Appendix B

Present and Potential Future Uses of Polymers by the Navy

The use of polymers by the Navy reflects the unique performance advantages potentially realizable from these materials (summarized in Table B.1). While each application poses different opportunities and challenges, certain general directions are apparent. Following the trend set in consumer products, the Navy also makes increasing use of polymers for relatively simple parts, such as hoses, pipes, and gaskets. Light weight, corrosion-resistance, and ease of manufacture provide the main impetus for the use of polymers in these applications, and the market share of polymers for such applications is anticipated to continue to grow steadily in the future.

Table B.1 Properties of Polymers

A DVANTAGES

C ONCERNS

High strength and stiffness/weight ratio

Corrosion-resistance

Low signature

Manufacturing flexibility

Variety of properties

Flexibility

Chemical stability

Low cost

Survivability in combat

Flammability and flame spreading

Release of smoke and toxic gases

Long-term durability

Repair problems (i.e., joints)

Resistance to high temperatures

The Navy also makes use of polymers in more critical and demanding applications, such as in load-bearing polymeric matrix composites, special coatings for signature control, coatings for corrosion reduction in waste-holding tanks, fuel storage tanks, and metal pipe linings, and so on, where polymers are often applied as part of a technology package to meet the needed performance criteria. This area provides significant opportunities for the Navy to improve the performance of its surface ships and submarines. For example, a lower-weight superstructure and hull mass would result in a lighter, smaller, and more stable vessel. In submarines, too, there are many potential applications for polymeric matrix composites, and there the achievement of a better balance in trim and an enhanced depth performance are often cited as potential advantages. Aside from the present use of advanced composites in bow domes, several applications external to the pressure hull will be evaluated, and several others, such as “intelligent” hulls with special embedded sensors, are under consideration by the Navy. An advantage of polymers for marine vessels is the low detectability by radar and the possibility of incorporating antifouling and/or drag-reducing agents.

The potential advantages listed in Table B.1 provide the driving force for an increased use of polymers, but their application is also tempered by concerns, as well as currently perceived or documented performance deficiencies in both normal use and battle conditions. Damage tolerance, for example, is of paramount importance for the use of polymers in structural components, and specifications define the length of time that structures under load must be able to resist fire with no “holing” or collapse. Another concern is smoke and toxic gases liberated by combat-initiated fires, as most fire casualties occur from smoke inhalation and impaired vision that prevent escape. While Federal Aviation Administration (FAA) tests indicate that a variety of specially treated composites performed better in a fire environment relative to aluminum and steel, it is also known that burning composite resins can generate smoke and noxious fumes. Finally, the experiences encountered with combat-initiated fires during the Falkland Islands and Persian



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Polymers Appendix B Present and Potential Future Uses of Polymers by the Navy The use of polymers by the Navy reflects the unique performance advantages potentially realizable from these materials (summarized in Table B.1). While each application poses different opportunities and challenges, certain general directions are apparent. Following the trend set in consumer products, the Navy also makes increasing use of polymers for relatively simple parts, such as hoses, pipes, and gaskets. Light weight, corrosion-resistance, and ease of manufacture provide the main impetus for the use of polymers in these applications, and the market share of polymers for such applications is anticipated to continue to grow steadily in the future. Table B.1 Properties of Polymers A DVANTAGES C ONCERNS High strength and stiffness/weight ratio Corrosion-resistance Low signature Manufacturing flexibility Variety of properties Flexibility Chemical stability Low cost Survivability in combat Flammability and flame spreading Release of smoke and toxic gases Long-term durability Repair problems (i.e., joints) Resistance to high temperatures The Navy also makes use of polymers in more critical and demanding applications, such as in load-bearing polymeric matrix composites, special coatings for signature control, coatings for corrosion reduction in waste-holding tanks, fuel storage tanks, and metal pipe linings, and so on, where polymers are often applied as part of a technology package to meet the needed performance criteria. This area provides significant opportunities for the Navy to improve the performance of its surface ships and submarines. For example, a lower-weight superstructure and hull mass would result in a lighter, smaller, and more stable vessel. In submarines, too, there are many potential applications for polymeric matrix composites, and there the achievement of a better balance in trim and an enhanced depth performance are often cited as potential advantages. Aside from the present use of advanced composites in bow domes, several applications external to the pressure hull will be evaluated, and several others, such as “intelligent” hulls with special embedded sensors, are under consideration by the Navy. An advantage of polymers for marine vessels is the low detectability by radar and the possibility of incorporating antifouling and/or drag-reducing agents. The potential advantages listed in Table B.1 provide the driving force for an increased use of polymers, but their application is also tempered by concerns, as well as currently perceived or documented performance deficiencies in both normal use and battle conditions. Damage tolerance, for example, is of paramount importance for the use of polymers in structural components, and specifications define the length of time that structures under load must be able to resist fire with no “holing” or collapse. Another concern is smoke and toxic gases liberated by combat-initiated fires, as most fire casualties occur from smoke inhalation and impaired vision that prevent escape. While Federal Aviation Administration (FAA) tests indicate that a variety of specially treated composites performed better in a fire environment relative to aluminum and steel, it is also known that burning composite resins can generate smoke and noxious fumes. Finally, the experiences encountered with combat-initiated fires during the Falkland Islands and Persian

