CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
Not a member yet
4735 research outputs found
Sort by
Volume changes measurement of elastomers using 3D DIC
Get PDFThe presented research aims at measuring the volume changes of elastomers using digital image correlation (DIC) in the 3D configuration (stereo DIC). The deformation measurement method in stereo configuration was applied during the mechanical testing of two types of test specimens (dumbbells, cylinders) in uniaxial tension. In this configuration, two cameras were used. The test specimens were measured up to a specified strain value, and the measured data were used to obtain the strain dependence of Poisson’s ratio and the bulk modulus, which are crucial for hyperelastic models. The measurement results reveal that the stereo DIC method provides relatively less scattered data in the low-strain regions for dumbbell-shaped test specimens and is suitable for measuring various test specimen shapes
Experimental validation of motion sensor Physilog®5 applied to shoulder joint
Get PDFThe main motivation of this paper is to verify the idea of using the Physilog®5 unit for the patients with shoulder movement difficulties. The attached sensor to the patient’s arm then measures motion during which the patient should follow certain paths. Finally, if a patient has difficulty with motion requirements, some typical pattern for their problem should emerge. By analysing these patterns, a database of typical problems could be created, which could assist doctors in determining a patient’s diagnosis.The experiment is focused on Physilog® concerning the 5th generation. The goal is to experimentally identify and verify the performance of this generation during relatively large motions of the upper limb. For this purpose, an experimental stand representing spherical joint with an accurate absolute position sensing is assembled and calibrated. Subsequently, the three Physilog®5 sensors are mounted on this stand at different positions
Effect of Copper Vapor on Radiation Properties of C4F7N Gas Mixtures
Get PDFC4F7N and its mixture with buffer gases are regarded as the most promising SF6-alternative gases in gas circuit breakers. The switching arc can severely ablate the electrodes, producing copper metal vapor that combine with the C4F7N gas mixture to chang radiation characteristics. This paper compares the net emission coefficient of C4F7N mixtures at various mixing ratios and assesses the effect of 20% copper vapor. It is found that adding copper vapor can greatly enhance radiation
Investigation of Plasma Parameters Using OES and Spectra Simulations
Get PDFThe radiation from the arc plasma ignited between the flat ends of copper electrodes in atmospheric pressure air at a direct current of 3.5 A is analyzed to determine the plasma temperature and composition. Side-on spectra in the range (430 – 650) nm are recorded using a CMOS camera connected to a spectrograph. The spectral emission coefficient is evaluated from the spectral radiance, which provides the radiator number density. The excitation temperature is obtained by applying the Boltzmann plot technique to at least two spectral lines and a series of radial positions in the midplane of the arc. Subsequently, the plasma composition is determined. The equation of radiative transfer is solved along lines of sight considered in the experiment. The spectral intensity of Cu I lines is computed and compared with the experimental ones. The arc properties are obtained by assuming axial symmetry and mapping the evaluated values in the midplane
Influence of Construction Period of Bridge Across Reservoir on Operation of Adjacent Power Station
Get PDFThe influence of the construction period of the bridge project across the reservoir on the adjacent power station includes not only the direct impact on the hydropower hub but also the impacts on the reservoir area, flood discharge, power station head, water diversion and sediment prevention, power generation operation, and other factors. In this paper, from the aspects of the power station operation, an evaluation index for the influence of the construction period of a bridge across a reservoir on the adjacent power station is developed, and an evaluation system is constructed. Based on the constructed evaluation system, the influence of the bridge construction period on the adjacent power stations is analyzed. This evaluation system provides a reference for the impact assessment of cross-reservoir bridge engineering on adjacent hydropower stations
MONITORING AND ANALYSIS OF CANTILEVER JACKING OF HIGH SLOPE PRESTRESSED CONCRETE CONTINUOUS BOX GIRDER
