Inverted Torsion Pendulum Research Articles

Mechanical spectroscopy measurements on SMA high-damping composites

High-damping materials have attracted much attention to solve problems such as acoustic pollution, nano-scale vibration isolations in electronic industry, vibration damping in civil engineering, etc. Shape memory alloys (SMAs), which intrinsically present high-damping capacity, are considered as alternative materials to the traditionally used polymeric ones, because they present better mechanical properties at moderate temperatures. A new kind of high-damping metal matrix composites has been produced by embedding a relatively high amount (approximately 60 vol.%) of Cu–Al–Ni SMA particles with metallic matrices (In, In + Sn). The damping properties have been characterized by mechanical spectroscopy, using an inverted torsion pendulum, as a function of temperature (150–400 K), frequency (0.01–3 Hz), and strain amplitude (2 × 10 −5 to 8 × 10 −5). The materials exhibit internal friction higher than 0.5 in a relatively wide temperature range. The ability of matching the temperature of maximum damping, through the composition of the SMA, opens new possibilities for designing high-damping materials for specific applications.

High-temperature internal friction in a Fe–38 at.% Al intermetallic

A new sub-resonant inverted torsion pendulum has been used to measure the internal friction and dynamic modulus of an Fe–38 at.% Al alloy as a function of temperature from 600 to 1350 K and constant oscillating frequency ranging from 0.01 to 3 Hz. Two internal friction peaks and a background increasing exponentially with temperature were observed. Both peaks overlap and have different shifts to lower temperatures with decreasing frequency indicating different involved relaxation mechanisms. We measured the activation parameters of the main peak. Finally we applied a recently proposed model to remove the high-temperature internal friction background and perform a spectra de-convolution to find the parameters characterizing both relaxations. The mechanisms responsible for both relaxations are discussed.

Temperature dependence of sound attenuation and shear modulus of ultra fine grained copper produced by equal channel angular pressing

The influence of temperature on shear modulus and internal friction in ultrafine-grained copper processed by equal channel angular pressing (ECAP) was investigated in the temperature range from 150 to 520 K. Acoustic measurements were performed on the inverted torsion pendulum at the frequencies of ∼18 and ∼45 Hz. An irreversible shear modulus increase and a concurrent decrease in sound attenuation were observed in the temperature region from ∼350 to 450 K on the first heating of specimens. The activation energy E ≈ 1.05 eV and the attempt frequency ν 0 ≈ 10 10 s −1 of the irreversible relaxation process were determined using the measurements at different heating rates. The overall decrease in the shear modulus in ECAP-processed copper was shown to be made up by two components: a temperature-independent and a temperature-dependent ones. The latter is accompanied with an additional internal friction of the relaxation type, which is reversible up to ∼350 K. An estimate of the activation energy for this reversible relaxation process was obtained. Possible mechanisms responsible for the anomalous behavior of the shear modulus and the sound attenuation in ultrafine-grained copper are discussed.

Relaxation resulting from atomic defects in quenched Fe-Al alloys

Two relaxational internal friction peaks in quenched Fe-Al alloys with different Al content have been investigated using a computer-controlled automatic inverted torsion pendulum through free-decay and forced vibration method. It has been shown that the two peaks (P1, 180℃ and P2, 340℃) appear only in the heating process and do not appear in subsequent in-situ cooling process. It is suggested that P1 resulted from the stress-induced reorientation of di-vacancies, which consists of the reorientation of nearest neighbour Fe-vacancies on the α and β (or γ) sublattice sites. The relaxation strength of P1 varies im-monotonicly with Al content and there is a maximum at about 25% Al(atomic percent). There is no P1 peak in the Fe-Al alloys with lower Al content since vacancies exist in the form of isolated vacancies. When Al content is over 25%, the number of vacancies on β and γ sites is reduced. Therefore, the nearest neighbour di-vacancies are decreased and the height of P1 peak declines. P2 originates from the stress-induced reorientation of FeAl-VFe dipoles under. P2 does not appear in the Fe-Al alloys with Al less than 22% since no FeAl anti-site atoms and FeAl-VFe dipoles are produced.

Shear Strain and Spontaneous Twisting of Ferroelastic Crystals Ba2NaNb5O15 and K2Ba(NO2)4

Using an inverted torsion pendulum, the peculiarities of low-frequency shear elastic and anelastic properties of the ferroelastic crystals Ba 2 NaNb 5 O 15 and K 2 Ba(NO 2 ) 4 have been investigated for various crystallographic oriented samples at temperature variation in the vicinity of their phase transition points. The work gives insight into the nature of the spontaneous shear strain behavior and spontaneous torque arising in the samples at the Curie point.

High-Temperature Internal Friction of Metallic Glasses with Widely Different Glass-Forming Ability

The internal friction (IF) of binary, ternary, quaternary, and quinary metallic glasses with widely different glass-forming ability (GFA) has been studied. A single-roller melt-spinning apparatus was used for preparing ribbon specimens. An inverted torsion pendulum was used in the IF measurement. The measurements were performed from room temperature, through the glass transition temperature, up to the crystallization temperature. The background IF monotonously increases with increasing temperature. The increase is of the thermal-activation type, and the activation energy E is determined. For alloys with higher GFA, the E value tends to be higher. IF is inversely proportional to the measurement frequency. The viscosity relaxation based on the Maxwell model is considered, and the relaxation time τ is determined. A linear relationship is seen between the logarithm of pre-exponential factor τ o and the activation energy E . Explanations of these results and discussions concerned are presented.

