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In this work, the guided wave de-bonding area-detecting technique was studied for application to containment liner plates in nuclear power plant areas. To apply this technique, an appropriate Lamb wave mode, symmetric and longitudinal dominance, was verified by the frequency shifting technique. The S0 2.7 MHz mm Lamb wave mode was chosen to realize quantitative experimental results and their visualization. Results of the bulk wave, longitudinal wave mode, and comparison experiments indicate that the wave mode was able to distinguish between the de-bonded and bonded areas. Similar to the bulk wave cases, the bonded region could be distinguished from the de-bonded region using the Lamb wave approach. The Lamb wave technique results showed significant correlation to the de-bonding area. As the de-bonding area increased, the Lamb wave energy attenuation effect decreased, which was a prominent factor in the realization of quantitative tomographic visualization. The feasibility of tomographic visualization was studied via the application of Lamb waves. The reconstruction algorithm for the probabilistic inspection of damage (RAPID) technique was applied to the containment liner plate to verify and visualize the de-bonding condition. The results obtained using the tomography image indicated that the Lamb wave-based RAPID algorithm was capable of delineating debonding areas.

The reflection and transmission problems of elastic waves through a partially saturated porous interlayer sandwiched between two elastic solid half-spaces are investigated. The partially saturated porous interlayer contains solid phase, gas phase and liquid phase. The solid frame is modeled by the fractional Zener model where the fractional order derivatives are used to describe the complex history-dependent viscoelastic behavior. Due to the coupled effects of the multiple fields, there exist three longitudinal waves and one transverse wave in the porous medium. The numerical results of reflection and transmission coefficients and the energy dissipation ratios are provided and shown graphically. The effects of the gas saturation, the interlayer thickness and the viscoelasticity of the solid frame are discussed based upon the numerical results. It is observed that the reflection and transmission coefficients and the energy dissipation ratios are affected noticeably by the gas saturation, the interlayer thickness and the viscoelasticity of the solid frame. In particular, there exists the characteristic gas saturation where the energy dissipation increases drastically.

This study considers granular crystals respectively with different three-dimensional microstructures categorized into a medium dense microstructure and two dense microstructures in one-sized and two-sized particles. Macroscopic micromorphic constitutive parameters are obtained for different granular crystals based on the micromechanics-based micromorphic model. Furthermore, two micromorphic wave modes are predicted for a plane strain problem, including coupled transverse-rotational and longitudinal waves. This study predicts obvious dispersions of micromorphic waves in different granular crystals. The widest frequency band gap is predicted for granular crystals with medium dense microstructure, and granular crystals with two dense microstructures have the same frequency band gap. The correlations are respectively obtained between frequency band gaps and void ratios, coordination numbers, characteristic lengths and micromorphic parameters. According to dispersion behaviors, correspondences between micromorphic and Cosserat waves are obtained. The simulations of dispersion curves based on the discrete element model are obtained to compare with the theoretical mircomorphic dispersion ones.

The detailed mechanism of supersonic mixing enhancement by a novel device is investigated computationally based on the Navier-Stokes equations. The device is a wall-mounted three-dimensional cavity, several parts of the rear face of which are cut out, and the lower wall of the cut-out part has a slope directed toward the injector from which the injectant is discharged. The flow structures and behaviors observed in the computational results are confirmed in the experimental results. Experimental information about the high-frequency (several tens of kHz) pressure oscillation in the cut-out part is acquired in this study using a pressure-sensitive paint (PSP) responding to rapid change in pressure. The computational results reveal that a hairpin-like vortex is formed inside the cavity. The vortex works on the shear layer across the cavity to deflect it upward. The deflected shear layer shields the injectant from the primary flow, which causes the injectant to penetrate deep into the primary flow. The computational results also clarify that the expansion and compression waves produced in the rectangular part of the cavity are delivered effectively to the injector along the slope of the cut-out part, which is confirmed in the PSP measurement results. The delivered waves actuate the jet issuing from the injector to fluctuate up and down periodically with a large amplitude.

An aim of current study is to analyze the contribution of reflected longitudinal waves to wave-induced fluid flow (WIFF) in the cracked porous solid. Initially, we investigate the time harmonic plane waves in cracked porous solid by employing the mathematical model proposed by Zhang et al. (2019) . The solution is obtained in form of the Christoffel equations. The solution of the Christoffel equations indicates that there exist four (three dilatational and one shear) waves. These waves are attenuated in nature due to their complex and frequency-dependent velocities. The reflection coefficients are calculated at the sealed pore stress-free surface of cracked porous solid for the incidence of P 1 and S V waves. It is found that three longitudinal waves contribute to WIFF and the contribution of these waves to the induced fluid in the cracked porous solid is analyzed using the reflection coefficients of these longitudinal waves. We analytically show that the fluid flow induced by these longitudinal waves is linked directly to their respective reflection coefficients. Finally, a specific numerical example is considered to discuss and to depict the impact of various parameters on the characteristics of propagation like phase velocity/attenuation, reflection coefficients and WIFF of longitudinal waves.

A tight-binding theoretical model which describes the vibration properties of a new type of mechanical metamaterial, the coupled-resonator phononic metamaterial (CRPM), is developed. This metamater...

