Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D. in Engineering Science - Mechanical Engineering)--University of California, Berkeley, June 1962. / TID-4500 (17th Ed.). Bibliography: l. 108-110.

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The split Hopkinson pressure bar has been used to study the acoustic isolation that can be achieved by inserting a compliant element into the sound path in an elastic system, and to study the dynamic response of the material comprising the compliant element. The specimens were inserted between two steel transducer bars. The incident stress pulse, of about 100 microsecond duration, was produced by striking the free end of one of the transducer bars by a round-headed striker bar. The incident pulse in the first bar and the transmitted pulse in the second bar were sensed by strain gages and displayed on an oscilloscope. The comparison of computed Fourier transforms (within the acoustic frequency range) of both the incident and transmitted pulses showed that in general a greater reduction in transmission of vibration across a specimen is achieved: i) by increasing the length of the specimen; ii) by using a material with a higher attenuation constant or higher viscous damping; iii) by increasing the impedance mismatch between the specimen and the steel transducer bars. Also, it was found that isolation is greater at high frequencies than at low frequencies. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The primary purpose of this thesis is to determine experimentally if the attenuation of small -amplitude elastic waves in metals is governed principally by a linear mechanism (i.e. one for which the principle of superposition is valid). The secondary purpose is to interpret the attenuation measurements in terms of existing theories on acoustic dissipation in solids. Attenuation measurements of the Fourier components of a Rayleigh pulse were compared with those of sinusoidal Rayleigh waves of the same frequency. One copper, one aluminum and two α-brass circular cylindrical shells were used, and Rayleigh waves propagating along the truncated edges of these tubes were studied. Rayleigh pulses were detected at strain levels of approximately four and forty microstrain in order to test for any amplitude-dependent effects accompanying the attenuation. The sinusoidal Rayleigh waves were detected at strain amplitudes between three and ten microstrain. For three out of the four tubes the results indicated that the dominant attenuation mechanism is a linear process in the frequency range from 100 to 500 kc/s and in the strain region from four to forty microstrain. For the copper tube, however, the scatter in the results is such that no definite conclusion could be drawn. For all four tubes the internal friction, 1/Q, increases with frequency. For some of them there is evidence of a relaxation peak, probably as a result of the Zener effect, superimposed on the general trend. Dislocation damping, as proposed by Koehler (1952) and later generalized by Granato and Lucke (1956), is suggested as a dissipative mechanism which could account for this general trend. Most of the internal friction values are found to be between 20 X 10¯⁵ and 100 X 10¯⁵. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Elastic wave propagation in a multilayered crust with causally or acausally attenuating layers is formulated directly in terms of linear systems theory. The solution of the linear systems analog determines the wave motions at the free surface, motions of all internal boundaries and the waveforms propagated into the mantle in response to plane P or S waves generated within the layering or entering into the crust. The particular problem solved is the determination of the response of an n-layered crust to teleseismic P or S waves incident with arbitrary angle at the crustal base. Trivial extensions of this problem would allow reflection solutions. Numerical solutions have been accomplished in both the frequency domain and the time domain. The Fourier solution restricted to a non-attenuating crust is equivalent to the standard Haskell matrix solution of elastic wave equations. Direct time domain solutions allow the syntheses of seismograms considering internal crustal absorption. For demonstration of the utility and advantages of the theory, the linear systems formulation has been applied to studies of the elastic wave response of the central Alberta crust using P waves from 6 teleseismic events. Frequency domain comparisons between the theoretical and experimental spectral amplitude V/H ratios have shown that, although the theoretical effect of attenuation within the crust can be considerable, little improvement in correlations between theory and experiment has been achieved by considering plausible crustal absorption models. Although significant similarities between the theoretical and experimental V/H ratios were found below 2 Hz, little correlation was apparent at higher frequencies. Background and scattering noise partly contributed to this effect and it is also probable that insufficient detail and accuracy was available for the model crustal sections. Time domain synthetic seismograms have been determined which well correspond to the early P coda of several of the experimental records. Assumptions on the event source motions and the mantle properties are required to determine incident P waveforms for these solutions. Causal attenuation within the crustal layering was included. Correlations between the synthetic seismograms and the experimental records has been found to decrease rapidly with time following the P onset. It is suggested that this effect is primarily due to background noise and possible scattering of the waves within the crust. Furthermore, it is probable that the waveforms used for these solutions based on the source motion and mantle attenuation assumptions were not sufficient. A major apparent advantage of the new formulation is that causal and acausal attenuation solutions are permitted in both the frequency and time domains. Also, the large body of communications theory mathematics can now be applied directly to the propagation problem and could prove useful in attempts at the solution of the non-normal incidence inverse problem. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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