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5/6/2008 | 2 MINUTE READ

USAF to provide funding for polyimide prepreg qualification

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The U.S. Air Force Research Lab (AFRL) is funding the qualification of a non-methylenedianiline (MDA) polyimide material for use in airframe and engine applications.

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The U.S. Air Force Research Lab (AFRL, Dayton, Ohio) has announced that it is funding the qualification of a non-methylenedianiline (MDA) polyimide material for use in airframe and engine applications. Both the Air Force and the National Center for Advanced Material Performance (NCAMP, Wichita, Kan.), which is coordinating this effort, believe that polyimide-based composite materials are a viable substitute for many aerospace parts currently made out of titanium.

The scarcity of raw material and high manufacturing costs associated with titanium make finding a substitute material attractive to the aerospace industry. Polyimide composites can replace titanium in many applications that require less than 500°F operating temperature while offering potential advantages such as lower cost and reduced weight. The advantages of a polyimide over epoxy and bismaleimide include a higher operating temperature, which may reduce or eliminate the need of thermal insulation in some applications.

The material property data acquisition and qualification test plan will generate basic material allowables typically needed for airframe and engine applications and material properties typically needed to establish material control. The available funding will be limited to the qualification of either one resin with two product forms or two resins with one product form.

The requirement for the high-temperature and high-pressure autoclave curing process will likely limit the number of companies participating in process equivalency. However, the need from the aircraft companies will inspire their suppliers and part fabricators to participate in equivalency due to the access they will gain to the data for use in designing parts. Currently, NCAMP has four companies interested in proposing materials for qualification.

The material submitted should have the following characteristics: 1. Non-MDA polyimide 2. Minimum of 450°F wet operating temperature; higher operating temperature is desirable 3. Easy to process; preferably require less than 200 psi autoclave pressure with low void content 4. Resistance to microcracking is desirable 5. High thermo-oxidative stability is desirable 6. High compression after impact strength is desirable 7. Demonstrated robustness in producing large panels (about 3 by 3 feet minimum) with bend radius, ply drop-offs, thick and thin sections, and integral stiffeners typically found in aircraft airframe structures is desirable 8. Demonstrated robustness in co-cure/co-bond applications is also desirable 9. Matured resin formulation and prepregging operation by July 2008 (i.e., able to lock down PCD under revision control by July 2008 to begin prepreg production) 10. Able to develop a robust cure cycle and test panel process specification by July 2008 (this will require some production experiments of small and large panels)

Once the materials have been proposed by suppliers, NCAMP will compile the information and send them to NCAMP voting members. The selection process and final decision on which material will be qualified should be finalized within a month.

Information: Visit the NCAMP website for more information.

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