Browsing by Author "Bakalova, Totka"
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- ItemComposite Performance Evaluation of Basalt Textile-Reinforced Geopolymer Mortar(MDPI, 2019-07) Chi, Hiep Le; Louda, Petr; Van, Su Le; Voleský, Lukáš; Kovačič, Vladimír; Bakalova, TotkaBasalt fiber is a novel type of inorganic fiber which is produced from the extrusion of natural vocalnic basalt rocks through their melting process at high temperature. So the quality and strength characteristics of basalt fiber depend mainly on both the quality of raw material and manufacturing processing. Basalt fabric-reinforced cementitious composites (FRCM) are a novel composite and an extensive scientific investigation is still ongoing for geopolymer composite. Based on three types of basalt textile with respect to various net sizes, the aim of this paper is to evaluate the flexural performance of basalt textile-reinforced geopolymer composite through the four-point bending test. The specimens of rectangular form with the dimension of 400 x 100 x 15 mm(3), reinforced with one to four layers of each type of basalt textile, were produced. They were then tested at the age of about 40 days after casting. On the other hand, the number of the specimens reinforced with four layers were considered to assess the mechanical strength of the specimens at longer periods of ageing time (60, 90, 150, 180 days). The experimental results showed that with the increasing number of reinforcing layers, the specimens significantly improved the mechanical strength, except for those reinforced with basalt textile of big net size. The specimens reinforced with basalt textile of big net size had no impact on post-crack mechanical strength, however, it helps to arrest the catastrophic brittle failure of the specimens; the failure of these specimens is due to localization of first crack. When the specimens were exposed to the further ageing times, the mechanical strength of the specimens were decreased over time. All the reinforced specimens have the same failure mode by flexural failure due to the rupture of fiber yarn in matrix, and no debonding of fiber yarn or a gradual peeling process of mortar matrix happened during testing.
- ItemFlexural Behavior of Carbon Textile-Reinforced Geopolymer Composite Thin Plate(MDPI, 2019-11-08) Le Chi, Hiep; Louda, Petr; Periyasamy, Aravin Prince; Bakalova, Totka; Kovačič, VladimírTextile-reinforced Portland cement-based concrete has been researched and developed over the last few decades. It was widely used in a different range of applications, such as repair and/or strengthening of structural elements, thin walls, lightweight structures, façade elements, and others. Due to its varied application, this study aims to develop the carbon textile-reinforced geopolymer composite. Specimens of rectangular form with the dimensions of 400 × 100 × 15 mm3 , reinforced with carbon textile, were produced. Four-point bending test was used to evaluate the effect of carbon textile on the mechanical strength of reinforced geopolymer composite based on the three factors: the different mortar compositions corresponding to the addition of the chopped basalt fiber (BF), the number of carbon textile layers, and the different thicknesses of the mortar cover layer. Besides that, a small part of the pull-out test was also considered to assess the adhesion strength at the interface between carbon textile and geopolymer mortar. The experimental results from the four-point bending test showed that the mechanical strength of composite specimens increased when the content of the chopped basalt fiber increased. With the increasing number of the textile layers, the specimens improved the flexural strength significantly. However, the flexural toughness of the specimens reinforced with three textile layers did not improve, as compared to those reinforced with two textile layers. The experimental results for the specimens related to the mortar cover thicknesses indicated that specimens with the mortar cover thickness of 2 mm provide the best strength. The experimental results from the pull-out tests showed that all the specimens have the same failure mode by slipping of the fiber yarn from the matrix.
- ItemA gyro-free system for measuring the parameters of moving objects(Slovak Academy of Sciences - Inst. Measurement Science, 2014) Dichev, Dimitar; Koev, Hristofor; Bakalova, Totka; Louda, PetrThe present paper considers a new measurement concept of modeling measuring instruments for gyro-free determination of the parameters of moving objects. The proposed approach eliminates the disadvantages of the existing measuring instruments since it is based, on one hand, on a considerably simplified mechanical module, and on the other hand, on the advanced achievements in the area of nanotechnologies, microprocessor and computer equipment. A specific measuring system intended for measuring the trim, heel, roll, and pitch of a ship has been developed in compliance with the basic principles of this concept. The high dynamic accuracy of this measuring system is ensured by an additional measurement channel operating in parallel with the main channel. The operating principle of the additional measurement channel is based on an appropriate correction algorithm using signals from linear MEMS accelerometers. The presented results from the tests carried out by means of stand equipment in the form of a hexapod of six degrees of freedom prove the effectiveness of the proposed measurement concept.
