Showing papers on "Lamb waves published in 1983"
231 citations
TL;DR: In this article, the dispersion of transverse elastic waves both perpendicular and parallel to the laminations of infinite and semi-infinite periodically layered media is studied and the displacement fields and dispersion relations for such waves are obtained analytically, and the latter are solved numerically to yield the corresponding dispersion curves.
Abstract: The propagation of transverse elastic waves both perpendicular and parallel to the laminations of infinite and semi-infinite periodically layered media is studied. The displacement fields and the dispersion relations for such waves are obtained analytically, and the latter are solved numerically to yield the corresponding dispersion curves. It is shown that a semi-infinite medium layered periodically parallel to its stress-free surface can support shear horizontal surface acoustic waves that have no counterpart in a homogeneous medium. Finally, the dynamical elastic Green's function for a semi-infinite medium layered periodically parallel to its stress-free surface is obtained, and its possible application to Brillouin scattering studies of the surface acoustic waves on such a medium is discussed.
202 citations
TL;DR: In this article, it was shown that a modified electron-acoustic wave exists in a plasma with distinct hot and cold electron components and the frequency of this wave depends strongly on the cold electron number density.
Abstract: It is shown that a modified electron-acoustic wave exists in a plasma with distinct hot and cold electron components. The frequency of this wave depends strongly on the cold electron number density. Solitons associated with the modified electron-acoustic waves are also discussed.
135 citations
TL;DR: In this article, a semi-infinite plate of homogeneous isotropic, linearly elastic material is considered and the problem of determining the reflected wave field is solved by the method of projection, a method developed by the authors for solving corresponding problems in elastostatics.
Abstract: A semi-infinite plate of homogeneous isotropic, linearly elastic material occupies the region x≥0, |y|≤1, -∞
109 citations
TL;DR: In this article, a theoretical treatment of magneto-atmospheric waves is presented and applied to the modelling of waves in the solar atmosphere and a dispersion relation is defined for wave propagation in a plane-stratified atmosphere when there are no plane-wave solutions.
Abstract: A theoretical treatment of magneto-atmospheric waves is presented and applied to the modelling of waves in the solar atmosphere. The waves arise in compressible, stratified, electrically conductive atmospheres within gravitational fields when permeated by a magnetic field. Compression, buoyancy, and distortion of the magnetic field all contribute to the existence of the waves. Basic linearized equations are introduced to describe the waves and attention is given to plane-stratified atmospheres and their stability. A dispersion relation is defined for wave propagation in a plane-stratified atmosphere when there are no plane-wave solutions. Solutions are found for the full wave equation in the presence of either a vertical or a horizontal magnetic field. The theory is applied to describing waves in sunspots, in penumbrae, and flare-induced coronal disturbances.
82 citations
TL;DR: In this article, the space-time acoustic wave motion generated by a two-dimensional, impulsive, monopole line source in a fluid/solid configuration with a plane boundary is calculated with the aid of the modified Cagniard technique.
Abstract: The space–time acoustic wave motion generated by a two‐dimensional, impulsive, monopole line source in a fluid/solid configuration with a plane boundary is calculated with the aid of the modified Cagniard technique. The source is located in the fluid, and numerical results are presented for the reflected‐wave acoustic pressure, especially in those regions of space where head wave contributions occur. There is a marked difference in time response in the different regimes that exist for the wave speed in the fluid in relation to the different wave speeds (compressional, shear, Rayleigh) in the solid. These differences are of importance to the situation where the reflected wave in the fluid is used to determine experimentally the elastic properties of the solid.
80 citations
TL;DR: In this article, the effect of quadratic elastic nonlinearity on the propagation of surface Rayleigh waves on an isotropic elastic solid is examined using the method of multiple scales and an approximate solution is obtained which is uniformly valid in both spatial directions as well as in time.
77 citations
66 citations
TL;DR: In this paper, the authors investigated transverse nonlinear waves in an one-dimensional lattice with elastic bonds under longitudinal stress taking into account a possibility of lattice rotations, and the main types of wave motion were found in the continuum approximation including helical waves and rotation discontinuities.
