Attenuation Of Longitudinal Ultrasonic Waves Research Articles

Low-temperature relaxation of various samarium phosphate glasses

Abstract Glasses constructed, (1 − x) (0.6595P2O5–0.0958ZnO–0.2447PbO) · xSm2O3 with x = 0.00, 0.0045, 0.0089, 0.0132, and 0.0261 mol%, had been created to investigate the attenuation of longitudinal ultrasonic waves at 2, 4, 6, and 14 MHz frequencies between 120 and 300 K. At a variety of temperatures, clear peaks of a large absorption curve have been seen. These peaks are dependent on the structure of the glass as well as the switching frequency. Maximum peaks have been shown to shift to higher temperatures, and the increase in overall frequency points to the presence of some kind of relaxation process. A thermally induced relaxation process is responsible for producing a calm approach, which has been identified as a result of this mechanism. A quiet approach has been defined as a consequence of a thermally triggered relaxation mechanism. The variance of the mean energy of activation of the mechanism counts on primarily the amount of Sm2O3 mol%. Such dependency has been evaluated based on the loss of normal linear solid form, attaining low dispersion, and a large allocation of Arrhenius kind relaxation through temperature-autonomous relaxation power. The measured acoustical energy of activation values have been quantifiably represented based on the number of loss centers (amount of oxygen atoms that now move at a double-well potential).

The eddy-current and ultrasonic investigations of the nickel-base superalloy the gas turbine engine blades after exploitation

The work carried out microstructural, eddy-current and ultrasonic studies of the material of spent blades of gas turbine engines made of nickel-base superalloy. To determine the degree of damage to the material of the spent blades, studies of the microstructure were carried out on a scanning electron microscope. It was found that γ' coagulation occurred in some specimens, which corresponds to overheated material. Acoustic studies of the material were carried out using the ultrasonic pulse echo method. Comparative analysis showed that in such specimens there is a significant decrease in the velocity of propagation and attenuation of longitudinal ultrasonic waves. It is found that the readings of the eddy-current flaw detector in overheated specimens differ more than twice in comparison with non-overheated specimens. This fact can be used for operational non-destructive testing of the actual state of the metal structure by the eddy current method with the aim of further safe operation of gas turbine engines.

Effect of thermal cycling on ferroelectric phase transition of PVDF-TrFE based composites as investigated by ultrasonic spectroscopy

ABSTRACTIn this paper we report on the investigation of longitudinal ultrasonic wave attenuation, velocity and ultrasonically induced piezoelectric voltage in P(VDF-TrFE) composites with fillers of conductive carbon nanotubes (CNT). Moreover, temperature dependences of ultrasonic attenuation in the composites were shown to be sensitive to thermal cycling over the ferroelectric phase transition.

On interrelation of damage accumulation in structural steels and physical parameters estimated by methods of acoustic emission and metal magnetic memory

The kinetics of microcrack accumulation at various stages of tension of smooth specimens of structural steels 20, 45, and 12Kh18N9T is studied. The microcrack length, the total number of microcracks, and the relative fraction of damaged surface are estimated, and a correlation of these characteristics with the time dependences of the acoustic emission parameters, the magnetic memory of metals, and the velocity and the attenuation of longitudinal ultrasonic waves is found.

Effects of sand aggregate on ultrasonic attenuation in cement-based materials

Ultrasonic wave attenuation measurements have been successfully used to characterize the microstructure and mechanical properties of inhomogeneous materials; these ultrasonic techniques have the potential to provide for the in-situ characterization of microstructure changes in cement-based materials due to damage. Recent research has applied acoustic scattering models to quantitatively predict ultrasonic attenuation for evaluating the air void content in hardened cement paste. The objective of the current research is to investigate the influence of sand aggregate on the ultrasonic attenuation as a first step towards a full simulation of more realistic microstructures in real concrete. Hardened cement paste samples containing sand aggregate of varying volume fractions are considered. The research employs an independent scattering model and a self-consistent effective medium theory to predict the scattering-induced attenuation of longitudinal ultrasonic waves by the sand inclusions distributed in the cement paste matrix. The predicted attenuation coefficients are compared with measured ones. It is observed that at low volume fractions, both models provide a good estimate of the total attenuation in the specimens. These results indicate that it is possible to use a physics-based model to quantify the effect of sand aggregate on ultrasonic attenuation.

