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Nov 1982

Volume 72, Issue S1, pp. S1-S108

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back to top Session E. Engineering Acoustics I: Specialty Materials
Invited Papers
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Specialty materials for underwater acoustics (A)

Robert Y. Ting

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S8-S8 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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In recent years, a majority of the failures of underwater transducers and sonar windows have been identified to be related to problems with the materials used in these systems. Most frequently, a design will successfully meet the initial performance requirement, but the device quickly fails after a short time of exposure to the service environment. The failure mechanisms often are attributable to the fact that the presently used materials are generally not optimized for long‐term operation and always poorly characterized for their aging properties. In many cases, material components for a transducer may be selected from different sources, and this results in serious compatibility problems. Furthermore, because of the proprietary nature of many commercial materials, the user has very little control over the quality of the material, which often shows large batch‐to‐batch variations. This nonreproducibility has made it extremely difficult to properly repair or replace the failed acoustic devices. In order to increase the readiness of present sonars and to improve the lift‐time performance requirement of future new transducers, it is necessary to understand materials' composition‐property relationship, to develop quality control techniques and to design new materials for optimum applications. In this presentation, the major problem areas will be addressed, and progress made in both the acoustically active and passive materials will be discussed.
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Twenty‐year life hydrophones (A)

A. C. Tims

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S8-S8 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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A particular hydrophone design application has been chosen to demonstrate that high reliability can be achieved through the use of reliability modeling, an in‐depth knowledge of transducer design, careful selection of materials, and good construction techniques. The reliability prediction for the design has been based upon random component failure with the assumption of a constant hazard rate. No consideration has been given to wear‐out failure. The design features that increase reliability are presented; alternate design approaches, predictions of lifetime based upon reliability modeling, choices of materials, and successful operation of hydrophones to date are discussed. It is expected that this hydrophone will demonstrate that sonar equipment can be made with reliability equal to space‐age equipment.
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Characterizing the impact of materials on transducer reliability (A)

R. Lowell Smith

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S8-S8 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Achieving high reliability for an acoustic device depends ultimately on its design, materials of construction, fabrication processes, testing, correct installation, and the environment and conditions of use. This paper focuses on evaluating the impact of materials on transducer reliability. It is sometimes appropriate to characterize materials reliability using the familiar exponential reliability, or constant hazard rate model. Commonly in the marine environment, however, degradation processes operate which imply instead wearout reliability descriptions. Attention is focused on distinguishing, characterizing, and representing the reliability impact of these two situations. Failure definition, failure mode, and service limit concepts are introduced and their implications explored. The interpretation of chemical kinetics and other physical rate processes as the microscopic bases for macroscopic reliability descriptions is investigated. Under favorable circumstances this leads to the availability of time compression techniques referred to as accelerated testing, as a reliability evaluation tool. Suggestions are made concerning how reliability methods may be used to reduce the scope of the overall product or device improvement problem. Examples illustrating the use and implications of materials reliability methodology are presented.
Contributed Papers
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Influence of chemical composition on dynamic properties of neoprenes for transducer applications (A)

Rodger N. Capps and Corley M. Thompso

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S9-S9 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Elastomeric materials are widely used in the construction of wet‐end sonar equipment. The viscoelastic nature of these materials causes them to possess and exhibit some extraordinary properties. Unless these properties are properly utilized, it can be disastrous to the performance of a transducer. Neoprenes are often used as components in transducers, due to the superior chemical and physical response properties of neoprene to many environments. However, the dynamic properties of neoprenes may often be inferior to those of other types of elastomers. Since these properties are important for transducer applications, they should be optimized, with additives being used to provide desirable chemical and physical properties. In this paper, the effects of carbon black type and loading and variation of base polymer on a series of neoprenes have been investigated. The dynamic moduli and loss tangents have been characterized for a number of these elastomers. Based on the experimental results, the suitability of these materials for transducer applications and the optimization of dynamic properties of transducer elastomers will be discussed. [Work supported by NAVSEA 63R.]
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Some considerations on resistivity and permeability in the design of a reliable transducer elastomer (A)

Corley M. Thompson

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S9-S9 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Neoprene elastomers are widely used as acoustic transducers but have rarely been optimized for their application. Electrical resistivity and water permeability are important properties in the design of a transducer elastomer. However, their dependency on the elastomer composite is generally unknown. A study was therefore designed to investigate the effects of different types and proportions of fillers on these pertinent physical properties. Three common neoprene types, each with a standard lead oxide cure system, were used. The dependency of resistivity on carbon black loading is found to be described by a sigmoidal curve for each carbon‐black type. Ramifications of the frequently specified properties such as shore hardness and tensile strength on the resistivity will be discussed. Changes in electrical resistivity with seawater exposure will also be described. The dependency of the water permeability of the neoprene on some of the composition parameters has been determined. The effects of both of these variables on transducer lifetime and reliability will be discussed. [Work supported by NAVSEA 63X.]
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Elastomers in Mulloka sonar staves (A)

