Effect Of Internal Friction Research Articles

Effect of internal friction on transformation twin dynamics in perovskiteSrxBa1−xSnO3(x=0.6,0.8)

The dynamics of transformation twins in ${\mathrm{Sr}}_{x}{\mathrm{Ba}}_{1\ensuremath{-}x}\mathrm{Sn}{\mathrm{O}}_{3}$ $(x=0.6,0.8)$ perovskite has been studied by dynamical mechanical analysis in three-point bend geometry. This material undergoes phase transitions from orthorhombic to tetragonal and cubic structures on heating. The mechanical loss signatures of the transformation twins include relaxation and frequency-independent peaks in the orthorhombic, and tetragonal phases, with no observed energy dissipation in the cubic phase. The macroscopic shape, orientation, and relative displacements of twin walls have been calculated from bending and anisotropy energies. The mechanical loss angle and distribution of relaxation time are discussed in terms of bending modes of domain walls.

Modelling the Bordoni peak†

In fcc metals, kink-pair formation in dislocation lines aligned along close-packed lattice directions can give rise to internal friction effects called Bordoni relaxation. The resulting internal friction peak is a superposition of several individual peaks, each with complex features. To study this behaviour, the differential equation describing the movement of dislocation segments by thermally activated kink-pair formation is solved numerically. It is assumed that the kink mobility is high. As a result, the movement is asymmetric, since the backward movement can occur by kink collapse without need of thermal activation. The influence of the external parameters, such as segment length, number of geometrical kinks, internal stress, amplitude and frequency of the applied stress and temperature on the position and shape of the internal friction peaks is studied. When the original configuration is in a bowed out state, the Paré condition is satisfied. Application of an external stress increases the magnitude of internal friction by aligning originally inclined dislocation segments in the direction of the Peierls valleys. †Dedicated to Prof. Frank. R. N. Nabarro on the occasion of his 90th birthday, on 7 March 2006.

Shearing flows of a dry granular material—hypoplastic constitutive theory and numerical simulations

In the present study, the Goodman–Cowin theory is extended to incorporate plastic features to construct an elasto-visco-plastic constitutive model for flowing dry granular materials. A thermodynamic analysis, based on the Muller–Liu entropy principle, is performed to derive the equilibrium expressions of the constitutive variables. Non-equilibrium responses are proposed by use of a quasi-linear theory, in particular a hypoplastic-type relation is introduced to model the internal friction and plastic effects. It is illustrated that the Goodman–Cowin theory can appropriately be extended to include frictional effects into the evolution equation of the volume fraction (i.e. the so-called balance of equilibrated force) and the equilibrium expression of the Cauchy stress tensor. The implemented model is applied to investigate conventional steady isothermal granular flows with incompressible grains, namely simple plane shear, inclined gravity-driven and vertical channel-flows, respectively. Numerical results show that the hypoplastic effect plays a significant role in the behaviour of a flowing granular material. The obtained profiles of the velocity and the volume fraction with hypoplastic features are usually sharper and the shear-thinning effect is more significant than that without such plastic effects. This points at the possible wide applicability of the present model in the fields of granular materials and soil mechanics. In addition, the present paper also provides a framework for a possible extension of the hypoplastic theories which can be further undertaken. Copyright © 2006 John Wiley & Sons, Ltd.

A strain-based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets

Numerical modelling of impact cratering has reached a high degree of sophistication; however, the treatment of porous materials still poses a large problem in hydrocode calculations. We present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation. In contrast to previous attempts (e.g., P-alpha model, snowplow model), our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure. Our new ɛ-alpha model requires only four input parameters and each has a physical meaning. The model is simple and intuitive and shows good agreement with a wide variety of experimental data, ranging from static compaction tests to highly dynamic impact experiments. Our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation. We present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity-scaled source size.

Energy absorption of a nanoporous system subjected to dynamic loadings

In a previous study [X. Kong and Y. Qiao, Appl. Phys. Lett. 86, 151919 (2005)], we analyzed the energy absorption behaviors of a nanoporous system subjected to quasi-static loadings. In this work, the performance of similar systems under dynamic loadings is investigated through a Hopkinson bar experiment. The energy absorption efficiency increases significantly with the loading rate, which is attributed to the effect of internal friction.

