TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: Potential acquisition program DDG1000

OBJECTIVE: To develop new affordable non-halogenated polymeric resin materials that have the improved structural, thermal and Fire, Smoke, and Toxicity (FST) behavior when compared to conventional brominated vinyl esters (Derakane 510A) which are currently in use by the U.S. Navy in topside structures. Special emphasis will be given to the structural and thermal characteristics of the polymeric system as they relate to high stress loading around joints, and fire, smoke and toxicity (FST). Equally important in the evaluation criteria will be the affordability of the process, and the compatibility with the carbon fibers.

DESCRIPTION: Organic matrix based composite materials offer a large number of advantages over conventional metals when applied to the naval environment. Composite materials can have the strength of steel at a fraction of its weight and will not corrode. The fatigue performance of composite materials is exceptional. While the material costs are higher than those of structural steel, the long term behavior combined with the low maintenance requirements can afford better total ownership cost (TOC) characteristics. Furthermore, these materials lend themselves to multi-functionality due to high degree of flexibility during fabrication which permits imparting additional properties such as RAM, EM window, etc.

Two major obstacles have impeded the wide dissemination of these materials across the fleet; the initial manufacturing cost and their poor FST performance. The poor FST performance limits the use of composite materials to topside unmanned structures. In addition, currently used vinyl esters have shown less than desirable compatibility with carbon fiber which is undesirable for use in high stress loading areas such as composite joints. The purpose of this effort will be to address these obstacles. While composite materials have been successfully used in aircraft structures because of the high performance requirements combined with their relatively small size, this has not happened with our ships. Not only are the amount of materials required to build ships 2 or 3 orders of magnitude larger than those required for aircraft fighter but also the strict mission requirements that exist on the materials to resist and contain fire for long periods of time have limited their use aboard ships.

NAVSEA has published Design Data Sheet (DDS-78-1) to facilitate the transition of the new composite materials in U.S. Navy shipbuilding. The material fire performance requirements described in this design data sheet are intended to provide consistent safety criteria for the application of composites aboard ships. These requirements have been developed based on Navy fire safety policy and international maritime standards for fire safety. Fire performance requirements for surface flammability, fire growth, smoke generation, fire gas toxicity, fire resistance, and structural integrity under fire have been established.

PHASE I: The technical team will include a nonprofit organization and a private sector business while the Government personnel will serve as advisors when requested or needed. During Phase I of the program, the technical team shall investigate relevant flame resistant chemistries that are compatible with carbon fibers (such as phosphorus based epoxy resins, benzoxazine chemistry, and others). The PI will demonstrate that: 1) The candidate resin system has mechanical properties that are comparable or better than those of standard epoxy systems as evidenced by mechanical tests such as Tension (ASTM D638), Compression (ASTM D695), Interlaminar Shear (ASTM D3846), Flexure (ASTM D790), Fracture toughness (ASTM D 5528), etc.; 2) The FST behavior of the candidate resin system shall be better than that of the standard brominated vinyl ester, and closer to a standard phenolic resin system as evidenced by fire tests such as heat release rates (ASTM E-1354), flame spread (ASTM E162), smoke generation (ASTM E-662), and fire gas toxicity (ASTM E-800); 3) The processability of the new resin system is comparable to that of vinyl ester systems in terms of room temperature or low temperature curing capability and low viscosity amenable to VARTM processing; 4) That the proposed resin system is compatible with carbon fiber reinforcement for structural applications. The PI will determine the resin manufacturing cost as a function of the material quantity.

PHASE II: During the Phase II the contractor will investigate alternative chemical routes to synthesize the resin system looking at improving yield and reducing manufacturing costs. Also, the contractor will fabricate carbon fiber reinforced composite materials of various sizes for testing. The PI will fabricate panels to characterize the mechanical, structural, and FST performance of the material. The FST performance testing will include ISO 9705 room corner fire tests, and UL-1709 fire resistance tests. A demonstration prototype such as the section of a composite mast, or a helicopter hangar, or a deckhouse will be fabricated. Cost estimates will be determined.

PHASE III: Large scale manufacturing of the resin will be optimized and documented in coordination with a NAVSEA program office and technical personnel. The PI will manufacture components for complete characterization in accordance with requirements and specifications recommended by the technical personnel of the Program Office, and, if successful, build a prototype for at sea trials including shock.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial ship, aviation industries, and transportation sector would benefit significantly from a material system of this nature as well. Fire smoke and toxicity are problems common to all structures where people live.

REFERENCES:
1. MIL-STD-2031 (SH), "Fire and Toxicity Test Methods and Qualification Procedure for Composite Material Systems Used in Hull, Machinery, and Structural Applications Inside Naval Submarines" (Feb 1991).

2. DDS-078-1: COMPOSITE MATERIALS, SURFACE SHIPS, TOPSIDE STRUCTURAL AND OTHER TOPSIDE APPLICATIONS � FIRE PERFORMANCE REQUIREMENTS, 11 August 2004

3. U. Sorathia, G. Long, M. Blum, J. Ness, T. Gracik; "Performance Requirements for Fire Safety of Materials in U.S. Navy Ships and Submarines", Proceedings of 46th International SAMPE Symposium and Exhibition, Volume 46, Book 2, May 2001.

4. Sorathia, U. and C.P. Beck, "Fire-Screening Results of Polymers and Composites," Proceedings of Improved Fire and Smoke Resistant Materials for Commercial Aircraft Interiors, National Research Council, Publication NMAB-477-2, National Academy Press, Washington, DC (1995).

5. Usman Sorathia, Naval Surface Warfare Center, USA, "N-Class Fire Resistant Divisions In U.S. Naval Surface Ships", Fire and Materials 2009, Interscience Publications, Greenwich, UK.

KEYWORDS: High stress loading, Fire, Smoke Toxicity, High Temperature Resins, Composites, VARTM

Questions may also be submitted through DoD SBIR/STTR SITIS website.