Changes In Ultrasonic Velocity Research Articles

Effects of the sweep rate of the magnetic field on the changes of ultrasonic wave velocity in magnetic fluid

An external magnetic field applied to a homogeneous magnetic fluid induces a change in its structure manifested as the appearance of chains of magnetic particles arranged along the direction of the field. This change implies changes in the acoustic and magnetic properties of the magnetic fluid such as the acoustic wave propagation velocity and coefficient of ultrasonic wave absorption, and in magnetisation. The paper reports results of a study on the influence of the magnetic field sweep rate and the magnetic fluid temperature on the value of ultrasonic wave velocity, proving that the degree of the aggregation of the magnetic particles (chain formation process) depends on the above-mentioned parameters.

Velocity Constants for Ultrasonic Stress Measurement in Prestressing Tendons

There is currently widespread use of high-strength steel tendons for prestressing and post-tensioning of concrete structures and as suspension cables for long-span bridges. Tendons normally consist of one or more seven-wire, helically wound steel strands or solid rods. There are more than 130,000 prestressed bridges in the United States that contain these tendons, and approximately 3,000 new bridges are constructed each year. The prestressing tendons are critical structural elements because the forces in the tendons counteract tensile stresses in the concrete that result from loads acting on a bridge. The tendons are frequently inaccessible for visual inspections and there is currently no accepted nondestructive evaluation technique to assess the condition of these tendons. The goal of this research is to examine ultrasonic stress measurement techniques for the condition assessment of prestressing tendons. This information could be used to compare the actual force in the tendon with its design values to determine if the tendon is performing below expectations. The focus of this paper is the characterization of the relationship between ultrasonic wave velocity and stress level in prestressing tendons. Measurements were made to determine constants that relate the change in ultrasonic velocity to the change in stress. The effects of dispersion in prestressing tendons, which act as circular waveguides for ultrasonic waves, are evaluated.

Optical Imaging in Scattering Medium by Detection of Ultrasonic Phase Shift Due to Light Illumination

A method using ultrasonic velocity change due to light absorption was investigated in order to realize practical optical computed tomography. The phase shift of ultrasonic wave was observed even in the medium with a scattering coefficient equivalent to that of the human brain when ultrasonic wave passed through absorption object under light illumination. The optical image of the absorption region in a scattering medium was reconstructed from the projection data of ultrasonic phase shift due to light illumination. The shape of the absorbing object hidden in the chicken tissue was recognized by detecting the ultrasonic phase shift due to light illumination.

Ultrasonic nondestructive material evaluation method and study on texture and cross slip effects under simple and pure shear states

Ultrasonic wave velocities propagating in a plastically deformed medium are known to depend upon its microstructural material properties. Therefore, the authors have proposed the theoretical modeling of an ultrasonic nondestructive method to evaluate plastically deformed states. In the present paper, we verify the proposed theoretical modeling of an ultrasonic nondestructive method and examine its accuracy by comparing the experimental results with the simulated subsequent yield surfaces, the longitudinal and transverse wave velocities under combined stress states of an aluminum alloy using internal state variables of an anisotropic distortional yield model which were determined to achieve a good fit for the experimental results of the longitudinal and transverse wave velocity changes under uniaxial tension test. As a special case, the velocity changes of longitudinal wave under pure shear state subjected to the combinations of tension and compression are also studied, it shows a different result compared with that of longitudinal wave velocity under torsional tests of thin thickness cylinders, i.e., simple shear state. The effects on ultrasonic wave velocity changes due to texture and cross slip under simple and pure shear states are studied via a finite element polycrystal model (FEPM).

On-line measurement of texture, thickness and plastic strain ratio using laser-ultrasound resonance spectroscopy

Laser-ultrasound resonance spectroscopy, a non-contact ultrasonic technique, was used to determine reliably and rapidly the crystallographic texture, the average plastic strain ratio, and the thickness of sheet metal on the production line. As with laser-ultrasonics, a short laser pulse is used to generate a wide-band pulse of ultrasound and a laser interferometer is used for its detection. In this paper, a large number of echoes are collected and analyzed together using Fourier techniques to measure the natural resonance frequencies in the thickness of the sheet. One longitudinal and two shear resonance frequencies were measured together with their harmonics. From these frequencies, two crystallographic orientation distribution coefficients, W 400 and W 420, are obtained, as well as a highly accurate measurement of the sheet thickness that is corrected for changes in ultrasonic velocity caused by texture variations. Using these coefficients, the average and in-plane twofold and fourfold variations of the plastic strain ratio, respectively r̄, Δ 2 r, and Δ 4 r, can be evaluated. These parameters are indications of the formability of metals sheets, which is of industrial interest. Measurements on 1 mm thick, low carbon steel sheets have shown the following measurement accuracies: r̄ to within ±0.08, Δ 2 r, and Δ 4 r to within ±0.1, and thickness to better than ±1 μm. On-line tests at LTV Steel Company showed that the sensitivity of the apparatus is sufficient to detect systematic variations in texture along the length of similar production coils and that the on-line repeatability for r̄ was of order ±0.02.

