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• Analytic algorithm for SH wave scattering near semi-elliptical crater. • The boundary of the crater is endowed with surface elasticity. • DSCF relative to wave frequency, incident angle and crater's aspect ratio. Cratering occurs inevitably on the surface of materials at all scales due to comprehensive factors. The presence of craters may have a significant influence on the mechanical performance of the surface of an elastic body. In this paper, we study the SH wave propagation in an elastic semi-infinite medium whose surface has a semi-elliptical crater. We explore the scattering of the SH wave by the crater when surface elasticity is incorporated in the model of deformation to account for possible small-scale effects of the crater. We obtain a series solution for the scattered wave function by employing the Mathieu functions in the corresponding elliptical coordinate system. We discuss in some numerical examples the dynamic stress concentration around the crater relative to the wave frequency and few geometric parameters. [ABSTRACT FROM AUTHOR]

Actuation of micro‐objects along unconstrained trajectories in van der Waals contacting systems—in the same capacity as optical tweezers to manipulate particles in fluidic environments—remains a formidable challenge due to the lack of effective methods to overcome and exploit surface friction. Herein, a technique that aims to resolve this difficulty is proposed. This study shows that, by utilizing a moderate power beam of light, micro‐objects adhered on planar solid substrates can be precisely guided to move in arbitrary directions, realizing sub‐nanometer resolution across extended surfaces. The underlying mechanism is the interplay between surface friction and pulsed opto‐thermo‐elastic deformations, and to render a biased motion with off‐centroid light illumination. This technique enables high‐precision assembly, separation control of nanogaps, regulation of rotation angles in various material‐substrate systems, whose capability is further tested in reconfigurable construction of optoelectronic devices. With simple set‐up and theoretical generality, opto‐thermo‐elastic actuation opens up an avenue for versatile optical manipulation in the solid domain. [ABSTRACT FROM AUTHOR]

The conventional reverse time migration utilizes regularly sampled computational grids to simulate wave propagation. Selecting the appropriate grid sampling is important for computational accuracy and efficiency. In general, the uniform-size grid cannot represent the complexity of the geology well. The grid may appear sparse in the low-velocity zone, especially in shallow depths where dispersion may occur. Conversely, it may appear excessively dense in the high-velocity zone, such as at greater depths or within a salt body, which results in higher computational memory and time consumption. To overcome these issues, we developed an efficient and accurate adaptive variable grid discretization method that automatically selects the vertical grid size based on the velocity, depth, and dominant frequency of the wavelet in elastic medium. Then we reformulated the elastic equations based on the adaptive variable grid by introducing a mapping relationship. To test the effectiveness, accuracy, and efficiency of the equation, we implemented it to both the forward propagation and migration of elastic wavefield. Synthetic numerical examples demonstrate that our proposed method can achieve elastic wavefield separation and no significant dispersion phenomenon. The multi-component imaging accuracy of reverse time migration is nearly equivalent to the traditional method, while significantly improving computational efficiency and saving storage space. [ABSTRACT FROM AUTHOR]

Abstract This study aims to develop a theoretical model for predicting the permeability of concrete in underground structures using compressive elastic waves. This research is motivated by the necessity of monitoring the permeability of concrete used in critical underground infrastructure, such as tunnels and radioactive waste disposal sites, to ensure their long-term safety. Increased permeability owing to crack generation can lead to groundwater inflow, undermining the structural integrity of these facilities. Traditional methods for permeability monitoring face challenges at depths of 500 m–1 km owing to high temperatures, high pressures, and limited space conditions. To address these issues, Biot’s model, which correlates the P-wave characteristics with the properties of porous media, was applied in this study. The P-wave velocity and attenuation were studied according to the permeability of concrete based on Biot’s model. Subsequently, concrete specimens were prepared to measure the permeability, P-wave velocity, and attenuation. The permeability results from the experiment were compared with those obtained from the model for validation. The findings indicate that the modified Biot’s model can effectively monitor permeability through elastic wave characteristics, offering a non-destructive and reliable method for assessing the condition of concrete structures in underground environments. This approach is expected to enhance the safety of underground infrastructure through accurate permeability monitoring.