To study the propagation characteristics and energy attenuation of different modal acoustic emission signals in wood, Zelkova schneideriana and Pinus sylvestris var.mongolica were used as test materials, and a test scheme was designed to separate surface transverse wave and internal longitudinal wave based on wave theory. The propagation characteristics of AE signal along the grain direction of wood was studied based on the discrete wavelet analysis, and then the energy attenuation model of AE signal was developed. The results show that when STW and ILW were propagated in wood, the energy of AE signal shows exponential decay with the propagation distance. STW has a more complex frequency domain distribution and more drastic time-frequency attenuation, and the propagation velocity of STW in Zelkova schneideriana and Pinus sylvestris var.mongolica was 1519.8 m.s−1 and 1118.8 m.s−1, respectively. The AE mode of ILW was relatively stable and always distributed in the low frequency band with fast propagation; the propagation velocity in Zelkova schneideriana and Pinus sylvestris var.mongolica was 6944.4 m.s−1 and 5168.4 m.s−1, respectively. Furthermore, the study shows that the propagation velocity of ILW is about 4.6 times that of STW in the same species of wood.

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.

For materials that have a matrix porosity at the microscopic scale, and an interconnecting fracture system at the mesoscopic scale, the double-porosity dual-permeability model provides a better prediction of seismic wave attenuation than the single porosity model, due to the flow exchange mechanism between these different size pores. The current work offers for the first time a numerical solution tool based on the method of fundamental solutions for problems of 3-D wave scattering and dynamic stress concentration around scatterers, such as cavities and embedded inhomogeneous inclusions, in an infinite double-porosity dual-permeability medium. The method of fundamental solutions is based on the spherical wave potentials representing three compressional waves and one shear wave. The accuracy and stability of the method are tested against other available results, and are demonstrated to be excellent. Wave scattering and dynamic stress concentration problems due to spherical cavity and poroelastic inclusion are then investigated for incident plane P1 and SV waves in the frequency domain. The research shows that the seismic responses are sensitive to the incident frequency, the boundary drainage condition, and material properties such as porosity.

In this paper, we report on surface-plasmon-resonance enhancement of the time-dependent reflection changes caused by laser-induced acoustic waves. We measure an enhancement of the reflection changes induced by several acoustical modes, such as longitudinal, quasi-normal, and surface acoustic waves, by a factor of 10–20. We show that the reflection changes induced by the longitudinal and quasi-normal modes are enhanced in the wings of the surface plasmon polariton resonance. The surface acoustic wave-induced reflection changes are enhanced on the peak of this resonance. We attribute the enhanced reflection changes to the longitudinal wave and the quasi-normal mode to a shift in the surface plasmon polariton resonance via acoustically induced electron density changes and via grating geometry changes.

This paper addresses the wave propagation problem within the context of the theory of materials with triple porosity under local thermal non-equilibrium. The time-harmonic wave solution is studied and the dispersion relation is explicitly established as an eighth-degree algebraic equation. It is shown that there are two shear waves undamped in time, that are non-dispersive and unaltered by the presence of the pore system or by thermal effects. Also, there are seven longitudinal wave solutions that are dispersive and damped in time: one longitudinal quasi-elastic wave, three longitudinal quasi-pore standing waves and three other longitudinal quasi-thermal standing waves. An illustrative simulation on a material like Berea sandstone shows that the effects of coupling triple porosity with local thermal imbalance and mechanical deformations leads to an increase in the propagation speed of the longitudinal quasi-elastic wave accompanied by an increase in its rate of decrease over time, as well as to a relaxation of the decrease in time for the quasi-pore and quasi-thermal standing waves.

In this study, a waveform modification method was proposed using a self-designed heating device combined with the split Hopkinson pressure bar (SHPB) technique for determination of dynamic behaviors of rock at high temperature. Firstly, the temperature gradient distribution on the incident bar was measured according to the variation of elastic modulus of the bar with temperature, and the relationship between the longitudinal wave velocity and temperature of the bar was obtained based on one-dimensional stress wave theory. The incident bar with a temperature gradient was divided into a series of microelements, and then the transmission coefficient of the whole incident bar was obtained. Finally, the stress wave was modified by the transmission coefficient from 25 °C to 600 °C. This method was used to study the dynamic properties of rock at high temperature, which not only preserves a classical SHPB device, but also effectively ensures the accuracy of the experimental results. A dynamic Brazilian disc experiment was carried out to explore the influences of loading rate and temperature on dynamic tensile strength of sandstone at high temperature using the proposed waveform modification method.

Diabetic patients have a higher risk of bone fracture than those without diabetes, despite a normal bone mineral density. This higher riskmay result fromthe deterioration of collagen because of glycation. The objective of this study was to investigate the elastic properties of glycated collagen using the micro-Brillouin scattering technique. Using single-layer uniaxial collagen films with a thickness of approximately $30~\mu \text{m}$ , the longitudinal wave velocities, propagating in the parallel andperpendiculardirectionswith respect to the collagen fiber orientation, were measured in dry and wet film specimens. The wave velocities in the glycated collagen specimens decreased as a function of glycation time. This decrease depended on the direction of collagen fiber alignment and wave propagation. The lowest velocity due to glycation in thewet filmswas foundwhen the ultrasound propagated perpendicular to the fiber direction. These results indicate that the glycation of collagen in the bone may also reduce bone elasticity and suggest that the effects of glycation on collagen films may be anisotropic.

The possibility of the localization of longitudinal waves in the intermediate frequency range in the edge transport barrier of a toroidal nuclear fusion facility is discovered. It is shown that such localized waves can be excited at the parametric decay of sub-megawatt ordinary microwave beams in experiments on electron cyclotron resonance heating of a plasma, which leads to the generation of anomalously scattered waves.

