Design, Optimization and Characterization of Hybrids of Boron Fiber and HM63 Carbon Fiber for Department of Defense Applications

Carbon fiber composites are strong in tension and significantly weaker in compression.  This effect is exacerbated as the modulus of the carbon fiber increases.  Boron fiber hybridized with carbon fiber mitigates this effect and creates a composite with a balanced set of mechanical properties. Specialty Materials has demonstrated for standard and intermediate modulus fibers. Only two high-modulus fibers are manufactured in the United States.  One is a carbon fiber called HM63 that has a modulus of 63 Msi and is manufactured by Hexcel in Salt Lake City.  The second is a boron fiber with a modulus of 62 Msi that is manufactured by a woman-owned small business in Lowell MA called Specialty Materials.  The unidirectional compression strength of polymer matrix composites (PMC) made with HM63 are in the 130 to 160 Ksi range significantly lower than PMCs made with intermediate modulus fibers.  For example, T1100 in TC350 provides a unidirectional compression strength of 273 Ksi.  Hybridizing T1100 with Specialty Materials 0.004-inch diameter leads to compression strengths of 465 Ksi which is a 41% increase in compression strength and it also results in a 50% increase in elastic modulus.  We believe that combining the boron fiber will HM63 will provide similar increases in compression strengths. The significant increase in both strength and stiffness allows more weight and volumetric efficiency since most composite structures get sized based on their compression properties in most applications.  The hybrids of boron and carbon fibers are commercially called Hy-Bor® which have been used on Department of Defense applications like General Atomics Gray Eagle and the Reaper variants of the Predator unmanned aerial vehicle.  Hy-Bor® won its way into the Predator Platform because of the higher compression strengths of the Hy-Bor® which consists of Mitsubishi’s MR40 fiber in NCT-301 Toughened Epoxy with Specialty Materials 0.004-inch diameter Boron fiber.  This combination allowed General Atomics to stiffen and strengthen the spar caps of the Predator allowing them to carry AGM-114 Hellfire missiles with minimal change in the aerodynamic characteristic of the aircraft.