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In order to study the propagation behavior of acoustic emission (AE) signals in wood, COMSOL 3D simulation models were established for four kinds of wood specimens, including Populus simonii, Castanopsis hystrix, Pinus sylvestris and Cunninghamia lanceolata. The elastic wave point source was simulated using a given displacement method, and then, the longitudinal propagation of the AE signal along the wood was analyzed with the help of the stress maps of the simulation process. The longitudinal wave velocity of the AE source was calculated by the time difference of arrival (TDOA) method with respect to the time difference between the two posi‐ tions of the AE source arriving at the surface of the model. The AE tests were carried out on the wood specimen under the same condi‐ tions and the longitudinal wave velocities were calculated. The final results were consistent with the simulation model. The results showed that the relative errors between the simulated and tested longitudinal wave velocities of Populus simonii, Castanopsis hystrix, Pinus sylvestris and Cunninghamia lanceolata were 1. 47%, 1. 04%, 0. 46% and 2. 33%, respectively. The simulation model can ob‐ jectively reflect the propagation behavior of the AE signals in wood, which provided a new way to visualize the propagation process of the AE signals in wood. However, the relative error of AE signal amplitude was large, and the model cannot objectively respond to the change rule of amplitude in wood. [ABSTRACT FROM AUTHOR]

For laser ultrasound in the thermoelastic mechanism, excitation of ultrasonic body wave signal is weak, it is not easy to realize the detection of deep defects inside the workpiece. While the ablation mechanism produces a high and practical ultrasonic signal-to-noise ratio, this paper is based on the generation mechanism of laser ablation excitation of ultrasonic waves, the establishment of laser ultrasound in the ablation mechanism in the aluminum plate excitation and propagation of ultrasonic numerical model, through the solution, obtained the ultrasonic acoustic field map, discussed the ablation mechanism of the laser ultrasonic body wave acoustic field directionality. Additionally, the preliminary verification of the validity of the model is presented. Then, in order to explore the application potential of high signal-to-noise ratio longitudinal waves in defect detection, defects of different depths are preset in the model for simulation calculations, and waveform and acoustic field analyses are performed on the simulation results to study the ultrasonic propagation paths inside the member and the interaction with the defects, and the transverse position and depth of the internal defects are judged by using B-scan imaging. Finally, experimental validation is carried out. The experimental results are highly consistent with the simulation model, and the defect experiments can qualitatively determine the location of internal defects and verify the practicality and accuracy of the model. [ABSTRACT FROM AUTHOR]

In ultrasonic nondestructive testing (NDT), accurately estimating the time of flight (TOF) of ultrasonic waves is crucial. Traditionally, TOF estimation involves the signal processing of a single measured waveform. In recent years, deep learning has also been applied to estimate the TOF; however, these methods typically process only single waveforms. In contrast, this study acquired fan-beam ultrasonic waveform profile data from 64 paths using an ultrasonic-speed computed tomography (CT) simulation of a circular column and developed a TOF estimation model using two-dimensional convolutional neural networks (CNNs) based on these data. We compared the accuracy of the TOF estimation between the proposed method and two traditional signal processing methods. Additionally, we reconstructed ultrasonic-speed CT images using the estimated TOF and evaluated the generated CT images. The results showed that the proposed method could estimate the longitudinal TOF more accurately than traditional methods, and the evaluation scores for the reconstructed images were high. [ABSTRACT FROM AUTHOR]

The elastic mechanical behaviour of materials is very important to the design and service safety evaluation of mechanical load components. In order to accurately measure the elastic mechanical behaviour of metal structures with a non-destructive testing way, a dual-mode bulk-wave electromagnetic acoustic transducer (EMAT) is developed for both ultrasonic longitudinal wave and shear wave measurement. The elastic modulus and Poisson's ratio of metals are directly obtained with the velocities of the longitudinal and shear waves. In order to improve the efficiency of electromagnetic acoustic transducer, the electromagnetic acoustic parameters were characterised and optimised by numerical simulation. The results show that the developed dual-mode EMAT can successfully excite and receive longitudinal and shear waves, and the elastic modulus and Poisson's ratio of different materials (copper, aluminium and steel) obtained through experiments using the developed dual-mode EMAT are very close to the reference values. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the reflection and refraction of an incident P wave or SV wave at the interface of a plane. The plane, which is divided into two halves, is an elastic medium M1 having an incident wave and a thermoelastic diffusion medium M2 with TPLT (i.e., three-phase-lag thermal) and TPLD (i.e., three-phase-lag diffusion) models. It has been noticed that two waves are reflected and four are refracted in an isotropic thermoelastic diffusion medium. Out of the four refracted waves, three are longitudinal waves: a quasi-longitudinal wave qP, a quasi-mass diffusion wave qV, a quasi-thermal wave qT and one is a transverse wave SV. If we consider the above waves first, the amplitude and energy ratio are calculated by using the surface boundary conditions and then graphically represented to compare the change in energy and amplitude ratio with the change in incident angle for three particular cases. The conservation of energy is depicted by verifying that all the energy sums up to unity. The considered problem has its application in earthquake engineering, astronautics, rocket engineering, seismology and many more engineering areas. [ABSTRACT FROM AUTHOR]