Non-destructive ultrasonic evaluation is one of the methods used for inspection in mechanical engineering. This method has diverse applications in various fields, including industry and medicine. The main purpose of this research is to identify a subcutaneous defect with ultrasonic waves. This is done by sending ultrasonic waves into the skin tissue and receiving backward echoes, simulating them using a software, and calculating the time difference using the speed of sound. In this research, the behavior of longitudinal and transverse waves is investigated in collisions with a defect by describing the genesis and application history as well as the principles and definitions of ultrasonic waves. In the test, first, the method of identifying the subcutaneous defect is explained. Then, the dimensions and stiffness of the defect are determined by analyzing the information obtained from the location. Using the 3.5-MHz probe, the defect was detected at a distance of 1.8 mm, indicating a high level of reliability compared to the sonography imaging device. This was while the 10-MHz probe failed to detect the defect just near the skin surface. The results confirm the choice of this method as a suitable method for detecting the subcutaneous defect.

In this paper, the second pulse ignition transient in a dual pulse solid rocket motor with elastomeric barrier pulse separation device has been conducted numerically. An in-house code has been developed to solve governing equations for unsteady compressible flow, heat conduction and structural dynamic. The solid propellant ignition and burning numerical models have been added. The fluid structure interaction is implemented by using the conventional serial staggered algorithm. The large deformation and expansion of the elastomeric barrier are addressed by the dynamic overset grid technology. The accuracy of the numerical method is validated by the experimental cases. Then, the detailed flow field development, pressure evolution, flame propagation characteristics in the combustion chamber, and the structural response of elastomeric barrier are analyzed carefully. The rupture-time and rupture-pressure of the elastomeric barrier are also obtained. The numerical results show that the elastomeric barrier deformation presents a small displacement at the front part and a large displacement at the rear section. The interaction of the compression waves and expansion waves from the convergent portion of the nozzle and from the motor head-end, as well as the supersonic annular jet flow in the combustion chamber, can induce obvious pressure rises with fluctuations and spikes. The first pulse free volume has a significant effect on the time to reach a steady state.

Salt rock is a crystalline material with a particular structure and different mechanical behavior. This inorganic material is a highly deformable rock, which shows creep under constant loads. This study attempts to estimate the properties and mechanical parameters of salt rock, such as uniaxial compressive strength, deformation modulus, Poisson’s ratio, internal friction angle, longitudinal wave propagation speed, and other related parameters by designing and performing the tests in accordance with valid standards in this context. Prismatic specimens were prepared from a salt rock dome, and the complete stress–strain curves in uniaxial compressive tests were determined. Comparison of salt rock strength and deformation characteristics with the brittle rock material shows significant difference between them. The results of tests have demonstrated the effect of the form of samples on their mechanical parameters. The ratio of the strengths under uniaxial loading of cylindrical samples to similar prismatic ones is about 0.83.

Acoustoelasticity is an inexpensive and reliable technique for measuring stresses in mechanical structures, provided the influencing factors are controlled. However, ultrasonic waves propagating inside solid bodies are affected by temperature, roughness, differences in microstructure, defects, and others. Non-uniformity is one of the most influential characteristics as it is difficult to evaluate. In this study, experiments were performed to assess the time-of-flight (TOF) of critically refracted longitudinal (Lcr) waves traveling in different regions of a unidirectional carbon-epoxy sample with allowable manufacturing non-uniformities using transducers of 1 MHz and 3.5 MHz to vary the depth of propagation. A phased array system (PAS) with transducers of 5 and 10 MHz was used to identify the regions with non-uniformities in the structure through the signal-to-noise ratio (SNR) and B-Scan images. The material under test is a unidirectional composite bar made of carbon fibers (HexTow® AS4) pre-impregnated with epoxy matrix (HexPly® 8552). The investigation shows that the TOF of the Lcr wave and the SNR results can be linearly related, for an optimized configuration. Therefore, the influence of non-uniformities can be removed from TOF using SNR values. Based on the results, a coupled PAS-Lcr ultrasonic system is proposed to measure stress in composites, including those with non-uniformities.

A simplified finite element method (FEM) simulation method has been established and validated for analyzing the sound absorption mechanism of structures with periodic axisymmetric cavities. Combined with genetic algorithm, the simplified FEM method is used to optimize the sound absorption coefficient of the structure containing periodic cylindrical cavities and variable cross section cavities. The result of variable section cavities is much better than the case of cylindrical cavities. The effect of cavity shape on sound absorption mechanism is discussed through energy dissipation, structure deformation and modal analysis of the absorption structures. It is found that the cavity structure resonances include bending vibration of the surface layer and radial motion of particles near the cavities. The radial motion also changes along the axial direction. Adding geometric design parameters of the cavity cross section are conducive to moving the radial mode to low frequency. The radial vibration has a great influence on absorption performance, which is more conducive to promoting the conversion of longitudinal waves into transverse waves with more energy dissipation. Finally, a better sound absorption performance is obtained by introducing the material parameter of Young's modulus into the optimization model, indicating that comprehensive consideration of geometry and material parameters for optimization is expected to obtain the desired sound absorption structure in engineering practice.

The paper studies the influence of the initial inhomogeneous thermal stresses on the dispersion of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder within the scope...

