Browsing by Author "Louda, Petr"

Now showing 1 - 20 of 49
  • Thumbnail Image
    Item
    Analysis of the Generation of Vibration Signals under Uniaxial Loading of Materials Using the Coherent Properties of Laser Radiation
    (MDPI, 2020-01-01) Louda, Petr; Sharko, Artem
    The present article describes the results of theoretical and experimental investigations of the force response of materials to external tensile stresses. The method used is based on remote precision measurements of the amplitudes of the harmonics of vibration signals and synchronous fixation of deformations under load. It was determined that the shape of the propagating acoustic signal depends not only on the bias time, but also on the frequency. In addition, fixation of the moments of occurrence of the vibrational signals and determination of the number of excesses in the amplitudes of harmonics over the discrimination level allows structural models to be studied in order to diagnose the strength properties of materials under dynamic loading of solids. The experimental setup consisted of a P100 Labtest-2 tearing machine providing a loading speed of 6.22 mm/min, a Polytech PSV–400 vibrometer including lasers, and a computer. Measurements were made at frequencies of 0.4, 1.6, and 40 kHz. An analysis of the mathematical models of the occurrence and propagation of acoustic signals in a material under load is presented, and the features of their application are reported. Transferring the moments of occurrence of vibrational signals to a strain diagram from the applied load allows the development of physical processes of hardening and destruction of materials to be traced. The occurrence of vibrational signals under load can be used as an information parameter for the diagnosis of developing defects in the structure of materials under load.
  • Thumbnail Image
    Item
    Aplikace plazmových nástřiků ze účelem snížení koeficientu tření a snížení lepivosti lepidla na dopravních válcích
    (Technická Univerzita v Liberci, 2004-01-01) Havel, Václav; Louda, Petr
    The present study is concerned with the requirement of the firm ONTEX s.r.o. ( Ltd. ) to devise a new lining of the compression rollers the characteristics of which should be equal to the lining employed now. The new lining ought to be fabricated by means of plasma coating. The lining used at present has been analysed in detail, and a similar lining has been created with the assistance of a special manufacturer. A further objective of the study is the comparison, and eventually, a proposal of sprayed plasma coatings serving to devise the co-efficient of friction, to be employed in the firm indicated above.
  • Thumbnail Image
    Item
    Composite Performance Evaluation of Basalt Textile-Reinforced Geopolymer Mortar
    (MDPI, 2019-07-01) Chi, Hiep Le; Louda, Petr; Van, Su Le; Voleský, Lukáš; Kovačič, Vladimír; Bakalova, Totka
    Basalt 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.
  • Item
    CREATION OF A 3D STRUCTURE BASED ON THE HIGH STRENGTH METALLURGICAL GRAPHENE®
    (2019-07-24) Kaczmarek, Lukasz; Kula, Piotr; Warga, Tomasz; Kolodziejczyk, Lukasz; Louda, Petr; Borůvková, Karolína; Niedzielski, Piotr; Szymanski, Witold; Voleský, Lukas; Pawlowski, Witold; Zawadzki, Piotr
    Herein, the results of a study focused on graphene in activation and cross-linking reactions with hydrazine are reported. The method provides an approach to the preparation of graphene-based materials, in this case, with a preset distance between individual layer and a relatively low ratio between the Raman G and D bands — D peak intensity/G peak intensity (ID/IG), ca. 1.81 (for unmodified High Strength Metallurgical Graphene® (HSMG® [Trade mark number: 013391669; Office for Harmonization in the Internal Market]), this ratio is 0.16). A 3D structure was created without a substrate (e.g. Si, SiO2 or polymer). This method allows for the preparation of a 3D graphene structure without the π–π interactions between individual layers.
  • Thumbnail Image
    Item
    Detekce vad pevnostních feromagnetických dílů pro strojírenský průmysl metodou magnetickou práškovou
    (Technická Univerzita v Liberci, 2006-01-01) Bartoš, Jan; Louda, Petr
    This work deals with non-destructive testing of machine parts by the magnetic particle method. The main aim of this work is the limit values determination of magnetisation process at chosen components. These limit values enable that we can safely find surface and near under-surface defects. These limit values are determined on the basis of tests which were made at different intensitiy levels of magnetising process.
  • Thumbnail Image
    Item
    Diamond-like carbon coatings for biomedical applications
    (1994-01-01) Mitura, Ewa; Mitura, StanisŁaw; Niedzielski, Piotr; Haś, Zdzislaw; Wołowiec, Remigiusz; Jakubowski, Andrzej; Szmidt, Jan; Sokołowska, Aleksandra; Louda, Petr; Marciniak, Jan; Koczy, B.
    The results of experimental studies on amorphous diamond carbon layers obtained by a new method of r.f. dense plasma chemical vapour deposition onto orthopaedic pins and screws are presented. Research on this subject which has been carried out over many years allows us to draw optimistic conclusions concerning the biomedical applications of diamond-like carbon (DLC). In particular, preliminary medical research on a new DLC-steel substrate system developed in 1992, which has just been concluded, is extremely promising. © 1994.
