Papers by Keyword: Internal Friction

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Authors: M.S. Blanter, V.V. Dmitriev, Andrei V. Ruban
Abstract: t is common knowledge that interstitial-interstitial interaction influence on the Snoek relaxation. We used a computer simulation of this effect in the Nb-O alloy to test the adequacy of various models of the O-O interaction and clarify the mechanism of this effect The energy calculations in the first twelve coordination shells have been performed by the projector augmented-wave (PAW) method as implemented in the Vienna ab initio simulation package (VASP). The energies have been calculated in different ways which vary in the method of determination the energy of non-interacting O-O pairs. The energies calculated on the various variants are similar but in one case there is O-O repulsion in all first twelve coordination shells, whereas in another one can see attraction in four of twelve shells. Internal friction Q-1 was calculated as a sum of the contributions from individual interstitial atoms in different environments, each of which being assumed to be the Debye function. It is assumed that long-range interaction of oxygen atoms affects the distribution of these atoms and the energy of each interstitial atom in the octahedral interstices before a jump and after a jump. The Monte Carlo method is used for simulating short-range order of interstitial atoms and for calculating values of energy changes. Comparison of the calculated temperature and concentration dependence of the Snoek peak with the published data showed that the PAW supercell calculation of the O-O interactions in Nb describes the behavior of the interstitial solid solution adequately. It proves also that the impact of interstitial atom concentration on the Snoek relaxation is connected to the mutual attraction of these atoms.
Authors: Hanuš Seiner, Petr Sedlák, Lucie Bodnárová, Michal Landa, Jitka Stráská, Miloš Janeček
Abstract: Resonant ultrasound spectroscopy (RUS) was applied to monitor the micro-cracking process occurring during cooling at polished surfaces of an ultrafine-grained AZ31 magnesium alloy. It was observed that although the net of micro-cracks covered only narrow regions along the edges of the sample, its appearance resulted in a strong increase of the attenuation of the free elastic vibrations, and was, thus, sensitively detectable from the evolution of the RUS resonant spectra with temperature. This approach enabled a reliable determination of the threshold temperature for micro-cracking.
Authors: Leszek B. Magalas, T. Malinowski
Authors: Xiao Hui Cao, Yu Wang
Abstract: By using a low frequency inverted torsion pendulum, the high temperature internal friction spectra of Al-0.02wt%Zr and Al-0.1wt%Zr alloys were investigated respectively. In Al-0.02wt%Zr alloy, the conventional grain boundary internal friction peak (Pg) is observed with some small unstable peaks. In Al-0.1wt%Zr alloy, the bamboo peak is observed to appear at the high temperature side of the conventional grain boundary internal friction peak. The conventional grain boundary internal friction peak decreased and moved to higher temperature. The bamboo peak owns an activation energy of 1.75eV. When average grain size exceeded the diameter of samples, Pb strength was reduced and its position was shifted to a lower temperature. Based on the grain boundary sliding model, Pg and Pb peaks were explained. Their dependence on annealing temperature and time was determined by considering the effects of contained Ce atoms and other impurities on the relaxation across grain boundary.
Authors: A. Stanislawczyk
Abstract: A new algorithm OMI (Optimization in Multiple Intervals) for the computation of the logarithmic decrement from exponentially damped harmonic oscillations is described. This method is shown to be effective and computationally compact for high damping materials. A comparison between the OMI algorithm and the four classical methods usually used in the computation of the logarithmic decrement is reported. The OMI algorithm yields high precision in the computation of the logarithmic decrement and the smallest dispersion of experimental points on the plots of mechanical loss spectra. The effect of the acquisition parameters and the experimental conditions on the results of computations of the logarithmic decrement and the relative error is discussed.
Authors: Ion Hopulele, Mihai Axinte, Carmen Nejneru
Abstract: Considering that, in Accordance with the Laws of Physics, the Sound Travels only through Elastic Bodies, the Main Characteristic of an Acoustic Material is the Elasticity. Classifying the Metallic Materials in this Regard is Quite Difficult, as the Elasticity is Characterized by more than One Component (static Elastic Modulus, Dynamic Elastic Modulus, Static Elastic Limit, Elastic Limit, Elastic Deformation Linearity, Damping Capacity). Best Acoustic Properties of some Metallic Materials are Widely Used in the Construction of Transducers, Musical Instruments, Bells Etc. for this Purpose, a Study on Three Metallic Materials was Conducted: a Cusn Alloy for Bells, a Cast Aluminum Alloy and a Martensitic Cast Iron. this Study Highlights both the Chemical Composition, Structure, Mechanical Properties and Damping Capacity of Sounds.
Authors: Igor S. Golovin, H.R. Sinning, J. Göken, Werner Riehemann
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