The paper is devoted to the numerical analysis of the reactive mixture explosion during the accidents at a launch site. The particular scenario concerns the explosion in the unconfined volume after accidental fuel release into the atmosphere. It is shown that the development of intrinsic flame instability results in the generation of compression waves, which occur to be intensified via the mechanism of thermo-acoustic instability. In turn, intensification of the compression waves leads to the formation of strong shock waves and even detonation in the case of a highly reactive mixture. The leading role in this process belongs to the transversal waves generated in the folds of the developed flame surface and propagated along the flame surface. It is the localization of the compression wave inside the reaction zone that causes amplification of the compression wave due to energy release.

For the accurate design of geotechnical structures subjected to static and dynamic loadings, precise estimation of elastic wave velocities and hence, small strain stiffness of soil is essential. However, the interpretation of elastic wave velocities propagating in deformed/sheared soil has not been comprehensively explored. In this research, shear (Vs) and compression wave velocity (Vp) measurements have been undertaken on three kinds of uniformly graded sands during drained triaxial compression by keeping minor principal stress constant. Planar piezoelectric transducers have been used to overcome the limitations associated with the more commonly used bender elements, such as distortion of transducers during specimen shearing. This technical note reveals that the increase of major principal stress in the wave propagation direction has a more significant influence on Vp in comparison to Vs. The axial strain (ea) at which peak Vs is noted is comparable to the ea at which specimen dilation or phase transformation takes place. The Vs values show a substantial drop after phase transformation, although there is an increase in the mean stress level. However, Vp increases even after specimen dilation takes place, and it is the major principal stress that dictates its evolution during triaxial compression. Moreover, for a given material and initial stress level, elastic wave velocities of specimens prepared at different initial densities approach one another during shearing and later merge at a large ea.

This paper studies weak solutions of the axial oscillations of the carbon nanotube modeled as an elastic nanobeam surrounded by an elastic medium. The model used combines Eringen’s theory of non-local elasticity and the equations of axial oscillations proposed by Aydogdu. Based on the Sturm–Liouville problem associated with this case, the weak solutions of the longitudinal waves in the carbon nanotube are determined.

Data from the Wildlife Liquefaction Array, which is located at southern California’s Imperial Valley in the USA, are analyzed. Variations in shear wave (Vs) and compression wave (Vp) velocities are identified during strong motions. Shear strains (γ) are computed from recorded acceleration time series between the sensors. All these variables are compared with the ground-surface accelerations and excess pore water pressure ratio (Ru) at different depths. Results show that Ru starts to accumulate when γ exceeds the threshold strain of 0.01–0.015%. Vs is negatively correlated to Ru and γ. Further investigation shows that Vs degradation depends on maximum horizontal shear strain with the different azimuthal angles at the same time window. By contrast, Vs reduction with Ru is caused by the decrease in effective stress; hence Ru reduces Vs regardless of the azimuthal angles. Vp degradation is limited compared with that of Vs under strong shaking, indicating that the constrain modulus is determined by the combination of soil skeleton and pore fluid.

The non-ordinary state-based peridynamic (NOSB PD) model has the capability of incorporating existing constitutive relationships in the classical continuum mechanics. In the present work, we first develop an NOSB PD model corresponding to the Johnson–Holmquist II (JH-2) constitutive damage model, which can describe the severe damage of concrete under intense impact compression. Besides, the numerical oscillation problem of the NOSB PD caused by zero-energy mode is analyzed and hence a bond-associated non-ordinary state-based peridynamic (BA-NOSB PD) model is adopted to remove the oscillation. Then, the elastic deformation of a three-dimensional bar is analyzed to verify the capability of BA-NOSB PD in eliminating the numerical oscillation. Furthermore, concrete spalling caused by the interaction of incident compression wave and reflected tension wave is simulated. The dynamic tensile fracture process of concrete multiple spalling is accurately reproduced for several examples according to the spalling number and spalling thickness analysis, illustrating the approach can well simulate and analyze the concrete spalling discontinuities.

A non-contact Laser-EMAT integrated system (LEIS) that uses a pulse laser as a generator and an Electromagnetic acoustic transducer (EMAT) as a detector is proposed. To explain the LEIS could simultaneously measure the width and the depth of metal plate, the finite element model (FEM) of the LEIS, which can describe the entire process from laser generates ultrasound to EMAT receives ultrasound, is established. In detail, the intensity ratios of Rayleigh wave, Shear wave and Longitudinal wave excited by laser under the consideration of three components, the particle displacement, the particle vibration velocity in out-plane direction and particle vibration velocity in in-plane direction, are focused. Combining the characteristics of the ratio and the EMAT as a velocity sensor, the Rayleigh wave and Longitudinal wave in the case of the particle vibration velocity in out-plane direction are chosen as the using waveforms, and the changes of directivity of various waveforms with laser parameters are studied. Furthermore, after the coil structure parameters and magnetic field direction of EMAT were reanalyzed and reconsidered, it is decided to use the coil with the wire spacing of 0.1 mm and a number of turns of 8 to combine with the transverse magnetic field to simultaneously detect the Rayleigh wave and Longitudinal wave generated by the laser. Finally, the signal-to-noise ratio of the two waveforms reach a balanced value, and can be clearly distinguished and extracted to achieve the purpose of measuring the depth and width of the metal plate at the same time.