In view of the non-destructive and non-contact features, laser ultrasonic (LU) technology has long been the effective method to detect tiny defects for laser powder bed fusion (LPBF) additive manufactured specimens. Of larger concern is the variation and the corresponding mechanism on tested results of LU detection as the property of LPBF additive manufactured specimen is changed. Aiming at the property of surface roughness, this work investigated the propagation characteristics of excited ultrasonic waves in LPBF additive manufactured 316L stainless steel with different surface roughness, as well as the interaction between ultrasonic waves and artificial submillimeter holes. Both numerical simulated and experimental study were conducted. Simulated results revealed that the amplitudes of longitudinal wave (L wave) and its echo wave L1 at the holes exhibited a discernible increase as the surface was coarser. The increase in surface roughness was detrimental to the resolution of defect detection as was expected from the increased amount of noise. LPBF fabrication and the subsequent LU pulse-echo detection were conducted for 316L stainless steel. Both B-scan and C-scan were able to detect the holes with the diameter of 0.6 mm. The speckle phenomenon deriving from the increase in surface roughness emerged, corresponding to the increased ultrasonic signal energy but deteriorated resolution of detected images. It is feasible to optimize LU detected effect by minimize the surface roughness of tested specimens.

For laser ultrasound in the thermoelastic mechanism, excitation of ultrasonic body wave signal is weak, it is not easy to realize the detection of deep defects inside the workpiece. While the ablation mechanism produces a high and practical ultrasonic signal-to-noise ratio, this paper is based on the generation mechanism of laser ablation excitation of ultrasonic waves, the establishment of laser ultrasound in the ablation mechanism in the aluminum plate excitation and propagation of ultrasonic numerical model, through the solution, obtained the ultrasonic acoustic field map, discussed the ablation mechanism of the laser ultrasonic body wave acoustic field directionality. Additionally, the preliminary verification of the validity of the model is presented. Then, in order to explore the application potential of high signal-to-noise ratio longitudinal waves in defect detection, defects of different depths are preset in the model for simulation calculations, and waveform and acoustic field analyses are performed on the simulation results to study the ultrasonic propagation paths inside the member and the interaction with the defects, and the transverse position and depth of the internal defects are judged by using B-scan imaging. Finally, experimental validation is carried out. The experimental results are highly consistent with the simulation model, and the defect experiments can qualitatively determine the location of internal defects and verify the practicality and accuracy of the model.

In ultrasonic nondestructive testing (NDT), accurately estimating the time of flight (TOF) of ultrasonic waves is crucial. Traditionally, TOF estimation involves the signal processing of a single measured waveform. In recent years, deep learning has also been applied to estimate the TOF; however, these methods typically process only single waveforms. In contrast, this study acquired fan-beam ultrasonic waveform profile data from 64 paths using an ultrasonic-speed computed tomography (CT) simulation of a circular column and developed a TOF estimation model using two-dimensional convolutional neural networks (CNNs) based on these data. We compared the accuracy of the TOF estimation between the proposed method and two traditional signal processing methods. Additionally, we reconstructed ultrasonic-speed CT images using the estimated TOF and evaluated the generated CT images. The results showed that the proposed method could estimate the longitudinal TOF more accurately than traditional methods, and the evaluation scores for the reconstructed images were high.

In this paper, a new and noncontact method with measuring longitudinal to shear wave velocity ratio by a dual-mode electromagnetic acoustic transducer is proposed for residual strain measurement in a metal structure without knowing its thickness. Firstly, the theoretical derivation of the ratio of longitudinal and shear wave velocities in electromagnetic ultrasound was conducted, and based on this, the effectiveness of the dual-mode bulk wave electromagnetic acoustic transducer was simulated. Secondly, the longitudinal and shear wave velocities of uniaxial stretched aluminum plates with different residual strains were measured using the established electromagnetic ultrasound experimental system. Finally, the ratio of longitudinal and shear wave velocities of specimens with different plastic deformations was analyzed, achieving quantitative non-destructive testing of residual strain in uniaxial tensile aluminum plates.

