and displacement data and elastic moduli are estimated as secant up to 10% deformation.

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