50 citations
TL;DR: In this paper, a homogeneous, isotropic elastic medium with initial axial stresses in two orthogonal directions is considered and the dynamic equations for superimposed small deformations are stated.
Abstract: A homogeneous, isotropic elastic medium having initial axial stresses in two orthogonal directions is considered. The dynamic equations for superimposed small deformations are stated. The propagation of plane waves in such a medium is discussed. It is shown that pure longitudinal and shear waves can propagate only in certain specific directions which are defined. The present analysis corrects a fundamental error in a recent paper in this Journal [J. Acoust. Soc. Am. 72, 255–263 (1982)].
43 citations
TL;DR: In this paper, a pair of IDT with 140μm period was applied to a composite Cu(3 μm)-ZnO (0.45 μm) film that is much thinner than the acoustic wavelength in a bulk material.
Abstract: Interdigital transducers (IDT’s) have been used to generate and detect ultrasonic Lamb waves in a composite Cu(3 μm)‐ZnO (0.45 μm) film that is much thinner than the acoustic wavelength in a bulk material. rf pulses of 29.0 and 1.31 MHz are applied to one of the pair of IDT’s with 140‐μm period, giving rise to a nondispersive quasi‐symmetric mode of phase velocity 4170 m/s and a dispersive quasi‐antisymmetric mode having a phase velocity of 184 m/s and a group velocity of 362 m/s, respectively. Possible applications to electronic signal processing and material studies are described.
TL;DR: In this paper, the interaction between ultrasonic Lamb waves and the region of rigid contact between two elastic layers is explored analytically, and it is shown that there exists a one-to-one relationship in the form of T∼d3 between the transmission coefficients T of the wave through a region of contact having diameter d. This problem is a model of two sheets welded in this region, and is of great practical importance in a nondestructive evaluation of welds.
Abstract: The interaction between ultrasonic Lamb waves and the region of rigid contact between two elastic layers is explored analytically. This problem is a model of two sheets welded in this region, and is of great practical importance in a nondestructive evaluation of welds. To uniquely define the dimensions of the region on the basis of the transmitted ultrasonic signal, the experimental conditions are selected in such a manner as to avoid resonance in the region of contact. Our experiments show that there exists a one‐to‐one relationship in the form of T∼d3 between the transmission coefficients T of the wave through a region of contact having diameter d.
TL;DR: In this paper, the normal mode solution of the scattered pressure due to a normally incident plane acoustic wave on an infinitely long, air-filled aluminum cylindrical shell in water is analyzed.
Abstract: The normal mode solution of the scattered pressure due to a normally incident plane acoustic wave on an infinitely long, air‐filled aluminum cylindrical shell in water is analyzed Our study yields a physical interpretation of normal mode contributions to the backscattering function The modes in the near‐soft (thin‐shell) region are compared to theoretical predictions and empirical observations Transitions from Rayleigh‐type surface waves to Lamb‐type waves are found to take place for thin shells A smooth transition of the first transverse wave on a thick shell to that of the first symmetric Lamb wave on a thin shell is shown to occur, and the inception of these thin‐wall modes is investigated as a function of shell thickness Also, the antisymmetric Lamb mode is shown to exist and its intermittent nature is examined
TL;DR: In this article, the propagation of large-amplitude, one-dimensional shear and compression waves in shocked solids of geophysical interest is studied and the experimental developments reported here are expected to be important to high pressure geophysics applications because they provide a direct measure of the shear modulus in the shocked state.
Abstract: Experimental techniques have been developed to study the propagation of large-amplitude, one-dimensional shear and compression waves in shocked solids of geophysical interest. Shear wave velocities and amplitudes can be directly measured along with the usual measurements on longitudinal waves. Although shear wave amplitude measurements do not approach the quality of the compression wave data, shear wave velocities can be measured to a precision of better than two percent. Experimental measurements to 90 kbar compressive shock stresses are reported in Al2O3. Within experimental scatter (±2%), our shear wave velocity data are in good agreement with the extrapolation of the ultrasonic measurements. The longitudinal measurements are in good agreement with earlier work. The experimental developments reported here are expected to be important to high pressure geophysics applications because they provide a direct measure of the shear modulus in the shocked state. The shear modulus is not only a more sensitive indicator of the solid state than the longitudinal modulus but in conjunction with the longitudinal wave data can provide the mean stress-volume relations for comparison with static data.
