HexTow IM7 continuous carbon fibre

HexTow IM7 is a continuous carbon fibre from Hexcel, supplied as an intermediate-modulus, PAN-based reinforcement fibre in 12,000-filament (12K) tows. It is a raw material for composite structures: the fibre is converted by weaving, prepregging, filament winding, braiding or pultrusion into laminates for load-bearing aerospace parts.

Hexcel describes IM7 as combining higher tensile strength and modulus with good shear strength, which lets structural designers reach larger safety margins in applications that are limited by either stiffness or strength. For UAV and eVTOL work, that means wing spars, fuselage shells, booms, rotor arms, landing gear and motor mounts where mass matters. The surface of the fibre is treated, and a sizing can be applied to raise interlaminar shear properties, handling and structural performance.

The typical fibre properties are a tensile strength of 5670 MPa, a tensile modulus of 276 GPa, an ultimate elongation at failure of 1.8% and a density of 1.78 g/cm³. A 12K tow weighs 0.446 g/m, has a cross-sectional area of 0.25 mm² and a yield of 2.24 m/g. The filament diameter is 5.2 microns, carbon content is 95.0% and the tow is never twisted. Thermal and electrical data for the yarn include a specific heat of 0.21 cal/g-°C, a thermal conductivity of 5.40 W/m-K, an electrical resistivity of 1.5 x 10-3 ohm-cm and a coefficient of thermal expansion of -0.64 ppm/°C. These are fibre values; the laminate result depends on resin, fibre volume and process.

As a reference for a laminate, the data sheet gives typical results with HexPly 8552 epoxy matrix at room temperature and 60% fibre volume: 0 degree tensile strength 2,723 MPa and modulus 164 GPa (ASTM D3039), flexural strength 1,862 MPa and modulus 152 GPa (ASTM D790), short beam shear strength 128 MPa (ASTM D2344), compressive strength 1,689 MPa, open hole tensile strength 428 MPa (ASTM D5766) and open hole compressive strength 337 MPa (ASTM D6484).

Processing depends on the sizing. Three options are listed: GP, compatible with epoxy, phenolic, vinyl ester, polyurethane, cyanate ester and BMI resins and recommended for weaving, filament winding and prepreg tape; G, for epoxy, phenolic and polyurethane resins and recommended for weaving and prepreg tape; and an unsized fibre that suits all resins for prepreg tape. Standard 12K packages are 3.6 kg (8,130 m) on a tube of 3 inch internal diameter, with a lighter 1.8 kg package also listed.

For qualification, IM7-G 12K with 0.25% sizing is qualified to the NMS 818 carbon fibre specification (NCAMP), so buyers can specify a standard aerospace-grade fibre without writing their own specification. Hexcel produces the fibre to its aerospace grade specification HS-CP-5000, and a Certification of Analysis is provided with each shipment.