Ultrasonic Monitoring of Nozzle and Cavity during Injection Moulding

Ultrasonic techniques are recognised as powerful sources of process information. Transducers are applied directly, are non-invasive, yet interrogate the entire melt cross-section, while data are available real-time. During injection moulding, two zones are considered: nozzle and cavity. In the nozzle, ultrasonic velocity measurement provides temperature and pressure information. Mean temperatures not observed by other techniques are detected. Previous extrusion based experience is used to address issues of high temperature transducer operation. In the cavity, changes in reflection coefficient and ultrasonic velocity provide information on mould filling and part cooling. Various mould geometries are monitored using a number of ultrasonic transducers.

Ultrasonic method for the whole blood coagulation analysis

The developed ultrasonic method is based on the experimentally established fact that the ultrasound velocity in a blood sample is changing in a specific way during the blood clotting process. For ultrasound velocity measurements pulse echo method was selected. Implementation of this approach has a few problems caused by small dimensions of the measurement cell. All elements of the cell contacting with the blood are made of biologically compatible materials. The length of Pd coated chamber is 5 mm, volume 0.2 ml. Data of measurements are stored and processed by PC. The ultrasound velocity in a sample is displayed as it changes in time during the experiment; the temperature is monitored as well. Application of the digital filtering allows to smooth the coagulation curve and reach the sensitivity up to ±3 cm/s. The coagulation curves were obtained at frequency 5 MHz and they represent peculiar stages of blood clotting characterised by their duration and ultrasound velocity differences. Fine structure of ultrasonic velocity changes is registered from the very beginning of the clotting to lysis. Such experiments were carried out using blood samples taken from a few hundred volunteers. For dynamic calibration and periodic checking of the measuring system the liquid medium in which acrylamide polymerisation reaction takes place is proposed as a reference liquid. Such a liquid mimics clotting blood from the point of view of ultrasonic velocity changes.

Velocity Constants for Ultrasonic Stress Measurement in Prestressing Tendons

There is currently widespread use of high-strength steel tendons for prestressing and post-tensioning of concrete structures and as suspension cables for long-span bridges. Tendons normally consist of one or more seven-wire, helically wound steel strands or solid rods. There are more than 130,000 prestressed bridges in the United States that contain these tendons, and approximately 3,000 new bridges are constructed each year. The prestressing tendons are critical structural elements because the forces in the tendons counteract tensile stresses in the concrete that result from loads acting on a bridge. The tendons are frequently inaccessible for visual inspections and there is currently no accepted nondestructive evaluation technique to assess the condition of these tendons. The goal of this research is to examine ultrasonic stress measurement techniques for the condition assessment of prestressing tendons. This information could be used to compare the actual force in the tendon with its design values to determine if the tendon is performing below expectations. The focus of this paper is the characterization of the relationship between ultrasonic wave velocity and stress level in prestressing tendons. Measurements were made to determine constants that relate the change in ultrasonic velocity to the change in stress. The effects of dispersion in prestressing tendons, which act as circular waveguides for ultrasonic waves, are evaluated.

A progressive damage model for ultrasonic velocity change caused by creep voids in copper

In order to investigate the creep voids–ultrasonic velocity relationships and the associated modeling, a series of crept copper samples are prepared and their ultrasonic velocities are measured. Velocities measured in three directions with respect to the loading axis are found to decrease nonlinearly and their anisotropy increases as a function of creep-induced porosity. A progressive damage model is developed to explain the observed void–velocity relationship, including the anisotropic behavior. In the model study we assume the creep voids as oblate spheroids and the axisymmetric orientation distribution of their minor axes with respect to the loading direction. We further assume that the void aspect ratio can vary as the creep advances. This model enables the determination of the average aspect ratio of voids for a given porosity content and provides a satisfactory agreement with experimental results over the whole creep life.

