• Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Journal of the Acoustical Society of America

SECTION LISTING

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Apr 1985

Volume 77, Issue S1, pp. S1-S108

Return to All Sections
back to top
RSS Feeds
back to top Session B. Physical Acoustics I: Solids
Contributed Papers
FREE

Acoustic methods of microstructure characterization (A)

R. Kline, H. Saghatchi, and C. Hsiao

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S3-S3 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
There has been a great deal of recent interest in using spectral analysis of backscattered ultrasonic signals to characterize material microstructure. As quantitative backscatter measurements can require signal averaging over several spatial orientations, a time consuming proposition, an alternative is needed. In this work the feasibility of using the spectral analysis of transmitted wideband signals was investigated. To precisely control grain size, samples were made by sintering glass beads of varying diameter. Porosity could be changed by altering the heat treatment of the samples. Results over the frequency range from 0.5–15 MHz are presented for specimens prepared with grain sizes ranging from 0.5–4 mm in diameter.
FREE

Generation of elastic ultrasonic waves by electric spark (A)

Doron Kishoni and Wolfgang Sachse

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S3-S3 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The ultrasonic elastic waves generated while an electric spark strikes a solid are investigated. Attention is given to the interaction with aluminum specimens and to cases where no apparent damage is observed. Several mechanisms are suggested as the source for the generated waves, and experiments investigating each of these mechanisms are described. It is found that the thermo‐elastic mechanism is of primary importance in the range of electric currents considered. As in the case of low energy laser‐generated ultrasound, the ablation mechanism becomes significant only at higher currents, when visible damage to the surface of the specimen is apparent. [Work supported in part by Materials Science Center at Cornell University.]
FREE

The quasicrystalline approximation and multiple scattering of waves in random media (A)

Vasundara V. Varadan and Vijay K. Varadan

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S3-S3 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The quasicrystalline approximation (QCA) was first introduced by Lax to break the infinite heirarchy of equations that results in studies of the coherent field in discrete random media. It simply states that the conditional average of a field with the position of one scatterer held fixed is equal to the conditional average with two scatterers held fixed, i.e., 〈ψ〉iji = 〈ψ〉ii. The QCA has met with great success for a range of concentrations from sparse to dense and for long and intermediate wavelengths. In this paper, the QCA is interpreted as a partial resummation of the multiple scattering series that includes only two body correlations and yields the same dispersion equation. Explicit improvements to the QCA are presented that still require only a knowledge of the two body correlation function.
FREE

Anomalous polarization of elastic waves in transversely isotropic media (A)

Michael Schoenberg and Klaus Helbig

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S3-S4 (1985); (2 pages)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The behavior of transversely isotropic elastic media is analyzed from both the kinematic (slowness surface) and dynamic (particle displacement) point of view. The relations for the slowness surfaces and wave front surfaces are derived in polar coordinates. Examination of the eigenvectors of the displacement equations of motion gives the relation for the polarization of the displacement vector associated with any plane wave. It is shown that the polarization of plane quasi‐P and quasi‐SV waves depends strongly on the sign of a particular elastic modulus, call it A, whereas the shape of the slowness surface is independent of the sign of A. When A is positive, which is the usual case, the particle displacement vector rotates in the same sense as the slowness vector. When A is negative, which is the “anomalous” case, the sense of rotation of the particle displacement vector is opposite to that of the slowness vector. Thus there is a direction in the medium for which the displacement vector associated with the quasi‐P sheet of the slowness surface is perpendicular to the slowness vector and that associated with the quasi‐SV sheet is parallel to the slowness vector. For both sheets the angle between the slowness vector and the displacement assumes all angles between 0 and π/2. This case even includes media that are “nearly” kinematically isotropic, i.e., characterized by spherical wave fronts emanating from point sources.
FREE

Vibration generation in and sound radiation from squealing chalk (A)

