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Specialty Materials Inc. (SMI, Lowell, Mass., U.S.) is emphasizing its line of boron monofilament and prepreg materials, as well as SCS silicon carbide (SiC) monofilament. Boron monofilament offers extremely high compression strength in excess of 400 KSI. In addition, it provides high composite tensile strength (220 KSI) and high tensile modulus (28 MSI). It also provides a positive coefficient of thermal expansion (CTE) for space applications, does not require coupling agents, and does not cause galvanic corrosion with aluminum.

Benefits to composite parts and structures conveyed by boron include a need for fewer plies (compared to all-carbon fiber) and a correlating reduction in debulk cycles. SMI says that when boron is combined with graphite for space applications, its positive CTE counteracts graphite’s negative CTE, resulting in zero CTE components. In addition, Boeing has issued a Boeing Material Specification for the use of boron epoxy as a repair material for commercial airplanes. Current major SMI customers include Israeli Aircraft Industries for F-15 tail sections, General Atomics for wing spar caps, and L3 Harris Technologies for space applications.

SMI also reports that it has teamed up with Toray Advanced Composites to offer its Gen-2 Hy-Bor materials, which combines boron monofilament with Toray’s T1100G carbon fiber in a variety of resin systems, including epoxy, cyanate ester, BMI and polyimide.

SMI says its SCS SiC fibers have excellent high-temperature mechanical properties for increasing the strength, stiffness and use temperature of titanium matrix composites, as well as providing toughness to ceramic matrix composites. In addition, it has been used commercially to increase the efficiency of the manufacture of solar cells used in photovoltaic modules. As a result, SMI says it is one of the few domestic suppliers of SiC fibers with production capacity. Its premier SiC fiber, SCS Ultra, reportedly has the highest creep rupture strength of any SiC fiber. A newer, smaller diameter version (3 mils) of SCS Ultra has recently been developed and is currently being evaluated by turbine engine manufacturers.