01 Jan 1983
TL;DR: In this article, it was shown that only two types of waves can be propagated through an unbounded elastic solid: a longitudinal (dilatational,P-) wave and a transverse (rotational, shear, S-) wave.
Abstract: When a mechanical disturbance propagates in an isotropic elastic body inertial and elastic properties control the velocity of the advance and the form of the disturbance frequently changes with progression depending upon the initial character of the displacement and the history of propagation. Elastodynamic theory shows that only two types of waves can be propagated through an unbounded elastic solid: a longitudinal (dilatational,P-)wave, and a transverse (rotational, shear, S-)wave. Particle motion in a P-wave (S-wave) is parallel (normal) to the direction of wave propagation. When the solid has a free surface or an interface between two different media surface waves may also be propagated. In layered structures several types of waves may be generated and propagated. In most practical engineering applications plane, cylindrical, and spherical waves form the majority of waves encountered.
TL;DR: In this paper, generalized ray theory for a thick plate driven by a step function point force is compared with experimental waveforms obtained on a glass plate using an improved piezoelectric displacement sensing transducer.
Abstract: Waveforms calculated by generalized ray theory for a thick plate driven by a step‐function point force are compared with experimental waveforms obtained on a glass plate using an improved piezoelectric displacement‐sensing transducer.
TL;DR: In this article, a finite element analysis for reflection of the fundamental symmetric Lamb wave at the free edge of a semi-infinite elastic plate is presented, and it is shown that the edge resonance phenomenon is very sensitive to the value of Poisson's ratio.
Abstract: A finite-element analysis is presented for reflection of the fundamental symmetric Lamb wave at the free edge of a semi-infinite elastic plate. It is shown that the edge resonance phenomenon is very sensitive to the value of Poisson's ratio. For a smaller value of Poisson's ratio, this phenomenon occurs at a lower frequency and the solutions vary more rapidly with frequency.
TL;DR: In this paper, a voltage sensor using a Lamb wave delay line oscillator is described, which consists of two pairs of interdigital transducers and one plate electrode at the central part of the device.
Abstract: A voltage sensor using a Lamb wave delay line oscillator is described. The device consists of two pairs of interdigital transducers and one plate electrode at the central part of the device. All of these transducers have the counter electrodes on the bottom surface of the substrate. The oscillation frequency of the device changes significantly with the voltage applied to the central plate electrode. Performances of the voltage sensor are given, including sensitivity and its frequency dependence.
TL;DR: In this article, phase gratings recorded sequentially by a reference wave and two object waves are studied with the aid of a coupled wave approach, and it is shown that waves not participating in the recording process may be present with large amplitudes at replay when the two object wave are sufficiently close to each other.
TL;DR: In this paper, the parametric mixing of two modulated surface acoustic waves propagating in opposite directions is studied with reference to nonlinear signal processing applications by the coupled mode theory of nonlinear surface waves.
Abstract: The parametric mixing of two modulated surface acoustic waves propagating in opposite directions is studied with reference to nonlinear signal processing applications by the coupled mode theory of nonlinear surface waves. In the case of propagation in opposite directions the combination frequency waves generated out of the nonlinear interaction of the two primary waves and their harmonics with one another do not satisfy the phase‐matching condition. Hence there exists no mode coupling between the primary waves. At the same time the amplitude of each combination frequency wave is proportional to the product of a harmonic amplitude of one of the interacting waves with a harmonic amplitude of the other wave. The variation of these harmonic amplitudes as functions of the slow scale variables are governed by two sets of coupled amplitude equations, each set pertaining to one primary wave and its harmonics. It is further shown that, in addition to surface wave modes, there also exist bulk wave modes in a certai...
TL;DR: In this article, the authors used stress as the dependent variable instead of the deformation gradient for simple elastic solids and showed that a combination of simple waves and/or shock waves is needed to satisfy the initial and boundary conditions.
Patent•
16 Dec 1983
TL;DR: In this article, a train of ultrasonic waves having a frequency and duration such that propagation takes place as Lamb waves is applied to an end portion of the sheath, and the echoes are detected.