H. L. Kuntz and R. D. Bruce

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S4-S4 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
Chalk squeal is a common phenomenon encountered in the classroom. The sound radiated from a chalk/blackboard system is possible because of two physical characteristics of the system. The first characteristic is that the frictional forces at the board and chalk interface are not constant when (stick‐slip phenomenon) steady, normal, and shear forces are exerted on the chalk. The second characteristic is that the resonances of the chalk are excited by the stick‐slip forces at the interface. A positive feedback system exists between the two characteristics and the vibrations are reinforced with the result that tonal squeal is generated. The resultant vibrations are called relaxational vibrations. Impedance measurement results are presented and compared to the radiated sound. The influence of the board characteristics are discussed. Methods of reducing chalk squeal are discussed. This work is important to the study of sound radiation from machinery operations, such as the honing of cylinders, which also exhibit relaxational oscillations. [Work supported by Department of Health and Human Services CDC/NIOSH Grant No. 1R43 OH01951‐01.]
FREE

On Lamb wave conversion effect of nondestructive evaluation of spot welds (A)

S. I. Rokhlin and Laszlo Adler

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S4-S4 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The interaction between ultrasonic Lamb waves and the region of rigid contact between two elastic layers is discussed. This problem is a model of two sheets welded in this region. The transmission of Lamb waves through such regions is estimated. The conversion of Lamb modes plays a major role. The effect of the temperature change in the welded region is also discussed. The effect of phase transformation in metal, metal melting, and solidification on wave transmission are described. Permanent address: Materials Engineering Department, Ben‐Gurion University of the Negev, P.O. Box 653, Beer‐Sheva, 84105 Israel.
FREE

Quantitative determination of porosity: Theory and experiment (A)

Kent Lewis, Shaio‐Wen Wang, Laszlo Adler, and James H. Rose

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S4-S4 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
When an ultrasonic wave propagates in a solid with a low concentration of voids the attenuation coefficient is proportional to the scattering cross section of each void multiplied by the number of voids [Gubernatis and Domany, Rev. Prog. QNDE 2A, 833 (1983)]. Exact calculation was carried out for the scattering cross section of elastic waves as a function of ka from spherical voids in several solids. A turning point between low and high ka values of the scattering cross section provides a turning point at ka = 1. This turning point depends only on the ratio of transverse to longitudinal velocity in the solids—can be used to calculate both the pore radius and their concentration. Experimental method was developed to measure attenuation coefficient as function of frequency using ultrasonic spectroscopy system. The theoretical model was successfully tested experimentally for several aluminum cast materials containing porosity up to 6% and with average radius for 10–150μ. [This work was supported by the Center of NDE operated by Ames Laboratory for the Air Force Wright Aeronautical Materials Laboratory.]
FREE

Application of elastic guided waves for interface properties characterization (A)

S. I. Rokhlin

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S4-S4 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
We discuss a new ultrasonic method for evaluation of interface properties. The method is based on utilization of the ultrasonic interface waves, for bonded semispaces and of Lamb waves for bonded layers. Using theoretical analysis we select experimental conditions in a manner such that the interface wave induces only shear stresses on the interface. This makes it possible to estimate the effective shear modulus of the interface. The effect of boundary conditions between layers on Lamb wave propagation and conversion is also considered. The transformation coefficients for Lamb waves conversion on the bonded and nonbonded regions between layers are derived and discussed.
FREE

Augmentation of acoustic transmission by a transition layer (A)

Mauro Pierucci

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S4-S4 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
It has already been reported by the author at a previous meeting [J. Acoust. Soc. Am. Suppl. 73, S95 (1982)] that certain types of transition layers can improve the transmission of acoustic waves from one medium to another. In this paper, conditions under which the transmissions of an acoustic wave is enhanced by the transition layer are presented. The case of a finite thickness elastic layer has been studied and it has been determined that at certain key frequencies, an optimum transition layer thickness exists which greatly improves the interaction between the two media.
FREE

Controlling plate radiation with Anderson localization (A)

