摘要:

The nearfield response of a thick viscoelastic plate at epicenter, off‐epicenter, and on the same side of the plate to a point step load acting normal to the surface is discussed. The integral expressions resulting from Fourier and Hankel transforms of the governing equations are evaluated by two procedures. An asymptotic evaluation of the frequency‐domain response is presented for high frequencies corresponding to ray arrivals. A numerical double inverse transform procedure is developed for obtaining exact time‐domain waveforms.

ISSN:0001-4966    

DOI:10.1121/1.397770

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The ray arrival behavior of an ultrasonic signal propagated through a thick viscoelastic plate is analyzed to determine the material dispersion and attenuation. Signal processing algorithms are developed and demonstrated with synthetic and real signals obtained in elastic and viscoelastic materials. Recovery of material properties is found to proceed reliably except for the case of attenuation recovery from real signals, where there were difficulties related to the use of a finite aperture receiver.

ISSN:0001-4966    

DOI:10.1121/1.397771

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The propagation of leaky Lamb waves in a plate consisting of a general balanced symmetric composite material is considered. The problem has been examined both analytically as well as experimentally. An exact solution for the dispersion equation was obtained. Numerical results for complex‐valued wavenumber were obtained for an isotropic material (aluminum) and a (0/903)sgraphite/epoxy laminate. Excellent agreement for the isotropic case and a satisfactory agreement for the anisotropic case between the theory and experiment were observed.

ISSN:0001-4966    

DOI:10.1121/1.397772

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The effect of topography on surface motion is studied in the case of incidentPandSVwaves and in presence of an explosive source. The discrete wavenumber‐boundary integral equation method is formulated for this case and is applied to the problem of diffraction of an elastic wave field by a ridge‐shaped topography. The amplitude of the scattered field, which mostly consists of surfacePwaves and Rayleigh waves, is strongly dependent on the steepness of the topography. The generation of surface waves by an explosion located in the vicinity of the ridge topography is studied and an increase in Rayleigh wave amplitude and a broadening of the Rayleigh pulse when the explosion occurs within the ridge is found.

ISSN:0001-4966    

DOI:10.1121/1.397773

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The acoustic scattering resonances of a solid elastic sphere are thoroughly analyzed in the low‐kafrequency region. No evidence is found to support the existence of the recently reported (1,1) Rayleigh wave dipole resonance.

ISSN:0001-4966    

DOI:10.1121/1.397774

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The necessity of nondestructively inspecting cast steels, weldments, composites, and other inherently anisotropic materials has stimulated considerable interest in wave propagation in anisotropic media. Here, the problem of an ultrasonic beam traveling in an anisotropic medium is formulated in terms of an angular spectrum of plane waves. Through the use of small angle approximations, the integral representation is reduced to a summation of Gauss–Hermite eigensolutions. The anisotropic effects of beam skew and excess beam divergence enter into the solution through parameters that are simply interpreted in terms of the slowness surface. Both time harmonic and pulsed solutions are discussed. Formulas are also presented for transmission of a beam through a curved interface between two media. Examples are given illustrating how this method may be applied to predicting beam patterns during ultrasonic inspections.

ISSN:0001-4966    

DOI:10.1121/1.397775

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Previous studies of scattering from multiple gratings of resonant compliant tubes in water determined that noncompliant, antisymmetric structural modes excited by evanescent waves severely degraded the reflectivity of closely packed gratings. Also, low‐frequency performance was diminished by transmission resonances due to the spring–mass–spring configuration of the two compliant gratings separated by a fluid mass. In this paper, encapsulating a single grating in a layer of elastomer whose shear properties are well below its rubber–glass transition region is shown to only reduce the maximum insertion loss. For two gratings, both the transmission resonances and the evanescent wave excitations are mitigated by encapsulation in a rubberlike material. Insertion loss performance with an encapsulant whose shear properties are in the rubber–glass transition region occurs at reduced bandwidths and shifted frequency responses. The mathematical model for gratings in fluid is extended to include the viscoelastic layer and calculations from this model are compared with experiments.

ISSN:0001-4966    

DOI:10.1121/1.397776

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The presence of texture can explain the anisotropy of ultrasonic propagation velocities in polycrystalline materials. This paper derives dispersion relations with which the phase velocities can be calculated for plate modes guided along an arbitrary direction in the plane of an orthorhombic sheet. The effect of texture is brought into the analysis through the crystallites’ orientation distribution coefficients (ODCs). The dispersion relations are split into two parts, one for theP–SVmotion and the other for theSHmotion. The result for the symmetricP–SVmotion approaches the angular variation in the velocity of the lowest (S0) mode with decreasing frequency. The anisotropy in Rayleigh surface wave velocity is also derived as a solution in the high‐frequency limit. These limiting solutions are useful for the nondestructive characterization of texture from ultrasonic velocity measurements.

ISSN:0001-4966    

DOI:10.1121/1.397777

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

In this paper, the acoustical behavior of circular ducts with nonuniform area functions is considered in terms of a corresponding scattering matrix. The elements of the scattering matrix denote the portions of reflected and transmitted waves of the mode orderkwhen a wave of mode ordernis incident. This way, the approach is able to treat wave modes of arbitrary order. When the tube under consideration consists of sections of constant cross‐sectional area, the method of calculation can be applied directly. Otherwise, the (continuous) area function has to be approximated by a corresponding step function; i.e., the tube is modeled by a certain number of contiguous sections (stepped duct approximation). In contrast to other publications, the area function is not restricted to be slowly varying along the tube axis. Losses as well as liners are simply taken into account by altering propagation constants and wave impedances, correspondingly. After derivation of the numerical algorithm, some examples of nonuniform ducts are investigated. The results are compared to some low‐frequency solutions. The accuracy of numerical results depends on some parameters occurring in the algorithm presented. The influence of different parameters on the resulting accuracy is investigated. Finally, the theory is verified by a measurement.

ISSN:0001-4966    

DOI:10.1121/1.397996

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Nonlinear propagation of sound waves generated by a directive ultrasound source in air is discussed theoretically and experimentally. The circular source of 21 cm in radius consists of 1410 small PZT bimorph transducers, whose resonance frequency is 28 kHz. For a single‐frequency wave excitation, sound pressures of the fundamental, second, and third harmonics are measured and are compared with the numerical results using a method of Aanonsenetal. [J. Acoust. Soc. Am.75, 749–768 (1984)]. Extending their initial condition to the case of a two‐frequency wave excitation, propagation curves and beam patterns of the difference frequency sound are obtained and compared with the measured data. All observations quantitatively agree very well with the numerical calculation. Nonlinear attenuation of spectral components by increasing the source pressure is clearly confirmed.

ISSN:0001-4966    

DOI:10.1121/1.397778

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP