Propagation Velocity Of Elastic Waves Research Articles

Acoustic Determination of Properties Possessed by Porous Titanium

To impart the optimal structure to a powder material and promote high mechanical properties, the production process is to be monitored at each step using nondestructive methods. Acoustic methods are believed to be promising in this respect. The parameters of acoustic fields are influenced by many factors that determine the structure and properties of powder materials. A relevant task is to improve acoustic methods for the identification and use of this influence. A model material is taken as an example to show the capabilities of a nondestructive acoustic method relying on integrated measurement of the propagation velocities of longitudinal, transverse, and rod elastic waves in studying the patterns peculiar to the powder structurization at the molding and sintering stages. The following problems that can be solved using this method are considered and experimentally confirmed: identify how the properties of the starting powders influence the characteristics of the final material, monitor the compaction and contact formation processes in the material, and identify features of these processes, which are manifested as uneven distribution of properties over the material and aftereffects and are stepwise. Additional criteria are proposed to increase the reliability and descriptiveness of the results. Analysis of the experimental data shows that the propagation velocities of bulk and rod elastic waves in different ways reflect the compaction and contact formation in powder materials. The differences are explained by the peculiarities of acoustic fields generated by various types of elastic waves.

Researches of the Seismic Properties of Clay Soils for Seismic Microzoning

The paper presents the results of seismoacoustic studies of soils on the example of samples of unsalted Sarmatian clays from the Northern black sea region. Samples of natural addition and humidity, as well as corresponding samples of soil particles were studied. Regression dependences of the longitudinal wave velocity on some indices of physical and mechanical properties of Sarmatian clays are revealed. The values of elastic wave propagation velocities determined as a result of ultrasonic investigations are used to calculate the increment of the seismic score and to map seismic microzoning, which is extremely important for ensuring the safety of construction in seismic areas. The obtained results can be used for seismic microzoning of any areas composed of clay swollen soils.

Применение стационарной гипопластической модели для моделирования движения сыпучей среды

Для моделирования движения гранулированной среды предложен вариант стационарной гипопластической модели. С целью решения задачи выбран метод сглаженных частиц, особенностью реализации которого является использование в расчетах комбинированного ядра, с малым параметром сглаживания. Выполнен расчет процесса обрушения песчаного столба и проведено сравнение полученных численных результатов моделирования с известными экспериментальными данными. Purpose. The aim of this study is а development of mathematical models that describe the complex motion of a granular medium in the process of its disintegration that allows evaluating the possibility of using a simplified stationary hypoplastic model to describe this process. Methodology. To describe the motion of a granular medium, the classical equations of motion and mass conservation were used. The calculation of the deviator of the stress tensor is performed within the framework of a simplified hypoplastic model. The work uses the hypothesis of a linear relationship between the pressure function and the density of the granular medium. This hypothesis is typical for smoothed particle methods, one of the variants of which is proposed for the numerical implementation of the problem. Results. A new mathematical model of the problem of the motion of a granular medium in the process of its disintegration is formulated. An algorithm for solving the problem based on the method of smoothed particles is proposed. The problem of disintegration of a sand pillar is solved numerically. A comparative analysis of the obtained solutions with experimental data is accomplished. Findings. Using the assumption that the propagation velocity of elastic waves that determine the stress-strain state in sand particles is much higher than the velocities of particles arising from sand shedding, an approximate model for calculating the stress state of a moving granular medium based on a stationary hypoplastic model is presented. To solve the problem, the method of smoothed particles with a small smoothing parameter was implemented with the help of a new combined interpolation core in the calculations. To verify the mathematical model and the selected method, the implementation of the smoothed particle method was performed and the problem of disintegration of the sand column was solved. The obtained solution of the problem shows satisfactory agreement with the experimental data.