2.25Cr1Mo0.25V steel has better high temperature strength than ordinary Cr-Mo steel, and has been widely used in nuclear and chemical environments such as nuclear energy and chemical industry. However, vanadium-added steel is still likely to cause hydrogen damage and requires early detection. Ultrasonic inspection has strong penetrating ability. It can detect thin plates with thickness of 1-2mm and steel structure of several meters long. In this paper, ultrasonic longitudinal wave was used to detect the amplitude and longitudinal wave period before and after hydrogen charging, and the change of wave velocity was obtained. The dynamic tensile test of the specimen before and after hydrogen charging was also carried out, and the elastic modulus and elongation of hydrogen before and after hydrogen charging were obtained. The relationship between ultrasonic signal and hydrogen embrittlement was also discussed in this paper.

An analysis of the focusing of an acoustic wave in a cylindrical channel filled with a pure liquid and a bubble liquid, separated by a spherical surface, as a result of its refraction at this interface is given. The influence of the frequency of an acoustic wave propagating in such a liquid–gas mixture as well as the radius of the bubbles and their volume content in it on the distance of focusing of this wave in the mixture was investigated. The conditions under which the focal distance of the acoustic lens formed in a liquid–gas mixture takes a maximum and a minimum values and an acoustic wave propagating in this mixture is focused or scattered in it were determined.

This study investigates the cracking mechanism of an elliptical bipolar linear-shaped charge blasting via theoretical analysis, experimentation, and numerical simulation. The results show that in the shaped charge blasting, due to the effect of the shaped jet in the direction of the shaped energy, a certain initial crack length is formed. In the action phase of the stress wave, the energy accumulation direction reduces the load required for crack initiation and propagation. The crack propagation length generated in the energy accumulation direction is greater than the nonenergy accumulation direction. The load value of the initial shock wave in the shaped energy direction is significantly greater, by about 1.64 times than the nonshaped energy direction, and the peak load acting time is earlier than the nonshaped energy direction. A large amount of impact explosion energy is consumed in the area close to the charged energy explosion due to the crushing area, regardless of the charged or noncharged energy direction. In the energy accumulation direction, the shock wave attenuation rate is faster in the near explosion area and the stress wave attenuation rate is slower in the mid and far areas of the explosion. The difference in the explosion load in the mid and far areas is small. In the nonconcentrated direction, owing to the reflected compression wave, the second stress peak appears in the nonconcentrated direction. However, its value is smaller than that of the initial shock wave peak.

Ultrasonic non-destructive techniques have been extensively used in various applications such as material characterization to extract important properties of materials. This work presents a non-contact hybrid system which integrates laser ultrasound and air-coupled transducer for generation and detection of guided waves. Furthermore, by adjusting the air-coupled transducer for an estimated angle, A0 S0 Lamb modes and longitudinal waves was detected in aluminum, stainless steel, and epoxy resin plates. Subsequently, the experimental measurements of dispersion curves are computed and Young’s modulus, thickness were calculated using inversion technique. Results show that the error percentage of Young’s modulus and thickness was about 7.60% and 9.26% for aluminum plate while the steel plate showed with 3.98% and 3.58%. Besides, the error percentage of Young’s modulus and thickness was about 4.05% and 5.88% for epoxy resin plate. The obtained experimental measurements were in good agreement with inversed material properties, which verified that the hybrid laser-air coupled ultrasonic technique can prove that the system is feasible, and the accuracy can be improved in the future to measure the material properties and geometrical character of metallic and polymer plates.

International audience; Abstract: The aim of this work is the detection of surface defects by the refracted longitudinal wave and the study of the parameters that influence the use of this wave in transmission and reflection modes in order to optimize the non-destructive testing (NDT) conditions with the LCR waves. For this, two types of defects are considered, cylindrical defects of different lengths 5 and 8 mm with depth of 10 mm and a rectangular groove of length 8 mm, width 2 mm and depth of 10 mm. The LCR wave was generated by transducers of center frequencies fc = 1 MHz and fc = 3.5 MHz with an inclination at a fixed-angle equal to 27° in aluminum. This study is divided into two parts. The first explains the changes in the signals caused by this interaction from a temporal point of view. The second part analyzes the energy losses induced on the spectrum. The reference signal is acquired in a defect-free sample. By comparison between the time signals and the respective reference signals, it has been found experimentally a decrease in the amplitude and a time shift of the LCR wave due to the presence of the defect. The sample spectra with a defect are modified relative to the spectrum obtained for the sample without defect, these are narrowed particularly for high frequencies. A shift of the centre frequency to lower values can also be noticed. The influences of the sensor frequency and the transmitter/receiver distance have been studied. When the frequency-sensor increases, the effects on the LCR wave by the defect increase. The study showed, that the increase in frequency allows the detection of smaller defects. Also, because of the inclination of the LCR beam, the choice of the distance between the transmitter and the receiver affects the defect detection. The reducing of the distance between the transmitter and the receiver improves the defects detection. The natures of the defects influence also the defects detection. In reflection mode, it is also possible to detected defect and the results found are satisfactory. Therefore this method is very effective because it identifies the defect and its location. © 2021, Pleiades Publishing, Ltd.

