Changes In Ultrasonic Velocity Research Articles

Stress-induced ultrasonic anisotrophy in Berea sandstone

Abstract Ultrasonic P- and S-wave velocities have been measured for propagation in three orthogonal directions through a sample of Berea sandstone as a function of maximum compressive stress applied perpendicular to the bedding plane. The sample was a 50mm cube and was stressed to peak in a new triaxial loading frame, with the principal stress components parallel to the bedding plane held constant at 4.1 MPa. The measured velocities are compared with velocities calculated for a medium containing an anisotropic orientation distribution of microcracks. With a recently developed technique, the P- and S-wave measurements can be inverted separately for the microcrack density and orientation distribution, thus enabling a consistency check to be made on current theories of elastic wave scattering by microcracks and fractures. Inversion of the measured velocities to obtain the microcrack orientation distribution function suggests the growth of cracks parallel to the direction of the maximum compressive stress. This supports the current view that failure is preceded by the growth of microcracks parallel to the direction of the maximum principal compressive stress. The large stress-dependent changes in ultrasonic velocities observed suggest the usefulness of ultrasonics for studying damage processes in sedimentary rocks.

Tunneling states in neutron-irradiated quartz: Measurements of the ultrasonic attenuation and velocity change.

We report the results of a systematic investigation of the tunneling states (TS's) in neutron-irradiated quartz. Measurements of the acoustic absorption and the variation of the velocity of sound were carried out as a function of temperature (0.3--300 K) and in the ultrasonic frequency range 200--700 MHz, on quartz specimens exposed to different neutron doses. From numerical fits of the data with the tunneling model, including Raman processes, the density of states P\ifmmode\bar\else\textasciimacron\fi{} and the coupling parameter ${\ensuremath{\gamma}}_{\mathit{l}}$ were determined independently. A comparison of the TS parameters obtained from both attenuation and velocity measurements with each other and with our previous ultrasonic-attenuation studies and with thermal-conductivity and vibrating-reed experiments shows that the results are qualitatively in agreement with each other, but indicates some shortcomings of the tunneling model, also observed in glasses. TS parameters deduced from experiments which probe TS's of different parts of the distribution function are systematically found to be slightly different. The results are further related to studies of the damage induced by neutron irradiation in quartz. The differences in dose units, used by different authors, are considered more closely, which leads to a consistent picture of the damage-related parameters and allows a more reliable comparison between the TS and the damage.

Ultrasonic velocity change with creep damage in copper

We studied the ultrasonic velocity change caused by the accumulative creep damage in polycrystalline pure copper after high-temperature tensile loading. The propagation velocities of bulk waves, longitudinal and shear waves polarized parallel and perpendicular to the stress direction, showed a strong sensitivity to intergranular creep controlled by grain-boundary cavitation and subsequent microcracking. The velocities decreased slowly with creep time up to approximately 60 pct of the lifetime, when the steady creep shifted to the tertiary creep. Beyond this point, they decreased at ever increasing rates until eventual failure. The total velocity changes amounted to several percent of the original velocities. The creep damage also caused velocity anisotropy in the shear waves. Evolution in the anisotropy revealed that formation of cavity arrays, cavity coalescence, and microcracking, which occurred preferentially on boundaries lying normal to the stress axis, were restricted to the last 20 pct of the lifetime. Metallography and measurements of porosity support the ultrasonic observations.

Correlation between cube strength, ultrasonic pulse velocity and volume change for oil well cement slurries

Four types of cement slurries used in cementing oil well casings have been examined to determine whether strength build-up during the first 24 hours after mixing can be predicted from measurements of ultrasonic pulse velocity and volume change. The pulse velocity method was found to be a useful predictive technique but there was no general correlation between bulk volume change and cube strength.

Ultrasonic studies of the relation between two-level-tunneling systems, oxygen content, and superconducting transition temperature in YBa2Cu3O7- delta.