A practical task of testing samples of various metals using the principles of nonlinear acoustics is being solved. A surface acoustic wave (surfactant), whose propagation process, due to nonlinear effects, is accompanied by generation of a wave of doubled frequency, was used for testing. An experimental device is used to monitor the structural state of a metal sample by recording a change in the nonlinear acoustic parameter (NAP). To excite surfactants, a wedge transducer with a resonance frequency of 1 MHz was used. The transmitted wave was recorded with a wedge transducer with a resonance frequency of 2 MHz. It has been shown that the NAP for the tested materials in the initial state has different values not only for materials belonging to different classes, but also for materials belonging to the same structural class and having different chemical compositions (12Kh17G9AN4 and 12Kh18N10Т). A plastic deformation by 2% does not lead to a NAP change for the AMg6 alloy and 12Kh17G9AN4, 20Kh13N4G9, and 10KhSND steels. The NAP change by 2% as a result of a plastic deformation for the 12Kh18N10T and 08Kh17N4M3 stainless steels is caused by a change in their phase compositions associated with the martensitic transformation. The presented data on the change in the NAP from early stages of the elastoplastic deformation to a predestruction for AMg6 and 10KhSND steels demonstrate the possibility of using it as a prognostic criterion for the limiting state of the material. [ABSTRACT FROM AUTHOR]

Elastic metamaterials with unusual elastic properties offer unprecedented ways to modulate the polarization and propagation of elastic waves. However, most of them rely on the resonant structural components, and thus are frequency-dependent and unchangeable. Here, we present a reconfigurable 2D mechanism-based metamaterial which possesses transformable and frequency-independent elastic properties. Based on the proposed mechanism-based metamaterial, interesting functionalities, such as ternary-coded elastic wave polarizer and programmable refraction, are demonstrated. Particularly, unique ternary-coded polarizers, with 1-trit polarization filtering and 2-trit polarization separating of longitudinal and transverse waves, are first achieved. Then, the strong anisotropy of the proposed metamaterial is harnessed to realize positive-negative bi-refraction, only-positive refraction, and only-negative refraction. Finally, the wave functions with detailed microstructures are numerically verified. [ABSTRACT FROM AUTHOR]

Incident particles in the Klein tunnel phenomenon in quantum mechanics can pass a very high potential barrier. Introducing the concept of tunneling into the analysis of phononic crystals can broaden the application prospects. In this study, the structure of the unit cell is designed, and the low frequency (< 1 kHz) valley locked waveguide is realized through the creation of a phononic crystal plate with a topological phase transition interface. The defect immunity of the topological waveguide is verified, that is, the wave can propagate along the original path in the cases of impurities and disorder. Then, the tunneling phenomenon is introduced into the topological valley-locked waveguide to analyze the wave propagation, and its potential applications (such as signal separators and logic gates) are further explored by designing phononic crystal plates. This research has broad application prospects in information processing and vibration control, and potential applications in other directions are also worth exploring. [ABSTRACT FROM AUTHOR]

Abstract Actuation of micro‐objects along unconstrained trajectories in van der Waals contacting systems—in the same capacity as optical tweezers to manipulate particles in fluidic environments—remains a formidable challenge due to the lack of effective methods to overcome and exploit surface friction. Herein, a technique that aims to resolve this difficulty is proposed. This study shows that, by utilizing a moderate power beam of light, micro‐objects adhered on planar solid substrates can be precisely guided to move in arbitrary directions, realizing sub‐nanometer resolution across extended surfaces. The underlying mechanism is the interplay between surface friction and pulsed opto‐thermo‐elastic deformations, and to render a biased motion with off‐centroid light illumination. This technique enables high‐precision assembly, separation control of nanogaps, regulation of rotation angles in various material‐substrate systems, whose capability is further tested in reconfigurable construction of optoelectronic devices. With simple set‐up and theoretical generality, opto‐thermo‐elastic actuation opens up an avenue for versatile optical manipulation in the solid domain.

The rock burst frequently occurs in the roadways with top coal, and the roof disasters are particularly severe under dynamic stress in China. In order to explore the classification and instability mechanisms of anchoring structures in the roadways with top-coal, analog simulation experiments, theoretical analysis, and data statistics were used under the engineering background of the large-area rock burst roof failure in the Working Face 301 of a mine in Shaanxi Province, China. The dynamic load response characteristics of the stress, displacement, and surface acceleration of the surrounding rock in the roadways with top coal were analyzed. The classification characteristics of the roof anchoring structure under the influence of top coal thickness and cables were studied. The stress response mechanism of the roadways with top coal under elastic waves was explored, and the instability mechanism of the anchoring “beam arch” structure was proposed. The rock burst resistance of the air-return roadway in the Working Face 301 was evaluated, and the corresponding optimization schemes for the “beam-arch” composite structure were proposed. The results show that ① the monitoring data of stress and displacement of the surrounding rock in the roadways with top coal under dynamic stress verify the existence of internal and external beam or arch anchoring structures in the roof. Due to the increase in the thickness of top coal, there is a transition from “beam” to “arch” in the anchoring structure of the inner layer of the roof; ② based on the relative relationship between the thickness of the top coal and the cables, the roof anchoring structure is divided into “superimposed-beam and arch” for thin top coal, “composite-beam and arch” for thick top coal, and “combined arch” for extra thick top coal. A critical thickness index for the transformation of thick coal beams from “beam” to “arch” is established; ③ the instability mechanism of the beam structure and the arch structure is that they fail after reaching their tensile and shear strength limits under dynamic and static stress, respectively. The amplification effect of the “beam-arch” composite structure on the load stress is significantly affected by its size; ④ the bearing strength of the inner arch in the "combined arch" structure is relatively low. Increasing the length of cables can increase the thickness of the inner arch, and the corresponding “combined arch” structure’s bearing strength increases significantly, which is consistent with the evaluation results of the rock burst resistance.