The influence of stress state, density and moisture on the dynamic properties of soil cement samples created by the method of deep soil mixing

The transformation of the properties of the bases by the method of deep soil mixing allows the construction of buildings and structures on sites with soft soils. As a rule, adverse geological conditions are accompanied by the presence of dynamic effects on the designed buildings. The objective of this research is to forecast changes in the mechanical properties of the base under dynamic loads. The object of study is the propagation velocity of elastic shear waves, since these parameters significantly affect the calculations of deformations and stability of earthquake-resistant industrial and civil buildings and structures, as well as objects of energy and transport construction. The paper contains a review of similar studies, on the basis of which the conclusions obtained during the experiments are further generalized. Based on the analysis of the results of laboratory tests performed by the authors of this work, by the method of low-amplitude torsion vibrations in a resonant column in the anisotropic triaxial compression mode, the influence of the density of soil cement samples, humidity, and additional load on the propagation velocity of elastic transverse waves is estimated. The paper provides a description of the essence of the research method, a review of the equipment on which special laboratory tests were performed. The tests were carried out on samples of unbroken soil cement taken from the base of a nuclear power plant (NPP) under construction. Dried samples of soil cement were investigated, and tests were carried out at full water saturation and at a given humidity. The anisotropic stress state of soil cement samples during triaxial tests in a resonance column was due to the features of the base of the designed NPP. Studies have shown that the most significant factor affecting the shear wave velocity is the additional vertical load. It is noted that with increasing density, the velocity of the shear waves decreases. Humidity is directly related to the density of soil cement and the amount of water in the pores, so the assessment of its effect on the dynamic properties of soil cement is similar to the effect of changes in density.

Justification of the effect of transitional modes on the quality of ready-made products when their treatment is used by plastic deformation methods from the position of the wave and auto vibration processes

Purpose. Substantiation of the role of longitudinal and transverse wave processes in the surface layers on the quality of finished products obtained by plastic deformation methods, such as cold rolling, stamping, running in, drawing and others. Research methodology. In the work, to describe the transients at the beginning of the interaction of the tool with the workpiece, a computational model was applied in which the surface layers of the workpiece are represented as a beam on an elastic base, loaded with suddenly applied tangential forces, often exceeding their critical values. The reasons for the occurrence of unstable dynamic states of such a beam, in which the integrity of the surface layers of the workpiece and parts may be disturbed due to the occurrence of supercritical stresses and deformation in the material of the outer layers, are investigated. Findings. The results were obtained on the definition of hazardous states of the surface layers of the workpiece, under the action of suddenly applied loads at the initial moments of the capture of the workpiece, as well as at the moments when the tool slips over the workpiece during the alignment of their speeds. Originality. It consists in the fact that the first dynamic problem was set and solved for the surface layers of the workpiece, represented as a two-support beam on an elastic base loaded with a suddenly applied longitudinal force, which can significantly exceed its critical value. Denoted areas of dynamic instability of the surface layers of the workpiece. The practical value of the work lies in the fact that the modes of operation of the metal forming machine and the parameters of the workpiece were identified under which conditions for obtaining products of insufficient quality may arise. As well as developed recommendations for improving the quality of finished products. Key words: metal forming, transients, longitudinal wave, shear wave, billet, loaded layer, overload coefficient, dynamic buckling, tool, rolling, knurling, drawing, hypothetical beam, impact, elastic wave propagation velocity.

Measuring the elastic wave velocity in the lens of the eye as a function of intraocular pressure using optical coherent elastography

The dependence of the elastic properties of the eye lens on the intraocular pressure is investigated in porcine eyes ex vivo. To measure the stiffness of the lens, the method of dynamic optical coherent elastography is used, in which the propagation velocity of surface elastic waves in the lens is measured using phase-sensitive optical coherent tomography. Measurement data show an increase in Young’s modulus of the lens by ∼30% with an increase in intraocular pressure from 10 to 40 mm Hg. This result allows us to conclude that the effect of intraocular pressure on the rigidity of the lens is less significant than on the rigidity of other eye tissues, such as the cornea and sclera. The method of optical coherent elastography makes it possible to measure the elastic properties of the lens without removing it from the eyeball and has considerable potential for clinical use.