We have examined the behavior of two-level-tunneling systems (TLS's) in the high-temperature superconductor ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ as a function of decreasing oxygen content, by measuring the temperature dependence of ultrasonic-velocity changes at low temperatures, T\ensuremath{\lesssim}1 K. We find the density of states of the TLS decreases with decreasing oxygen content and varies exponentially with both ${T}_{c}$ and oxygen content. We interpret these results in light of recent measurements on oxygen-vacancy ordering in oxygen-deficient ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. .AE

Electron and phonon interactions with two-level-tunneling systems in the high-Tc superconductor YBa2Cu3O7- delta and in niobium.

We have measured ultrasonic velocity changes with temperature (T\ensuremath{\le}1 K) to study two-level-tunneling systems (TLS) interactions with electrons and with phonons in the high-${\mathrm{T}}_{\mathrm{c}}$ superconductor ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ and in a niobium compact. In ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$, at T\ensuremath{\ll}${\mathrm{T}}_{\mathrm{c}}$, TLS relaxation is dominated by conduction electrons, as in normal metallic glasses. In niobium, at T\ensuremath{\ll}${\mathrm{T}}_{\mathrm{c}}$, this relaxation is dominated by phonons, as in other disordered, conventional superconductors. We also review recent specific-heat measurements in light of these results.

Ultrasonic-phase-velocity measurements in electron-irradiated quartz.

Precision measurements of the ultrasonic velocity change as a function of temperature were carried out in electron-irradiated quartz (dose=1.0\ifmmode\times\else\texttimes\fi{}${10}^{20}$ e/${\mathrm{cm}}^{2}$, E=3 MeV) for two frequencies: 648 and 480 MHz. Between 0.33 and 2 K, a frequency-independent logarithmic increase of the velocity is observed. The effect is very small, but clearly indicates the presence of the resonant interaction of tunneling states with phonons. The experiment shows that tunneling states of a two-state nature are present. In addition, the effect of the relaxation process on the velocity is observed and shows that the tunneling states are of the same nature as in glasses. A comparison with neutron-irradiated quartz indicates that similar tunneling states are induced by electrons and neutrons, in spite of the different disordering processes. It is suggested that the electron-induced Frenkel pairs provide the necessary freedom for rearrangements and rotations of the tetrahedra, which can be at the origin of the tunneling states.

A simple instrument for the measurement of small changes in ultrasonic velocity

In this instrument, the echoes are added to a continuous wave having a frequency 1.5 times that of the echoes. Changes in ultrasonic velocity result in a change of the added waveform. The relative velocity changes are given by the relative frequency changes required to restore the waveform. A relative accuracy of 2 parts in 106 can be easily achieved. This is an order of a magnitude better than the resolution of the pulse-echo overlap method.

Predicting failure in rocks and its implications for predicting earthquakes

In the laboratory rock failure can be predicted both in space and in time. The processes leading to failure are well understood and manifest themselves in measurable quantities. Ultrasonic velocity changes and surface strain anomalies are the most reliable indicators of the impeding failure. To a lesser degree and very much dependent on the deformation rate and the moisture content, acoustic emissions cluster in the vicinity of the failure shortly before the rupture occurs. The precursory failure zone has a linear dimension on the order of 1000 grain diameters. If the same physical mechanisms are involved in the Earth as failure is approached, then detailed velocity and surface strain measurements would greatly enhance our ability to predict earthquakes. With the realization of the Global Positioning System and a possible extension to a satellite holographic system, it is now possible to measure surface deformation inexpensively on a densely spaced grid.

Ultrasonic velocity change in sintered SiC and ain at low temperatures

Ultrasonic attenuation and velocity changes of sintered SiC samples with 1, 2, and 3 wt% AIN as the sintering additives are investigated as a function of temperature at low temperatures. Below ∼1K, the velocity increases logarithmically with temperature (lnT dependence). This lnT dependence of the velocity is one of the characteristics of amorphous materials. The results are analysed in terms of Two Level Tunneling System (TLS) model for amorphous solids. For comparison, sintered AlN was also studied and it was found that no detectable lnT dependence of velocity exists in this material. Available results suggest the existence of a relation between the disorder characterized by TLS detected at low temperatures and a reduction in the thermal conductivity at and above room temperature.