Ultrasonic Investigation of the Effect of Mixing Under Reduced Pressure on the Mechanical Properties of Bread Dough

ABSTRACTMixing is critical to attainment of a desirable gas cell distribution in dough. By varying mixer headspace pressure, changes in the mechanical properties of dough were investigated as a function of the dough's void concentration using low frequency (50 kHz) ultrasonic techniques. For the mixer used, this allowed the volume fraction of voids (Φ) to be varied from ≈0.01 to 0.08. The ultrasonic attenuation of longitudinal waves increased linearly with increases in Φ. If, as reported, pressure reductions during mixing decrease the number density of the voids but do not affect void size, the change in attenuation is proportional to the number of voids. By contrast, the velocity of longitudinal ultrasonic waves decreased dramatically with increasing Φ in the range 0.012 < Φ < 0.03, dropping from a value near that of water to values well below the velocity of sound in air. At higher Φ, the velocity decrease was less rapid. The longitudinal elastic modulus determined from these ultrasonic results shows that the mechanical properties of the dough are sensitive to the presence of gas bubbles. At low void fractions, the elastic behavior of dough is also influenced by changes in dough matrix properties.

Analysis of ultrasonic attenuation in particle-reinforced plastics by a differential scheme

Attenuation of ultrasonic longitudinal waves in some particle-reinforced polymer composites is studied theoretically by a micromechanical model based on a differential (incremental) scheme. A set of differential equations is established by which the attenuation spectrum of the composite can be computed from the known properties of viscoelastic matrix and elastic particles. For a composite reinforced with glass particles with radius 0.15 mm, the proposed scheme is shown to predict the attenuation in better agreement with the foregoing experimental results than the previous simplistic independent scattering model. Based on this scheme, the dependence of the longitudinal attenuation spectrum of a particulate polymer composite on the wavelength-to-particle radius ratio and the particle volume fraction is examined in detail. It is then shown theoretically that the attenuation of the composite decreases monotonically with the particle volume fraction when the particle radius is sufficiently small compared to the incident wavelength, while it shows non-monotonic particle-fraction dependence when the ratio of the particle radius to the wavelength is larger. To examine this theoretical finding from an experimental point of view, the longitudinal attenuation in a glass-particle-reinforced polyester composite with particle radius 0.0225 mm is measured for different particle volume fractions. The measured attenuation characteristics are shown to support the qualitative features of the theoretical prediction.

Resonance attenuation of ultrasonic waves in a superconductor with a moving vortex structure

Equations describing the interaction of ultrasonic waves with a moving vortex structure are derived. The addition to attenuation and the relative change in the velocity of longitudinal ultrasonic waves due to this interaction are calculated. It is found that when a longitudinal ultrasonic wave propagates along the direction of motion of the vortex structure and the velocity V of the structure is equal to half the velocity of the wave, then anomalous acoustic attenuation occurs and the contribution from the ultrasound-vortex interaction to the velocity of the ultrasonic wave vanishes. It is shown that if the vortex structure moves at a sufficiently high velocity, then (in contrast to the case of the structure at rest) a weakly damping collective mode propagating with velocity 2V arises in the structure. It is this mode that is responsible for anomalous attenuation of longitudinal ultrasonic waves.

Ultrasonic attenuation in cleand-wave superconductors

We consider the attenuation of longitudinal ultrasonic waves in a clean two-dimensional d-wave superconductor. We show that the attenuation coefficient is linear in temperature at low temperatures for all in-plane directions of the propagation of the ultrasound, and that the coefficient of the linear term can be used to determine the parameters crucial for the low temperature transport in these compounds.

