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Showing papers on "Lamb waves published in 2000"


Journal ArticleDOI
TL;DR: In this paper, a wave equation, derived using the acoustic medium assumption for P-waves in transversely isotropic (TI) media with a vertical symmetry axis (VTI media), yields a good kinematic approximation to the familiar elastic wave equation for VTI media.
Abstract: A wave equation, derived using the acoustic medium assumption for P-waves in transversely isotropic (TI) media with a vertical symmetry axis (VTI media), yields a good kinematic approximation to the familiar elastic wave equation for VTI media. The wavefield solutions obtained using this VTI acoustic wave equation are free of shear waves, which significantly reduces the computation time compared to the elastic wavefield solutions for exploding‐reflector type applications. From this VTI acoustic wave equation, the eikonal and transport equations that describe the ray theoretical aspects of wave propagation in a TI medium are derived. These equations, based on the acoustic assumption (shear wave velocity = 0), are much simpler than their elastic counterparts, yet they yield an accurate description of traveltimes and geometrical amplitudes. Numerical examples prove the usefulness of this acoustic equation in simulating the kinematic aspects of wave propagation in complex TI models.

500 citations


Journal ArticleDOI
TL;DR: In this article, the authors extended the multiple-scattering theory for elastic waves by taking into account the full vector character, and proposed a double-layer scheme to obtain the reflection and transmission matrix elements for the multilayer slab from those of a single layer.
Abstract: We extend the multiple-scattering theory for elastic waves by taking into account the full vector character. The formalism for both the band structure calculation and the reflection and transmission calculations for finite slabs is presented. The latter is based on a double-layer scheme which obtains the reflection and transmission matrix elements for the multilayer slab from those of a single layer. As a demonstration of applications of the formalism, we calculate the band structures of elastic waves propagating in a three-dimensional periodic arrangement of spherical particles and voids, as well as the transmission coefficients through finite slabs. In contrast with the plane-wave method, the multiple-scattering approach exhibits advantages in handling specialized geometries (spherical geometry in the present case). We also present a comparison between theory and ultrasound experiment for a hexagonal-close-packed array of steel balls immersed in water. Excellent agreement is obtained.

323 citations


Journal ArticleDOI
TL;DR: In this article, a nonlinear dispersive equation was derived for a system of incompressible hyperelastic rods with a vertical singular line in the phase plane, which leads to the appearance of shock waves.
Abstract: In the literature, it has been conjectured that solitary shock waves can arise in incompressible hyperelastic rods. Recently, it has been shown that this conjecture is true. One might guess that when compressibility is taken into account, such a wave, which is both a solitary wave and a shock wave, can still arise. One of the aims of this paper is to show the existence of this interesting type of wave in general compressible hyperelastic rods and provide an analytical description. It is difficult to directly tackle the fully nonlinear rod equations. Here, by using a non–dimensionalization process and the reductive perturbation technique, we derive a new type of nonlinear dispersive equation as the model equation. We then focus on the travelling–wave solutions of this new equation. As a result, we obtain a system of ordinary differential equations. An important feature of this system is that there is a vertical singular line in the phase plane, which leads to the appearance of shock waves. By considering the equilibrium points and their relative positions to the singular line, we are able to determine all qualitatively different phase planes. Those paths in phase planes which represent physically acceptable solutions are discussed one by one. It turns out that there is a variety of travelling waves, including solitary shock waves, solitary waves, periodic shock waves, etc. Analytical expressions for all these waves are obtained. A new phenomenon is also found: a solitary wave can suddenly change into a periodic wave (with finite period). In dynamical systems, this represents a homoclinic orbit suddenly changing into a closed orbit. To the authors9 knowledge, such a bifurcation has not been found in any other dynamical systems.