Acoustical characteristics of single-walled noncarbon nanotubes: Longitudinal and torsional waves

A study based on nonlocal continuum elastic theory is presented on the acoustic properties of single-walled noncarbon nanotubes, including boron nitride (BN), aluminum nitride (AlN), gallium nitride (GaN), aluminum phosphide (AlP), gallium phosphide (GaP), and boron (B) nanotubes. Elastic characteristics of the noncarbon nanotubes needed to describe the elastic waves propagation correctly have been defined previously. Two-dimensional densities (2D densities) for each type of noncarbon nanotubes are calculated. The values of propagation velocities of longitudinal and torsional elastic waves for proposed nanotubes with different diameter and chirality are obtained. Specific result is that in boron nanotubes sound propagates at a speed equal 54 km/s.

Structural and Collective Dynamics of Bi50Zn50 of binary metallic glass

In the present paper, structural properties, collective dynamics and elastic properties have been studied of Bi50Zn50 liquid metallic glass at a wide range of temperatures. Ashcroft and Langreth binary structure factor have been used to study for static structure factor and pair correlation function for present alloy. The collective excitation has been studied for longitudinal and transverses phonon modes based on our well-established model potential along with Hubbard and Beeby (HB) approach. These frequencies are expressed in terms of many-body correlation functions of atoms as well as of interatomic potential. The important ingredients in the present study are the pair-potential and pair-correlation functions. The local field correlation functions due to Hartree (H) and Farid et al (F) are employed to investigate the influence of the screening effects on the vibrational dynamics of Bi50Zn50 liquid metallic glass. The results for bulk modulus (BT), modulus of rigidity (G), Poisson’s ratio (ξ), Young’s modulus (Y), Debye temperature (ƟD), the propagation velocity of elastic waves and dispersion curves are reported. Good agreement with the experiment is observed for the structure factors and elastic properties results are consistent and confirm the applicability of model potential and self-consistent phonon theory for such studies.

Analysis of coiled stator ultrasound motor: Fundamental study on analysis of wave propagation on acoustic waveguide for coiled stator

In our research group, we previously developed a coiled stator ultrasound motor (CS-USM) for medical applications such as intravascular ultrasound (IVUS) devices. However, wave propagation on acoustic waveguides has not been investigated sufficiently in previous studies. In this study, we analyze the propagation velocity of elastic waves from the simulated the vibration displacement mode profile along a straight line acoustic waveguide via three-dimensional finite element method (FEM). Concerning results, elastic waves with vibration displacement along the thickness direction show dispersion characteristics corresponding to the a0 and a1 mode plate waves (Lamb waves) in the acoustic waveguide. Our theoretical hypotheses of the propagation velocities were closely borne out by experimental results. We further find that the dispersion characteristic is affected by the width of the acoustic waveguide. We believe that our findings can contribute to improved CS-USM designs for practical application.

An Acoustic Method for Evaluating the Quality of Thermal Processing of 44NKhTYu Alloy

A homogeneous fine-grained structure that provides required strength characteristics has been shown to form in the (44NKhTYu alloy) elinvar for the considered thermal processing mode. Experimental data are provided that demonstrate elasticity characteristics to remain constant within a temperature range from–70 to +70°С. The persistence of the propagation velocities of elastic waves in this temperature range makes it possible to use this regularity in the development of techniques for thermal-processing quality evaluation. The ratio of the velocities of longitudinal and shear elastic waves has been proposed as a “diagnostic parameter.” The possibility has been studied for using elastic waves to inspect 44NKhTYu-alloy characteristics after various thermal-processing modes.

Inspection of the lids of shallowly buried concrete structures based on the propagation of surface waves- PART II

The possibility of performing the inspection of an underground structure directly from the surface of the soil would be advantageous for the inspection of various type of underground utility structures present in modern cities. In part I, the behavior of elastic waves propagating in a soil profile containing a shallowly buried underground concrete utility structure was studied and it was found that it is possible to evaluate the condition of the surface of the lid of such structures based on the propagation velocity of elastic waves. The part II follows from the work that was previously performed to develop a nondestructive technique for the inspection of shallowly buried utility structures based on the propagation of elastic waves. First, the three-dimensional finite difference method implemented in the software Fast Lagrangian Analysis of Continuum was used to model an underground concrete structure to show how the presence of a manhole and of a pavement at the surface of the soil affect the propagation of elastic waves. Second, a receiver configuration typically used in three-dimensional seismic surveys is presented and its effectiveness is tested on three different existing underground structures. The signals collected during the field tests are analyzed independently in the velocity-frequency plane using an adaptive signal processing technique. The velocity-frequency representation of each signal is then used to identify the different elastic waves and to calculate their group velocities. Third, the variation of the group velocity at the surface of the three concrete structures is presented in the form of two-dimensional contour maps that enabled the detection of anomalies on the surface of two of these structures. Finally, it is shown how the collected data can be used to obtain a three-dimensional tomography representative of the condition of the surface of an underground structure.