Ultrasonic study of mechanically alloyed Co40Sn60

Ultrasonic velocity changes of mechanically alloyed Co40Sn60 are investigated as a function of temperature at low temperatures. It is found that the velocity increases logarithmically with temperature below ∼1 K, indicating the existence of features characteristic of the glassy state. With the two level tunneling system (TLS) model developed for amorphous materials, factors nM2 and K̃ are determined, where n is the density of states of TLS, M and K̃ are TLS coupling constants for phonons and electrons, respectively.

Real-time study of frequency dependence of attenuation and velocity of ultrasonic waves during the curing reaction of epoxy resin

The frequency dependence of the phase velocity and attenuation of ultrasonic waves were measured as a function of time during the polymerization (curing) reaction of epoxy resins. The phase velocity and attenuation were evaluated from the amplitude and phase spectra of ultrasonic signals transmitted through a layer of curing epoxy resin. The measurements were made in the frequency range of 2–20 MHz. From the experimental data follows an important conclusion: The attenuation coefficient increases linearly with frequency at all stages of the curing reaction from the viscous liquid to the solid state. The slope of the attenuation coefficient as a function of frequency is strongly dependent on the time of cure (degree of cure). The linear behavior of attenuation versus frequency suggests that the attenuation effect cannot be explained by classical viscothermal absorption or relaxation theory. This type of behavior (so-called hysteresis behavior) is poorly understood on the molecular level and was found previously for some highly viscous liquids, for solid polymers, and for biological tissue. The phase velocity data were evaluated from the phase spectrum of the transmitted signal. The ultrasonic velocity changes with time according to an S-shaped curve. It is also moderately dependent on the frequency.

Application of Ultrasonic Spectroscopy to Ferroelectric Phase Transition of VDF/TrFE Copolymer

An ultrasonic spectroscopic measuring system for higher temperature use was constructed by utilizing PVDF transducers and polyimide buffers. The system was successfully applied to simultaneous observation of the changes in ultrasonic velocity and absorption in a wide frequency range upon the ferroelectric phase transition of a VDF/TrFE copolymer (54 VDF mol%). The results revealed that the absorption becomes the highest and the velocity shows a sharp bend around the transition temperature of about 66°C. Further, frequency dispersion was observed for the degree of absorption and the temperature change in velocities.

Attenuation Stress Hysteresis Loops and Low‐Frequency Internal Friction Associated with Thermomechanical Breakaway of Dislocations

AbstractMeasurements of ultrasonic attenuation and velocity changes are performed on 5N aluminium during the application of a low frequency bias stress. The characteristics of the attenuation‐stress Δα = f(σ) loops are studied as a function of the repetition of loading, amplitude σm of loading stress, temperature, and pretreatment of the sample (prestrain, ageing time, or temperature). The results show that at least two kinds of dislocation‐point defect breakaway mechanisms are involved in the experiments. Then a model is developed in order to calculate from the attenuation‐stress hysteretic loop a low frequency internal friction decrement δα: peak events versus amplitude (δα = f(σm)) are thus observed, in good accordance with classical models of internal friction associated with breakaway of dislocations; the activation energy for depinning and the space between pinning points are deduced from these peaks and their evolutions are followed as a function of the pretreatment of the sample. In addition, although the internal friction decrements δα and δ, obtained directly from torsion pendulum, have some similar characteristics, a noticeable difference appears in the decrement levels which is especially explained by the characters of the solicitation in bias stress and torsion pendulum experiments, respectively, one sided and alternative; their effects are discussed in terms of dislocation mechanisms.