175 citations


Journal ArticleDOI
TL;DR: The transmission of Lamb waves across adhesively bonded lap joints is investigated using finite element analysis and provides a basis for the selection of modes for nondestructive evaluation of the bond region and for measuring the bond dimensions.
Abstract: The transmission of Lamb waves across adhesively bonded lap joints is investigated using finite element analysis. The studies consider three modes for excitation and reception, s0, a0, and a1, applied to lap joints consisting of parallel aluminum sheets bonded with an epoxy adhesive. Transmission coefficient results for a two-dimensional range of bond thicknesses and bond overlap lengths are presented for all three modes. The transmission coefficients are calculated from the spectra of the received and transmitted signals using an approach which is insensitive to the presence of multimode signals and reverberated signals, and which approximates to a power transmission coefficient. Detailed analysis is then performed for one of the modes in order to investigate the nature of the mode conversion in the overlap region of the joint. It is found that the relative amplitudes of the different modes which propagate in the overlap region can be estimated reliably and simply from the properties of the incident wave mode. As well as demonstrating the physics of the mode conversion behavior, the study provides a basis for the selection of modes for nondestructive evaluation (NDE) of the bond region and for measuring the bond dimensions.

155 citations


Journal ArticleDOI
TL;DR: The use of interdigital PVDF transducers for the quick inspection of large, plate-like structures is discussed in this paper, where the transducers are designed to excite a particular Lamb mode in the structure, the region of the structure that is insonified being controlled by the transducer design.
Abstract: The use of interdigital PVDF transducers for the quick inspection of large, plate-like structures is discussed. The transducers are designed to excite a particular Lamb mode in the structure, the region of the structure that is insonified being controlled by the transducer design. An example is given of the monitoring of an aluminium plate by a single, circular transducer operating in pulse-echo mode, the a0 Lamb mode at a frequency of about 1 MHz being transmitted and received. The transducer is split into segments so that the angular location of a reflector can be defined, the radial location of the reflector being determined from the time of arrival of the echo.

152 citations


Journal ArticleDOI
Younho Cho1
TL;DR: In this paper, a hybrid boundary element method aimed at analyzing Lamb wave scattering from defects can provide us with an excellent numerical tool for tackling complicated mode conversion phenomena under waveguide thickness variation, which can be used to improve inspection sensitivity and penetration power for a variety of practical NDE applications.
Abstract: The hybrid boundary element method aimed at analyzing Lamb wave scattering from defects can provide us with an excellent numerical tool for tackling complicated mode conversion phenomena under waveguide thickness variation. In this paper, utilization of hybrid boundary element modeling for specific Lamb wave mode incidence situations with special energy distributions along the structural cross section is proposed for estimating reflection and transmission from various scatterers, such as a step discontinuity and tapered parts of a waveguide, etc. Interaction of individual Lamb wave modes with scatterers that represent arbitrary thickness variation along the direction of guided wave propagation is investigated by calculating the scattered fields for varying incident modes, frequency, and scatterer shape. The mode conversion phenomena through step discontinuity in a plate are also experimentally explored. The theoretical predictions of reflection and transmission by boundary element methods and the utility of dispersion curves are compared with experiments for specific modes. Results in this paper can be used to improve inspection sensitivity and penetration power for a variety of practical NDE applications, notably those in which thickness variation is found. In addition, the feasibility of inspecting sections located behind a waveguide thickness variation region and subsequent mode control will also be discussed.

136 citations


Journal ArticleDOI
TL;DR: In this paper, the authors combine laser ultrasonic techniques with the two-dimensional Fourier transform (2D-FFT) to characterize adhesive bond properties and quantitatively track changes in the bonded specimens, as a function of age.
Abstract: This research combines laser ultrasonic techniques with the two-dimensional Fourier transform (2D-FFT) to characterize adhesive bond properties. The experimental procedure consists of measuring a series of equally spaced, transient Lamb waves in specimens consisting of aluminum plates joined with an adhesive bond. The frequency spectrum (dispersion curves) for each specimen are obtained by operating on these transient waveforms with the 2D-FFT. This study quantifies the effect of bond stiffness on the dispersion curves of two different bonded specimens (a single aluminum plate with an adhesive transfer tape attached to one side, and two aluminum plates joined with the same adhesive tape) and four adhesive bond conditions (un-aged, and three different aging temperatures and times). The proposed procedure consists of first determining the frequency spectrum of the Lamb waves that propagate in each of the two bonded specimens (plus a single plate); these measurements provide the dispersion curves for each specimen in their un-aged state. Degradation causes changes in the stiffness of an adhesive bond, which causes changes in the dispersion curves of the aged specimens. Experimentally measured dispersion curves are used to quantitatively track changes in the bonded specimens, as a function of age. Finally, these experimental results are interpreted in terms of an analytical model that replaces the adhesive bond layer with a linear spring boundary condition.