AbstractInteraction between two cavities and a linear crack subjected to elastic shear horizontally (SH) wave is investigated analytically in this work. Two cavities are buried in two bounded half spaces respectively and the cross-section of each cavity has a different shape. The media of two half spaces are isotropic and anisotropic respectively, and the complex function method is applied to first solve the wave equation in each medium. Then, with the help of image principle, Green’s functions and wave field expressions in each separated half space are constructed. Subsequently, utilizing “conjunction” technique, a series of Fredholm integral equations containing undetermined forces at the interface are obtained and reduced in order to be solved. Dynamic stress distribution is mainly considered to discuss the interaction between the cavities and the crack. Finally, a parametric study on dynamic stress concentration factor (DSCF) and dynamic stress intensity factor (DSIF) presents the interaction is affected by several dimensionless factors simultaneously. [ABSTRACT FROM AUTHOR]

This paper establishes the concept of elastic wave propagation in a multi-porous medium with different permeabilities by assuming there are n distinct pore fluid phases. The dynamic equation of motion of elastic wave propagation through this multi-porous medium is derived based on Lagrangian mechanics. In this regard, the generalized form of mass coefficients and then the energy loss due to the fluid phases in terms of dissipation coefficients are presented for low-frequency limits with the help of Darcy's Law of multi-phases system. The elastic coefficients of the constitutive equation in terms of compliance matrix are identified using a series of Gedanken experiments. Some significant results regarding the compressional and rotational waves in a multi-porosity medium are derived. The validation of the theory has been shown by comparing it with the existing theory of single and double porosity. It is observed that there are (n+1) compressional waves corresponding to solid and fluid phases, whereas only one rotational wave is associated with the solid phase. The concept of multi-porosity theory can contribute to a deeper understanding of wave behaviour in a porous medium. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature 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.)

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office 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.)

There have been many studies on the ground state of phononic crystals, but few studies on the nature of the excited state. In this paper, we introduce the asymmetric Klein tunneling method in phononic systems, which enables selective direction and control of elastic waves by inducing polarization through an external field in an artificial barrier. Using tight-binding theory, we systematically studied phononics in a super-honeycomb structure, demonstrating the anisotropic transition properties of excited state phonons through a matrix model involving the ground state’s s-type and the first excited state’s p-type wave functions. Additionally, we exploit the thermal sensitivity of epoxy to achieve localized thermal field-induced distortion of the bottom flat band, forming a tiled Dirac cone, and thereby creating a reconfigurable polarized artificial barrier in the elastic wave system. Elastic waves propagate in these systems with topological charge conservation. Combining this with the theoretical of excited-state phonons, we demonstrate asymmetric Klein tunneling with directional selectivity in the elastic wave carriers, and systematically investigate the performance of this tunneling. Furthermore, we design a four-port elastic waveguide based on the principle of asymmetric tunneling, which achieves exceptional directional selectivity of elastic wave signals by adjusting the polarization direction of barriers at the junctions. These studies not only extend the application of Klein tunneling in elastic wave systems but also open new research avenues for the study of elastic wave devices controlled by various external fields, showing direct application potential in elastic wave signal processing.

We consider the propagation of a harmonic elastic wave in a composite inclusion–matrix structure subjected to plane deformation. The interface between the inclusion and matrix is described by the complete Gurtin-Murdoch model with non-vanishing interface tension and interface stretching rigidity. We consider an inclusion of general shape and formulate the corresponding boundary value problem for the wave functions in the inclusion and matrix when a harmonic compressional or shear wave is incident on the edge of the matrix. The problem is then solved by series expansion methods for the case of a circular inclusion embedded in an infinite matrix. The series solution obtained is validated by checking its convergence and via comparisons with existing static and dynamic solutions for certain reduced cases. Numerical examples are presented for the case of a small-sized circular hole embedded in a soft matrix demonstrating the influence of surface tension on the incident wave-induced dynamic stress concentration in the matrix. We find that the presence of surface tension relieves the peak stress around the circular hole when the frequency of the incident wave is below a certain critical value, while it tends to intensify the peak stress for a high-frequency incident wave. [ABSTRACT FROM AUTHOR]