  • Thumbnail Image
    Item
    Effects Of Commercial Fibers Reinforced On The Mechincal Properties Of Geopolymer Mortar
    (Chemické Listy, 2012-01-01) Xiem, Nguyen, Thang; Louda, Petr; Kroisova, Dora; Kovačič, Vladimír; Hiep, Le, Chi; Nhut, Luu, Vu
    The essential objective of this work is to study the mechanical properties and microstructure of geopolymer mortar containing different kinds of fibers. Results show that the use of fibers as reinforcement in geopolymer mortar significantly improves the flexural strength and the hardness of the geopolymer mortar, reduces the amount of cracking and is also more lightweight than before.
  • Thumbnail Image
    Item
    Fire-Resistant Sandwich-Structured Composite Material Based on Alternative Materials and Its Physical and Mechanical Properties
    (2019-05-02) Hýsek, Štěpán; Frydrych, Miroslav; Herclík, Miroslav; Louda, Petr; Fridrichová, Ludmila; Van, Su Le; Chi, Hiep Le
    The development of composite materials from alternative raw materials, and the design of their properties for the intended purpose is an integral part of the rational management of raw materials and waste recycling. The submitted paper comprehensively assesses the physical and mechanical properties of sandwich composite material made from particles of winter rapeseed stalks, geopolymer and reinforcing basalt lattices. The developed composite panel is designed for use as a filler in constructions (building or building joinery). The observed properties were: bending characteristics, internal bonding, thermal conductivity coefficient and combustion characteristics. The results showed that the density of the particleboard has a significant effect on the resulting mechanical properties of the entire sandwich panel. On the contrary, the density of the second layer of the sandwich panel, geopolymer, did not have the same influence on its mechanical properties as the density of the particleboard. The basalt fibre reinforcement lattice positively affected the mechanical properties of sandwich composites only if it was sufficiently embedded in the structure of the particle board. All of the manufactured sandwich composites resisted flame for more than 13 min and the fire resistance was positively affected by the density of the geopolymer layer.
  • Thumbnail Image
    Item
    Flexural Behavior of Carbon Textile-Reinforced Geopolymer Composite Thin Plate
    (MDPI, 2019-11-08) Le Chi, Hiep; Louda, Petr; Periyasamy, Aravin Prince; Bakalova, Totka; Kovačič, Vladimír
    Textile-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.
  • Thumbnail Image
    Item
    FLEXURAL PERFORMANCE EVALUATION OF VARIOUS CARBON FIBRE FABRIC REINFORCED GEOPOLYMER COMPOSITE
    (UNIV CHEMISTRY & TECHNOLOGY, PRAGUE, TECHNICKA 5, PRAGUE 6, DEJVICE 166 28, CZECH REPUBLIC, 2020-01-01) Le Chi, Hiep; Louda, Petr
    In this paper; the results of an experimental investigation on the flexural behaviour, the mechanical properties, and the failure mode of a carbon textile reinforced geopolymer mortar composite subjected to four-point bending test are presented. The influence of various factors such as the type of the carbon fibre fabric, reinforcement ratio, dosage of the chopped basalt fibre on the flexural performance of the reinforced geopolymer composite is experimentally studied. The results reveal that the use of carbon fibre fabrics in the production of high-strength geopolymer matrix composites makes it possible for them to achieve a relatively high mechanical strength. Moreover, the value of the flexural strength and flexural toughness is strongly influenced by the reinforcement ratio and the mechanical properties of the fibre yarn of the carbon textile. The addition of the chopped basalt fibre (BF) plays an important role in both the improved mechanical strength and the failure mode of the geopolymer textile composites. The failure mode of all the specimens shows either a pure bending failure or a peeling off the concrete at the matrix/fibre interface due to the rupture of some filaments in the outer layer and the loss of the bonding strength of the fibre yarn in the matrix leading to the slippage of the fibre yarns within the matrix.
  • Thumbnail Image
    Item
    Geopolymerní kompozitní systémy na bázi termální siliky: studie postupu přípravy a mechanických vlastností
    (Technická Univerzita v Liberci, 2010-01-01) Hung, Tran Doan; Louda, Petr
    V této disertační práci jsou presentovány: 1) vlastnosti dvou geopolymerních systémů na bázi termální siliky spolu s dalšími typy funkčních aditiv 2) vlastnosdti komerčních vyztužujících vláken hodnocených za běžných podínek a to před tepelným namáháním a po tepelném namáhání až do 1000 stupňů C
  • Thumbnail Image
    Item
    Geopolymerní směsi pro tepelné izolace
    (Technická Univerzita v Liberci, 2012-01-01) Štefan, Martin; Louda, Petr
    The subject of this thesis is the use of geopolymer mixtures as insulating or protective elements when applied to wood. Geopolymers are not yet fully known, since previous research has been mostly in the field of mechanical properties. All measurements in this work are original. This work aims to define the basic thermal-insulating properties of geopolymers and indicate their potential application as fireproof protection in construction, engineering, etc. The theoretical part discusses generally geopolymers, their history, properties and uses. It also deals with materials that are used in the preparation of samples. The theoretical part can´t forget the burning properties of wood and general protection. In the experimental section describes the method of sample preparation, method of measurement, process evaluation of the measured values and then comparing the results
  • Thumbnail Image
    Item
    A gyro-free system for measuring the parameters of moving objects
    (Slovak Academy of Sciences - Inst. Measurement Science, 2014-01-01) Dichev, Dimitar; Koev, Hristofor; Bakalova, Totka; Louda, Petr
    The 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.