128 citations


Journal ArticleDOI
TL;DR: This article describes two potentially practical implementations of Lamb wave tomographic imaging techniques that can be optimized for in-the-field testing of large-area aircraft structures and the speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems.
Abstract: As the worldwide aviation fleet continues to age, methods for accurately predicting the presence of structural flaws—such as hidden corrosion and disbonds—that compromise airworthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. The work summarized here focuses on a variety of different tomographic reconstruction techniques to graphically represent the Lamb wave data in quantitative maps that can be easily interpreted by technicians. Because the velocity of Lamb waves depends on thickness, for example, the traveltimes of the fundamental Lamb modes can be converted into a thickness map of the inspection region. This article describes two potentially practical implementations of Lamb wave tomographic imaging techniques that can be optimized for in-th...

126 citations


Journal ArticleDOI
TL;DR: A unified spectral and temporal representation is introduced for nondIFFracting waves that spans the commonly considered nondiffracting wave solutions and is extended to include singular Neumann and Hankel waves, or Y waves.
Abstract: A unified spectral and temporal representation is introduced for nondiffracting waves. We consider a set of elementary broadband X waves that spans the commonly considered nondiffracting wave solutions. These basis X waves have a simple spectral representation that leads to expressions in closed algebraic form or, alternatively, in terms of hypergeometric functions. The span of the X waves is also closed with respect to all spatial and temporal derivatives and, consequently, they can be used to compose different types of waves with complex spectral and spatial properties. The unified description of Bessel-based nondiffracting waves is further extended to include singular Neumann and Hankel waves, or Y waves. We also discuss connections between the different known nondiffracting wave solutions, and their relations to the present unified approach.

112 citations


Journal ArticleDOI
TL;DR: A new signal processing approach was presented for acoustic emission source location using the dispersive waves in a thin plate using the wavelet transform to improve the accuracy of source location by utilizing the time-frequency data of the WT.
Abstract: A new signal processing approach was presented for acoustic emission source location using the dispersive waves in a thin plate. For wave propagation in dispersive media, the accuracy of source location can be improved by using the arrival times of a single frequency component in the output signals at an array of sensors. The wavelet transform (WT) was used to resolve this problem. By utilizing the time-frequency data of the WT, the frequency-dependent arrival time traveling with the group velocity was shown to be easily determined. Experiments were performed using a lead break as the simulated fracture source on the surface of an aluminum plate. Two plate modes corresponding to the S/sub 0/ and A/sub 0/ Lamb waves were identified, and their group velocities were accurately measured. The source location results based on the WT method agreed well with the true locations. The WT method was also compared with the cross correlation technique, and both methods provide similar results.

111 citations


Journal ArticleDOI
TL;DR: In this article, a hybrid boundary element method (BEM) and Lamb wave normal mode expansion (LWME) were used for defect characterization and sizing analysis, and the theoretical analysis was used to establish efficient guidelines for both data acquisition and feature selection in a pattern recognition analysis program of study.

Journal ArticleDOI
TL;DR: In this article, a comparison of various transducer elements for Lamb wave detection is made and the use of embedded 0-3 piezocomposite elements demonstrated, and it has been shown that using the S0 Lamb mode may enable a quantitative estimate of the degree of damage to be obtained.
Abstract: The use of smart damage-detection systems may have considerable benefits for equipment operators. As sensing elements for a health-monitoring array, piezoelectric elements offer potential benefits. In particular, 0-3 piezocomposite elements have been identified as good candidates since they offer the potential for embedment within the advanced fibre composites. Ultrasonic Lamb waves have been shown to offer a technique for large-area damage detection for composites. It has been shown that the use of the S0 Lamb mode may enable a quantitative estimate of the degree of damage to be obtained. A comparison of various transducer elements for Lamb wave detection is made and the use of embedded 0-3 piezocomposite elements demonstrated.