Physical basics of evaluating elastic characteristics of anisotropic composites by ultrasonic method

As a result of analyzing the generalized Hooke law and wave equations for an anisotropic medium, computational expressions have been derived for evaluating the elastic constants of orthotropic, transversely isotropic, and isotropic media using the propagation velocities of longitudinal and shear elastic waves measured with the pulsed ultrasonic method in the corresponding directions.

Elastic Properties of Zr<sub>50</sub>Cu<sub>43</sub>Ag<sub>7</sub> Bulk Metallic Glass Using Pseudopotential Theory

Using Hubbard-Beeby approach for phonon dynamics, in conjunction with our recently proposed model pseudopotential; phonon frequencies for longitudinal and transverse modes are computed and associated elastic properties of technologically important Zr-based Zr50Cu43Ag7 bulk metallic glass (BMG) are evaluated. Five different forms of the static local field correction functions, viz., Hartree etal. (H), Taylor et al. (T), Ichimaru and Utsumi et al. (IU), Farid et al. (F) and Sarkar et al. (S) are employed to investigate the influence of the screening effect on the vibrational dynamics of Zr50Cu43Ag7 BMG. Results for bulk modulus, modulus of rigidity, Poisson's ratio, Young modulus, propagation velocity of elastic waves and dispersion curves are studied. The theoretical computations are found to be in good agreement with the available experimental results, which confirms the use of our model pseudopotential to study elastic properties of such a glassy system.

Motion of a torsion pendulum immersed in a linear viscous liquid. Influence of wave phenomena

A cylindrical pendulum, which is suspended by an elastic rod or wire and immersed in a viscid liquid in a cylindrical container, can undergo rotating oscillations. The propagation velocity of vorticity perturbations in the gap between the cylinder and the container is assumed to be finite. This means that the acceleration of the liquid is characterized by not only the viscosity but also by a relaxation time constant. The propagation velocity of elastic torsional waves in the rod is assumed to be finite. The equations that describe the motion of such a complicated compound system are linear and have been solved in closed form. The solution shows that there is a considerable deviation between the exact solution and the simple quasi-steady solution. The most remarkable conclusion is that the classical quasi-steady solution for very weak damping is incompatible with the general solution. Propagation of elastic waves in the suspension rod and propagation of vorticity waves in the liquid have a great influence on the rotational motion of the pendulum. The purpose of this study is to formulate the criteria that make the classical quasi-steady analysis valid. The derived solution permits also measurement of viscosity and a conceivable relaxation coefficient of the liquid as well.

Phase-sensitive optical coherence elastography at 1.5 million A-Lines per second.

Shear-wave imaging optical coherence elastography (SWI-OCE) is an emerging method for 3D quantitative assessment of tissue local mechanical properties based on imaging and analysis of elastic wave propagation. Current methods for SWI-OCE involve multiple temporal optical coherence tomography scans (M-mode) at different spatial locations across tissue surface (B- and C-modes). This requires an excitation for each measurement position leading to clinically unacceptable long acquisition times up to tens of minutes. In this Letter, we demonstrate, for the first time, noncontact true kilohertz frame-rate OCE by combining a Fourier domain mode-locked swept source laser with an A-scan rate of ∼1.5 MHz and a focused air-pulse as an elastic wave excitation source. The propagation of the elastic wave in the sample was imaged at a frame rate of ∼7.3 kHz. Therefore, to quantify the elastic wave propagation velocity in a single direction, only a single excitation was needed. This method was validated by quantifying the elasticity of tissue-mimicking agar phantoms as well as of a porcine cornea ex vivo at different intraocular pressures. The results demonstrate that this method can reduce the acquisition time of an elastogram to milliseconds.