- ItemInfluence of electrospinning methods on characteristics of polyvinyl butyral and polyurethane nanofibres essential for biological applications(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2020) Havlíček, Karel; Svobodová, Lucie; Bakalova, Totka; Lederer, TomášThe diversity of nanofibre properties is caused not only by their chemical composition but also by the way of their preparation. In this study, we examine nanofibre properties resulting from five different electrospinning methods when using polyurethane or polyvinyl butyral. The five electrospinning methods examined were based on (a) alternating current (AC electrospinning) and (b) direct current (Rod electrospinning, Nanospider (TM) technology, Needle electrospinning, Centrifugal electrospinning). The results, based mainly on the evaluation of images from scanning electron and confocal microscopy, showed clear structural differences between the nanomaterials produced by the various methods. The fibres obtained by the AC method were predominantly fine and disordered with high porosity. In the case of DC methods, which are characterized by a significant difference in productivity, the nanofibers of an accurately defined thickness (Nanospider technology) or very oriented nanofibres with considerable surface roughness (centrifugal spinning) could be prepared. By selecting a suitable method, it should be possible to prepare required nanofibre structures (larger/smaller pore size, specific fibre diameters, etc.) for specific biological applications, sensors, filtration, cosmetic products, drug delivery systems etc. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
- ItemA kalman filter-based algorithm for measuring the parameters of moving objects(Slovak Academy of Sciences - Inst. Measurement Science, 2015) Dichev, Dimitar; Koev, Hristofor; Bakalova, Totka; Louda, PetrOne of the most complex problems in measuring equipment is related to the provision of the required dynamic accuracy of measuring systems determining the parameters of moving objects. The present paper views an algorithm for improving the dynamic accuracy of such measuring systems. It is based on the Kalman method. The algorithm aims to eliminate the influence of a number of interference sources, each of which is of secondary significance. However, their total effect can cause considerable distortion of the measurement signal. The algorithm model is designed for gyro-free measuring systems. It is based on one of the most widely used elements in the dynamic systems, namely the physical pendulum, due to which measuring systems of high dynamic accuracy and low cost can be developed. The presented experimental results confirm the effectiveness of the proposed algorithm with respect to the dynamic accuracy of measuring systems of this type.
- ItemMechanical properties of geopolymer foam at high temperature(2020-01) Le, Van Su; Szczypinski, Michal M.; Hájková, Pavlína; Kovačič, Vladimír; Bakalova, Totka; Voleský, Lukáš; Hiep, Le Chi; Louda, PetrIn this work, geopolymer foam composites containing waste basalt fibre (10, 30, and 50%wt) were exposed to elevated temperatures of 200, 400, 600, 800 and 1000 degrees C. With an increase in high temperature, the geopolymer foams material exhibits a decrease in compressive strength and bending strength. When heated above 600 degrees C, geopolymer foams materials exhibit a significant reduction in mechanical properties. It shows clearly with the naked eye that surface cracks in case of samples containing 10% of basalt filler. However, when increasing fillers with basalt fibres up to 30% and 50%, the cracking of the sample surface is no longer visible to the naked eye. Especially when the temperature increases, the mechanical properties also increase without decreasing in the sample of 50% by weighing to the binder. The results show that reinforcing the geopolymer foams with basalt ground fibre improves the mechanical properties at high temperatures.
- ItemA Model of the Dynamic Error as a Measurement Result of Instruments Defining the Parameters of Moving Objects(De Gruyter Open Ltd, 2014) Dichev, Dimitar; Koev, Hristofor; Bakalova, Totka; Louda, Petr;The present paper considers a new model for the formation of the dynamic error inertial component. It is very effective in the analysis and synthesis of measuring instruments positioned on moving objects and measuring their movement parameters. The block diagram developed within this paper is used as a basis for defining the mathematical model. The block diagram is based on the set-theoretic description of the measuring system, its input and output quantities and the process of dynamic error formation. The model reflects the specific nature of the formation of the dynamic error inertial component. In addition, the model submits to the logical interrelation and sequence of the physical processes that form it. The effectiveness, usefulness and advantages of the model proposed are rooted in the wide range of possibilities it provides in relation to the analysis and synthesis of those measuring instruments, the formulation of algorithms and optimization criteria, as well as the development of new intelligent measuring systems with improved accuracy characteristics in dynamic mode.