This study considers the propagation of harmonic plane waves in general anisotropic dissipative media. This propagation is governed by a complex slowness vector, which is resolved into a propagation vector and an attenuation vector. The attenuation part is decomposed into homogeneous attenuation and evanescent attenuation. This makes a generalised specification of slowness vector to represent (in)homogeneous propagation in (an)isotropic (an)elastic media. This specification applies to incident waves, scattered waves as well as surface/interface waves at the plane boundary of the medium. With the choice of involved parameters, this specification can represent the corresponding wave-fields in the absence of anisotropy and/or dissipation. This specification has been used to formulate a corrected procedure for the reflection of plane waves in a transversely isotropic piezothermoelastic medium. [ABSTRACT FROM AUTHOR]

To localize high-density polyethylene membrane leakage in operating landfills, a leakage localization method based on the wave velocity inversion model is proposed in this study. A double-layer acceleration sensor and elastic wave generator are placed under the high-density polyethylene membrane. First-arriving wave extraction is performed using a short-time average/long-time average method and an Akaike information criterion joint algorithm. When a high-density polyethylene membrane breakage signal is received, parameter information is extracted. An elastic wave with the same frequency as the breakage signal is emitted by the generator. The mean value of the wave velocity of the clay layer is calculated as the time-difference positioning wave velocity to determine the breakage point location. If no breakage signal is received, the generator emits a fixed-frequency elastic wave to invert the wave velocity of the leakage area, and a wave velocity tomography map is generated for leakage point localization. Leaky point shapes are identified in combination with soil moisture migration principles. The experimental results demonstrate that the error between the actual leakage coordinates and positioning coordinates meets the engineering requirements and that the inversion model can effectively identify block and slit leakage points. [ABSTRACT FROM AUTHOR]

In modern technological processes of metal forming, such as cold rolling, rolling and drawing, a significant proportion of energy supplied to the rolling device is irretrievably lost to friction and wear, as well as giving the workpiece a given shape (or dimensions) as a result of plastic deformation. To assess the nature of friction in such machines, the types of frictional interaction between the material of the processed workpiece and the tool were determined, taking into account the influence of lubricants. As it was established, during metal pressure treatment, there is both "dry" and "semi-liquid" friction. Even in the presence of lubricant in the kinematic pair: fiber-wire billet dry friction prevails. As practice shows - the occurrence of significant friction forces and forces of tension of the workpiece is caused by the presence of multiple deformation microroughnesses in the receiving part of the fiber, at its interaction with the moving workpiece. These microroughnesses (on the workpiece) are sheared and plastically deformed by the interaction of the contacting pair. Moreover, this deformation process is accompanied by a continuous wave background in the sound range. For intensification of rolling and drawing processes it is recommended to use, by analogy with vibration metal cutting treatment, vibration rolling and drawing, by installing additional vibrators acting in the direction of rolling or drawing on the applied fibers. The proposed vibrators operate, as a rule, in the ultrasonic range. Optimization of the rolling (drawing) unit operation is carried out by selection of amplitude and frequency of additional vibration, providing the required mode of machine operation, which realizes the transition from "dry" friction between wire and die to "semi-liquid" friction. Implementation of measures on creation of additional devices for ultrasonic drawing and rolling allows to reduce energy costs of the rolling and drawing operation, as well as to increase the wear resistance of the tool. [ABSTRACT FROM AUTHOR]

ABSTRACTFive different chocolate types (i.e. extra dark, dark, milk, white, and ruby) were characterized and compared for the acoustical and textural characteristics. Acoustic properties were described in terms of longitudinal and transversal wave velocities. These velocities were used for the evaluation of elastic constants namely Young modulus and Poisson ratio. The values of the Young moduli are significantly higher than those obtained using uniaxial compression and tensile tests. At the same time, the values of Poisson ratio are in reasonable agreement with results of these methods. Texture characteristics were evaluated using of the compression test at loading rates (crosshead velocity) 1, 10 and 100 mm/min. Results are presented in form of stress vs strain. The stress-strain dependences obtained from the compression test exhibited two different regions of the sensitivity of stress to the applied strain. The linear dependence stress- strain is taken as the evidence of the elastic behavior of the tested material. The extent of this region was given by the strain, which was the same for all tested chocolates. Its value increased with the loading rate. The stress-strain behavior in this region was only slightly dependent on the loading rate with exception of the ruby and dark chocolates. The stress-strain dependence in the following region was significantly dependent on the strain rate. Values of the strain rate sensitivity were evaluated. The order of the tested chocolates according to the values of stress at the given strain was identical with that obtained using of the elastic wave velocities.

