Mechanism Of Internal Friction Research Articles

Internal friction peak in bicrystals with different misorientations

The internal friction in pure aluminum bicrystals with misorientation angles ranging from 5.8\ifmmode^\circ\else\textdegree\fi{} to 44.0\ifmmode^\circ\else\textdegree\fi{} has been investigated. A substantial internal friction peak associated with a grain boundary (GB) appears at medium temperature in each of the bicrystals. The activation parameters of the peak reveal a distinct transition from low- to high-angle boundaries, indicating a structural transition. The difference in activation parameters between low- and high-angle GBs is interpreted by different mechanisms of internal friction.

Mechanism of internal friction in bulk Zr65Cu17.5Ni10Al7.5 metallic glass

Mechanism of internal friction in bulk Zr65Cu17.5Ni10Al7.5 metallic glass

Effect of Structure on the Damping Capacity and Mechanical Properties of Iron Alloys with Magnetomechanical Damping

The effect of the size of grains and magnetic domains on the damping capacity primarily determined by magnetomechanical damping is considered for iron alloys with the ferrite structure. The indeterminacy of the value of magnetomechanical damping in a single crystal and in large-grain polycrystals is considered. The effect of carbide, graphite, and ordered phases on the mechanical properties and damping capacity of ion alloys with predominantly ferritic structure and with other matrices is studied. The results of the study are generalized from the standpoint of structural mechanisms of internal friction.

Anelasticity and Damping of Thin Aluminum Films on Silicon Substrates

A new dynamic measurement system has been developed to investigate damping in thin metal films. This system includes a vacuum chamber, in which a free-standing bilayer cantilever sample is vibrated using an electrostatic force, and a laser interferometer to measure the displacement and velocity of the sample. With this equipment, internal friction as low as 10/sup -5/ in micrometer thick metal films in a temperature range from 300 to 750 K can be measured. Free-standing cantilevers with different frequencies have been fabricated using well-established integrated circuit (IC) fabrication processes. The cantilevers consist of thin metal films on thicker Si substrates, which exhibit low damping. From measurements of internal friction of Al thin films at various temperatures and frequencies, it is possible to study relaxation processes associated with grain boundary diffusion. The activation energy calculated from the damping data is 0.57 eV, which is consistent with previous research. This value suggests that the mechanism of internal friction in pure Al films involves grain boundary diffusion controlled grain boundary sliding. A model to describe these damping effects has been developed. By deriving an expression for the diffusional strain rate using a two-dimensional (2-D) Coble creep model, and modifying the conventional standard linear solid model for the case of bending, it is possible to give a good account of the observed damping.

Internal friction in metallic foams and some related cellular structures

Abstract Density, pore size and shape, chemical composition, pre-deformation, number of vibration, and air pressure influence damping of cellular metallic materials (CMM: foams with open and closed-cells, sponges and porous sintered metals). At least three ranges of amplitude domains of vibrations are distinguished with respect to internal friction mechanisms. The thermoelastic damping plays an important role in the range of amplitude-independent damping (Al- and Zn-based foams). The amplitude-dependent damping caused by reversible motion of dislocations is enhanced in porous structures by localised stresses. In case of magnetic CMM, the magnetomechanical effect can be an additional source of damping (Ni-based sponges). Up to a certain amplitude of deformation the damping is stable, i.e. practically does not depend on the number of vibrations. Beyond this limit, irreversible microplastic deformation (mpd) enhances the amplitude dependence; a model for damping in porous materials is discussed for this “microplastic” range. An additional time dependence due to fatigue processes is attributed to growth and movement of cracks.

Piezoelectric hysteresis analysis and loss separation

Losses in piezoelectrics are approached by considering a description of direct stress–charge displacement hysteresis. Shortcomings of the usual loss models (viscous and Rayleigh, taken separately) are briefly demonstrated. Then, a mixed model for piezoelectric losses superimposing viscous and Rayleigh types of descriptions is proposed and validated for a modified lead titanate and lead zirconate titanate (PZT). It is shown for PZT that viscous and Rayleigh-like loss contributions can be effectively separated by fitting the piezoelectric hysteresis loop with an expression combining the two lossy responses. The possibility to obtain all the necessary parameters that describe piezoelectric stress nonlinearity from one single piezoelectric loop is also demonstrated in the case of PZT. The origins of the mixed loss behavior are interpreted as arising from domain wall motion in terms of internal friction mechanisms and of pinning energy ranges.