Stabilization of metallic glass studied by internal friction measurement

The internal friction Q−1 and the oscillation frequency f of Zr–Ti–Cu–Ni–Be metallic glass specimens were measured using an inverted torsion pendulum with the free decay method. A single-roller melt-spinning apparatus was used for preparing the specimens. Isothermal annealing near the glass transition temperature Tg was performed to investigate the stabilization of the specimens. Q−1 decreased with annealing time t due to the stabilization. Q−1-vs-t was measured at various annealing temperatures Ta, and the values of relaxation time τ for the stabilization process were determined. The dependence of τ on Ta showed that the hydrodynamic behavior represented by the Vogel–Tammann–Fulcher form and the hopping behavior represented by the Arrhenius form were observed in high- and low-temperature regions, respectively. The crossover of the two behaviors was seen at a temperature near and somewhat higher than Tg. The result was discussed on the basis of the viscoelastic relaxation in glassy materials.

Influence of the matrix and of the thermal treatment on the martensitic transformation in metal matrix composites

New metal matrix composites were developed with a view to elaborating high-damping materials. These composites were produced by infiltrating a relatively high amount of Cu–Al–Ni shape memory alloy particles with soft metallic matrices. Details on the processing method as well as on the composite microstructure are given in the present paper. An inverted torsion pendulum was used to determine the damping capacity tan δ. High damping values were measured, what implies a promising future for these composites as high-damping materials. The influence of thermal treatments on the microstructure and on the thermoelastic martensitic transformation is discussed. The damping capacity of these materials is associated with the mobility of the martensite interfaces, and a synergetic interaction between the particles and the matrices is suggested.

Friction and relative energy dissipation in sheared granular materials

The oscillating cylinder of a low-frequency inverted torsion pendulum is immersed into layers of noncohesive granular materials, including fine sand and glass beads. The relative energy dissipation and relative modulus of the granular system versus the amplitude and immersed depth of the oscillating cylinder are measured. A rheological model based on a mesoscopic picture is presented. The experimental results and rheological model indicate that small slides in the inhomogeneous force chains are responsible for the energy dissipation of the system, and the friction of the grains plays two different roles in the mechanical response of sheared granular material: damping the energy and enhancing the elasticity.

Stabilization of Zr-base metallic glass studied by isochronal and isothermal annealing experiments

The internal friction Q −1 and the oscillation frequency f of a Zr–Ti–Cu–Ni–Be metallic glass specimen were measured using an inverted torsion pendulum with the free decay method. A single-roller melt-spinning apparatus was used for preparing the specimens. Two kinds of experiments have been performed. In the isochronal annealing experiment, temperature dependences of Q −1 and f were measured from the room temperature up to the crystallization temperature T x. The glass was found to become stabilized state by a long-time annealing near and below the glass transition temperature T g. In the isothermal annealing experiment, time dependences of Q −1 and f were measured at various annealing temperatures T a, and the relaxation time τ for the annealing process was determined. The dependence of τ on T a showed that the stabilization near T g could be due to the viscoelastic relaxation occurring in the glassy material.

Zero-Point Drift in Low-Frequency Mechanical Spectroscopy

The concept of the ‘zero-point drift’, ZPD, is introduced and analyzed on the basis of mechanical loss measurements carried out in a low-frequency mechanical spectrometer – inverted torsion pendulum. It is demonstrated that the ZPD, which modifies damped harmonic oscillations leads to false values of the logarithmic decrement computed from several widely accepted algorithms.

Extended capabilities of an inverted torsion pendulum

The complex elastic modulus, or its real component and the internal friction, are the mechanical variables that characterize the dynamic behaviour of linear viscoelastic materials. Free or forced oscillations produced by inverted torsion pendulums or rheometers are usually used to measure these variables. Linearity is checked sometimes by recording the stress vs. strain curve, otherwise by measuring whether the internal friction or any component of the dynamic modulus is independent of the strain amplitude. This paper demonstrates that the linear dynamic response of viscoelastic materials cannot be assured just by looking at the stress–strain amplitude detected by forced oscillation torsion devices. Furthermore, it is shown that internal friction measured at the resonance frequency of the experimental device provides an extremely accurate tool to determine the presence of nonlinear mechanical effects. This issue is shown for polycarbonate samples submitted to forced oscillations in a torsion pendulum working at resonance.

