ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2aUW25. Pressure effects on the dynamic and static properties of perforated elastomers used in underwater acoustics.

Stephane Beretti

DCN Ingenierie Sud, Dept. of Underwater Warfare, BP 30, 83800 Toulon Naval, France

Christian Audoly

DCN Ing. Sud., Toulon, France

Philippe Guillaussier

PONS, 13872 Aubagne Cedex, France

The microinhomogeneous materials made with air-filled cavities in viscoelastic matrices, have many possible uses in underwater acoustics including anechoic coatings, acoustic decoupling, or reflectors for arrays. Theoretical models are necessary to predict the acoustic properties of these materials by evaluating the properties of the equivalent homogeneous material, as a function of frequency, pressure, and temperature. During recent works an abnormal effect of the applied pressure on these materials was noted: The plot of the longitudinal sound speed and of the bulk modulus, versus static pressure, had the lowest value for 10 to 20 bars of applied pressure, instead of a regular increasing plot predicted by the models [G. Gaunaurd et al., 173--177 (1984)]. Different results, including test panel measurement in a tank, or measurement of the static and dynamic bulk modulus agree with this consideration. Theoretical models to predict the static and dynamic effective material properties as a function of the pressure were compared with these results.