The resilient modulus of subgrade should be estimated for pavement designs that undergo repetitive loading from vehicular movement. In this study, an in-situ modulus detector (IMD) with flat, wedge, and cone tips is employed to estimate the resilient modulus. The specimens with three different levels of water content are compacted, and the dynamic responses for two hammer drop heights are analysed. For all specimens, elastic waves are acquired to estimate the shear modulus and Poisson's ratio using bender and piezo-disk elements. The resilient modulus estimated from the IMD is compared with the lightweight deflectometer (LWD) modulus. The experimental results show a stronger relationship between the flat and wedge tips than between the cone and wedge tips. Furthermore, higher drop heights result in strong relationships between the resilient, shear, and LWD moduli. This study proposes an intrinsic design and verification of an IMD for reliable resilient modulus estimation in pavement design. [ABSTRACT FROM AUTHOR]

A type of artificial boundary layer for the numerical simulation of wave propagation, which is named the gradient viscoelastic (GV) boundary layer, is proposed in this study. The setting of the GV boundary layer was established according to the propagation behavior of the longitudinal wave in the elastic GV rod, the analytical solution of the longitudinal wave propagation in the GV rod was obtained via the Wentzel–Kramers–Brillouin (WKB) method, and the zero-reflection and attenuation condition was determined. The settings of the GV boundary layer in the 1D and 2D time-domain simulations were applied to numerical examples and then compared. Numerical results showed that setting the GV boundary layer in the structure could remarkably reduce the error caused by truncation, and the combined GV boundary and low-reflection (LR) boundary presented the best combination. These results provide a simple method for artificial boundary layer setting to solve numerical wave simulations in the time domain. [ABSTRACT FROM AUTHOR]

The article solves the problem of theoretically determining the deformable characteristics of railway ballast, considering its condition through mathematical modeling. Different tasks require mathematical models with different levels of detail of certain elements. After a certain limit, excessive detailing only worsens the quality of the model. Therefore, for many problems of the interaction between the track and the rolling stock, it is sufficient to describe the ballast as a homogeneous isotropic layer with a vertical elastic deformation. The elastic deformation of the ballast is formed by the deviation of individual elements; the ballast may have pollutants, the ballast may have places with different levels of compaction, etc. To be able to determine the general characteristics of the layer, a dynamic model of the stress–strain state of the system based on the dynamic problem of the theory of elasticity is applied. The reaction of the ballast to the dynamic load is modeled through the passage of elastic deformation waves. The given results can be applied in the models of the railway track in the other direction as initial data regarding the ballast layer.

Evaluating the subground properties during the initial stage of a construction of building is important in order to estimate the suitability of soil quality to the technical requirements of bearing capacity, resistance to stress, and strength. This study presented the evaluation of the geotechnical properties of soil intended for the construction of Max IV facility of Lund University, performed in fieldwork and laboratory. The in situ methods included drilling boreholes, core sampling and assessment, crosshole measurements, and borehole logging. The laboratory-based measurements were performed at Swedish Geotechnical Institute and combined seismic measurements of drill cores, determination of the uniaxial compressive strength (UCS), and examination of material property: sieve analysis and natural moisture content. UCS was evaluated with regard to velocities of elastic P-waves. The synchronous light test by X-ray diffraction was performed for qualitative analysis of mineral composition of samples. The study applied integrated approach of the diverse geophysical methods to solve practical tasks on the evaluation of foundation strength and geotechnical parameters. This study demonstrated the benefits of integrated seismic and geophysical methods applied to soil exploration in civil engineering for testing quality of foundation materials.

The aim of this paper is to test a simple damage model of a cohesive granular medium to study the relationship between the damage and velocity of elastic waves. Our numerical experiments of edometric compression show that the microscopic deformation quickly becomes very heterogeneous, while our simulations of elastic waves propagation show that a small amount of damage induces a dramatic decrease in the elastic velocity. This shows that cohesive discrete media are very sensitive to strain field heterogeneity, and that the wave velocities in these media can measure subtle transient deformation processes, such as earthquake initiation phases.

Integral equations of a number of problems of diffraction of elastic waves on defects, located on the layers interface in plane-parallel layered media, are considered by the method of the over-determined boundary value problem. Solvability conditions for over-determined problems are written in terms of impedance matrices. Various options for finding approximate solutions of integral equations of diffraction problems are considered. [ABSTRACT FROM AUTHOR]

In this work, a stable node-based smoothed finite element method with TBC (SNS-FEM-TBC) is proposed to solve the scattering of elastic plane waves by a two-dimensional (2D) homogeneous isotropic elastic medium. First, using Helmholtz decomposition, two scalar potential functions are introduced to divide the Navier equation into Helmholtz equations with the coupled boundary conditions for the elastic scattering problem. Second, based on the analytical solutions of Helmholtz equations, TBC operators are deduced. Then, the gradient Taylor expansion is used to construct the stability term to deal with the instability of the original NS-FEM, the gradient of the solution is expressed into a linear formulation through approximating the node-based smoothing domain as a circle. Finally, based on smoothed Galerkin weak formula, the SNS-FEM-TBC formula of linear algebraic system with linear smoothing gradient is derived. Numerical examples show that SNS-FEM can obtain more stable and accurate solutions than standard FEM. Moreover, the convergence rates of L 2 and H 1 semi-norm errors of SNS-FEM are faster. [ABSTRACT FROM AUTHOR]