The insufficient strength of the fixed releasable press joints in the inner rings of the bearings with the pins of the wheelset axles leads failures of axle boxes. During the operation it is possible to change the bearing strength of the bearing rings, which may result in grinding of an axle pin part, fretting corrosion and ring rotation. In order to control the integrity of the ring on the axis pin, the most promising is implementing the acoustic methods. Such methods are based on the correlation between the reflection coefficient of ultrasonic waves at the boundary with the rolling surface of the ring and its stress-strain state (and, as a consequence, the integrity). The reflected ultrasonic waves contain information on the parameters of the contact liquid layer and the acoustic properties of the ring material. The goal of the research is to study the effect of the contact fluid layer between the transducer and the tested samples from different materials on the parameters of the recorded signal during ultrasonic testing. Throughout the research, an original combined transducer was manufactured. Testing of samples from various materials by ultrasonic echo method testing was carried out. The amplitude-frequency characteristics of the signals reflected from the studied samples are obtained. The reflection coefficients of longitudinal waves reflected from the boundary “transducer – test sample” at frequencies of 2.5 and 5 MHz were experimentally determined. The correlation between the reflection coefficient and the grinding degree of the transducer and the test sample is determined.

Two waves model where shock wave is combined with rarefaction wave appearing in laser ablation due to metal-nonmetal transition effect is investigated using conservation laws for mass and momentum fluxes for the steady-state regime of the process. This approach permits to obtain the relation between front velocities of the waves which shows that the rarefaction wave can be rather slow compared with the generated shock wave.

To understand the in-plane elastic character of ultrasonic waves in the skull, longitudinal wave velocities were studied in the MHz range using a conventional pulse technique. Taking advantage of the thickness of swine skulls, anisotropic in-plane wave velocity changes in the outer and diploe layers were experimentally investigated using structural information measured by X-ray computer tomography (CT). The velocities in the thin inner layer were difficult to measure. The main trabecular alignment (MTA) in the thick swine diploe layer was almost perpendicular to the thickness direction and changed with position inside the skull. The degree of anisotropy of in-plane longitudinal wave velocity ranged 1.07-1.33 in both outer and diploe layers, depending on position and swine sample. The angle of the fastest velocity in the outer layer was different from that in most parts of the diploe layer. Anisotropic character in the diploe layer gradually changed with position in the thickness direction.

Two ultrasonic measurement methods for pressure calibration to 4.4 GPa in a multi-anvil apparatus by measuring the travel times of longitudinal wave as a function of pressure are reported. The firs...

In the reinforcement of the structure of carbon nanotubes, irregularities may occur as consequences of manufacturing defect, servicing reckless, environmental damages, etc. Hence, it is of great importance to deal with various constructions of single-walled carbon nanotubes to study wave propagation. This study is the first attempt to show the impacts of the surface irregularity on waves propagating in a single-walled carbon nanotube (SWCNT) using Donnell thin shell approach. A new closed-form of the characteristics equation is derived. The results show that, the presence of surface irregularities effects the natural frequency of longitudinal waves propagating in the single-walled carbon nanotubes. In this work, the theoretical investigation and numerical results are important to predict the phenomenon of wave propagation in irregular single-walled carbon nanotubes, which can be used as a useful reference for the designs of Nano drive devices, Nano oscillators and Nano sensors.

Ultrasonic measurements were used to characterize the setting process of glass-ionomer dental cement (GIC) and to evaluate the effect of temperature on the setting time and mechanical properties. The ultrasonic method has the potential to be an ideal new tool for direct, real-time evaluation of the GIC setting reaction, providing detailed information on the evolution of their parameters as a function of setting time. The cement paste was prepared following the manufacturer’s instructions, from polycarboxylic acid and fluoroaluminosilicate glass, then inserted into cylindrical molds (8.0 mm in diameter and 3.0 mm in thickness). The cement mixing and the measurements of the acoustic properties were carried out at three different temperatures. The setting behavior was analyzed by monitoring changes in the ultrasonic velocity of the longitudinal wave. The results obtained show that the increase in temperature considerably accelerated the setting reaction. It was concluded that the proposed method is very effective in evaluating the setting reaction when an external energy source is applied and that the addition of heat energy to the setting almost sets GIC on command and improves their early mechanical properties.

The influence of nonlinear wave structures on the local hardness of an ice field of a dynamic type of formation is studied. Wave structures are formed by the interference of flexural–gravitational and longitudinal waves. The source of oscillations is coherent radiation in the ice itself. The difference in the local hardness of ice in the nodes and antinodes of standing waves (up to 60%) is explained by the dynamic metamorphism of ice. The dependences of the local ice hardness on the coordinates in the longitudinal and transverse profiles of the ice field have the form of periodic curves. The texture scales were determined, and the phase surface of the wave structures was constructed, which is not monochrome and reflects the spatial heterogeneity of the strength properties of the ice field. The effect of the wave action depends on the conditions at the interface between the ice and the pool walls. The influence of wave structures on the strength properties of the ice field as one of the possible factors of the spatial variability of ice under various modes of occurrence in situ is quantified.

Based on the results of laboratory studies, the frequency of 35 Hz in longitudinal waves and 20 Hz in circular waves is the optimum frequency that can increase the maximum oil recovery. Coreflooding test results before the vibration effect can increase oil production by 51.96% and reduce the residual oil saturation by 59.03%. The surprising results when the vibration effect was applied to the coreflooding test method with P wave types continuously succeeded in increasing oil production by 60.54%, intermittent P waves by 63.53% and circular waves by 64.76%, while also reducing Sor by 48.49% in continuous P waves, intermittent P waves at 44.81% and C waves at 43.3%. The P wave type vibrational method has an increase in oil gain by 16%, intermittently by 22%, Sor reduction by 18% and 24%, in circular wave oil gain increases by 25%, and Sor decreases by 27% from before the vibration effect given. Besides vibration can change the physical properties of rocks, among others; permeability has increased by 7% using P waves continuously, intermittently by 31% and C waves by 4%; porosity of 5.88% with P waves continuously, intermittently of 6.46% and circular waves of 4.63%; grain size before vibration of 45.16 μm after vibration using continuous P waves of 42.01 μm, intermittently of 47.98 μm, and circular of 50.46 μm; changes in oil composition to contain more alkanes, and lack of aromatic compounds; oil viscosity increased by 3% with continuous P waves, intermittent of 5%, and circular 61%. The new point from this paper is analyzing the vibroseismic effect by using SEM images in terms of the watershed segmentation of the Rabbani algorithm compared to lab results, which have an error rate of under 2%, and a review of oil composition by the GC-MS method.