This study investigates the Slepyan–Palmov (SP) model, which describes plane longitudinal waves propagating within a medium comprising a carrier medium and nonlinear oscillators. The primary objective is to analyze the integrability properties of this model. The research entails two key aspects. Firstly, the study explores the group invariant solution by utilizing reductions in symmetry subalgebras based on the optimal system. Secondly, the conservation laws are studied using the homotopy operator, which offers advantages over the conventional multiplier approach, especially when arbitrary functions are absent from both the equation and characteristics. This method proves advantageous in handling complex multipliers and yields significant outcomes. [ABSTRACT FROM AUTHOR]

The paper reports on a dynamic finite element simulation of the propagation of longitudinal elastic waves in cylindrical plates and Pochhammer waves in rods. The simulation shows that in cylindrical specimens of compact shape, a single longitudinal wave first propagates till unloading waves from their lateral surfaces start to interact, and then, two types of longitudinal elastic waves propagate at a time. In rods, first comes a longitudinal elastic wave, and then, two concurrent waves—a longitudinal elastic wave and a Pochhammer wave—due to the effect of unloading from their lateral surfaces. With the example of aluminum, it is demonstrated in which range of geometric parameters the elastic properties of near-compact specimens cannot be analyzed by ultrasonic methods. [ABSTRACT FROM AUTHOR]

On-stream inspections are the most appropriate method for routine inspections during plant operation without undergoing production downtime. Ultrasonic inspection, one of the on-stream inspection methods, faces challenges when performed at high temperatures exceeding the recommended 52 °C. This study aims to determine the ultrasonic velocity and attenuation with known material grade, thickness, and temperatures by comparing theoretical calculation and experimentation, with temperatures ranging between 30 °C to 250 °C on low-carbon steel, covering most petrochemical equipment material and working conditions. The aim of the theoretical analysis was to obtain Young's modulus, Poisson's ratio, and longitudinal velocity at different temperatures. The experiments validated the theoretical results of ultrasonic change due to temperature increase. It was found that the difference between the experiments and theoretical calculation is 3% at maximum. The experimental data of velocity and decibel change from the temperature range provide a reference for the future when dealing with unknown materials information on site that requires a quick corrosion status determination. [ABSTRACT FROM AUTHOR]

Equations that describe elastic wave propagation in a fracturing solid are obtained. It is shown that a solution to an equation for the velocity potential of longitudinal waves of acoustic emission can be represented as the superposition of the fields of an ensemble of radiating cavities known as monopoles. The monopole ensemble parameters are selected so as the structural characteristics of a medium with cavities barely differ from those of a solid. [ABSTRACT FROM AUTHOR]

Plane longitudinal waves propagating in a Slepyan-Palmov medium that consist of a carrier medium and an ensemble of nonlinear oscillators are considered. The system of equations of dynamics is reduced to one equation for the longitudinal displacement of the carrier medium. The propagation of harmonic waves is analyzed depending on the change in the system parameters characterizing the relative density and dissipation in the medium. It is shown that only periodic waves can exist among nonlinear stationary waves. The influence of the parameters of nonlinearity and the relative density of the material on the limits of the maximum possible deformation, shape and wavelength has been studied. [ABSTRACT FROM AUTHOR]

Percussive drilling is considered an efficient approach for penetrating hard formations. Understanding the responses and mechanical properties of rocks while being impacted and crushed by rock drills is essential for further improving their penetration efficiencies. This paper examines the consecutive impacts between the drill bit and rock, which are induced by the waves reflected in the drill rod after an initial hammer impact. Firstly, the loading and unloading principle for consecutive impacts is proposed. Based on this principle and one-dimensional (1-D) longitudinal wave propagation, a 1-D bit-rock interaction dynamics model is subsequently established. This model considers switches between the states of impact and separation, to instantly predict rock responses. Selecting marble as a representative material, the findings from the 1-D theoretical model and three-dimensional (3-D) Finite Element Method (FEM) simulations indicate that the number of repeated crushing impacts, which substantially contribute to the final penetration displacement, increases as the wavelength or the baseline level of f c (dimensionless crushing threshold force) in a rock decreases. f c is related to the loading rate, and its baseline level diminishes with decreasing impact energy (waveform amplitude). Due to the increases in f c and loading stiffness for short waves, the overall increasing trend of the final penetration displacement with decreasing wavelength weakens. A suitably-short wave with a high dimensionless exponential growth rate r or a long wave with approximately a unit of r can lead to a relatively-high final penetration displacement. In addition, we find that the dynamic loading and unloading stiffness and crushing threshold force have specific relationships with the penetration displacement and rock loading rate. [ABSTRACT FROM AUTHOR]

This study investigates the Slepyan–Palmov (SP) model, which describes plane longitudinal waves propagating within a medium comprising a carrier medium and nonlinear oscillators. The primary objective is to analyze the integrability properties of this model. The research entails two key aspects. Firstly, the study explores the group invariant solution by utilizing reductions in symmetry subalgebras based on the optimal system. Secondly, the conservation laws are studied using the homotopy operator, which offers advantages over the conventional multiplier approach, especially when arbitrary functions are absent from both the equation and characteristics. This method proves advantageous in handling complex multipliers and yields significant outcomes.