Uniaxial stress dependence of the elastic wave propagation near normal—incommensurate phase transition in (NH4)2ZnCl4

The effect of uniaxial σ2 stress on the velocity and attenuation of longitudinal ultrasonic wave propagating along the [001] direction in an NH4)2ZnCl4 crystal was studied in the vicinity of the orthorhombic — incommensurate phase transition. A stress induced shift of the transition temperature is dT1/dσ2= 0.2 K/MPa. Application of stress greater that 5 MPa results in the appearance of additional anomalies of velocity and attenuation, which are interpreted as manifestations of a new phase induced by uniaxial Stress.

Anelastic relaxation due to OH pairs in NbZr alloys

In the last 30 years several studies have been made to understand the relaxation mechanisms of the hydrogen atoms present in transition metals and their alloys. In this work, we observed the stress-induced ordering of hydrogen atoms around the interstitial oxygen atoms near the niobium matrix atoms. We studied this relaxation process by measuring the attenuation of longitudinal ultrasonic waves. These measurements were made in Nb1.0%Zr polycrystalline alloys at 10 and 30 MHz, pure and doped with 0.7 and 4.2 at.% hydrogen. The results revealed a thermally activated relaxation structure around 202 K and 235 K for 10 MHz and 30 MHz respectively. This relaxation structure increases with increasing hydrogen concentration.

Ultrasonic, dielectric and mechanical investigation of kaolin-filled styrene-butadiene rubber mixed with a new bifunctional ingredient

A new product named Ismacorr 141 has been prepared from raw linseed oil and aniline. It is mainly used as a corrosion inhibitor for overhead distillation towers. Since the main constituents of this compound are oil and aniline, it may be useful as a bifunctional ingredient (antioxidant/plasticizer) for rubber formulations. The effect of Ismacorr 141 on the physico-mechanical and dielectric properties of SBR mixed with kaolin has been studied. The change in attenuation of longitudinal ultrasonic waves has been measured as a function of frequency and temperature. The data have been analysed and the results showed a relaxation phenomenon of the β-relaxation type. The activation energies for such processes were calculated and found to be related to the plasticization of the samples. The velocity of the ultrasonic longitudinal waves through the different samples has also been measured.

Effect of new additives on the ultrasonic attenuation and mechanical properties of styrene–butadiene rubber

AbstractThe change in attenuation of longitudinal ultrasonic waves has been measured as a function of frequency and temperature for styrene–butadiene‐rubber (SBR) mixed with Ismacorr 141 as plasticizer and antioxidant. Analysis of the results showed relaxation processes and the activation energies for these processes were calculated and found to be related to the plasticization of samples. Also the velocity of the ultrasonic longitudinal waves through different samples was measured. The effect of Ismacorr 141 on the physical and mechanical properties of SBR was also studied.

Ultrasonic investigation in KTaO3

The anomalous ultrasonic attenuationα c of longitudinal waves propagating along (100) direction in KTaO3 has been analyzed above the phase transition temperature in the frequency range 150–300 MHz in the paraelectric phase. The attenuation of longitudinal ultrasonic waves in KTaO3 is primarily due to a strong interaction with thermally-excited phonons in the soft mode. Frequency and temperature variations of attenuation are discussed.

Dislocation relaxation in aluminium single crystals at 10 MHz frequency

Abstract Dislocation relaxation, namely the Bordoni peak, in the three principal planes of a high-purity aluminium single crystal has been studied by measuring the ultrasonic attenuation of longitudinal waves at a frequency of 10 MHz using a conventional ultrasonic single-ended pulse-echo technique. The crystals of <100>, <110>, or <111> orientation were deformed by compression, and the temperature dependence of the ultrasonic attenuation was measured after applying resolved shear stresses ranging up to 60N mm−2. The results lead to the following conclusions: (i) The temperature of the Bordoni peak is essentially independent of the orientation; (ii) the temperature of the peak decreases up to a resolved shear stress near 28 N mm−2 and then increases slightly for higher prior stresses; (iii) the peak height increases with increasing deformation; and (iv) a subsidiary peak at the lower temperature side of the Bordoni peak (the Niblett-Wilks peak) appears only at low deformations.