In order to study the instability propagation characteristics of the liquid kerosene rotating detonation wave (RDW), a series of experimental tests were carried out on the rotating detonation combustor (RDC) with air-heater. The fuel and oxidizer are room-temperature liquid kerosene and preheated oxygen-enriched air, respectively. The experimental tests keep the equivalence ratio of 0.81 and the oxygen mass fraction of 35% unchanged, and the total mass flow rate is maintained at about 1000 g/s, changing the total temperature of the oxygen-enriched air from 620 K to 860 K. Three different types of instability were observed in the experiments: temporal and spatial instability, mode transition and re-initiation. The interaction between RDW and supply plenum may be the main reason for the fluctuations of detonation wave velocity and pressure peaks with time. Moreover, the inconsistent mixing of fuel and oxidizer at different circumferential positions is related to RDW oscillate spatially. The phenomenon of single-double-single wave transition is analyzed. During the transition, the initial RDW weakens until disappears, and the compression wave strengthens until it becomes a new RDW and propagates steadily. The increased deflagration between the detonation products and the fresh gas layer caused by excessively high temperature is one of the reasons for the RDC quenching and re-initiation.

Reference blocks for loading the bearing rings on the car wheelset axle journals have been developed and manufactured, and a hydraulic test rig for loading bearing rings that simulates their press fitting on the axle has been certified. A mathematical model of a method for evaluating mechanical stresses in a bearing ring using acoustoelastic method with chord-type sounding has been created and solved, with the variation of the angle between the wave propagation direction and the axis of the principal mechanical stresses taken into account. The acoustoelasticity coefficient of a longitudinal wave in ShKh15 steel was determined experimentally when loading the bearing ring. Interference fit measurements of bearing rings were performed with the loading reference blocks using acoustoelasticity method.

Mode-coupled vibrations in a thickness-shear (TSh) mode and laterally finite film bulk acoustic resonator (FBAR) with one face in contact with Newtonian (linearly viscous and compressional) liquid are investigated. With boundary conditions and interface continuity conditions, exact dispersion curves in FBAR sensors contacting with two kinds of liquids are obtained, and they are compared with the dispersion curves in a bare sensor without liquid contact. Frequency spectra, describing mode couplings between the main TSh modal branch and undesirable modal branches, are calculated by employing weak boundary conditions at lateral free edges constructed based on the variational principle. Mode shapes of mechanical displacements in both the sensor and liquid layer are presented, and mode transformations are observed due to the liquid contact and lateral edge effect. The effect of liquid thickness on frequency spectra is also studied. Numerical results reveal that the generation of shear wave in the liquid layer results in the shifts of spectrum curves along the frequency axis and hence it is the main factor of frequency shifts of FBAR sensors. The compressional wave causes the shifts of spectrum curves along the lateral aspect ratio axis. Then for a given FBAR sensor, the liquid thickness changes could also cause frequency shifts. Therefore, desirable vibration modes should be chosen based on the frequency spectra to avoid strong mode couplings and to eliminate frequency shifts induced by the liquid thickness changes in real applications.

In order to reveal the propagation characteristics and hazards of a gas explosion in urban drainage pipeline, the dynamic evolution of a methane deflagration in a closed water-containing pipeline was numerically simulated based on Computational Fluid Dynamics (CFD). The interaction mechanism between water oscillation and flame development during the methane deflagration was such revealed. The results show that the presence of water accelerates the flame propagation in the forward accelerating stage. However, the water generally played a significant role in inhibiting the flame propagation because of its cooling and blocking effects. And the flame acceleration may be enhanced with the water present if a longer tube is employed. The shear force generated by the compression wave acting on the stagnant water surface provides the most primitive power for the movement of water, which creates ripples in the calm water. The obstacles and the reciprocating motion of the compression wave make the water ripple and evolve into lifting thin water columns. The shearing effect of high-speed gas flow evolves the water columns into discrete water droplets. This evolution process of the water body increases the contact area between water and flame, thus blocking the transfer of heat and the expansion wave, inhibiting the self-sustained flame propagation, leading to its gradual extinction.

Longitudinal wave propagation in carbon nanotubes has been investigated by using Rayleigh-Bishop rod model and nonlocal strain gradient elasticity theory in the present study. Size dependent govern...

