摘要:

The resonance method has been used to study the attenuation and dispersion of the first longitudinal mode of propagation and the dispersion of the first flexural mode of propagation of elastic waves in a cylindrical, aluminum alloy (24ST) rod.Qwas found to decrease monotonically from 2.5×105to 1.2×105as the frequency increased from 0.84 to 100 kc. Longitudinal and flexural phase velocities are compared to Pochhammer‐Chree theory dispersion curves. Agreement of experimental and theoretical curves is within 0.3%. Similar agreement is obtained when normal flexural modes computed by a modified Timoshenko theory are compared to the experimental resonant frequencies. Measurements of torsional mode frequencies indicate dispersion does not exceed approximately 0.01% in the frequency range of approximately 0.5 to 100 kc.

ISSN:0001-4966    

DOI:10.1121/1.1908417

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

For the diffraction of electromagnetic waves from a standing sound wave, the amplitudes of the first diffraction order are calculated from Born's approximation. If the wavelength of the electromagnetic signal is made comparable to the acoustic wavelength, the first diffraction order vanishes periodically with increasing width of the sound beam because of a destructive interference of scattered waves. The sound‐perturbed medium becomes also slightly anisotropic. The diffraction of microwaves by a standing sound wave in oil is measured as a function of sound frequency and polarization of the electromagnetic wave.

ISSN:0001-4966    

DOI:10.1121/1.1908419

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Frequency equations of simple axisymmetric axial shear and simple axisymmetric radial vibrations were obtained for a soft elastic cylinder with a hard, thin, elastic skin. The soft core is treated on the basis of the three‐dimensional exact equations of elasticity while the thin skin is regarded as a membrane. Numerical frequencies for the first several modes for various values of the skin thickness were tabulated and their implications discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908421

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The transient behavior of shock mountings disturbed by steplike displacements that invoke large departures of mount stiffness from linearity is described theoretically and compared with the behavior of an ideally linear mounting. The influence of mount damping upon the transient motion of the mounted item is discussed in detail.For the majority of step rise times considered, a mount that softens upon compression and is not heavily damped is shown to reduce both the acceleration and displacement experienced by the mounted item below the values observed for a linear mounting or, as is normally the case in practice, a mount that stiffens upon compression. The reduction in acceleration can be comparable with 10 db for quite a wide range of step rise times. It is frequently the magnitude of the acceleration to which the likelihood of damage to the contents of the mounted item may be related.

ISSN:0001-4966    

DOI:10.1121/1.1908423

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Dynamic shear compliance measurements on a vulcanized natural rubber stock have been carried out from 50 to 5000 cps as a function of static elongation in the range 0–400%. Above 300% elongation several very large resonance dispersions appear in the region 1000–2000 cps, but at lower elongations no such resonances are observed. The appearance of mechanical resonance dispersion thus coincides with the development of oriented crystallinity in the stretched rubber as shown from x‐ray diffraction data. On the other hand, the magnitudes of the dispersions decrease with increasing elongation above 300% whereas x‐ray measurements indicate the amount or extent of crystallinity increases with stretching above 300% elongation. The resonances thus clearly decrease as the crystallinity becomes more perfect or more extensive and hence appear to reflect theimperfectionsof the crystalline regions formed by elongation rather than the crystallinity itself. Observed changes in the compliance spectrum with time at each elongation also favor this view. Broad retardation dispersions were observed when the rubber was allowed to contract back to elongations below 300% after long times above 300%. These are tentatively ascribed to an extended amorphous state in which the rubber molecules are kept partially extended by very small randomly oriented crystalline regions which persist for some time after retraction. Another interesting feature of the results is an apparent correlation between the percent crystallinity determined from x‐ray diffraction and the reciprocal of the general level of storage compliance 1/J′ at frequencies well below or well above the dispersion region.