Development of a High-speed Electromagnetic Repulsion Mechanism for High-voltage Vacuum Circuit Breakers

This paper presents a design and testing of a new high-speed electromagnetic driving mechanism for a high-voltage vacuum circuit breaker (VCB). This mechanism is based on a high-speed electromagnetic repulsion and a permanent magnet spring (PMS). This PMS is introduced instead of the conventional disk spring due to its low spring energy and more suitable force characteristics for VCB application. The PMS has been optimally designed by the 3d non-linear finite-elements magnetic field analysis and investigated its internal friction and eddy-current effect. Furthermore, we calculated the dynamic of this mechanism coupling with the electromagnetic field and circuit analysis, in order to satisfy the operating characteristics—contact velocity, response time and so on, required for the high-speed VCB. A prototype VCB, which was built based on the above analysis shows sufficient operating performance. Finally, the short circuit interruption tests were carried out with this prototype breaker, and we have been able to verify its satisfying performance.

A Bending Mode Analysis for Growing Microtubules: Evidence for a Velocity-Dependent Rigidity

Microtubules are dynamic protein polymers that continuously switch between elongation and rapid shrinkage. They have an exceptional bending stiffness that contributes significantly to the mechanical properties of eukaryotic cells. Measurements of the persistence length of microtubules have been published since 10 years but the reported values vary over an order of magnitude without an available explanation. To precisely measure the rigidity of microtubules in their native growing state, we adapted a previously developed bending mode analysis of thermally driven shape fluctuations to the case of an elongating filament that is clamped at one end. Microtubule shapes were quantified using automated image processing, allowing for the characterization of up to five bending modes. When taken together with three other less precise measurements, our rigidity data suggest that fast-growing microtubules are less stiff than slow-growing microtubules. This would imply that care should be taken in interpreting rigidity measurements on stabilized microtubules whose growth history is not known. In addition, time analysis of bending modes showed that higher order modes relax more slowly than expected from simple hydrodynamics, possibly by the effects of internal friction within the microtubule.

The annealing and aging effects of high temperature internal friction in pure aluminum

Abstract By using an inverted torsion pendulum we investigated the effects of annealing and aging on high temperature internal friction in pure aluminum. In 99.9 wt.% aluminum we found only one internal friction peak, and its height decreased gradually and finally disappeared with increasing annealing temperature. In 99.993 wt.% aluminum, two internal friction peaks were observed; one vanished and was accompanied by the appearance and development of the other with increasing annealing temperature. The later peak was reproducible during the annealing–aging–annealing cycle. In 99.999 wt.% aluminum, only one internal friction peak was found and the peak height decreased when the specimen was aged at room temperature. We think that the high temperature internal friction peaks in pure Al originate from the stress relaxation across grain boundary and the annealing and aging effects on them were associated with the condensing of impurities on grain boundaries and depend on the interaction of impurities with grain boundaries.

Experimental study of the effects of amplitude-dependent internal friction in a sandstone bar resonator

Results of an experimental study of the effects of amplitude-dependent internal friction (nonlinear loss, resonance frequency shift, and sound-by-sound damping) in an acoustic bar resonator made of sandstone are presented. The measurements were carried out for the first five longitudinal modes of the resonator. The analytical description of the observed effects is performed within the framework of the phenomenological equations of state that include hysteretic and dissipative components of nonlinearity. The parameters of the hysteretic and dissipative components of sandstone nonlinearity are obtained from a comparison of the experimental data with analytical dependences describing the nonlinear effects.

Acoustic resonance widening in GW detectors: detailed modelling of the dissipation processes

Internal friction effects are responsible for line widening of the acoustic resonance frequencies in mechanical oscillators and result in damped oscillations of its eigenmodes with a decay time Q/ω. We study the solutions to the equations of motion for the case of spherical oscillators, to be used as the next generation of acoustic gravitational wave detectors, based on various different assumptions about the material's constituent equations. Quality factor dependence on mode frequency is determined in each case, and a discussion of its applicability to actual gravitational wave detectors is made on the basis of available experimental evidence.