Journal ArticleDOI
TL;DR: This modeling technique allows the determination of the amplitude of each Lamb mode excited in a composite plate with surface-bonded or bulk-embedded piezoelectric elements and can be used to design and optimize these "sensitive materials".
Abstract: Thin piezoelectric transducers attached to or embedded within composite structures could be used for in situ structural health monitoring. For plate-shaped structures, the useful ultrasonic vibration modes are Lamb waves. Preliminary testing has already demonstrated the suitability and practical feasibility of such integrated transducers, but better control of the generation of Lamb modes seems to be necessary. Therefore, an original modeling approach has been developed, which can be used to design and optimize these “sensitive materials.” This modeling technique allows the determination of the amplitude of each Lamb mode excited in a composite plate with surface-bonded or bulk-embedded piezoelectric elements. The method consists of a coupling of the finite element method (FEM) and the normal modes expansion method. The limited finite element mesh of the transducer and its vicinity enables the computation of the mechanical field created by the transducer, which is then introduced as a forcing function int...

Journal ArticleDOI
TL;DR: This study demonstrates that the reassigned spectrogram is capable of distinguishing multiple, closely spaced Lamb modes in the ultrasonic frequency range.
Abstract: This brief note reports on a study that applies the reassigned spectrogram (the reassigned energy density spectrum of the short-time Fourier transform [STFT]) to develop the dispersion curves for multimode Lamb waves propagating in an aluminum plate. The proposed procedure first uses the spectrogram to operate on a single, laser-generated and detected waveform to develop the dispersion relationship for this plate. Next, a reassignment procedure is used to refine the time-frequency resolution of the calculated dispersion curves. This reassignment operation clarifies the definition of the measured modes. This study demonstrates that the reassigned spectrogram is capable of distinguishing multiple, closely spaced Lamb modes in the ultrasonic frequency range.

Journal ArticleDOI
TL;DR: In this article, the sequence of microscopic fracture mechanisms in locally loaded cross-ply carbon-fiber composites was studied by analyzing acoustic emission (AE) signals in combination with the modal analysis of Lamb waves, using microscopic and ultrasonic examination of the specimen after load interruption.
Abstract: The sequence of microscopic fracture mechanisms in locally loaded cross-ply carbon-fiber composites was studied by analyzing acoustic emission (AE) signals in combination with the modal analysis of Lamb waves, using microscopic and ultrasonic examination of the specimen after load interruption. The first 70 AE events were analyzed, which were detected during the initial loading segment when the first sudden load drop and gradual load recovery were observed. Characteristics of the detected waves were compared with the S 0 - and A 0 -mode Lamb waves produced by a spot- or line-focused YAG laser. The internal damage progression of the composite specimen was determined to be the fiber fracture in the front lamina, transverse cracks in the mid-lamina, delamination and splitting.

Journal ArticleDOI
TL;DR: A new acoustic nondestructive method using Lamb waves as a probe is presented, and two methods for reconstructing the image of the inspected structure are proposed.
Abstract: A new acoustic nondestructive method using Lamb waves as a probe is presented. These waves are generated and received by an ElectroMagnetic Acoustic Transducer (EMAT). The position of flaws in the structure under test is computed from the time of arrival of the main peak of the reflected signal. Due to the noisy nature of the received signal, we use a wavelet transform algorithm to extract the required time information. The main advantage of such a multi-scale method of signal analysis is to be suitable for peak detection problems especially in highly noisy environments. We explain how we proceed to do the feature extraction, and we propose two methods for reconstructing the image of the inspected structure. Results of real-world ultrasonic Lamb waves signal analysis are presented. In addition, to test the noise robustness of the method, the case of synthetic noisy signals is also treated.