D. Oldfield

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S9-S9 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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This paper will present a case study of the use of elastomers in the underwater transducer array of the Australian designed Mulloka sonar system. The successful long‐term operation of the sonar depends upon correct choice of materials to keep the interior of the array staves dry. A combination of factors led to severe corrosion inside the prototype staves which were subsequently refurbished with a butyl rubber coating over a cast polyurethane rubber membrane. Later laboratory studies showed that the sprayed butyl rubber coating was much more permeable to water vapour than a brushed coating. The rate of increase of relative humidity inside the array whilst in service with the Royal Australian Navy correlated well with the rate predicted from laboratory measurements. Experience with the prototype array clearly indicated the need for a much less permeable system for the production version. The design eventually adopted consisted of a pre‐vulcanized bromobutyl rubber membrane bonded to the transducer heads and to the stave housing. The stave was then encapsulated in polyurethane to maintain the integrity of the rubber/metal bonds. A limited amount of accelerated testing of actual staves gave moisture permeation results in good agreement with laboratory data. These results lend further support to the view that moisture ingress should not be a problem during the service lifetime of the transducer array.
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Water permeation through elastomer laminates (A)

Patrick E. Cassidy

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S9-S9 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Neoprene and EPDM elastomers were used to measure the permeation rates of distilled water and salt water at 23°, 40° and 60 °C. For laminates, the rates were measured in both directions. The laminates showed a directional dependence of permeation rate and rates lower than the arithmetic mean of the two single layers. Effect of temperature on permeation rate had an Arrhenius type behavior and the activation energies fall within the range for those membranes that follow activated transport mechanism. Tentative mechanisms were proposed for the directional flow behavior in regard to concentration‐dependent permeation.
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Fabrication of nonorthotropic axially stiffened polyurethane mandrels for use in fiber optic hydrophones (A)

S. Africk, P. Jameson, and A. Ordubadi

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S9-S9 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Ideally, extended hydrophones consisting of optical fibers wound on a compliant cylinder have high radial compliance to maximize sensitivity per unit length and high axial stiffness to minimize effects of longitudinal dynamics to assure uniform frequency response. Bendability is also desirable in certain applications. A set of nonorthotropic mandrels consisting of polyurethane cylinders with embedded axial steel wires have been fabricated. These include two levels of stiffening and polyurethanes of four degrees of hardness. Several aspects of the molding technique used, including process selection, mold design, air bubble requirements, and adhesion of the elements are described.
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Tonpilz head mass studies (A)

George R. Douglas and Charles R. Wilson

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S9-S9 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Alumina and composites of graphite/epoxy were used as head mass materials in two separate applications. In the first application alumina and composites of graphite/epoxy head masses were used to produce a low mechanical Q, high electroacoustic efficiency transducer. The initial results show that graphite/epoxy composites especially have great promise as head mass material because of its light weight and high tensile strength. In the second application an alumina head mass was used in a dual mode transducer. This configuration consists of an array of smaller tonpilz elements mounted in the head mass of larger tonpilz elements. This unique method required a very stiff secondary head mass to transfer acoustic energy (without storing strain energy) to the primary radiating surface of the smaller elements. Work in first application was sponsored by Westinghouse in‐house R&D Program of FY 81 & 82. [The work in second application was supported by the dual mode transducer program Navy contract No. N00140‐80‐R‐6916.]
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Pressure release study of materials and configurations applicable to large sonar transducer (A)

Charles R. Wilson

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S9-S10 (1982); (2 pages)

Online Publication Date: 12 Aug 2005

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Polyimide and polyester elastomer reinforced with 20% random glass were developed and tested as a pressure release material for sonar transducer applications. Tonpilz‐type transducers using these materials as a pressure release were subjected to various high pressure conditions and intensive qualification tests including acoustic, extraneous noise, and shock. The results show that both polyimide and polyester elastomer reinforced with 20% random glass are excellent, cost efficient, pressure release configurations that can replace existing belleville springs and sonite pressure release systems now in use. [Work supported by Sonar Transducer Reliability Improvement Program FY 80 under Navy contract No. N00173‐79‐C‐0390.]
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The speed of sound in epoxy resin blends and composites (A)

Robert E. Montgomery, Fred J. Weber, David F. White, and C. M. Thompson

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S10-S10 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Sound speeds in two types of diamine‐cured epoxy resin blends were determined as functions of frequency, temperature, and composition, and the feasibility of impedance matching through the addition of microballoon fillers was also demonstrated. A filled resin system based on a diglycidyl ether of poly (propylene glycol) was shown to possess a mass density near 1.0 g/cm3 and propagate sound at speeds near 150 m/s, while a resin system based on a diglycidyl ether of bisphenol A exhibited sound speeds and specific acoustic impedances about twice those of water. Although the incorporation of microballoons slightly increased sound speeds, the corresponding density reductions resulted in a net decrease of the specific acoustic impedance in all instances. [Work supported by NAVSEA 63R.]
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