Acoustoelastic stress measurement of wood in bending - A new attempt at determining stress conditions of wood

The changes in ultrasonic wave velocity propagating in wood normal to the direction of applied stress were investigated experimentally. On the basis of the experimental results, bending stress distributions in wood specimens were estimated acoustoelastically by carrying out measurements of ultrasonic wave velocity. The investigation showed that ultrasonic waves changed speeds only a little, due to the applied stress. Acoustoelastic constants determined from the results of the experiment were used to express the percentage change in ultrasonic wave velocity as a function of the applied stress. The velocity change was seen to also depend on the mode of the ultrasonic wave. Bending stress distribution estimated acoustoelastically agreed well with stress measurements using the strain gauge method and results of numerical calculations. The results of the study show conclusively that the acoustoelastic phenomenon can be applied to determine stress conditions of wood, and it is expected that the method presented here will in the near future be developed into a useful, practical technique for stress measurement of wood.

Texture and Cross Slip Effects on Ultrasonic Wave Velocity Changes Under Simple and Pure Shear States.

Although stress and strain states are same in simple and pure shear states, longitudinal wave velocity changes propagating in the plastically deformed medium under simple and pure shear states are apparently different each other according to authors' theoretical and experimental research works. The objective of this paper is to discuss the effect on ultrasonic wave velocity changes due to texture and cross slip under simple and pure shear states via finite element polycrystal analysis. In small plastic deformation range, in spite of quite different longitudinal wave velocity changes under simple and pure shear states, the texture developments and transverse wave velocity changes under both states are similar each other. That suggests dependence of transverse wave velocity on texture. Next, the multiplicative amounts of intersected slides between primary and secondary slip systems, which relates closely to the amount of cross slip, under simple and pure shear states are examined. The result, i.e., this multiplicative amount under pure shear state is larger than that under simple shear state, means the point defects induced by cross slip are much easier to introduce under pure shear state than under simple shear state and suggests that the point defects induced by cross slip may cause quite different longitudinal wave velocity changes.

Comparison of Ultrasonic Pole Figures Based Upon Ultrasonic Nondestructive Evaluation Method With Pole Figures Based Upon FEPM.

The ultrasonic wave velocities in a polycrystalline aggregate are sensitively influenced by texture changes due to plastic deformation, and their relationship was systematically analyzed by Sayers. According to Sayers's proposed model, it is possible to construct ultrasonic pole figures via the crystallite orientation distribution function (CODF), which can be derived by using ultrasonic wave velocity changes. In the previous paper, the Sayers's model was examined by experimental work and the effect of plastic deformation on texture development of an aluminum alloy specimen was studied by using ultrasonic pole figures as one of its applications. In the present paper, the ultrasonic pole figures based upon Sayers's model are constructed under various loading conditions of uniaxial tension, pure torsion, biaxial tension-compression, biaxial compression and biaxial tension, respectively. To examine its accuracy and reliability, the ultrasonic pole figures are compared with ones analyzed by the finite element polycrystal (FEPM), which has already been considered as a well-developed technology for the analysis of microstructural behaviors due to plastic deformation. The results show a remarkable qualitative similarity among the two methods.

Two types of tunnelling state in fast-neutron irradiated bulk silicon?

Ultrasonic attenuation measurements were performed on fast-neutron irradiatedbulk silicon. The data are analysed in the framework of the tunnelling model.Good agreement was found with the results obtained from earlier measurementsof the changes in ultrasonic velocity, performed on the same samples, and thepresence of tunnelling states in this material was confirmed. More detailedanalysis however gives an indication of the presence of two different typesof tunnelling state.

Ultrasonic Evaluation of Spall Damage of Carbon Steel under Repeated Impact.

Plate impact tests were repeated up to three times on carbon steel. The spall damage within the target plate was evaluated with a low frequency scanning acoustic microscope as well as ultrasonic velocity, attenuation (amplitude change of B 2 to B 1 echo) and backscattering intensity. The spall damage generated by the first impact have increased in its density and sizes by the second impact of which stress is higher or lower than the first impact stress. Small cracks once generated have been extended by lower impact stress in successive impacts. The change in B- and C-scan images under repeated impact are well correlated with the change in ultrasonic velocity, attenuation and backs-cattering intensity. These methods give us an advanced means to evaluate nondestructively spall damage and to make clear the mechanisms of the spall damage growth under repeated impacts.