Elastic wave has wide applications, such as signal processing, sensor, and communication. It is highly desired to control the propagation of elastic wave efficiently. Inspired by various topological phenomena in electronic systems, robust transports of elastic wave have attracted much attention. In this paper, we review the recent progress on elastic wave topologies, including elastic quantum spin Hall effect, valley Hall effect, Weyl semimetal, higher-order topology, and other topological effects. Finally, we give some brief outlooks on elastic wave topologies. Three-dimensional topological materials and non-Hermitian physics for elastic waves are yet to be explored. Due to the strong intrinsic nonlinearity, it is an ideal platform to investigate nonlinear properties in nanomechanical structures. In addition to passive materials, active materials may be introduced to realize tunable multifunctionalities. Topological elastic materials have promising prospects in device applications. [ABSTRACT FROM AUTHOR]

Recently, microbial biopolymer-based soil treatment (BPST) has gained attention for its application in environmentally friendly soil stabilization, particularly for enhancing the strength and stability of fine-grained soils. However, the effects of BPST on clay's compressibility (consolidation) and expansion (swelling) behaviors remain unclear. This study used xanthan gum, a microbially produced polysaccharide with anionic charges, to stabilize kaolinite clay. The effect of xanthan gum BPST on the consolidation and swelling behavior of cohesive kaolinite clays was assessed through a series of experimental tests, including one-dimensional consolidation tests with elastic wave measurements, swelling tests, environmental scanning electron microscopy, and unconsolidated-undrained triaxial tests. The formation of xanthan gum hydrogels induces pore-clogging, resulting in a delay in the consolidation process, increased energy dissipation, and compressibility. Furthermore, the interaction between kaolinite and xanthan gum improved the undrained shear strength of kaolinite soils, thereby reducing the consolidation time required for a specific bearing capacity. This study demonstrates the possible application of controlling hydraulic conductivity, seismic stabilization, and rapid surface stabilization. However, additional drainage is necessary for in situ applications. [ABSTRACT FROM AUTHOR]

In this work, we propose a design of a double-scatterer structure to achieve complete conversion for elastic bulk waves. Every unit of the elastic metamaterial slab contains a pair of scatterers with a relatively oblique direction. When the slab attaches on a semi-infinite solid background, it can completely convert the normal incident longitudinal wave into the reflected shear wave, or vice versa. The conversion can be attributed to the in-phase coupling of the double scatterers' quadrupolar resonances. The coupled two quadrupoles could interact with the background and bring oblique displacements. Consequently, the oblique displacements generate horizontal displacements for reflected waves. [ABSTRACT FROM AUTHOR]

In this paper, a real-time leak source localization method based on convolutional neural network (CNN) of elastic wavefield images and spatio-temporal correlation analysis (STCA) is developed for the pressure vessel leakage. This method uses a single sensor array coupled to the wall to collect the elastic wave data excited by the leak source. Besides, the distance $R$ and the direction $\theta $ between the leak source and the sensor array are calculated based on CNN and STCA respectively, to finally obtain the location ( $R$ , $\theta$ ) of the leak source. In this paper, the digital twin model of the experimental platform is established, the training set is obtained by the finite element simulation, and the CNN model applied to the elastic wavefield images is studied and constructed. The experimental results show that the maximum locating error is 1.46 cm and the average locating error is about 0.56 cm within the range of a 1 m2 experimental plate based on the method proposed in this paper.

Piezoelectric semiconductor (PS) materials possess piezoelectric and semiconducting dual properties. Due to the interaction between piezoelectricity and semiconducting property, the performance of a p–n junction made of PS materials can be manipulated by an applied mechanical load. In this paper, we theoretically investigate the manipulation of a PS p–n junction by an elastic longitudinal wave. The total voltage in the PS p–n junction is physically regarded as consisting of the applied voltage, the built-in voltage through the depletion region, and the induced piezoelectric voltage. Based on this, we present a modified current equation for the PS p–n junctions with travelling elastic waves. The tuning effect of elastic waves with different frequencies and amplitudes on the current-voltage characteristics and the optical power output of the PS p–n junction is studied. Numerical results show that the elastic wave has a tuning effect on the electrical behaviors of the PS p–n junctions, and the performance of the PS p–n junction-based semiconductor devices can be effectively manipulated by an elastic wave. Such a wave-based controlling approach belongs to a non-contact way. It provides a theoretical guidance on the designing of wave-based semiconductor devices. [ABSTRACT FROM AUTHOR]