Journal ArticleDOI
TL;DR: In this paper, a particle-based model for the simulation of wave propagation is presented, which is based on solid-state physics principles and considers a piece of rock to be a Hookean material composed of discrete particles representing fundamental intact rock units.
Abstract: Summary A particle-based model for the simulation of wave propagation is presented. The model is based on solid-state physics principles and considers a piece of rock to be a Hookean material composed of discrete particles representing fundamental intact rock units. These particles interact at their contact points and experience reversible elastic forces proportional to their displacement from equilibrium. Particles are followed through space by numerically solving their equations of motion. We demonstrate that a numerical implementation of this scheme is capable of modelling the propagation of elastic waves through heterogeneous isotropic media. The results obtained are compared with a high-order finite difference solution to the wave equation. The method is found to be accurate, and thus offers an alternative to traditional continuum-based wave simulators.

Proceedings ArticleDOI
TL;DR: In this article, the authors used the Jacobian matrix for high frequencies (5-40 Hz) to measure the dispersion curve sensitivity of the Rayleigh wave to earth model parameters.
Abstract: Summary The Rayleigh-wave phase velocity of a layered earth model is a function of frequency and four groups of earth parameters: compressional (P)-wave velocity, shear (S)-wave velocity, density, and thickness of layers. For the fundamental mode of Rayleigh waves, analysis of the Jacobian matrix for high frequencies (5-40 Hz) provides a measure of dispersion curve sensitivity to earth model parameters. S-wave velocities are the dominant influence of the four earth model parameters. With the lack of sensitivity of the Rayleigh wave to P-wave velocities and densities, estimations of these parameters can be made for a layered earth model such that dispersive data vary predominantly with S-wave velocities (Xia et al., 1999a). This thesis is valid for higher modes of Rayleigh waves as well. Experimental analysis indicates that energy of higher modes tends to become more dominant as the source distance becomes larger (Park et al., 1999a). In some cases, higher mode data are necessary since shorter wavelength components of fundamental mode Rayleigh waves are obscured by these higher frequency data where higher modes of Rayleigh waves dominate. As well, our modeling results demonstrate at least two quite exciting higher mode properties. First, for fundamental and higher mode Rayleigh wave data with the same wavelength, higher modes can “see” deeper (longer than the wavelength) than fundamental modes (normally shorter than the wavelength). Second, higher mode data can increase the resolution of the inverted S-wave velocities. A much better S-wave velocity picture can be produced from inversion of surface wave data if higher-mode data are included. Real world examples show how resolution can be improved.

Journal ArticleDOI
TL;DR: In this article, the authors compare two kinds of devices, a classical delay line device and a resonant device, and the behavior of these devices has been controlled using optical visualization of vibration modes.
Abstract: Lamb waves, especially the A 0 mode, can be used to build sensors able to operate in contact with liquid. Nevertheless, some difficulties remain for practical devices. First, we discuss the relevance of the electromechanical coefficient. We present the element of choice of the device characteristics and the piezoelectric material. We compare two kinds of devices, the first is a classical delay line device and the second a resonant device. The behavior of these devices has been controlled using optical visualization of vibration modes. Furthermore, the performance of the devices is experimentally tested and advantages of the resonant device are shown.

Journal ArticleDOI
TL;DR: In this paper, surface mounted piezoelectric devices were excited with a tone burst of few cycles generating a propagating stress wave along the structure, which was used for the detection of delaminations in composite laminates.
Abstract: The present paper examines the application of low frequency Lamb waves for the detection of delaminations in composite laminates. Surface mounted piezoelectric devices were excited with a tone burst of few cycles generating a propagating stress wave along the structure. Experiments were carried out on composite beam specimens, for which wave propagation distances over 2 m were achieved and artificially induced delaminations as small as 1 cm2 were successfully identified. The feasibility of employing piezoelectric devices for the development of smart structures, for which a small and lightweight transducer system design is required, has been demonstrated. Finite element results of wave propagation in wide plates are also presented.