The aim of the work. The problem of numerical simulation of longitudinal, transverse and surface waves on the free surface of an elastic half-plane is considered. Methods. To solve the non-stationary dynamic problem of elasticity theory with initial and boundary conditions, the finite element method in displacements was used. Using the finite element method in displacements, a linear problem with initial and boundary conditions was led to a linear Cauchy problem. A quasiregular approach to solving a system of second-order linear ordinary differential equations in displacements with initial conditions and to approximating the area under study is proposed. The method is based on the schemes: point, line and plane. The study area is divided by spatial variables into triangular and rectangular finite elements of the first order. According to the time variable, the study area is divided into linear end elements with two nodal points. The Fortran-90 algorithmic language was used in the development of the software package. Results. Some information is given about numerical modeling of elastic stress waves in an elastic half-plane with a concentrated wave action in the form of a Delta function. The estimated area under study has 12 008 001 nodal points. A system of equations consisting of 48 032 004 unknowns is solved. The change of elastic contour stress on the free surface of the half-plane at different points is shown. The amplitude of Rayleigh surface waves is significantly greater than the amplitudes of longitudinal, transverse, and other waves with a concentrated vertical action in the form of a triangular pulse on the surface of an elastic half-plane. After surface Rayleigh waves, a dynamic process is observed in the form of standing waves.

The problem of numerical modeling of bending waves in an aboveground oil pipeline under nonstationary seismic action is studied. To solve the unsteady dynamic problem of elasticity theory with initial and boundary conditions the finite element method was applied. Using the finite element method in displacements, a linear problem with initial and boundary conditions was led to a linear Cauchy problem. A quasi-regular approach to solving a system of linear ordinary differential equations of the second order in displacements with initial conditions and to approximation of the studied domain is proposed. The technique is based on the schemes: point, line and plane. The area under study is divided by spatial variables into triangular and rectangular finite elements of the first order. According to the time variable, the area under study is divided into linear finite elements with two nodal points. The algorithmic language Fortran-90 was used in the development of the software package. The problem of the effect of a plane longitudinal wave in the form of six triangles on an elastic half-plane to assess physical reliability and mathematical accuracy is considered. A system of equations consisting of 8 016 008 unknowns is solved. The calculation results are obtained at characteristic points. A quantitative comparison with the results of the analytical solution is taken. Furthermore, the problem of the impact of a plane longitudinal seismic wave at an angle of 90 degrees to the horizon on an aboveground oil pipeline is considered. The seismic impact is modeled as a Heaviside function, which is applied at a distance of three average diameters from the edge of the pipe. The calculation results were obtained at the characteristic points of the object under study. A system of equations consisting of 32 032 288 unknowns is solved. Bending waves prevail in the problem under consideration.

The problems of elastic wave propagation in the micropolar porous materials have been attempted under the interaction of micro-rotation tensor and porous distribution in this material. We obtain the existence of three coupled longitudinal and two coupled shear waves propagating with different phase speeds. Numerically, the phase speed and attenuation of five basic waves are computed. We consider the incident plane waves at the boundary of micropolar porous materials, then the dispersive nature of the incident waves is studied and the existence of critical angle for the incident shear wave is found. The amplitude and energy ratios of various reflected waves for the incident coupled longitudinal and shear waves are obtained analytically and numerically. Further, the influence of different material parameters is studied using dispersion relation and the relevant numerical values. [ABSTRACT FROM AUTHOR]

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Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A laser-EMAT ultrasonic longitudinal wave resonance thickness measurement method based on surface constraint mechanism is proposed. • The influence of surface constraint mechanism, irradiation laser source parameters, and EMAT receiving coil dimensions on the accuracy and amplitude of resonance method thickness measurement are analyzed. • Achieve accurate and rapid detection of the thickness thinning of stepped aluminium plates and the thickness of 500 ℃ high-temperature metal thin-walled parts. In this paper we propose a novel ultrasonic longitudinal wave resonance method for measuring the thickness of metal walls using a laser-electromagnetic acoustic transducer (Laser-EMAT). The method is based on the surface constraint mechanism (SCM) of the material and is expected to be capable of accurately detecting local thinning of metal walls in a non-contact manner and at high temperatures. Based on finite element analysis of laser-EMAT ultrasonic resonance measurement of aluminum alloy thickness, we investigated the effects of such key factors as SCM, irradiation parameters of laser source, and the size of EMAT receiving coil on the accuracy of thickness measurement (resonance frequency position) and on the amplitude of the resonance wave. Both numerical simulations and experiments are conducted to demonstrate that the measurement accuracy of the proposed method is not affected by SCM, irradiation laser source parameters, and EMAT receiving coil size, and that accurate detection of stepped aluminum plates with thickness thinning from 3.0 mm to 0.5 mm is achieved. Furthermore, we were able to perform rapid detection of aluminum thin plate thickness at 500 °C temperature with an EMAT lift-off of 5.0 mm and achieved a relative experimental error as small as 3.40 %. The results obtained in this study showed that the proposed method performed well in non-contact measurement of metal thinning in harsh environment of high temperature. [ABSTRACT FROM AUTHOR]

