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3/5/2014 | 3 MINUTE READ

Carbon fibers, prepregs

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Hexcel is introducing several new products, including a new high-modulus carbon fiber and two new carbon fiber prepregs. Also on display will be a 400-mm thick carbon fiber laminate.

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Hexcel (Stamford, Conn.) is adding to its range of IM and AS carbon fibers with the launch of a new high-modulus carbon fiber, called HexTow HM63. It is said to have the highest tensile strength of any HM fiber and provides good translation of fiber properties in a composite, including superior interlaminar shear and compression shear strength. It is reportedly suitable for any high-stiffness, high-strength applications including space, satellites, UAV, commercial aerospace and helicopters. It also meets the requirements for premium sports and recreation applications including F1, marine craft, bikes and fishing rods. At JEC Europe, Hexcel will display a thermoset carbon fiber cable for yacht rigging manufactured by Future Fibres using  HexTow HM63.

Also new is HexPly M92, a prepreg that is said to combine all the major benefits achieved individually with other 125°C/257°F-cure epoxy resins in one new “multi-purpose” system. Benefits include hot/wet Tg performance of 115°C/240°F, allowing HexPly M92 to operate at higher service temperatures from a lower-cost 125°C cure. The system is self-adhesive to honeycomb, making it suitable for sandwich structures as well as monolithic components.  Other benefits include high toughness, fire resistance, low exotherm, long out/tack life and the ability to cure by vacuum bag. HexPly M92 is available in a range of prepreg forms (woven and unidirectional tape). At the show, Hexcel will display a helicopter rotor hub cap fairing manufactured by Airbus Helicopters. This oven-cured part is a honeycomb sandwich structure in which the prepreg is bonded directly to the non-metallic core, without additional adhesive. Airbus Helicopters estimates weight savings of 8 to 15 percent with use of HexPly M92, depending on the helicopter type.

To further extend the use of thermoset resins in mass-produced composite parts, Hexcel has developed HexPly M77, a rapid-curie epoxy prepreg that allows automotive components and sports goods to be press-cured in a two-minute cycle at 150°C/302°F at 80 bar pressure. The low tack of HexPly M77 enables the prepreg to be cut by laser cutter; the individual plies can then be oriented, assembled and consolidated into a flat preform by robot. Once in the mold, HexPly M77 has an optimized gel time that allows the resin to flow into the contours to produce the precise geometries required. A high Tg of 125°C means cured parts can be demolded while hot for a faster production cycle. This rapid-cure product, with a six-week outlife at room temperature, is available in various forms including unidirectional or woven reinforcements and heavy tow fibers.  It is also supplied as HexMC, Hexcel’s high-performance carbon fiber/epoxy compound developed for compression molding processes.  HexMC is ideal for the series production of complex parts with thickness variation, sharp angles or parts that require inserts to be integrated into the molding process such as screw threads.  

HexPly M79 was developed to meet industry requirements for a faster and lower temperature curing prepreg for thick laminates. It evolved from HexPly M10, Hexcel’s established prepreg resin for marine structures and wind blades. A number of cure cycle options are possible for HexPly M79, including a very low temperature cure of 8 to 10 hours at 70°C/158°F, or a more rapid cure cycle of just 4 to 6 hours at 80°C/176°F. HexPly M79 also has an out life at room temperature of at least 6 weeks.

Also on Hexcel’s stand at JEC Europe, visitors can see what Hexcel says is the thickest carbon prepreg laminate ever made. The layup of 695 plies of HexPly M79 600-gsm carbon UD tape, with Hexcel’s grid technology, is 400 mm/15.7 inches thick. It was cured in 6 hours at 80°C. 

Hexcel debuted its HiTape advanced dry carbon fiber reinforcements at JEC Europe 2013; the material returns in 2014 after further development. HiTape allows preforms to be manufactured in a fully automated layup process, with high deposition rates. Parts produced with HiTape and Hexcel’s HexFlow infusion resins can be up to 30 mm/1.2 inches thick with a 58 to 60 percent fiber volume content, resulting in mechanical properties that are as high as those achieved with primary structure prepregs. To demonstrate the potential of HiTape, Hexcel has worked with Aerolia SAS and Coriolis Composites to design and manufacture an aircraft fuselage panel demonstrator that will be on display at JEC Europe 2014. The fuselage panel is a self-stiffened skin that was designed by Aerolia to meet the mechanical performance requirements for primary structures. Coriolis Composites developed the dry automated fiber placement (AFP) process for the full-scale fuselage skin demonstrator; the dry preforms were made at Compositadour’s facilities. The HiTape preform skin and stiffeners were infused with HexFlow RTM6 resin at Hexcel’s new Applications Laboratory in Les Avenieres, France, using a co-infusion process that was developed in-house. Hexcel says the resulting fuselage panel demonstrates that parts made with HiTape and HexFlow RTM6 meet the high mechanical performance requirements for primary structures, including toughness. 

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