- ItemQuality assessment of milling technology and the biocidal effects of SiO2 or TiO2 nanoadditives in cooling lubricant emulsions(2019-08-13) Bakalova, Totka; Svobodová, LucieNanoparticles (NPs) of TiO2 or SiO2 (size of 10–25 nm) added to a cooling lubricant emulsion (CLE) have a positive effect on the machining process due to a reduction in the average friction coefficient, a reduction in the variance of the measured values and a reduction in the wear of the cutting tool resulting in increased durability. The functional properties of NPs were evaluated using two different CLEs – CLE1 with the majority content oxygen molecule and various amines; and CLE2 composed of oxygenated organic compounds comprising glycols and higher alcohols. Conventional face milling was selected as the machining process type with the cutting speed 119 m min−1; rotor speed 600 rpm; feed per tooth 0.1 mm; feed rate per minute 60 mm; depth of cut 1 mm and width of cut 40 mm. The addition of spherical SiO2 NPs and TiO2 NPs with a flat surface texture with smooth edges led to a reduction in wear, in the sticking region there was no evidence chipping, cracking or peeling of the coating. The different compositions of CLE1 and CLE2 influence the biocidal effects of the NPs on bacteria cells; CLE1 with SiO2 of 56.6%, and with TiO2 of 18.4%; CLE2 with SiO2 of 26.5%, and with TiO2 of 55.3%. The presence of NPs in the CLEs does not increase the cytotoxic effect on mouse fibroblast cells; however, the composition of CLE1 and CLE2 affects the cytotoxicity for mouse fibroblast cells; CLE1 has an up to 59.6% higher cytotoxic effect than CLE2.
- ItemTHERMAL CONDUCTIVITY OF REINFORCED GEOPOLYMER FOAMS(UNIV CHEMISTRY & TECHNOLOGY, PRAGUE, TECHNICKA 5, PRAGUE 6, DEJVICE 166 28, CZECH REPUBLIC, 2019) Le, Van Su; Hájková, Pavlína; Kovačič, Vladimír; Bakalova, Totka; Voleský, Lukáš; Le, Chi Hiep; Seifert, Kevin Ceccon; Peres, Amanda Pereira; Louda, PetrReinforced geopolymer foams were studied in this work as potential building materials. It has been widely assumed that for a given thermal conductivity. [W center dot m(-1)center dot K-1], geopolymer foams can have a lighter density than other materials. The study sought to test this assumption by comparing the thermal conductivity between geopolymer foams. The thermal conductivity. was measured using an ISOMET 2014 device. In all the experiments, the geopolymer foams were obtained by adding aluminium powder and several combinations: silica fume and fine sand reinforced by short basalt fibres. Curing was carried out at room temperature and then in a furnace at 70 degrees C. After the curing process, the properties of the samples were tested at 7 and 28 days. The results show that the thermal conductivity, porosity, compressive strength, flexural strength and density for all of the tests ranged in the following values: 0.13 - 0.359 W center dot m(-1)center dot K-1; 41.8 - 62.5 %; 1.94 - 9 MPa; 0.96 - 2.93 MPa; 546 - 1028 kg center dot m(-3), respectively. It was proven that the filler in the geopolymer foams has a significant influence on the mechanical and physical properties of the tested samples.
- ItemVliv materiálových a technologických parametrů obrábění na napětí v povrchové vrstvě a vlastnosti dynamicky namáhaných strojních součástí(Technická Univerzita v Liberci, 2010) Bakalova, Totka; Jersák, JanDisertační práce se zabývá analýzou nově vzniklých povrchů ocelových materiálů po obrábění z hlediska integrity povrchu. Těžiště této disertační práce spočívá v experimentální tenzometrické analýze nově vzniklých funkčních povrchů laboratorních vzorků i speciálně připravených segmentů reálných strojních komponent. Výsledky těchto analýz jsou diskutovány z hlediska technologického i metodického v závislosti na proměnných parametrech opracování.