A variety of polyimide composite materials produce cost-effective alternatives to cast-metal parts. Edited by Jean M. Hoffman The bushings, bearing pads, and splines in the 10-stage, high-pressure compressor of the Rolls-Royce BR710 turbofan engine are made from Vespel polyimide. These parts are exposed to temperatures up to 525°F yet need no lubrication. Double and triple tube clamps for an aircraft engine are made from reinforced Vespel CP. They attach hydraulic, hot air, and electrical lines onto the engine compressor housing. The clamps withstand operating temperatures on the order of 500°F. Variable stator vane bushings made from Vespel CP are used in the high pressure section of the compressor in a aircraft engine. The laminate withstands temperatures in excess of 675°F. Aerospace companies often select new materials based on their ability to make designs simpler, more durable, easier to maintain, and more economical to produce. To meet these goals, designers have often converted cast-metal parts to those made from polyimide composites. These materials have matured and are gaining wider acceptance in industrial and commercial applications. But unlike high-performance polymers that also developed through military programs, polyimide composites have been a tougher sell for commercial applications. Designers historically hesitated specifying advanced composites as metal replacements because their manufacturing processes are less mainstream and often more expensive than conventional polymers. However, it's often these nonconventional manufacturing techniques that, when understood and employed early, give designers more freedom to customize the composite for an application. The fillers or fibers and polyimide matrix of advanced composites may be combined using a variety of fabrication processes. The combination generally depends on part count, size, and complexity, and the required physical or mechanical properties. This ability to selectively tailor composite constituents such as fillers of graphite and MoS2 or reinforcement fibers is generally easier and more affordable than
Polymer and plastic composites are strengthened with fibers, fillers, particulates, powders and other matrix reinforcements to provide improved strength and/or stiffness. Examples include fiber reinforced plastics (FRPs), sheet molding compounds (SMCs), bulk molding compounds (BMCs), pre-preg materials, and fabricated composite parts.
Fibers and filaments consist of bulk, chopped fibers or strands and continuous monofilaments of materials and are used in reinforcing composites as well as other specialized electrical and thermal applications.
Metal matrix composites (MMC) consist of a metal and one or more other materials, typically a ceramic or organic compound. They provide superior specific strengths and good strength-to-weight ratios, resist fire and moisture, and are can be used over a wide range of temperatures. MMCs also provide resistance to radiation and excellent electrical and thermal conductivity.
Thermoplastic composites offer, based on their high specific strength and stiffness, alternative solutions with significant weight reduction compared to traditional metal and metal alloy parts.
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