Journal ArticleDOI
TL;DR: In this article, the authors studied the effect of one or two thermal relaxation times on the reflection plane harmonic waves of a homogeneous, isotropic, and thermally conducting elastic solid.
Abstract: We discuss the reflection of thermoelastic plane waves at a solid half-space nearby a vacuum. We use the generalized thermoelastic waves to study the effects of one or two thermal relaxation times on the reflection plane harmonic waves. The study considered the thermal and the elastic waves of small amplitudes in a homogeneous, isotropic, and thermally conducting elastic solid. The expressions for the reflection coefficients, which are the ratio of the amplitudes of the reflected waves to the amplitude of the incident waves are obtained. It has been shown, analytically, that the elastic waves are modified due to the thermal effect. The reflection coefficients of a shear wave that incident from within the solid on its boundary, which depend on the thermoelastic coupling factor and included the thermal relaxation times, have been found in the general case. The numerical values of reflection coefficients against the angle of incidence for different values of thermal relaxation times have been calculated and the results are given in the form of graphs. Some special cases of reflection have also been discussed, for example, in the absence of thermal effect our results reduce to the ordinary pure elastic case.

Journal ArticleDOI
TL;DR: In this paper, a theoretical framework for wave propagation in infinite homogeneous elastic plates of unrestricted anisotropy is developed, which exploits the propagator matrix which is the exponential of the fundamental elasticity matrix underlying Stroh9s formalism of anisotropic elastodynamics.
Abstract: A theoretical framework is developed which describes wave propagation in infinite homogeneous elastic plates of unrestricted anisotropy. The approach exploits the propagator matrix which is the exponential of the fundamental elasticity matrix underlying Stroh9s formalism of anisotropic elastodynamics. The matrices of plate impedance and admittance are introduced, and their analytical properties are established, which appear fruitful for computing and analysing the plate wave spectra. On this basis, the dispersion equation can be cast into the form of a real equation involving the monotonic function, whose zeros and poles are the wave velocities in a given plate subjected to different boundary conditions (traction–free or clamped faces). It is proved that three fundamental wave branches exist for any orientation of wave propagation in an anisotropic plate with traction–free faces, and that those branches are missing if one or both faces are clamped. The intrinsic symmetry of the wave motion in an arbitrary plate is revealed. The general formalism is applied to elaborate the long–wavelength low–frequency approximation for a (thin) free plate of unrestricted anisotropy. The frequency–dispersive wave velocities, displacements and tractions at the onset of the fundamental wave branches are derived explicitly. The conditions for the extreme velocity values and some other useful universal connections are determined for an arbitrary thin plate, and exemplified for specific anisotropy cases.

Proceedings ArticleDOI
12 Jun 2000
TL;DR: In this paper, the authors present a review of work conducted at The University of Strathclyde in collaboration with several European partners into the feasibility of Lamb wave inspection, addressing issues of Lamb Wave generation, propagation, defect interaction and detection.
Abstract: Ultrasonic Lamb waves have been investigated extensively for damage detection in advanced composite materials. They are particularly suitable for proving thin plate structures of large area, where the Lamb wave approach offers a considerable saving in time over through-the-thickness inspection. However the potential complexity of the propagation can introduce significant difficulties to the technique. We present a review of work conducted at The University of Strathclyde in collaboration with several European partners into the feasibility of Lamb wave inspection. Specifically we will address issues of Lamb wave generation, propagation, defect interaction and detection.

Journal ArticleDOI
TL;DR: The problem of detecting damage in composite plates is addressed here using L amb waves and novelty detection, and the method of novelty detection is used to produce an automatic diagnostic tool which can operate on measured time data.
Abstract: The problem of detecting damage in composite plates is addressed here using L amb waves and novelty detection. Damage can be inferred from the scattering and modification of the Lamb wavefield as it passes through a defect. In order to produce an automatic diagnostic tool which can operate on measured time data, the method of novelty detection is used. This depends on establishing a description of normality which then allows subsequent signals to be flagged as anomalous if they deviate from normal condition. Three methods of novelty detection are illustrated: two statistical methods and one neural. The methods are demonstrated on experimental data captured from two composite plates.