Measurement of the small filling levels in closed steel container systems is still a challenge. Ultrasound, however, is a sensitive and non-invasive technique and is suitable for online monitoring. This study describes a new ultrasonic sensor system for sensing small filling levels using longitudinal and surface acoustic wave analysis. The sensor system consists of one transducer for the longitudinal wave analysis and two transducers for the longitudinal and surface acoustic wave analysis. All transducers were mounted to the outer wall of the steel container, ensuring non-invasiveness, and a filling level ranging from 0 to 5 cm was investigated. Combining both approaches, a consistent determination of small filling levels was achieved for the entire measuring range (R2 = 0.99). [ABSTRACT FROM AUTHOR]

We consider the modulation instability of quasiharmonic longitudinal waves propagating in a homogeneous rod immersed in a nonlinearly elastic medium. The dynamic behavior of the rod is determined by the Mindlin–Herrmann theory, which refines the technical theory of rods. The accuracy of the model is ensured by describing the motion of the rod particles in the transverse direction and rejecting the hypothesis that the transverse strains due to the axial extension or contraction are proportional to the longitudinal strain. The system of equations describing the longitudinal vibrations of the rod reduces to a single nonlinear fourth-order equation for the longitudinal displacement of the rod particles. The multiscale method is used to derive the nonlinear Schrödinger equation, which is one of the basic equations of nonlinear wave dynamics. The Lighthill criterion is used to determine the domains of modulation instability. It is shown how the boundaries of these domains move as the parameters characterizing the elastic properties of the rod material and the medium nonlinearity change. The influence of the parameters of the system on the wave packets and the main parameters of envelope solitons (amplitude, speed, width) is analyzed. [ABSTRACT FROM AUTHOR]

The paper deals with the issue of modelling elastic wave propagation using the discrete element method (DEM). The case of a longitudinal wave in a rod with a circular cross-section was considered. A novel, complex algorithm consisting of the preparation of models and simulation of elastic waves was developed. A series of DEM models were prepared for simulations, differing in discretisation and material parameters. Additional calculations with the finite element method (FEM) were performed. Numerical wave signals were obtained from each simulation and compared with experimental results to choose the best DEM model based on the correlation between the waveforms. Moreover, dispersion curves were prepared for each model to verify the agreement with the Pochhammer-Chree wave propagation theory. Both experimental and theoretical approaches indicated the same model as the most suitable. The analysis results allowed stating that DEM can be successfully used for modelling wave propagation in structural rods. [ABSTRACT FROM AUTHOR]

We study the problem of propagating longitudinal waves in an elastic rod connected to a locally damaged foundation through a thin elastic layer. The motion of the rigid foundation blocks is considered predetermined. We formulated the initial-boundary problem for the Klein–Gordon equation with a discontinuous right-hand side. The nonstationary fields of displacements, velocities, and deformations were investigated by the Laplace integral transformation method. Examples of sudden divergence of fragments of the foundation by a given value and their mutual separation at a constant speed are considered.

The longitudinal wave propagating in an elastic rod with a variable cross-section owns wide engineering background, in which the longitudinal wave dissipation determines some important performances of the slender structure. To reproduce the longitudinal wave dissipation effects on an elastic rod with a variable cross-section, a structure-preserving approach is developed based on the dynamic symmetry breaking theory. For the dynamic model controlling the longitudinal wave propagating in the elastic rod with the variable cross-section, the approximate multi-symplectic form is deduced based on the multi-symplectic method, and the expression of the local energy dissipation for the longitudinal wave propagating in the rod is presented, referring to the dynamic symmetry breaking theory. A structure-preserving method focusing on the residual of the multi-symplectic structure and the local energy dissipation of the dynamic model is constructed by using the midpoint difference discrete method. The longitudinal wave propagating in an elastic rod fixed at one end is simulated, and the local/total energy dissipations of the longitudinal wave are investigated by the constructed structure-preserving scheme in two typical cases in detail. [ABSTRACT FROM AUTHOR]