Effects of stress on magnetically induced velocity changes for ultrasonic longitudinal waves in steels

Effects of both uniaxial tensile and compressive stresses on the magnetically induced velocity changes for 10-MHz ultrasonic longitudinal waves were investigated in specimens of ASTM A-36, SAE 4340, and HY-80 steels. The magnetically induced ultrasonic velocity changes were found to exhibit characteristically different stress effects depending on the magnitude and sign, i.e., tensile or compressive, of the stress and the relative orientation between the stress and applied magnetic field . The effects of a compressive stress were particularly distinctive producing a prominent minimum in the velocity changes as a function of the applied magnetic field. The observed stress dependence of the magnetically induced velocity changes is qualitatively explained considering the effect of the stress and the magnetic field on the rotational motion of the domain magnetization caused by the propagating ultrasonic waves due to the magnetoelastic coupling.

Effects of plastic deformation on magnetically induced ultrasonic wave velocity changes in steel

Effects of a uniaxial tensile plastic deformation on magnetically induced velocity changes for 10-MHz ultrasonic longitudinal waves in a specimen of SAE 4340 steel were investigated. The velocity change as a function of the applied magnetic field, measured after plastic deformation under uniaxial tension, was found to be similar to that obtained under uniaxial compression before deformation, suggesting the presence of a residual compressive stress in the plastically deformed specimen. This finding agrees with other reported results.

Frequency Modulator using Ultrasonic Vibrator

An ultrasonic bulk wave delay line oscillator is presented composed of a piezoelectric vibrator and an amplifier. The field effect of the oscillation frequency is explained in terms of the ultrasonic wave velocity change by higher order elastic effect which is generated with inner stress by piezoelectric effect. A stress coefficient K and a field coefficient K e 31 resulting from the higher order elastic effect are obtained as K=1030×10-6 MPa-1 and K e 31=1.77×10-3 cm/KV, respectively.

Electron-Phonon Coupling Constant of the Oxide Superconductor BaPb1-xBixO3

By means of measurements of the ultrasonic attenuation and velocity change, we have derived the magnitude of McMillan's parameter λ of the oxide superconductor BaPb 1- x Bi x O 3 ( x =0.20–0.25). In this derivation we have assumed that the interaction between the conduction electrons and the sound waves is of the deformation potential type and the magnetic field dependent part of the attenuation at T < T c is contributed from the normal conduction electrons. The value obtained is λ∼0.85 for the sample with T c =10.5 K. It is shown that a relatively large deformation potential constant | V d |=2.0 eV, which is 2.7 times larger than the Fermi energy and comes into λ in square, counterbalances the small density of states of this material and consequently leads to a reasonably large magnitude of λ for this rather semimetallic material.

RESIDUAL STRESS CHARACTERIZATION WITH AN ULTRASONIC/MAGNETIC TECHNIQUE

A potentially useful new technique for residual stress characterization in ferromagnetic material is described. The unique feature of this technique is the measurement of small changes in ultrasonic wave velocity by the application of external dc magnetic field in the material under various stress conditions. It was found, in steel, that the fractional change in the natural velocity Delta W/W of waves propagating along the external field direction is affected by the uniaxial stress applied in the same axis. External compression lowers the slope of the Delta W/W curve in the low field region, while external tension generally does the opposite. For most cases, the slope in this region falls below zero under external compression. The result of measurements in specimens with residual stress shows exactly the same tendency.

Ultrasonic properties of transducer backings

For non-destructive testing applications it is often necessary to limit the number of cycles in a pulse produced by ultrasonic transducers. Usually a backing with a high ultrasonic attenuation and with an acoustic impedance chosen to match that of the piezoelectric active element of the transducer is employed. The acoustic properties of the commonly used tungsten/Araldite backings are compared theoretically with those of composites made by pressing tungsten powder with a powder of a plastic metal. The change in ultrasonic velocity and attenuation due to scattering by the tungsten particles is investigated and the dependence on frequency is determined.