Bulletin N08-01    April 29, 2008 Air Force to provide funding for polyimide prepreg material qualification   The U.S. Air Force Research Lab is funding the qualification of a non-methylenedianiline (MDA) polyimide material for use in both airframe and engine applications. Both the Air Force and NCAMP, who 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: Non-MDA polyimide Minimum of 450ºF wet operating temperature; higher operating temperature is desirable Easy to process; preferably require less than 200 psi autoclave pressure with low void content Resistance to microcracking is desirable High thermo-oxidative stability is desirable High compression after impact strength is desirable Demonstrated robustness in producing large panels (about 3' by 3' minimum) with bend radius, ply drop-offs, thick and thin sections, and integral stiffeners typically found in aircraft airframe structures is desirable Demonstrated robustness in co-cure/co-bond applications is also desirable 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) 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.   Film Adhesive Screening Programs The U.S. Air Force Research Lab is also interested in funding a limited amount of testing to screen for compatible film adhesives for cocure and cobond applications with the prepregs currently undergoing NCAMP qualifications. Companies currently participating in NCAMP qualification and equivalency programs have been asked to submit suggestions for film adhesives that are compatible with the prepregs currently being qualified, including ACG MTM45-1, Cytec 5215, Cytec 5250-5, Cytec 977-2, Hexcel 8552, Newport 4708, Nelcote E752, and Tencate TC250. The film adhesives will be chosen by material users to finalize the selection.  Two film adhesives per prepreg resin system will be tested.  The test panels will be fabricated in the NIAR Composites and Advanced Materials Laboratory.   As a screening program, there will be no FAA involvement and material allowables will not be generated. In addition, adhesive material specifications will not be created since they are not qualification programs.  A detailed adhesive information data sheet to document the adhesive pedigree information will be included in the final report. The final report will only contain test results and observations.   Cocure composite sandwich structure The National Center for Advanced Materials Performance is located at the National Institute for Aviation Research at Wichita State University. Stemmed from the NASA AGATE shared composite material property database program, NCAMP’s goal is to take the composites industry to a self-regulating level similar to that achieved by the metals industry. This involves working with industry organizations such as the Composite Materials Handbook 17 on data archival, the American Society for Testing and Materials D30 committee on composite test methods, the Society of Automotive Engineers on aerospace material specification development, the Performance Review Institute on product assessment and certification and Nadcap on audit criteria; all aiming at creating a framework covering material property data acquisition, qualification and property control that will be acceptable to the FAA and Department of Defense. This framework must be self-sustaining, both financially and technically, while being managed by the aforementioned non-profit organizations with minimal FAA and DoD oversight. This ambitious goal requires a strong level of support and participation from industry and government.