The article solves the problem of theoretically determining the deformable characteristics of railway ballast, considering its condition through mathematical modeling. Different tasks require mathematical models with different levels of detail of certain elements. After a certain limit, excessive detailing only worsens the quality of the model. Therefore, for many problems of the interaction between the track and the rolling stock, it is sufficient to describe the ballast as a homogeneous isotropic layer with a vertical elastic deformation. The elastic deformation of the ballast is formed by the deviation of individual elements; the ballast may have pollutants, the ballast may have places with different levels of compaction, etc. To be able to determine the general characteristics of the layer, a dynamic model of the stress–strain state of the system based on the dynamic problem of the theory of elasticity is applied. The reaction of the ballast to the dynamic load is modeled through the passage of elastic deformation waves. The given results can be applied in the models of the railway track in the other direction as initial data regarding the ballast layer. [ABSTRACT FROM AUTHOR]

In this work, the duality of mechanical Kagome lattices with internal microstructures is studied and its non-Abelian characteristics of wave packet evolution are discussed. Based on Bloch's theorem, the dynamical and duality matrices are obtained during elastic wave propagation. By regulating the twisting angles of the Kagome lattices and internal microstructures, global twofold degeneracy and unequal Berry phase can be obtained. A fourfold degeneracy appears at Γ point when the mechanical metamaterial is subjected to a special twisting state. Numerical calculations of non-Abelian mechanics and duality are performed, in which band structures with special twisting angles are the same. In addition, the solution of the Wilson operator is derived by the elastic wave equation and gauge transformation, which has non-exchangeable product and leads to the non-Abelian Berry curvature. If the time-reversal symmetry is broken, non-commutative elastic wave responses can be generated. The generalized polarization and wave propagation become different when the acting sequences of external forces are exchanged. [ABSTRACT FROM AUTHOR]

In this paper, the effect of boundary slip on the reflection and refraction of elastic waves at the interface of fluid-saturated porous media is investigated based on the virtually enlarged pore (VEP) model. The theoretical formula for the energy reflection and refraction of elastic waves is derived by introducing a potential function. The dependence of energy reflection and refraction coefficients on permeability and pore fluid viscosity is investigated using the VEP model. The numerical results are obtained and displayed graphically. It is observed that boundary slip has a noticeable effect on the energy reflection and refraction coefficients of elastic waves. The boundary slip effect makes the energy reflection and refraction coefficients more sensitive to the permeability and the viscosity of pore fluid. Article Highlights: Reflection and refraction of elastic waves are studied based on the VEP model The influence of boundary slip effect on the reflection and refraction coefficients is investigated. Reflection and refraction coefficients are more sensitive to permeability and viscosity based on the VEP model. [ABSTRACT FROM AUTHOR]

Consistent transmitting boundaries for time‐domain analyses of scalar‐ and elastic‐wave propagation in horizontally layered anisotropic or transversely isotropic waveguides are developed. Governing equations and corresponding consistent nodal forces are derived for scalar and elastic waves in layered waveguides for which finite‐element discretization is considered in the vertical layering direction. Auxiliary variables for the horizontal derivatives and integrals of displacements are introduced to modify the governing equations and the nodal forces. The desired consistent transmitting boundaries applicable to time‐domain analyses of scalar‐ and elastic‐wave propagation in isotropic and anisotropic waveguides are then derived. The transmitting boundary for a scalar wave satisfies the criteria for an accurate and well‐posed boundary condition and shows convergent, accurate, and stable behaviors for a variety of scalar‐wave propagation problems in waveguides. Although the boundary for an elastic wave is demonstrated as convergent and stable for elastic‐wave propagation problems in waveguides, limited accuracy is observed in the numerical examples. Nevertheless, the newly proposed approach is expected to provide another way to solve elastic‐wave propagation problems. [ABSTRACT FROM AUTHOR]

The problem of determining the shape of an object from knowledge of the far-field of a single incident wave in two-dimensional elasticity was considered. We applied an iterative hybrid method to tackle this problem. An advantage of this method is that it does not need a forward solver, and therefore, the exact boundary condition is not essential. By deriving the Fréchet derivatives of two boundary operators, we established reconstruction algorithms for objects with Dirichlet, Neumann, and Robin boundary conditions; by introducing a general boundary condition, we also established the reconstruction algorithm for objects with unknown physical properties. Numerical experiments showed the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, elastic waves generated from a SKD11 (HV670) steel specimen under various corrosive solutions were investigated. The frequency characteristics of the waves, as well as how hydrogen aggregation and crack propagation affected these characteristics, were studied using time-frequency analysis conducted in LabVIEW. The waves detected were either in a low frequency band, below 40 kHz, or in a high frequency band, above 60 kHz. The low frequency waves below 40 kHz were caused by hydrogen aggregation and corrosion, while the high frequency waves above 60 kHz were caused by crack initiation and propagation due to HAC. Inspection by SEM confirmed that the grains and cracks were caused by HAC via hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Particulate polymer composites (PPCs) are widely applied under different elastic wave loading conditions in the automobile, aviation, and armor protection industries. This study investigates the elastic wave propagation behavior of a typical PPC, specifically a Cu/poly (methyl methacrylate) (PMMA) composite, with a wide range of particle contents (30–65 vol. %) and particle sizes (1–100 μm). The results demonstrate an inflection phenomenon in both the elastic wave velocity and attenuation coefficient with increasing volume content. In addition, the inflection point moves to the direction of low content with the increase in particle size. Notably, the elastic wave velocity, attenuation, and wavefront width significantly increased with the particle size. The inflection phenomenon of elastic wave propagation behavior in PPCs is demonstrated to have resulted from particle interaction using the classical scattering theory and finite element analysis. The particle interaction initially intensified and then reduced with increasing particle content. This study elucidates the underlying mechanism governing the elastic wave propagation behavior of high particle content PPCs and provides guidelines for the design and application of wave-absorbing composites. [ABSTRACT FROM AUTHOR]