  • Thumbnail Image
    Item
    Hodnocení biochemických vlastností polykrystalického diamantu
    (Technická Univerzita v Liberci, 2007-01-01) Wluka, Marcin; Louda, Petr
    Work is realized as a part of the international programme MNT ERA-Net. The aim of this programme is an estimation of technological process of microfluidics diamond device making (producing) as well as detection of surface and geometry of three-dimensional structures defects. Theoretical part concerns description of production process of the polycrystalline diamond device to sequentioning of DNA. Practical part contains microstructure silicon matrix as well as diamond chips geometry and surface profile done by applying the modern microscopic techniques - LM, SEM as well as profilometrical analysis of state and shape of the surface.
  • Thumbnail Image
    Item
    Hodnocení fyzikálních vlastností kompozitních systémů s geopolymerní matricí
    (Technická Univerzita v Liberci, 2009-01-01) Jasiczek, Michal; Louda, Petr
    The following master's thesis deals with the evaluation of composites based on geopolymer matrix using three types of reinforcement: fiber glass, carbon fiber and basalt fiber. The theoretical part describes the genesis and chemistry of geopolymers as well as main characteristics of the fibers used in the manufacture of composites on their basis. The hitherto known properties and successful applications of geopolymer composites have been also presented. The experimental part describes process of composite manufacturing and description of conducted researches. The results allow an assessment of the physical properties of geopolymer composites essential for evaluation of their practical application.
  • Thumbnail Image
    Item
    Hodnocení útlumu elektromagnetického pole transparentním materiálem
    (Technická Univerzita v Liberci, 2014-01-01) Buřič, Jiří; Louda, Petr
    Tato práce je zaměřena na možnosti stínění elektromagnetického pole s ohledem na několik parametrů - cena, schopnosti tlumit elektromagnetické pole a transparentnost stínění. Součástí práce byla také rešerše v oblasti elektromagnetického pole. Metody jak to dělají a z jakých materiálu. Cílem bakalářské práce bylo navrhnout nové možnosti u transparentního stínění elektromagnetického pole.
  • Thumbnail Image
    Item
    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.
  • Item
    Influence of carbon coatings origin on the properties important for biomedical application
    (1996-01-01) Mitura, StanisŁaw; Niedzielski, Piotr; Jachowicz, Dariusz; Langer, Małgorzata A.; Marciniak, Jan; Stanishevsky, Andrei Vladimirovich; Tochitsky, Eduard I.; Louda, Petr; Couvrat, Patrice; Denis, Michel; Lourdin, Pierre
    The purpose of the present study was to investigate the properties of a carbon layer depending of the origin of applied methods. Quasiamorphous carbon coatings prepared by ion beam methane decomposition by RF dense plasma and vacuum pulsed arc deposition were applied to stainless steel implants used in surgery. The studies of carbon films as coatings for implants in surgery were aimed on the investigations of biological resistance of implants, histopathological investigations using laboratory animals, tests of corrosion resistance, measurements of mechanical properties and a breakdown test in Tyrod solution. The comparison of the properties of the coating produced by these methods shows very good biotolerance and biocompatibility of all of the coatings. They are not corroded in physiological fluids. From the other side they have different properties, especially electrical and optical, and are not influenced on medical applications. The obtained results prove that the implants coated by all the methods mentioned are a very good material for medical use.
  • Thumbnail Image
    Item
    The Influence Of Modified Fly Ash Particles By Heating On The Compressive Strength Of Geopolymer Mortar
    (Chemické Listy, 2012-01-01) Xiem, Nguyen, Thang; Louda, Petr; Kroisova, Dora; Trung, Nguyen, Duc; Thien, Nguyen
    N. Xiem, P. Louda, D. Kroisova, N. Trung, and N. Thien (Department of Material Science, Faculty of Mechanical Engineering, Technical University of Liberec, Czech Republic): The Influence of Modified Fly Ash Particles by Heating on the Compressive Strength of Geopolymer Mortar In this study, 2 types of fly ash from Czech Republic power plants were investigated with respect to composition. Fly ashes particles are heated at high temperature up to 1000 degrees C to remove the contaminant (unburnt carbon) and the color become brighter can be observed by a naked eye. However, the high processing temperatures can slightly influence on the final properties of the fly ash and geopolymer mortar. After heating fly ash particles at 1000 degrees C, the compressive strength of samples can be reduced slightly when comparing with original fly ash.
  • Thumbnail Image
    Item
    A kalman filter-based algorithm for measuring the parameters of moving objects
    (Slovak Academy of Sciences - Inst. Measurement Science, 2015-01-01) Dichev, Dimitar; Koev, Hristofor; Bakalova, Totka; Louda, Petr
    One 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.