National Repository of Grey Literature 32 records found  beginprevious23 - 32  jump to record: Search took 0.01 seconds. 
Determination of mechanical properties of low carbon and low alloy steels via small punch tests at room and low temperatures
Závodský, Peter ; Pantělejev, Libor (referee) ; Válka, Libor (advisor)
The presented diploma thesis deals with an innovative material test, so called Small Punch Test. There are main principles, advantages and limitations of the test stated in the thesis. There are stated also correlation procedures in order to obtain standard mechanical properties. A test fixture design has been done in order to perform test procedures at temperature range from 80 to 25 °C. Twelve experimental curves have been obtained from the test and typical quantities have been evaluated. The different accuracy of correlations with standard mechanical properties has been obtained using different correlation equations.
Determination of material volume expansion
Silvestr, Jiří ; Rozsívalová, Zdenka (referee) ; Frk, Martin (advisor)
This Bachelor’s thesis deals with the temperature dependence of the density of solid and liquid materials. First of all I measured the density of solid and liquid materials, from which I made an overview. In the next section I focused on application of volumetric and length expansion in practice and made a table of densities of materials and their appropriate temperature coefficients of volumetric or length expansion. Last section focuses on the practical measurement with one of the methods and their automation.
The Temperature Dependence Of The Specific Conductivity Of Electrolytes for Lithium - ion Batteries
Svoboda, Petr ; Sedlaříková, Marie (referee) ; Máca, Josef (advisor)
This thesis deals with the measurement of the temperature dependence of the specific conductivity of aprotic electrolytes for lithium - ion batteries. Samples that consisted of a mixture of aprotic solvents and salts with alkaline metals were prepared. Sulfolane in combination with another aprotic solvent was used in a mixture of solvents in all cases. Furthermore this thesis deals with the determination of the apparent activation energy of solvents and mixtures of solvents.
Monitoring properties of nanocomposites on base epoxy
Libra, Miroslav ; Rozsívalová, Zdenka (referee) ; Polsterová, Helena (advisor)
The present thesis deals with the study of nanotechnology in the field of composite materials (nanocomposites). Furthermore, the production, composition and electrical properties of these materials. Samples for the experiment are made of epoxy resin as matrix and titanium dioxide TiO2 as fillers with different benefits. Are the measurements the temperature dependence of permittivity, loss factor and internal resistivity.
Measurement of Parameters of Piezoelectric Active Elements for Acoustic Emission Sensors
Fialka, Jiří ; Erhart,, Jiří (referee) ; Sedlák, Petr (referee) ; Beneš, Petr (advisor)
The doctoral thesis discusses the measurement of parameters of piezoelectric (PZT) materials and the influence of temperature on their stability. In the introductory sections, the author briefly explains the piezoelectric effect and its use; simultaneously, methods for the preparation of piezoelectric materials and the measurement of their properties are presented to illustrate the analyzed problem. The experimental part of the thesis describes the procedure of measuring and calculating the complete matrix of material coefficients from samples of PZT ceramics. The applied set of piezoelectric samples complying with relevant European and world standards was made in the form of thin plates, thin discs and cylinders, via gradual modification of the large disc. The NCE51 and/or the older PCM51 ceramics obtained from the company Noliac Ceramics were used in determining the complete matrix and describing the measurement method. Both these types are soft piezoceramics composed from a solid solution of lead zirconate and lead titanate with the general chemical formula of Pb(Zr1-x,Tix)O3. The real crystallographic structure and chemical composition of the samples were confirmed by X-ray diffraction spectroscopy and energy dispersive spectroscopy (EDS), respectively. The frequency method was used for the measurement and calculation of all material coefficients. An Agilent 4294A impedance analyzer and a set of measuring tweezers marketed as “Tweezers Contact Test Fixture 16334A” were used in the process. Fast determination of the entire matrix of coefficients without any special requirement for the preparation of the samples to be measured was tested and verified. The charge coefficients