Journal ArticleDOI
TL;DR: In this article, the use of Lamb waves was investigated to ensure health monitoring of foam core sandwich structures by a system based on ultrasonic methods, the propagation mechanisms were analyzed and reveal leaky waves properties.
Abstract: With intent to ensure health monitoring of foam core sandwich structures by a system based on ultrasonic methods, the use of Lamb waves is investigated. The propagation mechanisms are analyzed and reveal leaky waves properties. Moreover, the wave sensitivity to damages induced by low-velocity impacts is tested and the feasibility to detect debonding and foam failure is evaluated.

Book ChapterDOI
01 Jan 2000
TL;DR: In this article, the authors focus on the propagation of stress waves in engineering materials, and the particular case when the suddenly applied disturbance is mechanical, e.g., an impact force, the resulting waves in the medium are referred to as "mechanical stress waves" or simply "stress waves".
Abstract: When a localized disturbance is applied suddenly into a medium, it will propagate to other parts of this medium. The local excitation is not detected at other positions of the medium instantaneously, as some time would be necessary for the disturbance to propagate from its source to other parts of the medium. This simple fact constitutes a general basis for the interesting subject of “wave propagation”. Well-cited examples of wave propagation in different media include, for instance, the transmission of sound in air, the propagation of a seismic disturbance in the earth, the transmission of radio waves, among others. In the particular case, when the suddenly applied disturbance is mechanical, e.g., an impact force, the resulting waves in the medium are due to mechanical stress effects and, thus, these waves are referred to as “mechanical stress waves”, or simply “stress waves”. Our attention in this text is restricted to the study of the propagation of stress waves in engineering materials.

Journal ArticleDOI
TL;DR: The first experimental evidence of coherent backscattering enhancement for transient elastic waves propagating in a two-dimensional chaotic cavity is reported, and the spatial shape of the coherent back scattering enhancement is well predicted by a generalization of the existing theory.
Abstract: We report the first experimental evidence of coherent backscattering enhancement for transient elastic waves propagating in a two-dimensional chaotic cavity. The time-integrated squared amplitude at the point source is twice as large as at the other points around the source. Contrary to analogous optical experiments, this effect is already clearly observable on a single realization. Especially, the spatial shape of the coherent backscattering enhancement is well predicted by a generalization of the existing theory.

Journal ArticleDOI
TL;DR: In this paper, shear-induced wave conversion has a wide range of potential applications for monitoring and determining the magnitude of shear stress acting on fractures in geologic and engineered materials.

Journal ArticleDOI
TL;DR: This work presents an easy way to deduce the tensorial transfer and Green functions for Lamb waves generated in isotropic elastic plates and allows the avoidance of laborious calculations for each kind of Lamb waves source.
Abstract: This work presents an easy way to deduce the tensorial transfer and Green functions for Lamb waves generated in isotropic elastic plates. These functions could be applied to obtain the response of each propagating mode in the ensemble of excited modes arising from any sort of pulsed excitation (wedge transducers, lasers, etc.). The transfer function is based on modal analysis development. Not only is it easy to manipulate but also allows the avoidance of laborious calculations for each kind of Lamb waves source. Theoretical predictions are compared with those of Viktorov [I. A. Viktorov, Rayleigh and Lamb Waves (Plenum, New York, 1967)] and with experimental measurements of Lamb waves generated by the wedge-transducer method.

Journal ArticleDOI
TL;DR: In this article, a hierarchy of wave equations for axially symmetric elastic rods is derived by series expansions in the radial coordinate, and the dispersion relation and the displacements for these approximations and for Love's equation are compared with the lowest branch of the exact Pochhammer-Chree equation.
Abstract: The derivation of one-dimensional wave equtions for axially symmetric waves in elastic rods is discussed. By series expansions in the radial coordinate a hierarchy of wave equations are derived. As the lowest reasonable approximation the usual simple wave equation for the rod is recovered. At the next level a fourth order wave equation is obtained. The dispersion relation and the displacements for these approximations and for Love's equation are compared with the lowest branch of the exact Pochhammer-Chree equation. An excitation with a shear force is also solved and compared among the theories.