The propagation of the longitudinal waves in a single-walled carbon nanotube (SWCNT) considering the effects of thermoelastic damping is investigated in this Letter. The cylindrical shell is considered and the Donnell–Mushtari–Vlasov approach is utilised. The thermoelasticity governing equations are derived based on thin shell theory. Analytical expressions for the quality factor (Q-factor) of thermoelastic damping are presented for plane stress and strain conditions. The numerical results are presented to investigate the influence of some parameters on Q-factor of thermoelastic damping, such as the length of a nanotube, nanotube thickness and the ambient temperature. In addition, the dispersion curve of the longitudinal waves propagation in the SWCNT under the effects of thermoelastic damping is plotted. It can be seen that the Q-factor is proportional to the length and thickness of the SWCNT. It means that the increase in both length and radial thickness of the nanotube makes the Q-factor increase. For the final observation, it should be noted that the ambient temperature has an inverse effect on the Q-factor for the SWCNT. It means that the increase in ambient temperature makes the Q-factor decrease. These results can be helpful in the design of resonators and nanodevices.

In this study, with the meso-scale model reliably validated in our previous work (Construction and Building Materials, 2018), the waveform features of plain concrete under various loading conditions and especially with considering stress non-equilibrium are reliably reproduced and predicted. Associating with waveform features, the violation indicator of the specimen stress equilibrium in the split Hopkinson pressure bar test is identified for concrete-like damage softening materials. The concrete material behaviors for stress non-equilibrium are further analyzed, e.g. the dynamic increase factor (DIF) and damage development, etc. The conception of “damage failure volume” is introduced, and a new method of defining the development of concrete dynamic damage is given in the numerical study. What’s more, the “compression wave” and “double peak” phenomena observed in the experiment are further interpreted based on the means of numerical simulation. Waveform features how to reflect the concrete material properties is also concluded. The results show that, the disappearance of the “double peak” phenomenon of reflection curve under high strain rate can be regarded as the indicator of the violation of stress equilibrium. After the violation of the stress equilibrium, the relevant DIFs of the concrete specimen will not change significantly. Especially, the concrete specimen will turn into structural response from material response. The conception of “damage failure volume” can well explain the generation of the “double peak” phenomenon of the reflection curve. The “compression wave” phenomenon of reflection curve under lower strain rates is derived from the unloading expansion recovery of the concrete specimen. Furthermore, under the same loading condition, the amplitude of the first peak of the reflection curve can be used as the evaluation standard of the bonding quality between mortar and aggregates.

Pulmonary diseases and injury lead to structural and functional changes in the lung parenchyma and airways, often resulting in measurable sound transmission changes on the chest wall surface. Additionally, noninvasive imaging of externally driven mechanical wave motion in the chest (e.g., using magnetic resonance elastography) can provide information about lung stiffness and other structural property changes which may be of diagnostic value. In the present study, a comprehensive computational simulation (in silico) model was developed to simulate sound wave propagation in the airways, parenchyma, and chest wall under normal and pathological conditions that create distributed structural (e.g., pneumothoraces) and diffuse material (e.g., fibrosis) changes, as well as a localized structural and material changes as may be seen with a neoplasm. Experiments were carried out in normal subjects to validate the baseline model. Sound waves with frequency content from 50 to 600 Hz were introduced into the airways of three healthy human subjects through the mouth, and transthoracic transmitted waves were measured by scanning laser Doppler vibrometry at the chest wall surface. The computational model predictions of a frequency-dependent decreased sound transmission due to pneumothorax were consistent with experimental measurements reported in previous work. Predictions for the case of fibrosis show that while shear wave motion is altered, changes to compression wave propagation are negligible, and thus insonification, which primarily drives compression waves, is not ideal to detect the presence of fibrosis. Results from the numerical simulation of a tumor show an increase in the wavelength of propagating waves in the immediate vicinity of the tumor region., Graphical Abstract

Shear wave elastography (speed and dispersion), local attenuation coefficient slope and homodyned-K parametric imaging were used for liver steatosis grading. These ultrasound biomarkers rely on physical interactions between shear and compression waves with tissues at both macroscopic and microscopic scales. These techniques were applied in a context not yet studied with ultrasound imaging, that is, monitoring steatosis of force-fed duck livers from pre-force-fed to foie gras stages. Each estimated feature presented a statistically significant trend along the feeding process (p values

In this paper, an experiment is proposed to select longitudinal ultrasonic waves as the physical agent in the detection of tensile stress states. The delay time in the back-wall echo travel presents a relation with the strain usually considered in tensile tests. From an algebraic manipulation procedure, this time interval is the fundamental quantity in the proposed method. The theoretical development initiates from the sound velocity in the unstressed state and employs a perturbative method to quantify the changes in the time-of-flight due to both the dimension modifications and the acoustoelastic effect. In addition to Armco iron and rail steel, this study applies its mathematical model to metal-matrix composites of aluminium and SiC particles at different temperatures. The scheme requires one transducer to perform the corresponding measurements to evaluate if a metallic material is under tensile stress.

It is quite important for the detection and evaluation of material early degradation in order to ensure the durability and integrity of the key engineering components. The collinear wave mixing method is an effective and promising technique capable of detecting and localizing damage in materials. This research reports an investigation for evaluating and locating material plasticity damage in a metallic material by using collinear mixing wave technique. It is found that a third, resonant shear wave would be generated when the resonant condition of two collinear shear and longitudinal waves is satisfied. By controlling the triggering times of the signals that excite the primary waves, this wave mixing method is capable of scanning the cylindrical metallic specimens. Distributions of the amplitudes of resonant shear waves along the specimen can thus be obtained. Experimental study and numerical simulation show that amplitudes of the resonant shear waves are significantly increased at the plastic damage zone compared with that at the undamaged zone with same position on the specimen. It is demonstrated that this wave mixing technique has great potentials for identifying and evaluating the locations of the plastic damage zone in engineering.