In this work, we design a twisting metamaterial for longitudinal-torsional (L-T) mode conversion in pipes through exploring the theory of perfect transmodal Fabry-Perot interference (TFPI). Assuming that the axial and radial motions in pipes can be decoupled, we find that the metamaterial can be designed in a rectangular coordinate system, which is much more convenient than that in a cylindrical system. Numerical calculation with detailed microstructures shows that an efficient L-T mode conversion can be obtained in pipes with different radii. In addition, we fabricate mode-converting microstructures on an aluminum pipe and conduct ultrasonic experiments, and the results are in good agreement with the numerical calculations. We expect that the proposed L-T mode-converting metamaterial and its design methodology can be applied in various ultrasonic devices. [ABSTRACT FROM AUTHOR]

Despite a significant number of theories of friction and wear, the issue of wave formation on contacting surfaces and in the zone ahead of the moving part has not yet received a sufficiently deep justification. Based on accumulated theoretical and experimental data, it is generally accepted to consider the groups of theories: 1) geometric, 2) molecular (adhesive), 3) deformation, 4) combined [1]. The most widespread opinion is that friction is caused by plastic extrusion of the material and the destruction of welding bridges (F. R. Bowden and D. Tabor), which is also confirmed by the hypothesis of Ernst and Margent, where friction is caused by adhesion (at the molecular level and surface roughness). At the same time, the experimental results of F. R. Bowden and D. Tabor indicate that the effect of friction depends on both the adhesion forces and the deformation of the material in the thin surface layer. As a result of the application of significant compressive forces and tangential frictional forces, a large amount of energy is released at the contact of two bodies, and with weak heat exchange with the environment, high gradients of temperature changes occur, and in the case of metal parts, under certain conditions, the welding effect of both individual micro-uniformities and contact surfaces in general, which is confirmed by research results [2]. [ABSTRACT FROM AUTHOR]

Biomechanical properties of soft tissues are important indicators of tissue functions which can be used for clinical diagnosis and disease monitoring. Elastography, incorporating the principles of elasticity measurements into imaging modalities, provides quantitative assessment of elastic properties of biological tissues. Benefiting from high-resolution, noninvasive and three-dimensional optical coherence tomography (OCT), optical coherence elastography (OCE) is an emerging optical imaging modality to characterize and map biomechanical properties of soft tissues. Recently, acoustic radiation force (ARF) OCE has been developed for elasticity measurements of ocular tissues, detection of vascular lesions and monitoring of blood coagulation based on remote and noninvasive ARF excitation to both internal and superficial tissues. Here, we describe the advantages of the ARF-OCE technique, the measurement methods in ARF-OCE, the applications in biomedical detection, current challenges and advances. ARF-OCE technology has the potential to become a powerful tool for in vivo elasticity assessment of biological samples in a non-contact, non-invasive and high-resolution nature.

Metamaterials with low-frequency band gap have always been the focus of research. For this reason, many researchers have proposed many structural design schemes. In this paper, an innovative star-shaped hybrid metamaterial structure is proposed. Based on Bloch's theorem and finite element method, a dynamic model of the proposed structure is established, the band gap characteristics of the proposed structure are analyzed, and the generation mechanism of band gap is discussed with the mode shape of specific frequency. Then, the propagation characteristics of elastic wave in the proposed structure are analyzed by using the dispersion surface and group velocity images, and the attenuation region of vibration transmission in the finite periodic structure is consistent with the frequency range of band gap. Finally, the relationship between band gap and structure parameters is explored. The results show that the proposed structure has good band gap characteristics in the frequency range of 1000 Hz, the lowest frequency of band gap reaches 60.207 Hz, and the total band gap width accounts for 54.463%. This research opens up an ideological route for the design of low frequency metamaterial structures.