微視的モデルによる巨視的な応力-ひずみ特性発現機構の解析

In order to understand how the macroscopic stress-strain properties of metallic materials are caused by their microscopic structures, we mathematically analyze a microscopic model which describes the dynamics of the materials by applying the theory of soliton system. We treat the typical atomic chain model which includes topological defects and consists of the thermal effect, the interactions of atoms, the friction from the environment and the external force. Moreover, we extend the chain model as a microscopic model by considering the effects of work hardening and internal friction. The dynamics of the microscopic model are given by the extended thermal overdamped sine-Gordon equation and a coupled equation. Solving the pair of equations by the perturbation expansion, we derive the macroscopic stress-strain response. In the static case, we show that inelastic behavior is displayed by the microscopic model and that it is derived from the effects of work hardening and internal friction. In the dynamic case, the shape of the hysteresis loop obtained by the microscopic model qualitatively corresponds to well-known experimental data better than that of the typical rheological model. We analytically show the effect of the work hardening and the interal friction on the hysteresis loop.

Effect of Internal Friction on Biofilament Dynamics

We consider biofilaments-flexible multimolecule structures common in cell biology-and show how "internal" friction associated with either conformational fluctuations or with fluid flow through narrow pores inside the filaments can dominate the external hydrodynamic friction usually considered to be the main energy dissipation process. The signature of this is wave-number-independent relaxation time of bending fluctuations. Preliminary experimental data for bending fluctuations of single folded (mitotic) chromosomes display these dynamics.

Fatigue resistant silicon nitride ceramics due to anelastic deformation and energy dissipation

To investigate the link between internal friction and fatigue resistance of sintered silicon nitride at elevated temperatures, impulse excitation, torsion pendulum and uniaxial tension–compression tests were performed. At low stress-amplitudes, an internal friction peak is observed and associated with the glass transition of amorphous intergranular phases (IGPs). This peak constitutes a reliable means of energy dissipation for otherwise brittle ceramics. The high amplitude uniaxial tests have revealed a new and much larger internal friction effect than previously could be expected from low amplitude test results. Rheological analysis indicates that the underlying deformation is truly anelastic. Within the investigated stress-amplitude range (30–150 MPa), the damping is shown to increase linearly with stress-amplitude. As a consequence, energy dissipation in a cyclically loaded component will increase locally at stress concentrations such as crack tips. This results in an increased crack propagation resistance, and explains earlier observations of a positive fatigue effect in sintered silicon nitride at high temperature.

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.

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

The amplitude-independent mechanical quality factors (reciprocal internal frictions) of the binary alloys 98Cu–2Be and 94Cu–6Be, and the commercial alloys Cu–Be “10” (C17 500), phosphor bronze “A” (C51 000), and silicon bronze “A” (C65 500) were measured in the temperature range 50 mK–300 K. This study was motivated by the need to identify materials with very low acoustic losses, which could be used for the fabrication of resonant-mass detectors of gravitational radiation. Data were obtained from measurements of 1 kHz torsional modes of mechanical resonators configured to minimize extraneous internal friction effects. Flexural mode measurements at 9 kHz gave substantially the same quality factor for the 94Cu–6Be as seen at 1 kHz from 50 mK to 10 K. The measured quality factor of this alloy of about 40 million at 50 mK is the largest that has ever been observed in a copper alloy. High resolution resonator frequency data below 10 K are shown to exhibit a temperature dependence which has been associated with dislocation motion in pure elemental metals.

Aging Characterization of Adhesives and Bonded Joints by Non-Destructive Damping Measurements

Long term performance of adhesive joints in various environments is the main concern of bonding technology in both military and civil applications. Joint strength can be greatly degraded by aging. Periodic non-destructive strength evaluation of bonded devices is, thus, a critical necessity for quality assurance. Developing a tool for non-destructive testing of joint strength in bonded devices is the long-term goal of the present study. The method revealed here is application of vibration analysis, concentrating on the damping behavior of the tested object. Contrary to other non-destructive evaluation methods, which indicate only the presence of defects, this method is sensitive mainly to the material properties, thus can assess material degradation. In this case, the property of interest is the strength. In stage 1 of this research (Shiloh et al., 1996) it was shown that aging of adhesives and bonded joints can be evaluated non-destructively by vibration analysis, based on the internal friction (damping) effect. Good correlation between the specific damping capacity (SDC) and the shear strength of bonded joints was determined. In stage 2 (Shiloh et al., 1998), an additional step towards the target application was achieved, by broadening the range of the tested specimen. Additional adhesives and adherends as well as various geometries and sizes of the bonded joints were tested. The effect of the following factors was established: adhesive aging or shear strength, adherends, temperature, sample size [up to diameter of 356 mm (14")] and sample shapes (flats and rings). The results show that the method is most promising. For more reliable wide-ranging guidelines, theoretical analysis by numerical simulation of vibrational stresses is required.

