CompositesWorld
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103 CompositesWorld.com Spickenheuer's team has since employed a similar five-step design process to redesign and replace two aluminum attach- ments for the rear wing of a racecar, using variable-axial CFRP. e original aluminum part weighed 397g. e main load case was a 750N downforce. Five TFP CFRP wing attachment designs were compared, as was a more conventional quasi-isotropic, multiaxial composite design. In numerical calculations, the best TFP variable-axial design increased mass-specific part stiff- ness compared to the multiaxial CFRP part by 68% and reduced weight by roughly 50%. However, compared to the original metal part, specific stiffness was increased by 236% while mass was cut by almost 75%. e TFP CFRP part was designed as a sandwich structure to improve out-of-plane bending stiffness. is was achieved by stitching one of the two required symmetrical preforms onto a 4-mm thick layer of Lantor Composites' (Veenendaal, e Neth- erlands) Cormat XM, a glass fiber fleece that contains hollow polymer microspheres with a honeycomb pattern imprinted on the surface to promote resin flow. e second preform was stitched onto a 108-g/m² woven glass fabric. Both preforms used the same UHM carbon fiber and polyester stitch yarn featured in the rec16 bow riser. A one-sided mold, adapted for the preforms' nonhomoge- neous thickness distribution, was used to avoid mechanical coupling between in-plane and out-of-plane responses. Because only a few parts were needed, tooling cost was minimized by 3D printing a plastic master from which a silicon rubber lower mold was pulled (Fig. 3, lower left image). e durable, heat-resistant material provided a self-releasing surface; no additional parting agent was required. e attachment preforms were bagged and infused with the same room-temperature epoxy resin used in the bow riser. A 10-hour cure was followed by a 10-hour postcure at 60°C. Finished parts were trimmed, holes were drilled and the parts were attached to the Elbflorace racer SophE, which won its competition in 2016. "We have demonstrated how to combine TFP variable-axial composites with an optimization loop that couples FEA and refinement of the fiber path," says Spickenheuer, "and proven its ability to produce extremely lightweight, high-performance composite structures." Design for TFP Read this article online | short.compositesworld.com/rec16Riser Read more online about TFP | short.compositesworld.com/7QEhsvZ0 CW senior editor Ginger Gardiner has an engineering/ materials background and more than 20 years of experience in the composites industry. ginger@compositesworld.com FIG. 3 TFP at home with disruptive technology A Tajima dual-head TFP machine stitches mirror copies of Preform A for the rec16 recurve bow riser, using carbon fiber and polyester stitch yarn (top photo). Aluminum tooling was used to achieve the bow riser's many openings, out-of-plane 3D shape and integrated metal inserts with a high-quality surface finish (center). Tooling costs for another project — a racecar's CFRP rear wing attachments — were reduced dramatically by 3D printing a plastic master from which a silicon rubber lower mold was created and used to resin infuse the parts (bottom).