Stress induced ordering due interstitials in Nb–4.7 at.%Ta

The presence of interstitial elements in metals cause strong changes in their physical, chemical or mechanical properties. These interstitial impurities interact with the metallic matrix atoms by a relaxation process known as stress induced ordering. Relaxation processes give rise to a peak in the internal friction spectrum, known as Snoek effect. The presence of substitutional solutes has a strong influence on Snoek effect, particularly if the substitutional solute element is the one, which interacts with the interstitial element. Anelastic spectroscopy measurements provide information of the behavior of these impurities in the metallic matrix. In this paper, polycrystalline samples of Nb–4.7 at.%Ta alloy have been analyzed in the as-received condition. Measurements of anelastic spectroscopy were carried out using an inverted torsion pendulum, operating with frequency of 2.0–30.0 Hz and in a temperature range between 300 and 700 K. It was observed the presence of a relaxation structure that have been attributed to stress induced ordering due to interstitial atoms around atoms of the metallic matrix. The relaxation structure have been decomposed in its constituent peaks, what it allowed to identify the following relaxation processes: Ta–O, Nb–O and Nb–N.

On the Internal Friction of Ti<sub>50</sub>Ni<sub>25</sub>Cu<sub>25</sub> Particle/Al Smart Composite

The Ti50Ni25Cu25 particle/Al composite was fabricated with 30 vol.% Ti50Ni25Cu25 particles by hot pressing and followed by extruding methods. The internal friction (IF) measurements of the composite were carried out on an inverted torsion pendulum. Ti50Ni25Cu25 particles embedded in Al matrix improve the damping capacity of the composite. The internal friction behavior of Ti50Ni25Cu25 particles is consistent to that of the Ti50Ni25Cu25 bulk material. The mismatch of thermal expansion coefficients between Ti50Ni25Cu25 and Al contributes to the damping capacity of the composite. A high damping capacity of the composite could be obtained at low vibration frequency and large vibration amplitude.

二相ステンレス鋼溶接金属における水素とシグマ相の相互作用

The effect of sigma phase on hydrogen embrittlement in 329J3L duplex stainless weld metal was studied. In addition, in order to clarify the mechanism, hydrogen behavior was also investigated by means of internal friction and fractography technique. The internal friction measurements were conducted over the temperature range from 77K to 373K by using an inverted torsion pendulum for a frequency of about 1.5Hz. After hydrogen charging, almost hydrogen can be diffused easily into the austenite through the ferrite and ferrite/austenite interfaces. Consequently, a sharp significant peak due to hydrogen in austenite was detected at 245K in the as-welded specimen. In the case of as-welded specimen a little reduction of strength was recognized, while the significant loss of strength was observed in the weld metal containing significant sigma phase after hydrogen charging.The sigma phase clearly accelerated hydrogen embrittlement. In the hydrogen-charged specimen containing significant sigma phase, the internal friction analysis revealed that hydrogen entered in the sigma phase lattice and hydrogen was also trapped sigma/austenite phase boundaries. Furthermore, on the fracture surface, the many secondary cracks associated with interaction between sigma phase and hydrogen were observed. Therefore, it could be concluded that sigma phase itself and sigma/widmanstatten austenite phase boundaries were preferential hydrogen cracking sites. It was found that the reduction of notch tensile strength was mainly attributed to many secondary cracks associated with hydrogen and sigma phase.

Influence of Al content on Zener relaxation in Fe-Al alloys

The effect of Al content on the Zener relaxation peak in annealed Fe-Al alloys has been investigated using a computer-controlled automatic inverted torsion pendulum through free-decay and forced vibration method. It has been shown that alloys with medium Al contents show strong relaxation while lower or higher Al content leads to relatively weak Zener relaxation peak. The relaxation in Fe-Al alloys originates from the next-nearest-neighbor atom-pairs and their interaction instead of the nearest-neighbor atom-pairs. The latter may not produce the Zener relaxation because of the ordered-structure formed, which suppresses Zener relaxation.

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.

Low-Frequency Elastic and Anelastic Properties of the Ferroelectric-Ferroelastic PbFe0.5Nb0.5O3 Ceramics with Magnetic Ordering

Low-frequency elastic and anelastic properties of the ceramic PbFe0.5Nb0.5O3 were investigated by the inverted torsion pendulum in the temperature range including the Neel (TN) and Curie (TC) temperatures. The shear modulus and the internal friction anomalies observed in the vicinity of TN are due to magnetostriction connection between a strain and magnetic spin ordering. The electric field effect on elasticity of the sample in the vicinity of TC was found.

Dielectric and Elastic Properties of Relaxor PbMg1/3Nb2/3O3

Anomalous behavior of the low-frequency elastic and anelastic properties of the ceramic PbMg1/3Nb2/3O3 was found by the inverted torsion pendulum within the temperature range corresponding to the diffused phase transition. This transition was also observed via dielectric measurements, which allowed finding the dielectric constant anomaly of the relaxor type.

Elastic and Anelastic Properties of the Ceramics PbFe0.5Nb0.5O3: Anomalies Near T C and T N

Low-frequency elastic and anelastic properties of the ceramic PbFe0.5Nb0.5O3 were investigated by the inverted torsion pendulum in the temperature ranges including the Curie and Neel temperatures. Correlation between elastic and dielectric properties was found to take place within the diffuse ferroelectric phase transition. The shear modulus and the internal friction anomalies observed in the vicinity of TN are due to magnetostriction connection between a strain and magnetic spin ordering.