119 単純せん断と純粋せん断状態における超音波速度変化に及ぼす集合組織と塑性スピンの影響(材料力学III)(オーガナイズドセッション(a)材料力学・材料強度に関する新展開)

Although stress and strain states are same in simple and pure shear states, longitudinal wave velocity changes propagating in the plastically deformed medium under simple and pure shear states are apparently different each other as the results of authors' theoretical and experimental research works. The objective of this paper is to discuss the effect on ultrasonic wave velocity changes due to texture and cross slip under simple and pure shear states via finite element polycrystal analysis. First the texture developments under both states are studied and the results suggest the dependence of transverse wave velocity changes on texture in the small plastic deformation range. Next, the multiplicative amounts of intersected slids between primary and secondary slip systems, which relates closely to the amount of cross slip under both states are calculated and the results show that the point defects induced by cross slip are much easier to be introduced under pure shear state than that under simple shear state, this suggests that the point defects induced by cross slip may cause quite different longitudinal wave velocity changes.

Ultrasonic velocity changes in bulk neutron-disordered silicon

Measurements of the changes in ultrasonic velocity were performed on bulk single-crystalline silicon irradiated with fast-neutron doses up to 1.7×10 21 and 3.2×10 21 n/cm 2 ( E>0.1 MeV). Compared to the unirradiated material, a large additional effect is observed at low temperatures the behavior of which is similar to the predictions of the tunneling model. Together with results previously obtained from attenuation measurements and Raman spectroscopy, this result puts the presence of tunneling states in high coordinated bulk silicon clearly in evidence.

Sensitivity of Ultrasonic Attenuation and Velocity Change to Cyclic Deformation in Pure Aluminum

The average dislocation density Λ and loop length L in cyclically deforming Al were derived from the measurement of ultrasonic attenuation and velocity change. With the increase of the cycle number, Λ increases at first and then decreases a little after passing a maximum, while L decreases monotonously. At low cyclic strain amplitudes less than 10—4, and L Λ almost do not change with cycle number. These results show that the measurement of ultrasonic attenuation and velocity change is a useful method to determine the parameters Λ and L in the process of cyclic deformation.

Evidence for a structural change in TSMG Y123 at 225 K

This paper reports on an ultrasonic study at 85 kHz and 485 kHz of melt-textured Y123 (YBa 2Cu 3O 7− δ ) where a possible structural change has been identified in the 220 K region. Work on oxygenated and partially deoxygenated samples has shown that the change is associated with oxygen in the samples and that the activation energy for the process is 110 meV. The conclusions are based on a qualitative and quantitative description of ultrasonic attenuation and ultrasonic velocity changes in the material as a result of slow thermal cycling and quenching experiments.

Effect of particle size distribution upon specific surface area and ultrasonic velocity in sintered ceramic powders

The changes in ultrasonic sound wave velocity and specific surface area which occur as a result of sintering have been correlated for several zinc oxide and alumina powder systems. Particle size distribution is shown to have a significant effect upon the nature of this correlation. Powders with narrow particle size distributions exhibit a nearly linear relationship between the surface area reduction and the longitudinal wave velocity over much of the initial and intermediate stages of sintering. In contrast, powders with broad particle size distributions exhibit a significant reduction in the specific surface area, with little increase in the ultrasonic velocity, during the early stages of sintering. This behavior is attributed to the differences in the thermodynamic driving forces for sintering of the different sized particles. These data also indicate that in powder compacts containing broad particle size distributions, the apparent elastic moduli, as manifested in the ultrasonic velocity, are dominated by the larger particles. The present work contributes to the understanding of the dynamic behavior of sintering powder compacts in terms of the ultrasonic velocity, which may be determined non-intrusively during processing. This understanding may facilitate the use of ultrasonic techniques for real-time monitoring and controlling of the sintering process in ceramic power compacts.

変形中の多結晶純銅における超音波音速と減衰の非接触・連続モニタリング

Changes in ultrasonic velocity and attenuation were studied by noncontact and continuous measurement method for polycrystalline pure copper during deformation. This measurement, involving two ultrasonic waves at the same time, has been made possible by electromagnetic acoustic resonance (EMAR). Use of an electromagnetic acoustic transducer (EMAT) can isolate the attenuation within the plate specimens. The method relies on the Lorentz force mechanism to couple the EMAT and the specimen surfaces and then eliminates the extra losses, which otherwise occur in the use of the piezoelectric transducers. Ultrasonic velocity and attenuation changes are interpreted in terms of the dislocation behavior and the acoustoelastic effect. The changes in dislocation density and loop length can be analyzed using dislocation damping theory. Pure third-order elastic canstants, which are free from the velocity change due to the dislocation movement, can also be derived and compared with the existing experiments.