The relevance. Currently, for construction of oil and gas wells, the most effective tool are bits reinforced with PDC (polycrystalline diamond cutters). These bits work on cutting–chipping principle, as the cutting is the most effective among all the mechanisms of rock destruction, due to the fact that the tensile strength of the rock and chipping is much less than its compressive strength. The analysis of the state of spent drill bits reinforced with PDC plates shows that they work out their life not fully, as a part of the cutting PDC elements fails due to chipping. The variety of forms of chips in shape and size requires classification, identification of the reasons of occurrence and determination of loads that lead to their occurrence. In addition, the scrapping of plates or their loss significantly affects the final technical and economic performance of drilling exploration and production wells. Solving the issues of improving the quality of bits by reducing the number of breakdowns will help to improve the economic efficiency of work in extraction and exploration of minerals. The aim of the study is the sizing platform chips for possible classification depending on the thickness of the shear layer of rock cutting element, and determining the causes of torsional and longitudinal vibrations in the drill string, causing breakage of the PDC offered a constructive change of drill bits reinforced PDC plates, warning the appearance of self-oscillations in the drill string. Objects: cutting elements of drill bits reinforced with PDC plates with a flat front face and PDC with a convex front face, chips of PDC plates on drill bits arising during drilling. Methods: experimental and analytical method of research on laboratory samples and on spent drill bits reinforced with PDC plates. Result. Based on the analysis and generalization of the results of the laboratory studies of the PDC plate breakdown occurrence causes and their nature the authors have developed the number of technical and technological solutions that prevent the occurrence of torsional and longitudinal self-oscillations in the drill string, and increase the efficiency of rock-cutting tools reinforced with PDC plates.

Wave propagation in a system of two arbitrary fluids separated by a contaminated interface in the form of an insoluble monolayer is investigated. The effects of four parameters (density ratio, R ; kinematic viscosity ratio, V ; Marangoni number, P ; and squared wave-Reynolds number, σ) on the solutions of a comprehensive dispersion relation for these waves are analyzed. In the first part of the manuscript, several special cases are considered wherein the comprehensive dispersion relation is modified to a simple polynomial equation and its numerical solutions are obtained for σ ∈ [ 0 , 1 ]. A bifurcation is observed at σ = σ b in two of the solutions in each case; and the system is shown to be overdamped for σ < σ b , and underdamped for σ > σ b . The relative influences of { R , V , P } on σ b are also analyzed, and it is found that in general, σ b is a strong function of { R , V } , but a weak function of P. In the second part of the manuscript, numerical solutions of the comprehensive dispersion relation are obtained for waves in a decane-water system, in the limit of { P ≫ 1 , σ ≫ 1 } ; and these solutions are classified to correspond to a transverse wave or to a longitudinal wave. The presence of a maximum/minimum in the frequency of oscillation and in the damping rate is observed for the transverse/longitudinal waves. For both the transverse and longitudinal wave modes, the relative deviation of the numerical solution (obtained from the comprehensive dispersion relation) from the respective approximate solution (obtained from a simple dispersion relation) is calculated. The relative deviation, though small, cannot be neglected because it accounts for the effects of elasticity and of capillarity/gravity; and disregarding it in the analyses will fail to yield the inherent maximum/minimum in the frequency of oscillation and in the damping rate for the transverse/longitudinal waves. • Solutions of a comprehensive dispersion relation involving { R, V, P, σ } — the density ratio, kinematic viscosity ratio, Marangoni number, squared wave-Reynolds number, are analyzed. • A bifurcation in present in the solutions and the system transitions from an overdamped regime to an underdamped regime at the bifurcation point, σ b. • The location of the bifurcation, σ b , is strongly dependent on { R,V }; and weakly dependent on P. • For { P ≫ 1 , σ ≫ 1 } , the comprehensive dispersion relation has two coupled solutions — one corresponding to a transverse wave and the other corresponding to a longitudinal wave. • Numerical solutions (obtained from the comprehensive dispersion relation) are compared with corresponding approximate solutions (obtained from simple dispersion relations for both waves). • The numerical solutions deviate from the corresponding approximate solutions slightly — this deviation, though small, cannot be neglected, because it produces results consistent with the physics. • For the transverse waves, this small deviation accounts for the effects of interfacial elasticity, and leads to the maximization of their oscillation frequency and of their damping rate. • For the longitudinal waves, this small deviation accounts for the effects of gravity/capillarity, and leads to the minimization of their oscillation frequency and of their damping rate. [ABSTRACT FROM AUTHOR]

With the advancement of aberration correction techniques, transcranial ultrasound imaging has exhibited great potential in applications such as imaging neurological function and guiding therapeutic ultrasound. However, the feasibility of transcranial imaging varies among individuals because of the differences in skull acoustic properties. To better understand the fundamental mechanisms underlying the variation in imaging performance, the effect of the structure of the porous trabecular bone on transcranial imaging performance (i.e., target localization errors and resolution) was investigated for the first time through the use of elastic wave simulations and experiments. Simulation studies using high-resolution computed tomography data from ex vivo skull samples revealed that imaging at large incidence angles reduced the target localization error for skulls having low porosity; however, as skull porosity increased, large angles of incidence resulted in degradation of resolution and increased target localization errors. Experimental results indicate that imaging at normal incidence introduced a localization error of 1.85 ± 0.10 mm, while imaging at a large incidence angle (40°) resulted in an increased localization error of 6.54 ± 1.33 mm and caused a single point target to no longer appear as a single, coherent target in the resulting image, which is consistent with simulation results. This first investigation of the effects of skull microstructure on transcranial ultrasound imaging indicates that imaging performance is highly dependent on the porosity of the skull, particularly at non-normal angles of incidence. [ABSTRACT FROM AUTHOR]

