Acoustical and dynamic mechanical measurements were carried out on a commercial polyurethane rubber, DeSoto PR1547. The sound speed and attenuation were measured over the range from 12.5 to 75 kHz and 3.9 to 33.6 degrees C. Shear modulus was measured from 10(-4) to 2 Hz and -36 to 34 degrees C. The peak heights of the shear loss tangent varied with temperature, demonstrating thermorheological complexity. At higher temperatures, time-temperature superpositioning could be applied, with the shift factors following the Williams-Landel-Ferry equation. From the combined acoustical and mechanical measurements, values for the dynamic bulk modulus were determined. Moreover, superposition of the bulk modulus data was achieved using the shift factors determined from the dynamic mechanical shear measurements. Finally, this work illustrates the capability and the working rules of acoustical measurements in a small tank.

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Strain relaxation functions have been obtained for boron trioxide glass in its transformation region by digital correlation of a scattered optical beam and by pressure jump relaxation measurements utilizing a recently developed acoustic densitometer. The results confirm that the light−scattering correlation data is a measurement of the isothermal constant stress compressibility function. These measurements, together with previous ultrasonic results, cover a temperature region for B2O3 in which the structural relaxation time changes by more than 13 orders of magnitude.

An actuator—sensor tile has been developed for use in studies examining the issues involved in actively controlling the reflection and transmission characteristics of generic underwater structures. The tile is 25 cm square and contains a full area actuator, acoustic pressure sensor, and (acoustic particle) velocity sensor. This paper presents the predictive models used in the tile design. Issues addressed include transducer performance, spatial sampling, near-field sensing, internal resonances, and both direct and extraneous coupling mechanisms, all of which can contribute to complicate the system transfer functions. The acoustic characteristics of the final tile were evaluated at the NRL Laboratory for Structural Acoustics (LSA) and these results are compared with predictions.

Ultrasonic absorption has been measured in acetic acid–acetone mixtures in the concentration range 5.47M acetic acid to 17.38M (glacial). The frequency range covered was 0.5–30 MHz, and all the systems fit a single relaxation mechanism. It is demonstrated that the chemical process responsible for the relaxation is an equilibrium of the form D ⇄ lim krkf C, where D and C are believed to be the “closed” (two H bond) and “open” (one H bond) forms of the acetic acid dimers. This scheme gives a quantitative fit of the ultrasonic data and complete thermodynamic and kinetic parameters if the rate constants are assumed to be viscosity dependent.