of the piezoelectric material were confirmed by direct methods including the laser interferometer technique, the vibrometric method, and the procedure utilizing changes of the force applied to the sample. The advantages and disadvantages of the methods were compared and defined based on measurements and their results. The main part of thesis was focused on the behavior of piezoelectric material at high temperatures near the Curie point. Depolarization performed by means of a high temperature approaching the Curie point constitutes a significant yet hardly measurable material property of PZT ceramics. Commonly available vibrometric methods (d33-meters) do not appear to be suitable for the measurement of temperature dependencies, and for that reason the frequency technique was used. The piezoelectric charge coefficient, whose value can be effectively measured via the above-discussed frequency method, was selected as the indicator showing the depolarization state in the applied piezoelectric ceramics. The accuracy of the procedure was verified via comparison of the vibrometric method in cylinders of the NCE51 ceramics with different sizes, which are designed for the longitudinal length mode. The result is an optimized measurement methodology which facilitates accurate determination of the Curie temperature, namely phase transition to the cubic crystallographic structure. The experiment also proved the applicability of progressive, controlled depolarization of PZT ceramics via high temperature, and it also enabled us to define the temperature limits at which there occur irreversible changes of the piezoelectric properties of piezoceramics. In the measured NCE51 and PCM51 materials, the limit for the irreversible changes was equal to 95% of the Curie temperature.
Dynamic viscosity of electroinsulating liquids
Míka, Petr ; Rozsívalová, Zdenka (referee) ; Frk, Martin (advisor)
This work deals with persepective environmentally friendly electroinsulating liquids. Important properties of currently used electroinsulating liquids are listed. Physical nature of viscosity of liquids and its temperature dependance are described and methods of its measuring are listed. Also temperature dependance of density is described from physical point of view. Measurement of density and of temperature dependance of viscosity of chosen vegetable and mineral oils was performed. On the basis of this measurement was calulated the activation energy of these samples. Two methods of dynamic viscosity measurement were used for some samples.
Influence of the temperature on hydrophobic domain quality in a biopolymer-surfactant system.
Hnyluchová, Zuzana ; Kopuletá, Ema (referee) ; Mravec, Filip (advisor)
The temperature dependence on polarity has been investigated by fluorescence spectroscopy with pyrene as a probe. Pyrene was chosen thanks to its unique sensitivity to polarity of the medium. As a biopolymer was chosen 73 kDa and 1,4 MDa hyaluronic acid. Emission spectra of pyrene were measured as a function of temperature in aqous solution of CTAB in a presence and absence of sodium chloride. The results show, that the addition of specific concentration of hyaluronic acid to the sample with CTAB, mostly doesn´t have effect to change increasing/decreasing slope of polarity with the temperature.
Ab initio calculations of temperature dependent resistivity for transition metals
Wagenknecht, D. ; Turek, Ilja ; Carva, K.
The effect of phonons on electrical resistivity has been simulated by considering random displacements of atomic nuclei from their equilibrium positions together with a frozen-potential approach. The developed theory has been applied successfully to late transition metals (Fe, Ni, Rh, Pd, Pt).
Temperature dependence of mineralization of organic matter in litter, humus layer and mineral soil from watersheds of Certovo and Plesne lake
JAROŠOVÁ, Eva
In this study soil samples from watersheds of two Bohemian glacial lakes, Plesne and Certovo were analysed. Respiration by heterotrophic soil organisms as the main source of CO2 efflux from soils was measured during long-term laboratory incubation at four different temperatures. The aim of the thesis was to describe a temperature dependence of C mineralization and make a comparison of results among examined places.
Influence of the flow temperature on the hot-wire heat transfer
Antoš, Pavel
A set of calibration curves of the hot-wire was observed at various fluid temperatures.Measurements were performed on the special calibration rig. There is a dimensionless expression of the heat transfer in the paper.

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