مدل سازی و اثبات پلی یورتان به عنوان یک عامل جاذب آکوستیک در زیر آب Modeling and validation of polyurethane based passive underwater acoustic absorber

I. INTRODUCTION Materials that efficiently dissipate a substantial portion of the acoustic intensity of a propagating wave are in general known as attenuating materials. Such materials are essential for providing a stealth coating for ships and submarines. Also they are useful for anechoic lining of water filled tank facilities used for calibration and evaluation of underwater acoustic devices. It is important to develop damping materials suitable for these applications.1–۴ In many situations, the maximum damping obtainable with a single material may not be sufficient; rather a combination of different layers of materials is required. Several methods are employed to improve the damping capacities of polymers. Interpenetrating polymer networks (IPNs) are a class of polymers that are reported to give a broad range of damping.5,6 These are materials with microheterogenous morphology and are different from polymer blends or composites. The loss modulus peaks characteristic of the individual polymers merge in an IPN and result in a broad band of frequencies over which a higher loss modulus is observed. This has been one of the common techniques used by researchers to broaden the effective damping range of polymers. However, for the purpose of underwater acoustic attenuation, the material should be compatible with water in terms of the acoustic impedance. Use of multilayer absorbers has become increasingly important in noise abatement.7–۹ This is particularly so in situations wherein damping a broad range of frequencies is essential. To cater to futuristic requirements for underwater materials and to design and evaluate them, an ability to model and predict performance of different configurations is essential. Modeling can afford theoretical optimization of performance with respect to material configurations, thickness of different graded layers, and effect of size and concentration of various fillers. For a multilayer absorber development, this approach will enable low cost manufacturing of high performance materials leading to new structures and devices.10–۱۲ In the present work, an acoustically transparent polyurethane (EPU) and its interpenetrating polymer network with polydimethyl siloxane (PDMS) were used. Acoustic behavior of these materials was modeled using ATILA, a commercial finite element modeling (FEM) code developed by ISEN, Lille, France.13 The modeling results were compared with the experimental results obtained using a water-filled pulse tube facility. II. EXPERIMENTAL A. Materials Raw material components of an EPU were received from Rand Polyproducts, Pune, India, and the silicone raw materials were from M/s Anabond Ltd., Chennai, India. For EPU, the resin: hardener ratio was kept at 100:40. The materials were mixed thoroughly and degassed for about 2 min to remove air bubbles, trapped during mixing. This polyurethane (PU) was cured at room temperature after pouring into a mold. This PU is designated as EPU in this study. For realizing the IPN, PDMS components, Anabond 1217 A, B, and C were mixed according to predetermined compositions (97:3:6). This was reacted with PU prepolymers at room temperature with proper mixing. The PDMS: EPU composition was fixed at 1:1. The IPN was formed as a result of the simultaneous room temperature polymerization of both PDMS and EPU components. The material densities were measured using a densimeter model Mirage MD 200 S (A & D Company Ltd, Tokyo, Japan).