Get PDFDue to the rapid development of the transportation industry and economy, an increasing number of bridges have been unable to meet the demands of traffic. Demolishing and rebuilding bridges can lengthen the construction period, waste a lot of resources, and increase construction costs. Based on the lifting renovation project of the old Harbin Dongsan Ring Expressway viaduct, this paper combines finite element analysis and on-site testing to analyze the construction process. The bridge alignment, elevation, and deviations were monitored during the construction process, and a correction system was developed to address such issues. Structural analysis was conducted to evaluate the internal forces when uneven jacking occurred. The construction process described in this paper can effectively solve the jacking problems of urban continuous bridges with large tonnage, high slopes, and heights. The successful implementation of the jacking retrofitting project has verified the reliability of the measures taken
Ageing of Technical Air and Technical Air with 7.5% C5-Fluoroketone by Free-Burning Arcs
Get PDFThis paper reports on the effect of ageing by free-burning arcs in 7.5% C5-fluoroketone (C5-FK) with 92.5% technical air in comparison to that in technical air (80% N2, 20% O2) at 1.3bar absolute pressure. The gases are aged by applying a series of arcs dissipating an accumulated energy of around 315kJ. It is found that the arc voltages in technical air and technical air with C5-FK are in the same range and do not vary significantly as a function of ageing or current amplitude (∼40-900 A). Contact erosion in both mediums is found to be similar if the discharge procedure is same. However, erosion increases significantly if ageing is performed in a short contact gap that needs more arcing operations to achieve similar level of arcing energy accumulation. Furthermore, gas decomposition by-products are analysed using gas chromatography coupled with mass-spectrometry
NMM 2022 Nano & Macro Mechanics
No full textThe 13th conference Nano & Macro Mechanics was held in Prague, in September 15, 2022.
The main objective of the conference is to bring together researchers, students and engineers devoting their work to comuting and experimental mechanics in different areas of engineering applications on a common platform.
The conference key topics were following:
Testing of building materials at the nano and macro level.
Destructive and non-destructive methods for determining the mechanical properties of building materials.
Relationships between material parameters at nano and macro level.
Numerical simulation of behavior of structures and materials.
Computational and experimental dynamics and mechanics.
Material research for steel, building materials, glass, woods, textiles, and composites.
Analyses of constructions.
Computational methods for analyses of the constructions.
Biomechanics.
Scientific comittee:Tomáš PlachýPavel TesárekPavel PadevětPetr BittnerAleš JíraJan VorelLenka MezerováMichal ŠejnohaBořek Patzák
Local organizing comittee:Petr BittnerTomáš PlachýPavel PadevětPavel TesárekOndřej ZobalBarbora MužíkováZdeněk Prošek
Guarantor of the peer review process:Pavel Padevět
Guarantor of the language editing:Tomáš Plach
Modelling of laminated glass interlayer by fractional viscoelasticity
Get PDFFractional calculus, i.e. the theory of derivatives and integrals of non-integer order, can be efficiently used for the theoretical modelling of viscoelastic materials. Our research is focused on the polyvinyl butyral which is used as an interlayer for the laminated glass. Polyvinyl butyral can be classified as a viscoelastic material and the introduction of the fractional viscoelasticity seems to be appropriate tool for its description. This paper briefly introduces the springpot element and its connection into more complex theoretical models. We mainly consider the generalized Maxwell model in its standard and fractional form and show their application by fitting the data obtained by experimental analysis
Bacterially induced calcite formation at the surface of recycled concrete
Get PDFThe construction industry is one of the main sources of greenhouse gas emissions, and portland cement production is responsible for approximately 8 % of anthropogenic CO2 emissions. Microbially induced calcium precipitation (MICP) has the potential to partially replace cement or modify the properties of materials that would otherwise not find use in construction, for example, in concrete recycling. MICP might be an environmentally friendly method to improve the properties of recycled aggregates and form conglomerates from the finest fractions. In this paper, factors influencing MICP’s ability to solidify recycled concrete fines are thoroughly investigated. Calcium carbonate precipitate crystals produced by the bacterium Sporosarcina pasteurii were analyzed using scanning electron microscopy and energy dispersive spectroscopy