The present study aimed to investigate the elastic properties of functionally graded materials using ultrasonic bulk wave velocity features. To this end, three Al 2 O 3 –Al FGM samples were fabricated by spark plasma sintering method at three different temperatures (1050 °C, 1400 °C, and 1450 °C). In addition, two homogenous aluminum and alumina samples were fabricated to evaluate the properties of the initial materials using the initial powders. Ultrasonic pulse-echo technique was applied on fabricated samples in order to measure the longitudinal and transverse wave velocities. The elastic properties of the graded samples were obtained by wave velocity features and Archimedes density. The alumina and aluminum elastic modulus were measured as 394 and 70 GPa, respectively. The results indicated that increasing the sintering temperature from 1050 °C to 1400 °C and 1450 °C leads to considerable improvement in the average elastic modulus. The average elastic modulus of the graded bundle sintered at 1450 °C (308 GPa) was about 8.5% higher than that of the one sintered at 1400 °C (284 GPa). The microstructure analogies of samples illustrated micro-voids and phases agglomeration in all samples. The highest wave attenuation was observed in the graded sample with the lowest sintering temperature, i.e., the largest number of micro-voids caused the highest energy absorption in the graded bundle sintered at 1050 °C. [ABSTRACT FROM AUTHOR]

This research presents the theoretical and experimental studies for cylindrical and conical periodic structures to control longitudinal wave motion. Many relevant researches exist to stop and pass a certain frequency wave without active devices with periodic structures called metamaterials. To modify or control longitudinal wave propagation, i.e., passing or blocking mechanical wave within specific frequency ranges, repeated mass-spring systems or metamaterials can be applied. By integrating a few identical structural components to form a whole structure, it is possible to make a mechanical filter for wave propagation. Most studies rely on straight bar with cylindrical structure. Thus, with a unit cell that have a cylindrical and conical structure, this research presents the extensions toward the studies of the wave motions for straight and curved bars with finite element simulations and experiment studies. The results show that the hybrid cylindrical and conical periodic structures can be effective in terms of wave motion control and stiffness. [ABSTRACT FROM AUTHOR]

The results of the first stage of ultrasonic studies of the metal structure of pipelines of thermal power plants in operation are presented. The tests were carried out on metal of steel grades 15Kh1M1F and St20 with different operating life (operating time). The metal samples were subjected to metallographic analysis, the received data (the average grain size the distribution variance ) was used for theoretical calculation of the parameters of ultrasonic pulses of the bottom signal in metal. Quantitative data were obtained on the effect of the thickness of the couplant layer (the gap) between the transducer and the test object at operating frequencies of 5.0, 7.5 and 10 MHz for various values of the average grain size in metal. Examples of calculated and experimental pulses and signal spectra for a frequency of 5 MHz are given. [ABSTRACT FROM AUTHOR]

[Display omitted] • The realizable and controllable topological interface state of longitudinal wave in magnetostrictive PC beams is studied. • The magnetic and elastic fields in a unit cell are not uniformly distributed and closer to the real condition in the proposed nonlinear model. • The frequency and location of topological interface state can be modulated by adjusting magnetic, stress and thermal loadings. • The magneto-mechanical-thermal coupling tunability of longitudinal wave topological transport has been experimentally verified. Topological phononic crystals (PCs) have attracted increasing attention owing to their elastic wave topological transmission with high robustness, backscattering suppression, and defect immunity. However, the effective regulation of the topological interface state of elastic waves in multi-field environments remains a challenge, particularly in the magneto-mechanical-thermal coupling field. In this study, a magnetostrictive PC beam composed of Terfenol-D and aluminum rods was designed to dynamically manipulate the topological interface state of longitudinal waves when the system was subjected to magnetic, mechanical, and thermal loadings. First, the Zak phase transition of the band gap was induced by simply controlling the magnetic field distribution of a unit cell based on the nonlinear magneto-mechanical-thermal coupling constitutive characteristics of magnetostrictive materials. The frequency of the Zak point was also significantly affected by pre-stress and temperature. Subsequently, the controllable topological interface state of the longitudinal wave was successfully observed at the interface of magnetostrictive PC beams in a multi-field environment without altering the structure. The results showed that the frequency and location of the topological interface state could be dynamically tuned by magnetic, stress, and thermal loadings. The robustness of the topological interface state was also investigated. Finally, the magneto-mechanical-thermal coupling tunability of longitudinal-wave topological transport was experimentally verified for the proposed magnetostrictive PC systems. This study provides an effective method for the active modulation of elastic wave topological transmission and the development of novel tunable topological devices. [ABSTRACT FROM AUTHOR]

