Underwater Acoustic Absorption Characteristics of Composites of Wood, Rubber, and Steel
PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB
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In this experimental investigation, the underwater acoustic absorption characteristics of composites of various species of wood, rubber, and steel were determined under low hydrostatic pressure and over a frequency range of 10 to 50 kHz. The test samples included a thin steel plate, closed-cell bubble rubber Rubatex, hemlock, fir plywood, white pine, redwood and Saper-T rubber. Composites of these materials were tested in a semi-anechoic water tank, where the technique used to determine the incident and reflected pressure amplitudes was the tone-burst method. The complex reflection factor for normal incidence, calculated from the standing waves measured in front of each sample at discrete frequencies, was determined for each composite over the frequency range of interest. The bubble rubber-steel composite was found to have the highest reflection factor over the frequency range of measurement however, when reversed steel-bubble rubber, very low reflection factors were measured, but the data were difficult to repeat. Consistently low reflection factors R approximately 0.5 were measured for the fir plywood-steel-bubble rubber composite and for the Saper-T rubber-steel-bubble rubber composite. In general, the other soft woods evaluated were found to be resonant-type absorbers, although the broadband reflection factor did decrease by approximately 20 to 30 percent when a layer of Saper-T rubber was included in the composite.
- Laminates and Composite Materials