ISSN:0001-4966    

DOI:10.1121/1.1908425

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Because of the many resonances, plates have an extremely small driving‐point impedance, add accurate measurements are difficult to perform. Some of the fundamental difficulties that accompany such measurements are illustrated by experimental results. Measurements performed with thin, rectangular plates show that the asymptotic laws of vibration and sound radiation predict, within the range of experimental error, the characteristic impedance and the sound radiation of plates. The theoretical prediction that damping would have no appreciable effect on either the characteristic impedance or the background level of the radiated sound pressure was found to be accurate.

ISSN:0001-4966    

DOI:10.1121/1.1908427

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

This report treats the free and forced vibrations of infinitely long, thick and thin cylindrical shells surrounded by water. Exact elasticity theory is used to treat unpressurized shells and an approximate shell theory is employed to treat the effects of static pressure, internal fluid, and structural damping. Comparisons are made between the results of the exact and approximate theories.

ISSN:0001-4966    

DOI:10.1121/1.1908429

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Spectra of sound‐pressure amplitude versus frequency in the range 1.1 to 2.4 kc have been obtained at regular intervals in shallow (10 ft) water during two periods of extended observation. The acoustical data have been presented in the form of contour diagrams of sound‐pressure amplitude versus frequency and time as coordinates and compared with water conditions.The form of the contour diagrams permits differentiation between field‐structure variation and variation in attenuation although differentiation between the associated processes has not been possible. Temporal variation in the vertical sound‐velocity profile produced only small changes in the gross features of the field structure, as inferred from the contour diagram, for up to the first three modes of propagation. For frequencies above 1.6 kc (i.e., when three or four modes were stimulated) the variations in field structure were prominent. Attempts have been made, with little success, to explain periods when the received signal was strongly attenuated in terms of vertical sound‐velocity structure.

ISSN:0001-4966    

DOI:10.1121/1.1908431

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Frequency spectra of the underwater noise produced by cavitating submerged water jets were determined experimentally for nozzle diameters from38to112 in., efflux velocities from 40 to 175 ft/sec, and ambient pressures up to 2 atm. When cavitation is barely incipient, the rms sound pressure varies with differences in the manner of handling the water prior to a run; this variation of sound pressure is presumably due to changes in the nuclei content of the water. When, however, the cavitation index is sufficiently small, cavitation is well advanced, and then the radiated sound is independent of the manner of treating the water. For this condition a simple relation is found to exist among the noise spectra when they are plotted as dimensionless functions of those physical quantities which determine the flow.

ISSN:0001-4966    

DOI:10.1121/1.1908433

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Piezoelectric ceramic elements in high‐power acoustic transducers are subjected to high static as well as dynamic stress. This is particularly true of well‐matched transducers operating in deep water, since the static stress in the piezoelectric element may be several times the water pressure. The present study was undertaken in an effort to determine the effects of static compressive stress on the piezoelectric properties of two commercial lead titanate zirconate compositions, PZT‐4 and PZT‐5, and of two barium‐titanate compositions, commercial Ceramic B (a barium calcium titanate), and the composition 88 wt% barium titanate, 12 wt% lead titanate (BaPb12Ti). The permanent effects of stress exposure, determined at zero stress after exposure to a given stress, were found to be more severe with stress parallel to the polar axis than with perpendicular stress, as expected. Under maintained stress, however, the effects of perpendicular stress are more severe. PZT‐4 and BaPb12Ti, generally better suited for use as radiating transducers, show effects dependent upon exposure time but independent of the number of stress cycles. Ceramic B and PZT‐5 show effects dependent upon the number of stress cycles and less dependent upon the total period of stress exposure. Of the compositions tested, PZT‐4 and BaPb12Ti were least affected by high static stress, suffering relatively little from exposure to stress as high as 15 000 psi. Of these two compositions. PZT‐4 has markedly higher coupling (k33∼0.64 compared to 0.365) and therefore offers higher transducer bandwidth.

ISSN:0001-4966    

DOI:10.1121/1.1908435

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP