Returning to the discussion on F-22, traditional aircraft materials such as aluminum and steel make up about 1/5 of the F-22's structure by weight. The high performance capabilities of the F-22 requires the significant use of titanium (42 % of all structural materials by weight) and composite materials (24 % by weight), which are both stronger and lighter weight than traditional materials, and offer better protection against corrosion. Titanium also offers higher temperature resistance.
Materials such as Thermoplastic, BISMALEIMIDE (BMI) resins and Titanium (Ti-62222) create its own unique engineering challenges. Thermoplastic is made from sheets of graphite fibers held together by resin, this is baked in an autoclave while nitrogen is pumped in to raise pressure forcing the fibers to blend with the resin. BISMALEIMIDE (BMI) resins are also cooked in an autoclave without the need for vacuum and pressure but both BMI and Thermoplastics present the same problem of air bubbles forming within the layers of resin and graphite weakening the structure. In addition, it is important to achieve the correct crosslinks density (linking of polymer chains) too high crosslink density results in brittleness too low will reduce strength achieving the right crosslink density largely depends on the materials and the resin.
Defective composites are unusable and must be discarded; the success of this procedure is dependent upon the quality of raw materials (fiber and resin), the process and efficiency of the machines used during the operation. A majority of the raw materials and tools are dual use technology and is aggressively export controlled.
I re-emphasize capability is not just limited to technical capability and know-how it is the ability of a nations infrastructure to support a complex fifth generation fighter program simply because the manufacturing tolerance for a 5-generation fighter is much more stringent a structural anomaly during the thermal curing process will weaken the air frame and compromise stealth.
The process of cooking and the use of auto-clave for producing thermal-cured composites is by no means new this technology has been around for over forty years. Despite this some of the well known issues with thermal-curing such as resin timeout, auto-clave size limit and tooling cost of the auto-clave and associated test equipment is yet unresolved. The use of thermal-curing is perhaps cost justified for building two prototypes but will be cost prohibitive for building over three hundred airplanes needed by both Russia and India. This was recognized by DARPA several years ago that more sophisticated techniques were needed to reduce cost and eliminate wastage due to defects.
The problems with thermal curing particularly the size restriction imposed by the auto-clave is resolved by a newer technique that uses a high energy electron beam(EB) rather than heat, to initiate polymerization and cross-linking. This technique was first introduced in the US in 1994 by Northrop Grumman and Lockheed Martin with the IATA program (Integrated Airframe Technology for Affordability). The fuselage of the F-18 E/F was built entirely by EB curing at the Northrop Grumman facility. The use of EB require a different epoxy resin, unlike thermal resins, EB resins can be stored at room temperature and is cured under vacuum pressure only an additional benefit of EB curing is resistance to micro-cracking and moisture absorption. The use of EB technique is now wide spread it has been widely adopted by Boeing, Lockheed, Dassault and EADS.
EB is not known to have been used in Russian military or civilian programs, penetration of this technology in the Russian aviation sector will be visible in the form of airplane components that require sophisticated production techniques a good example of such a component is the laminated polycarbonate bubble canopy I do not recall ever seeing a Russian fighter with a bubble canopy.