Effects of microstructure on the internal friction of carbon–carbon composites

Internal friction directly depends on the microstructure of material. For carbon–carbon composites made up of fibers, matrix and interface, internal friction mechanisms involved are more complex. In present work, the effects of microstructure on the internal friction in carbon–carbon composites are studied. During the Chemical Vapor Infiltration (CVI) process, the internal friction in carbon–carbon composites decreases with the increasing of density. The experimental result does not accord with the equation for conventional composites. Considering the porous structure and non-full ideal interfacial adhesion in carbon–carbon composites, we develop a modified equation for the quantitative description of internal friction, which shows good agreement with the experimental results. Furthermore, internal friction related to pyrolytic carbon matrix, fibers and interface are discussed, respectively, which gives us a fundamental understanding on the internal friction in carbon–carbon composites. Among these internal friction mechanisms, interfacial internal friction is of special interest, as it causes some abnormal internal friction phenomena in carbon–carbon composites.

Effects of content and particle size of Si crystal on damping property of powder forged Al–Si alloy

The effects of the Si content and Si crystalline size on the damping properties of powder forged (PF) Al–Si alloys has been investigated using a fast Fourier transformation (FFT) analyser. A quantitative image analysis method was used successfully to determine the mean diameter and distribution of Si crystals in the aluminium alloy. The damping capacity greatly depends on the mean diameter of Si crystals. The value of δ for heat treated specimens with Si crystals of 2–5 μm is 4 to 25 times less than that for the as forged specimens with Si crystals of 1–5 μm. This indicates that the vibration is absorbed at the interface between the Si particles and the aluminium matrix by a mechanism of internal friction. Therefore, a fine distribution of Si crystals and/or elimination of crystal coarsening should contribute to improved damping.

Theory of amplitude-dependent internal friction and acoustoplastic effect in shape memory alloys

Mechanisms of amplitude-dependent internal friction and the acoustoplastic effect in shape memory alloys are discussed in terms of the previously developed theory of diffuse thermoelastic martensitic transformations. The amplitude dependences of these effects are found for different temperatures and applied stresses.

Internal friction behavior of carbon–carbon composites

The fundamental internal friction behavior of carbon–carbon composites is studied. Two internal friction mechanisms are proposed according to the special internal friction characteristics in carbon–carbon composites. A thermoelastic mechanism, which is independent of amplitude, mainly leads to the internal friction increase with increasing frequency. The other is a static hysteresis mechanism that internal friction depends on the amplitude but is independent of frequency. Moreover, it is very interesting that some abnormal internal friction phenomena can be observed. The variation characteristics of internal friction and dynamic modulus versus temperature in carbon–carbon composites are quite different from other materials. This special behavior may be a result of interfacial CTE effects, as well as the coordination effects of the individual response of the fibers, matrix and interface of carbon–carbon composites. Finally, the validity of internal friction analysis methods for densification process monitoring and non-destructive inspection of carbon–carbon composites is discussed for the first time. The results indicate that internal friction testing methods have great potential for monitoring process and inspecting components of carbon–carbon composites non-destructively.

The mechanism of low frequency internal friction in concentrated Cu-Al and Cu-Zn alloys

The mechanism of low frequency internal friction in concentrated Cu-Al and Cu-Zn alloys

The mechanism of low frequency internal friction in concentrated Cu-Al and Cu-Zn alloys

Abstract The present paper attempts to give a detailed theoretical analysis of the mechanism for a relaxation peak of internal friction which occurs around 210K in concentrated Cu-Al and Cu-Zn alloys at about 1 Hz. It is shown that the observed peak is a superposition of two components, which are respectively induced by the overall motion of extended dislocations (acoustical mode) and the relative motion between two partials (optical mode). Assuming that the solute atom-vacancy pairs on dislocation lines act as mobile pinning agents damping the motion of dislocations, the evaluated peak temperature is close to the observed one.

Internal friction and relaxation mechanism of F-doped SiO 2 glasses

The internal friction and the Young's moduli of pure SiO 2, SiO 2 –4 mol% F and –8 mol% F glasses were measured in the temperature range of 1.6–250 K. The temperature dependencies of the internal friction were not different except for their peak values, which showed differences of a few percent at 35 K. In contrast, the Young's moduli of F-doped SiO 2 glasses were 7.5% (–4 mol% F) and 15% (–8 mol% F) less than that of pure SiO 2 glass, respectively. Both temperature dependencies were analyzed on the basis of Debye relaxation by the distributed double-well potential model.