Elastic wave propagation and time history analysis in FG nanocomposite cylinders reinforced by carbon nanotubes using a hybrid mesh-free method

Purpose – The purpose of this paper is to propose a hybrid mesh-free method based on generalized finite difference (GFD) and Newmark finite difference methods to study the elastic wave propagation in functionally graded nanocomposite reinforced by carbon nanotubes (FGNRCN). The presented hybrid mesh-free method is applied for a thick hollow cylinder, which is made of FGNRCN and excited by various mechanical shock loadings. Design/methodology/approach – The FG nanocomposite cylinder is assumed to be under shock loading. The elastic wave propagation is obtained and studied for various nonlinear grading patterns and distributions of the aligned carbon nanotubes. The distribution of carbon naotubes in FG nanocomposite are considered to vary as nonlinear function of radius, which varies with various nonlinear grading patterns continuously through radial direction. The effective material properties of functionally graded carbon nanotube are estimated using a micro-mechanical model. Findings – The mechanical shock analysis of FGNRCN thick hollow cylinder is carried out and the dynamic behavior of displacement field and the time history of radial displacement are obtained for various grading patterns. An effective hybrid mesh-free method based on GFD and Newmark finite difference methods is presented to calculate the average velocity of elastic wave propagation in FGNRCN. The average velocity of elastic wave propagation is obtained for various grading patterns and various kinds of volume fraction. The effects of some parameters on average velocity of elastic wave propagation are obtained and studied in detail. Originality/value – The calculation of elastic radial wave propagation in a FGNRCN thick hollow cylinder is presented using a hybrid mesh-free method. The effects of some parameters on wave propagation such as various grading patterns of distribution of carbon nanotubes are studied in details.

Measurement of elastic wave propagation velocity near tissue surface by optical coherence tomography and laser Doppler velocimetry

We demonstrate a new technique for measuring the velocity of elastic waves propagating near a tissue surface by swept-source optical coherence tomography (OCT). We establish a theory for estimating the elastic wave velocity from the OCT images taken with a slow mechanical scanning, which is experimentally verified using agar and tissue samples. The elastic wave velocity measured by this technique agrees well with previous results and that measured with a laser Doppler velocimeter. We also carry out some trial measurements of the elastic wave velocities of several tissue samples by this method.

탄성파의 매질 내 이동속도 산정방법 비교

탄성파의 매질 내 이동속도 산정방법 비교

Condition assessment of PC tendon duct filling by elastic wave velocity mapping.

Imaging techniques are high in demand for modern nondestructive evaluation of large-scale concrete structures. The travel-time tomography (TTT) technique, which is based on the principle of mapping the change of propagation velocity of transient elastic waves in a measured object, has found increasing application for assessing in situ concrete structures. The primary aim of this technique is to detect defects that exist in a structure. The TTT technique can offer an effective means for assessing tendon duct filling of prestressed concrete (PC) elements. This study is aimed at clarifying some of the issues pertaining to the reliability of the technique for this purpose, such as sensor arrangement, model, meshing, type of tendon sheath, thickness of sheath, and material type as well as the scale of inhomogeneity. The work involved 2D simulations of wave motions, signal processing to extract travel time of waves, and tomography reconstruction computation for velocity mapping of defect in tendon duct.

Wave motion in auxetic solids

The effect of auxeticity on the velocity of elastic wave propagation is investigated herein for isotropic solids. Three types of dimensionless wave velocities are proposed for investigating longitudinal waves in prismatic bars, plane waves of dilatation, plane waves of distortion, and surface waves. Results show that the velocity of surface waves is slightly less than that of plane waves of distortion for conventional solids, but the difference becomes large for auxetic solids. The velocity of longitudinal waves in prismatic bars is higher than that of plane waves of distortion for conventional solids but the gap narrows for solids of the low auxetic range of −0.5 < ν < 0. The velocity of longitudinal waves in prismatic bars become lower than that of plane waves of distortion for intermediate auxetic range of −0.733 < ν < −0.5, and lower than that of surface waves for high auxetic range of −1 < ν < −0.733.