CompositesWorld
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CompositesWorld.com 47 Illustration / Karl Reque Bloodhound SSC Carbon Fiber Composite Air Brakes for Bloodhound SSC Supersonic Racecar › FEA modeling of aluminum vs. composite air brake panels showed that composites ofered better frequency response, and thus, less vibration when deployed. › FEA and computation fuid dynamics (CFD) models showed bias plies (±45°) would reduce bending and defection in the composite air brakes. › The composite sandwich-construction air brake "door" panel is one quarter the weight of an aluminum version, yet ofers comparable braking power. fapping. Given these parameters, a modeling and design efort was carried out to determine the best material choice. A fnite element analysis (FEA) model of the air brake door was constructed — using HyperMesh and HyperWorks from Altair Engineering Inc. (Troy, MI, US) — by using the mid-plane surface from the air brake door CAD model and creating a 2D element mesh on that surface, explains Edwards. "Mid-plane models were also created in a similar way for each of the four hinge attachments in order to accurately represent the stifness of the entire assembly during modal analysis." Next, aerodynamic loading on the doors was derived from the results of computational fuid dynamics (CFD) analysis, using Flu- ent, a sofware package that is part of the ANSYS numerical simula- tion package from CAE Associates Inc. (Middlebury, CT, US). (CFD with Fluent also played a big role in other aspects of the vehicle, and infuenced the design of the front wheels, the shape of the nose, the jet engine intake, rear wheel fairings and the wing.) For the airbrakes, Fluent used fve combinations of door position and velocity, begin- ning with the conservative assumption that the door would deploy at the car's top speed of 450 m/sec, to calculate air-pressure loads to input to the FEA model. Beyond solid aluminum plate, modeled materials were sandwich constructions, with skins made from Cy- tec Aerospace Materials' (Tempe, AZ, US) unidirectional MTM49-3 carbon prepreg tape, featuring high-modulus M46J carbon fbers from Toray Industries (Tokyo, Japan), and a Cytec MTM49-3 woven 2x2 twill prepreg made with Toray T700 fbers. Core material was an aluminum honeycomb from Hexcel (Stamford, CT, US). "For the material analyses, the 0° fber direction was aligned perpendicular to the door hinge line in the plane of the air brake door," says Ed- wards. He used standard bolt group theory to determine the loads at the three metallic hinge positions, and spread the loads from the hinges to the doors with the use of "spider" nodes within the FEA model, so named because of the way the nodes are connected to each other to simulate load transfer. DEFLECTION vs. WEIGHT vs. VIBRATION Atkins compared a number of sandwich panel confgurations, in terms of skin and core thickness, with the solid aluminum (Figs, 1 & 2, p. 48). "Early analysis showed that in the composite designs, the maximum defection was occurring at the corner furthest from the actuator attachment," says Edwards, "We had to increase overall stif- ness, and the potential composite layups were altered to include a greater number of ±45° plies." Tis strategy was confrmed by the modal analyses (a study of how the doors would react under vibra- tional excitation), using the Radioss solver in Altair's HyperWorks ±45° facesheet plies reduce defection Each door is 40 mm thick, 0.6m 2 in area, and weighs only 19 kg (vs. the 70-kg aluminum version) Rear metallic structure supports Eurojet EJ 200 engine and fve Nammo rockets Forward body/ fuselage skin is carbon fber composite construction Air brake "door" is a sandwich construction of aluminum honeycomb core between carbon fber prepreg facesheets Carbon composite air brake deploys at 1,300 kmh to slow the car