Abstract: Defective fuel elements in an assembly immersed in a liquid are detected using ultrasonic absorption. A train of ultrasonic waves having a frequency and duration such that propagation takes place as Lamb waves is applied to an end portion of the sheath. The echoes are detected. Transmission and detection are repeated for different frequencies. Some frequencies are in a range corresponding to absorption by water which may be contained in the sheath. Other frequencies correspond to a range for which there is an echo at a mechanical defect of the sheath, such as a crack.
TL;DR: In this paper, the authors used a prestressed piezoelectric sandwich transducer with a titanium stepped mechanical amplifier, the small end of which was the piston that produced the high-amplitude motion inside the tube.
Abstract: This paper is concerned with an investigation of the nonlinear behavior of sinusoidal plane progressive acoustic waves of finite amplitude in air at a frequency of about 21 kHz. The various stages in the distortion of the wave have been experimentally studied and the results compared with theoretical models. The experiments were done in a tube 5.5 m long and 8‐mm internal diameter with an absorbing termination. The acoustic source used was a prestressed piezoelectric sandwich transducer with a titanium stepped mechanical amplifier, the small end of which was the piston that produced the high‐amplitude motion inside the tube. This source was capable of generating a nearly pure sinusoidal wave at sound pressure levels up to about 155 dB (re: 0.0002 μbar). Interestingly, as compared to previous reports on this field, the use of a high frequency has allowed the study of all the propagation regions (including the old age region) of the wave using a short length tube.
01 Aug 1983
TL;DR: An acoustical-ultrasonic technique was used to demonstrate relationships existing between changes in attenuation of stress waves and tensile stress for an eight ply 0 degree graphite-epoxy fiber reinforced composite as discussed by the authors.
Abstract: An acoustical-ultrasonic technique was used to demonstrate relationships existing between changes in attenuation of stress waves and tensile stress for an eight ply 0 degree graphite-epoxy fiber reinforced composite. All tests were conducted in the linear range of the material for which no mechanical or macroscopic damage was evident. Changes in attenuation were measured as a function of tensile stress in the frequency domain and in the time domain. Stress wave propagation in these specimens was dispersive, i.e., the wave speed depends on frequency. Wave speeds varied from 267 400 cm/sec to 680 000 cm/sec as the frequency of the signal was varied from 150 kHz to 1.9 MHz which strongly suggests that flexural/lamb wave modes of propagation exist. The magnitude of the attenuation changes depended strongly on tensile stress. It was further observed that the wave speeds increased slightly for all tested frequencies as the stress was increased.
TL;DR: In this article, the diffraction of a plane wave by an infinite elastic plate stiffened by a doubly periodic set of rigid ribs of moderate wave dimensions is studied, and the problem is reduced to an infinite quasiregular system of linear algebraic equations, and their solution describes the amplitudes of the waves propagating from the plate into the fluid.
TL;DR: For the Love wave and the Rayleigh wave the power flux and the energies are evaluated and the group velocity is determined by the dynamic method and verified to be identical to that obtained by the kinematic method as mentioned in this paper.
Abstract: For the Love wave and the Rayleigh wave the power flux and the energies are evaluated, and, therefrom, the group velocity is determined by the dynamic method and is verified to be identical to that obtained by the kinematic method. A proof based on a variation theorem is also provided to show in a general way that the kinematic and the dynamic methods yield identical results for the group velocity of the surface elastic waves.
TL;DR: In this article, an integral transform method is used to find the solution of the equation of motion from the linear theory for a homogeneous, isotropic elastic material, which reduces the problem into an integral equation.
Abstract: This paper deals with the propagation of shear waves in a wave guide which is in the form of an infinite elastic strip with free lateral surfaces. This strip contains a Griffith crack. An integral transform method is used to find the solution of the equation of motion from the linear theory for a homogeneous, isotropic elastic material. This method reduces the problem into an integral equation. It has been observed that only shear waves with frequencies less than a parameter-value, depending on the width of the wave guide, can propagate. The integral equation is solved numerically for a range of values of wave frequency and the width of the strip. These solutions are used to calculate the dynamic stress intensity factor, displacement on the surface of the crack and crack energy. The results are shown graphically.