Browsing by Author "Pechočiaková, Miroslava"

Now showing 1 - 5 of 5
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    Concept of a polishing tool based on viscoelastic properties for midspatial frequencies suppression on aspheric surfaces
    (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 1000 20TH ST, PO BOX 10, BELLINGHAM, WA 98225 USA, 2019-11-01) Procháska, František; Matoušek, Ondřej; Tomka, David; Beneš, Jiří; Pechočiaková, Miroslava
    We focus on the subaperture polishing tool concept development for suppressing midspatial frequencies (MSF) arising from computer numerical control machining of aspherical optical surfaces. The selective effect in the MSF range is achieved by setting the tool viscoelastic properties so that rigidity increases in the frequency-domain generated by the rotational tool movement over the aspheric surface with the MSF while the tool remains flexible in the lower frequency range associated with tool radial direction movement. The mechanism of MSF removal is discussed in detail, including in terms of elasticity module frequency dependences, and is also experimentally verified. In order to monitor and optimize viscoelastic properties, especially in regard to frequency dependences, the dynamic mechanical analysis method has been developed and applied and is presented in the paper as well.
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    Impact of Flax and Basalt Fibre Reinforcement on Selected Properties of Geopolymer Composites
    (MDPI, 2020-01-06) Frydrych, Miroslav; Hýsek, Štěpán; Fridrichová, Ludmila; Van, Su Le; Herclík, Miroslav; Pechočiaková, Miroslava; Chi, Hiep Le; Louda, Petr
    The submitted paper deals with the physical and mechanical properties of geopolymer composite materials reinforced with natural fibres. For this study, we aimed to develop a geopolymer composite reinforced with long flax fibres, which were implemented in the geopolymer in the form of a nonwoven fabric that reinforced the structure of the geopolymer over the entire thickness of the board. In order to compare the properties of the developed composite with natural fibres, a geopolymer without fibres and a geopolymer reinforced with basalt fibres were also produced. The monitored mechanical properties were impact bending, bending strength and compressive strength. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and microscopic analysis were also carried out. The results clearly showed the positive effect of the addition of natural fibres on impact bending and bending strength. However, the addition of natural fibres in the form of a nonwoven fabric significantly increased the variability of the properties of the developed composites. In addition, a different pattern of joint failure was noted between geopolymer reinforced with flax fibres and geopolymer reinforced with basalt fibres.
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    Solid and microcellular polylactide nucleated with PLA stereocomplex and cellulose nanocrystals
    (SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS, 2020-03-01) Borůvka, Martin; Běhálek, Luboš; Lenfeld, Petr; Brdlík, Pavel; Habr, Jiří; Wongmanee, Sorasak; Bobek, Jiří; Pechočiaková, Miroslava
    Blending polylactide (PLA) with poly(d-lactide) (PDLA) and cellulose nanocrystals (CNC)-based stereocomplex (SC) nanohybrids presents practical approach to produce fully biobased blends and nanocomposites with enhanced properties. This paper investigated the nucleation effect of PLA/PDLA and PLA/PDLA-g-MAH/CNC nanohybrids at low loading levels on the non-isothermal crystallization, morphology, as well as thermal and thermo-mechanical properties of PLA-based samples. Neat PLA, blends and nanocomposites were produced by conventional and microcellular injection molding. Nitrogen (N-2) in a supercritical state was used as the physical blowing agent for preparation of microcellular samples. CNC-based SC showed superior nucleating efficiency compared to SC nucleating agents. However, low mold temperature resulted in relatively low degree of crystallinity (similar to 15%). In addition, decrease in cell size and increase in cell density of microcellular samples have been observed after introduction of both nucleating agents. Slight increase in mechanical properties of nucleated samples compared to neat PLA has been ascribed to the higher degree of crystallinity. Despite these, decrease in all mechanical properties of microcellular samples has been noticed when compared to solid counterparts. Furthermore, dynamic mechanical analysis (DMA) reveals subsequent foaming and dramatic decrease in dimensional stability of microcellular samples above glass transition temperature (T-g). The storage modulus in a glassy region has been improved in both solid blends and nanocomposites. In addition, shift of T-g due to restricted chain mobility of PLA due to retarded relaxation of amorphous regions due to SC interactions has been observed.
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    The impact of wear on mechanical properties of roving
    (IOP PUBLISHING LTD, DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND, 2018-01-01) Pechočiaková, Miroslava; Novotná, M.
    The paper deals with the influence of mechanical wear out on the resulting mechanical properties of roving. The paper deals with the scraping of roving from inorganic fibres. Glass, carbon and basalt roving are used for this experiment. Rovings are mainly used for the production of composites. The preparation of the roving for processing into composites includes their coiling of the supplied large coils on the coils used in the manufacture. With this rewinding, mechanical damage to roving can occur, which could result in loss of strength. The aim of this work is to determine whether the values of the mechanical properties change depending on the wound generated during winding. For this purpose, a special Cycle Abrasion Apparatus has been developed to simulate wiping during winding. The work is first aimed at finding the optimal measurement procedure on the Abrasion Apparatus. Further, the results of weight loss, loss of strength, particle removal and measurements on the Zweigle G522 instrument are processed.
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    Vliv vlákenné výztuže na mechanické vlastnosti omítkových kompozitních materiálů
    (Technická Univerzita v Liberci, 2014-01-01) Kryšková, Petra; Pechočiaková, Miroslava
    Diplomová práce s názvem Vliv vlákenné výztuže na mechanické vlastnosti omítkových kompozitních materiálů je rozdělena do tří částí. V rešeršní části jsou popsány a definovány obecně kompozitní materiály. Dále se tato část věnuje popisu omítek a vláken vhodných pro jejich vyztužení. V experimentální části je řešena příprava omítkových kompozitů včetně vlákenné výztuže a popis jednotlivých zkoušek, které byly zvoleny pro testování mechanických vlastností omítkových kompozitů vyztužených skleněnými nebo čedičovými vlákny. Část nazvaná diskuze výsledků obsahuje číselné, slovní i grafické vyjádření výsledků testů a jejich shrnutí.