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High modulus carbon fibre and advanced pre-pregs

Hexcel Composites : 27 March, 2014  (New Product)
In addition to launching a new carbon fibre and aerospace pre-preg, Hexcel at JEC 2014 promoted some recent applications in aerospace and industrial markets.
High modulus carbon fibre

Hexcel is launching a new high modulus carbon fibre, called HexTow HM63. This has the highest tensile strength of any HM fibre and provides excellent interlaminar shear and compression shear strength. It is therefore ideal for high stiffness and strength-critical 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.
On display was a thermoset carbon (TSC) cable for yacht rigging manufactured by Future Fibres, using HexTow HM63 high modulus carbon fibre for low weight, high break strength and resistance to impact.
Pre-preg for aerospace structures
HexPly M92 is a pre-preg, available in a wide range of pre-preg forms (woven and UD tape), that combines the major benefits achieved individually with other 125C curing epoxy resins in one new “multi-purpose” system. These benefits include excellent hot wet Tg performance of 115C, allowing the material to operate at higher service temperatures from a lower cost 125C 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, a long out/tack life and the ability to cure by vacuum bag. 
On display was a helicopter rotor hub cap fairing manufactured by Airbus Helicopters. This oven-cured part is a honeycomb sandwich structure in which the pre-preg is bonded directly to the non-metallic core, without any additional adhesive. Airbus Helicopters estimates that weight savings of 8 to 15% will be achieved by manufacturing this part from HexPly M92, depending on the helicopter type.
“Snap Cure” pre-preg
To further extend the use of thermoset resins in mass produced composite parts Hexcel has developed HexPly M77, a rapid-curing epoxy pre-preg that allows automotive components and sports goods to be press-cured in a two-minute cycle at 150C  and 80 bar pressure.
The low tack of HexPly M77 enables the pre-preg to be laser cut into precise shapes. The individual plies can then be oriented, assembled and consolidated into a flat preform by robot. Once in the mould, HexPly M77 has an optimised gel time that allows the resin to flow into the contours to produce the precise geometries required. The high Tg of 125C enables the cured parts can be demoulded while hot for a faster production cycle.
This rapid-curing product, with a six-week outlife at room temperature, is available in various forms, including unidirectional or woven reinforcements and heavy tow fibres. It is also supplied as HexMC, a high performance carbon fibre/epoxy compound developed specifically for compression moulding processes. HexMC is ideal for series production
of complex shaped parts with thickness variation, sharp angles - or parts that require inserts such as screw threads to be integrated into the moulding process.
Low temperature cure pre-preg for wind blades and marine
HexPly M79 was developed to meet industry requirements for a faster and lower temperature curing pre-preg for thick laminates. It has evolved from HexPly M10, the long-established and widely used pre-preg 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 8-10 hours at 70C, or a more rapid cure cycle of just 4-6 hours at 80C. With previous systems, it could take 10 hours to cure a laminate at 80C. HexPly M79 also has a very long out life at room temperature of at least six weeks.
When HexPly M79 carbon fibre UD pre-preg is used in conjunction with Hexcel’s patented grid technology, a void content in the cured laminate of less than 1% is achievable, regardless of the part thickness.
At JEC visitors saw what is claimed to be the thickest carbon pre-preg laminate ever made. The lay-up of 695 plies of HexPly M79 600gsm carbon UD tape with Hexcel’s grid technology is 400mm thick – and it cured in just six hours at 80C. The very low exotherm of HexPly M79 allowed the temperature to be increased more quickly in the mould, resulting in a shorter cure cycle.
Aircraft fuselage panel demonstrator
HiTape advanced dry carbon fibre reinforcements combine automated processing with out-of-autoclave infusion. HiTape allows preforms to be manufactured in a fully automated lay-up process, with high deposition rates. Parts produced with HiTape and Hexcel’s HexFlow infusion resins can be up to 30mm thick with a 58 to 60% fibre volume content, resulting in mechanical properties that are as high as those achieved with primary structure pre-pregs.
For aircraft primary structures, Hexcel has worked with Aerolia SAS and Coriolis Composites to design and manufacture an aircraft fuselage panel demonstrator. The fuselage panel is a self-stiffened skin that was designed by Aerolia to meet the mechanical performance requirements. Coriolis Composites developed the dry automated fibre placement process for the full scale fuselage skin demonstrator - and 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, close to Lyon, using a co-infusion process that was developed in-house.
The resulting fuselage panel demonstrates that parts made with HiTape and HexFlow RTM6 meet the high mechanical performance requirements for primary structures, including toughness. HiTape is cost-effective and highly automated to enable aircraft designers to meet future cost and build rate targets, while retaining the weight-saving benefits that are achieved with pre-pregs.
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