J. D. Maynard

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S4-S4 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
When a plate is stiffened with a periodic array of ribs, the normal modes of the system are extended and structural vibrations may travel long distances with little scattering. If the rib array is made random, then structural vibrations become localized within a distance inversely related to the degree of randomness. This effect, analogous to a phenomenon in solid state physics, is referred to as Anderson localization. At the present time we are using nearfield acoustic holography to study the possibility of controlling sound radiation from ribbed plates through the effects of Anderson localization. Results from a one‐dimensional system will be reported. [Work supported by ONR and NASA.]
FREE

Diffraction by acoustically penetrable scatterers (A)

James E. Copeland and O. Martin Milner

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S4-S5 (1985); (2 pages)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The problem of acoustic diffraction by nonrigid scatterers in water was treated both theoretically and experimentally. A theoretical model of diffraction by a matrix of square or rectangular blocks was developed. The Helmholtz integral equation was solved by making Kirchhoff‐type approximations that relate surface pressure to transmission and reflection coefficients calculated from the Brekhovskikh layered media model. Experimental measurements of pressure amplitude and phase difference were made on the shadow side of matrices of metal blocks. The blocks were insonified by sound waves of frequencies 2500 and 3500 Hz. An array of three hydrophones on the shadow side of a matrix sensed diffracted pressure amplitude and phase as a function of distance between the matrix and the hydrophones. Comparison of model predictions and experimental data shows good agreement. The agreement for small hydrophone‐matrix separations becomes better with increasing ka where 2a is the outside dimension of the matrix. [Work supported by NAVSEA, Code 55N and DTNSRDC Code 1933.]
FREE

Acoustic intensity by intuition (A)

J. E. White

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S5-S5 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
For a plane sinusoidal acoustic wave, we know that average intensity is directed perpendicular to the wave front and uniform in magnitude. For two identical plane waves at right angles, intensity must be directed at 45° and be increased by √2. Wrong! For a standing wave, we realize that average intensity is zero. For two standing waves at right angles, the average intensity must surely be zero. Wrong again! Measurements in a 4‐ft by 8‐ft enclosure confirmed the circulating flow of energy which can exist. In an elastic solid, average intensity is perpendicular to the wave front for both compressional and shear plane waves. When a plane shear wave and a plane compressional wave at the same frequency travel in the same direction, one would expect the direction of average energy flow to be perpendicular to the wave fronts. Actually, the direction of average intensity as a function of distance oscillates about the perpendicular. It is clear that intuition based on linear theory may lead one astray when applied to a nonlinear phenomenon like intensity.
FREE

Numerical calculations for resonance scattering by an elastic sphere in an elastic medium (A)

D. Brill and G. C. Gaunaurd

J. Acoust. Soc. Am. Volume 77, Issue S1, pp. S5-S5 (1985); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
In an earlier paper [J. Acoust. Soc. Am. Suppl. 1 76, S9 (1984)] we developed the complete RST formulation for an elastic sphere in an elastic medium under shear and compressional wave incidences. We also showed how that work contained a variety of simpler cases that we have studied in the past, such as, a fluid‐filled cavity in an elastic matrix, an elastic sphere in water, a gas bubble in a liquid, etc, … as particular cases. We now develop the entire computational machinery of the RST and show the many useful plots that it can produce. These numerical displays include: (a) The SEM‐type poles with their relation to the various types of surface waves that they generate. The Franz‐zeros also fall under this category. (b) The graphs of the five types of scattering amplitudes (i.e., fpp, fps, fsp, fss, ftt) that are pertinent to this elastic problem. (c) Their decomposition into partial waves or normal modes, (d) The decomposition of the partial waves into backgrounds and resonances, (e) The informative three‐dimensional plots of the response surface of all the scattering amplitudes, in the mode‐order and frequency domains, and, (f) The dispersion plots for the phase velocities of the various surface waves. All this is done for two material combinations (i.e., epoxy sphere in steel and steel sphere in epoxy) for which two different types of backgrounds are required to isolate the modal resonances. All displays are constructed in wide nondimensional frequency bands that include the resonance region for which λ≈a. Physical interpretations of all plots are given.
Return to All Sections
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close