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Polymers Table B.2 Polymer Uses by the Navy M ATERIALS P RESENT A PPLICATIONS N EW A PPLICATIONS U NDER C ONSIDERATION Structural Composites Radar domes Rocket motor casings Shipboard ventilation Pump casings and impellers Piping Composite masts Acoustic isolation Ducts Piping for fluid handling Submarine pressure bottle Fairwater Elastomers Adhesives Sonar domes Hoses (water and fuel) Sealants (fuel and water tanks) Conductive sealants (electromagnetic shielding) Lubricants External tiles for submarine hulls Vibrational damping (engine and motor mounts) Electrical insulation Tires, belts, bushings, gaskets, seals Binders for propellants Foams Protective cover for hydraulic actuators Plastics Deck houses Railings Shrapnel screens Body armor Insulating foams Interior fittings Floors   Nonstructural Coatings Anticorrosion Antistatic Nonskid Signature control (stealth) Interior lining of pipes Fuel storage tank lining Biocompatible coatings Controlled drug release Anti fouling Drag-reducing Films Packaging Biodegradable bags for trash disposal Skin grafts Membranes for soil Filtering Ultrafiltration Textiles Uniforms Cushions Bandages Ropes Optical fibers

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Polymers Gulf wars, and the fire-induced melting of an aluminum-based superstructure on the USS Belknap, a guided-missile cruiser, following a collision with the USS Kennedy, have contributed to this continuing debate. As stated in Table B.2 , listing polymer uses by the Navy, polymeric matrix composites and advanced composites composing one or more stiff, high-strength reinforced fibers with a compatible resin system are already used for many Navy applications, such as radar domes, rocket motor casings, and aircraft structural parts. In many such cases, materials and manufacturing technology developed for and applied in the automotive, commercial aircraft, and consumer products industries can be, and in the past have been, usefully applied to meet the Navy's needs. However, many potential applications either have more demanding performance requirements or are unique to the shipbuilding industry and to the Navy, in particular. A successful use of advanced composites in more critical load-bearing shipboard structures will likely pose many scientific as well as technological challenges, including the further improvement of existing manufacturing methods as well as the development of new ones. In addition, there is a great need to supplement laboratory testing of potentially useful composite structures by realistic on-board evaluation using vessels dedicated for such purposes. Considerable experience has already been gained in Europe with mine hunter ships built with glass and polyester composite hulls, and the construction of a much larger ship from advanced composites is being undertaken in Japan. The U.S. Navy has build several minehunting ships with glass-reinforced plastic hulls fabricated under a license to U.S. industry from an Italian firm. The Navy also has informal and formal procedures for test and evaluation of research products and has designated two submarines for such purposes. There should be opportunities for early shipboard evaluation of new technology and materials, including advanced composite structures and other polymer-containing systems. Another area of much significance is coatings for corrosion-resistance (including biocorrosion), reduction of signature and drag, and other purposes. While such coatings are extensively used by the Navy, the panel believes that there are many new opportunities to improve the performance of coatings and to extend their range of applications, e.g., the reduction of flammability, as discussed above. Finally, new scientific advancements have opened the door for the use of polymers in biomedical applications, which may provide future benefits to Navy personnel. This is a relatively new field, but skin grafts, biocompatible coatings, and controlled drug release applications are already being tested.