Ultrasonic absorption and dielectric properties of natural rubber-furnace black mixtures: γ-irradiation effects

The change in attenuation of longitudinal ultrasonic waves has been measured as a function of frequency and temperature for natural rubber samples loaded with semi-reinforcing oil furnace black (SRF) in increasing quantities and vulcanized with either mercaptobenzo-thiazol (MBT) or N-oxidethylene benzothiazol sulphenamide (OBTS) after being subjected to natural ageing for 8 years. One relaxation process was noticed in the range of frequency where the activation energy was calculated. Also, the dielectric constant ε′ and dielectric loss ε′' have been investigated for those samples in the frequency range from 10 2 to 10 5 Hz at room temperature (∼25°C). The results are compared with those previously obtained. The effect of 50 MR γ-irradiation on the dielectric properties of those samples was also studied and the results are interpreted.

Environmental effects and relaxation in natural rubber

AbstractThe change in attenuation of longitudinal ultrasonic waves has been measured as a function of frequency and temperature for natural rubber samples loaded with intermediate super abrasion furnace (ISAF) in increasing quantities and vulcanized with N‐oxidiethylene benzotriazol sulfunamid (OBTS) after being subjected to natural aging for 5 years. Three relaxation processes, namely α, β, and γ, were noticed. The activation energy for each process was calculated and the results are discussed. Also, the dielectric constant ε′ and dielectric loss ε″ have been investigated for those samples after being immersed in various water media. The measurements were carried out in the frequency range from 100 Hz up to 100 kHz and at room temperature (∼ 28°C). The results are compared with each other and the differences are interpreted.

Ultrasonic attenuation in antiferromagnetic chromium - vanadium alloys

Details of the temperature dependence of the attenuation of ultrasonic longitudinal waves in chromium-rich vanadium crystals are presented. The attenuation curves exhibit an oscillatory shape around the Neel temperature in contrast to the sharp peak observed in unalloyed chromium at that temperature.

Attenuation of longitudinal ultrasonic wave near the diffuse phase transition in CdF 2

The attenuation of a longitudinal ultrasonic wave propagating in the [111] direction in CdF 2 is studied as function of temperature from 300K to 1030K. An ultrasonic attenuation peak has been observed for the first time near 983K. This peak is used to define the diffuse transition temperature (T c = 983 K) in CdF 2 which is well below its melting temperature of 1372K. The Arrhenius activation energy of anion motion above T c was obtained from the temperature dependence of the attenuation and the theory of the dynamics of the coupled crystalline-cage-charged-liquid fluctuations. The elastic constant, C 11+2 C 12+4 C 44) 3 , measured simulataneously with the ultrasonic attenuation displays a large decrease near 983K in addition to the nearly linear decrease in the elastic constant with temperature.

Ultrasonic investigation in the eutectic mixture acetamide + sodium thiocyanate

The attenuation of ultrasonic longitudinal waves in the eutectic mixture CH3CONH2+ NaCNS has been measured in the temperature range 255.2–303.2 K and frequency range 5–105 MHz, and the velocities of propagation at 298.4 K for 5 and 15 MHz have been obtained. A distinct structural relaxation process was found in the measured area. Comparing these results with previously reported shear results (G. Berchiesi, G. Vitali, P. Passamonti and R. Plowiec, J. Chem. Soc., Faraday Trans. 2, 1983, 79, 1257), the variation of the loss modulus, M″, as a function of frequency was determined. Agreement was found with theoretical expectations; however, the influence of the eutectic relaxation process, which takes place in the same area, is evident. Additional shear measurements performed at 10 MHz showed this influence to be stronger than at the higher frequencies reported previously.