Papers by Author: Zuzanka Trojanová

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Authors: J. Dosoudil, Zuzanka Trojanová, Pavel Lukáč, František Chmelík
Authors: D. Blažek, Peter Palček, Zuzanka Trojanová, Jakub Porubčan
Abstract: The aim of this work is to study the Amplitude Dependent Internal Friction (ADIF) of magnesium alloy AZ31 at room temperature at the frequency 20kHz. The internal friction of AZ31 at room temperature is mostly influenced by mechanical cycling at strain amplitudes in the microplastic deformation region. An excited state of the AZ31 alloy, which can be associated with a higher internal friction and lower dynamic modulus than usual state, was found immediately after mechanical cycling. When the strain amplitude drops, the diffusion of solute atoms restores the Zener atmosphere and the internal friction relaxes exponentially with the second root of time. The measurement methodology and obtained results are presented.
Authors: Zuzanka Trojanová, Michael Bosse, Gerhard Ziegmann, Agnieszka Mielczarek, Hans Ferkel
Abstract: Internal friction in ultra-fine grained Mg with 3vol% of Graphite was measured by forced vibration method at low frequencies of 0.1, 0.5, 1.0, and 2.0 Hz over a temperature range from room temperature to 753 K with continuous heating. The specimens were prepared by milling procedure in an inert atmosphere and subsequent compacted and hot extruded. Two developed peaks in the internal friction spectrum were obtained at temperatures ≈ 350 K and ≈ 550 K. While the position of the first peak is frequency dependent, the second peak position is stable, independent of measuring frequency. The activation energy of the low temperature peak was estimated. In the light of internal friction measurements, the high temperature internal friction peak is attributed to the generation and motion of dislocations produced by the difference in the coefficient of thermal expansion between the Mg matrix and Gr phase at the matrix–particle interfaces.
Authors: Pavel Tofel, Josef Sikula, K. Hajek, Zuzanka Trojanová, L. Bumbalek
Abstract: New non-destructive testing (NDT) method is based on the effect of the ultrasonic vibrations on the electron transport in samples with macroscopic defects as cracks or defect centers affecting electrical conductivity. On the frequency given by the subtraction of exciting frequencies new intermodulation signal appears. Its value is given by electric resistance modulation by the defects and un-homogeneities in the sample structure. In our experiment we used the ultrasonic actuator with frequency fU when the period of wave is longer than the dielectric relaxation time in analyzed sample. In this case the effects of electron bunching by ultrasonic wave are negligible. The ultrasonic wave length is much larger than the electrons mean free path and the wave period is much longer than the mean free time among the electrons collision with scattering centers and defects. Then the electron transport is described by the quasi-steady state transport equation in one-electron approximation. Because of the requirement of charge neutrality, no net AC electric current with the ultrasonic wave frequency fU can be carried by the wave. Similar situation exists for samples excited by standing ultrasonic waves. The electrical conductivity varies with time due to that the cracks geometry is changed with frequency of the ultrasonic vibration. The sample conductivity is affected mainly by the presence of cracks and defects boundaries perpendicular to the electric current density vector. In our experiment the amplitude of ultrasonic vibration is so low that no new cracks are generated and then the proposed testing method belongs to NDT.
Authors: Pavel Lukáč, Zuzanka Trojanová, Werner Riehemann, B.L. Mordike
Authors: Pavel Lukáč, Tibor Donič, Mária Chalupová, Peter Palček, Zuzanka Trojanová, Eva Tillová, Stanislav Rusz, Ronald Bastovansky
Abstract: Magnesium alloy EZ10 was deformed in tension at temperatures from room temperature up to 400 °C with an initial strain rate of 2.7x10-3 s-1. Deformation tests showed a rapid decrease of the tensile yield strength at temperatures higher than 300 °C. Microstructure of the deformed samples was analysed with light microscope. Fracture mechanisms were estimated using scanning electron microscopy.
Authors: Zuzanka Trojanová, Pavel Lukáč, Zoltán Száraz
Abstract: The deformation behaviour of the ternary magnesium alloy AX41 (4%Al-1%Ca-balance Mg) were investigated in uniaxial tension tests at temperatures between 20 and 300 °C and at an initial strain rate ranging in the order 10-4 s-1. The yield stress of the alloy is very sensitive to the testing temperature. Stress relaxation tests were performed with the aim to reveal physical base of deformation processes.
Authors: Pavel Lukáč, Zuzanka Trojanová, Zdeněk Drozd
Authors: Zuzanka Trojanová, Zdeněk Drozd, Pavel Lukáč, S. Kúdela
Authors: Zuzanka Trojanová, M. Pahutová, J. Kiehn, Pavel Lukáč, Karl Ulrich Kainer
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