The mechanism of dynamic internal friction during creep

A new mechanism of dynamic internal friction during creep has been proposed. In addition to the energy dissipated due to the motion of dislocations, we suggest that the energy dissipated due to the formation of new dislocations during deformation has to be taken into account. We show that the latter component plays an important role in the dynamic internal friction, and is responsible for the appearance of the Q −1-t peak and the amplitude effect. The predictions derived from this mechanism are in agreement with experiments. Based on the analyses in this study, some useful information can be deduced from the internal friction data.

Mechanisms of internal friction in a cu-zn-ai shape memory alloy

The internal friction in a Cu-Zn-AI shape memory alloy has been studied in various microstructural states in a wide range of stress amplitude. Simultaneous measurements of the corresponding shape change indicate correlations between internal friction and the deformation mechanisms. It is found that the observed stress-amplitude dependence of the internal friction cannot be represented by a single formalism. Rather, in different ranges of stress amplitude, where the internal friction mechanisms are different, separate formalisms are applicable. The comparison of the experimental results with a previously developed theory is presented.

Anomalous elastic and inelastic properties of erbium in c-axis hexagonal direction

The Young's modulus E and internal friction Q -1 as functions of temperature in the region 4.2-380 K have been studied in detail for a sample of erbium single crystal oriented in the c-axis direction. Unique technique of flexural auto vibrations of a thin sample-bar on sound frequencies (∼ 1 kHz) was used for these investigations. Anomalous behavior of E( T) and Q -1( T) curves was found, not only in the well known conventional magnetic transition points Δ 1 ≈ 19 K, Δ B ≈ 53 K and Δ 2 ≈ 84 K, but also in points of successive transitions between commensurate structures in the temperature region 27–42 K. At least five such transition points were unambiguously stated. Magnetic part of the Young's modulus E m has been theoretically computed from paramagnetic region data. Various possible mechanisms of internal friction in erbium are also discussed.

A relaxation-defect concentration model for internal friction in BSCCO between 78 K and 160 K

Ultrasonic internal-friction and velocity measurements at 85 kHz in single crystals of Bi 2Sr 2CaCu 2O have provided evidence for the occurence of a phase change at 165 K and for two further internal-friction mechanisms which occur between this temperature and 80 K. Quantitative measurements have closely fitted a relaxation-defect concentration model we have developed. This model is further supported by slow temperature-cycling and quenching experiments which yield an activation energy of approximately 24±2 meV associated with the relaxation process.

On internal friction mechanisms in hydrogen charged stable austenitic stainless steel

The internal friction method is used to obtain data on hydrogen diffusion parameters and hydrogen interactions with other solutes as well as crystal lattice defects in a hydrogenated austenitic stainless steel. Such information is important, for example, for development of hydrogen embrittlement mechanisms of the metallic materials. The application of the internal friction data needs, however, adequate understanding on the nonelastic mechanical response mechanisms in the hydrogenated austenitic steels. In spite of the numerous studies, the nature of the internal friction peaks in hydrogen charged steels is still a controversial issue. Furthermore, the high-fugacity electrolytic hydrogen charging commonly used in the internal friction experiments results in a marked concentration gradients of hydrogen, formation of hydride-like phases and damage of the crystal lattice in the surface layers of material. The hydrogenated surface layers may contribute to the internal friction which is also discussed in a number of papers and needs further investigation. The subject of the present study is the mechanistic analysis of the internal friction spectra observed at low temperatures in an electrolytically charged stable austenitic stainless steel.

Acoustic quality factor of aluminum alloys from 50 mK to 300 K

Measurements of the acoustic quality factor (reciprocal internal friction) of commercial aluminum alloys 2090, 5056, and 6061 in a torsional vibrational mode at a frequency of 1 kHz in the temperature range from 50 mK to 300 K are reported. The temperature dependence of the mode frequency, which is a measure of the shear modulus of the material, is also given. The quality factor (Q) of all alloys exhibited the highest values at the lowest measurement temperature. A heat-treated sample of the 5056 alloy gave the highest Q of 6.5×107 at 53 mK. Maximum Q values of 8.9×106 in 2090 and 6.5×106 in 6061 were observed. Internal friction mechanisms which may explain the measured Q values are discussed. The results provide support for the planned construction and operation of very sensitive 50-mK aluminum-alloy bar gravity-wave detectors.

Internal friction mechanism near the ferroelastic phase transition in YBa2Cu3O7−6

Abstract It is shown that at infralow frequencies near the ferroelastic phase transition point of YBa2Cu3O7-6 ceramics fluctuation mechanism responsible for the internal friction takes place and that tetragonal-orthorhombic phase transition is the first-order one.