Aging Characterization of Adhesives and Bonded Joints by Non-Destructive Damping Measurements

Long term performance of adhesive joints in various environments is the main concern of bonding technology in both military and civil applications. Joint strength can be greatly degraded by aging. Periodic non-destructive strength evaluation of bonded devices is, thus, a critical necessity for quality assurance. Developing a tool for non-destructive testing of joint strength in bonded devices is the long-term goal of the present study.The method revealed here is application of vibration analysis, concentrating on the damping behavior of the tested object. Contrary to other non-destructive evaluation methods, which indicate only the presence of defects, this method is sensitive mainly to the material properties, thus can assess material degradation. In this case, the property of interest is the strength.In stage 1 of this research (Shiloh et al., 1996) it was shown that aging of adhesives and bonded joints can be evaluated non-destructively by vibration analysis, based on the internal friction (damping) effect. Good correlation between the specific damping capacity (SDC) and the shear strength of bonded joints was determined.In stage 2 (Shiloh et al., 1998), an additional step towards the target application was achieved, by broadening the range of the tested specimen. Additional adhesives and adherends as well as various geometries and sizes of the bonded joints were tested. The effect of the following factors was established: adhesive aging or shear strength, adherends, temperature, sample size [up to diameter of 356 mm (14")] and sample shapes (flats and rings).The results show that the method is most promising. For more reliable wide-ranging guidelines, theoretical analysis by numerical simulation of vibrational stresses is required.

Flexural composite oscillators for the measurement of anelastic and elastic properties of solids at frequencies of 1 to 10 kHz

Longitudinal composite oscillators for measuring internal friction, piezoelectric modulus, and strain modulation effects are usually limited to a frequency range of 30 to 200 kHz. If the same crystals are vibrated in flexure, a longitudinal strain can be introduced with the resonance frequency below 3 kHz while at the same time keeping the inherent high Q of the composite system. This paper develops the theory for the strain amplitude and damping for the flexural composite oscillator made up of two quartz crystals plus specimen and, if appropriate, spacers. This high Q technique of vibrating in flexure has applications for strain modulation and damping experiments.

Fracture Analysis By Distinct ElementMethod, Introducing Symmetrical Analysis

Although the Distinct Element Method has been approved as a strong tool for analysis of both granular and solid media, but there is some shortcomings which the main ones are need for large memory and time for computation. In order to increase the efficiency of this method some new concepts have already developed. Here, anew concept for the DEM analysis of symmetric structures is introduced. New boundary conditions are defined for the elements near and on the axis of symmetry. By analyzing only half of the structure the computation and the memory needed for computation will be half. The developed concept is verified by fracture analysis of a concrete beam under two point-loads. The case study is done by comparison between analysis of the whole beam and the analysis of the half of the beam. A parametric study is also done for investigation on the effects of internal friction and the cohesion on the concrete beam behavior, using the developed symmetrical analysis.

Internal Friction and Photoacoustic Effects in A2B6 and A2B7(HgI2) Single Crystals at Different Levels of Ultrasound Strain Amplitude

A comparison of effects in damping and Young modulus under the influence of illumination for ZnSe and HgI 2 demonstrates quite different mechanisms of photoacoustic interaction in the crystals: a drift of photocarriers in the electric field which arises due to piezoelectricity for the first case and a dislocation pinning mechanism for the second one. Spectral responses of the photoacoustic effect in both amplitude independent and dependent damping range are presented for mercury iodide crystals. The newly found acousto- and photo-optic effects in the luminescence spectrum of HgI 2 allow one to specify the photosensitive dislocation pinning centre as an exciton state of carriers on a stoichiometric point defect of the lattice (iodine ur mercury vacancy or interstitial).