• A three-dimensional helical metamaterial tapered rod with power-law radius is proposed. • Complex band analyses and experimental results demonstrate a broad omnidirectional bandgap with strong wave attenuation capacity. • Wave mode coupling and conversion open up different bandgap types in helical structure. • Complete bandgap can be tuned via adjusting geometric parameters of tapered helical rod lattice. Tapered metamaterials have drawn much attention due to the inherent advantage of vibration reduction. However, the bandgap performance in most traditionally periodic structures is only restricted to a single direction. In this paper, aiming at opening up the complete bandgap both in flexural and longitudinal directions, we propose a novel type of three-dimensional helical metamaterial tapered rod with a power-law radius. Complex band analyses and vibration transmission results demonstrate that this metamaterial possesses a broad complete bandgap and several single-directional flexural bandgaps. The formation mechanisms of two bandgap types are also revealed. The complete bandgap is created by the combination effect between the local resonance and Bragg scattering effect. The mode transformation phenomenon immediately takes place before and after this complete bandgap. On the other hand, below the complete bandgap, single-directional bandgaps are generated by the separation effect between the neighboring modes which belong to different dominant directions. It can also be found that the wave attenuation capacity in the complete bandgap is far more significant than that of the single-directional one. Meanwhile, by increasing the initial radius or reducing the residual radius, a stronger local resonance effect can enlarge the complete bandgap and improve the attenuation capacity for evanescent waves. To validate the dynamic characteristics, different tapered rod metamaterials are fabricated and tested. A good agreement can be observed between the numerical predictions and experimental results. Based on these analyses, the three-dimensional helical metamaterial tapered rod paves a promising way for realizing excellent omnidirectional wave attenuation. [ABSTRACT FROM AUTHOR]

• Quasi-static components (QSCs) induced by longitudinal waves in isotropic pipes are numerically investigated. • The experiment is carried out to validate the existence of QSCs. • The generation of different levels of corrosion on the surface of the aluminium pipe is investigated. • The sensitivity of QSCs to corrosion is examined by nonlinear acoustic parameter. In this paper, the quasi-static component (QSC) generation of longitudinal waves propagating in an isotropic pipe is investigated numerically and experimentally. The three-dimensional (3D) finite element (FE) simulations are first carried out to gain physical insights into the characteristics of QSC generation from longitudinal wave travelling in an isotropic pipe with weak material nonlinearity. By applying the axial displacement excitation in the FE model, L(0, 1) mode and L(0, 2) mode are excited simultaneously. Then, the generated QSC pulses are extracted using the phase reversal approach for analysis. It is found that the QSC pulses generated by L(0, 2) mode and L(0, 1) mode are L(0, 1) mode. Meanwhile, the shapes of QSC pulses at different locations are extracted and compared. In this study, a data pre-processing method is proposed to handle numerically calculated and subsequent experimentally measured displacement signals, and a nonlinear acoustic parameter is defined to evaluate the incipient damages. After that, an experiment is conducted to measure the QSCs induced by the propagation of longitudinal waves in an aluminum pipe. The experimental results indicate that the propagation of longitudinal waves in the aluminum pipe can induce the QSCs. Different levels of corrosion are created on the surface of the aluminum pipe and are assessed by the generated QSCs. The results show that the nonlinear acoustic parameter has a monotonically increasing trend with the growing severity of corrosion. The QSCs generated by longitudinal wave can be used to detect and evaluate the early-stage surface corrosion in the aluminum pipe. [ABSTRACT FROM AUTHOR]

This article discusses ultrasound echo examination of the liquid volume inside a metal enclosure using noncontact electromagnetic acoustic transducers (EMATs) from outside the tank. Because only longitudinal sound waves exist in liquids, a novel and powerful EMAT design (kA currents in small coils) with a specifically enhanced transduction of longitudinal ultrasound is presented. Different wall materials (aluminum, steel, and stainless steel) and working frequencies are considered. A particular challenge, in addition to the already weak EMAT signals across an air gap, is the highly reflective interface between the metal wall and liquid because the acoustic impedances of the two media differ considerably. With thicker metal walls (here, 3mm), only either low frequencies < 100 kHz or frequencies close to the corresponding thickness resonance of the wall (here, about 1 MHz) are more suitable. The higher frequencies are preferred, as they show advantages due to a directed beam profile, shorter wavelengths in the liquid, and an overall better pulse fidelity. The simultaneous operation of several and closely neighboring EMATs demonstrates the feasibility of more demanding detection tasks, ultimately leading toward a 3-D localization inside the liquid using a noncontact EMAT array with eight independent elements. [ABSTRACT FROM AUTHOR]