Cranfield, 2024

As part of the Composites Module of the Master Course "Advanced Motorsport Engineering," a carbon fibre wing with specific set of plies and materials had to be manufactured and tested with a standarised 3-point bending test to determine if it complies with the mechanical requirements to be utilised as a vehicle wing for downforce. Prior to the experimental testing, utilising compliance matrices equation and others, we had to make an accurate of the maximum load it could take before the wing had a severe deflection.

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Each team (composed of 6 engineers) had to make an carbon fibre wing composed of different types of skin and core. In this case, the composition of the airfoil was as shown below:

Woven skins with an UD ply, single flax C spar.

Skin: 4 plies MTC510, 42%, 3K HS Twill, 245 gsm, 1250 mm wide woven carbon fibre prepreg, 0.23 mm per ply all 0/90 = 0.96 mm thick, plus the UD ply of MTC510 HS 300gsm = 0.3 mm ply, making a total thickness of 1.25 mm.

Spar: C section flax fibre FF-PP-UD-110-40-90 FLAXPREG, spar web at the deepest section, flange facing the trailing edge, 6 layers = 1.2 mm, flange width = 30 mm.

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Utilising the rule of mixtures, laminate theory, plate constitutive equations, and other equations/theories, it was determined that the maximum deflection of the airfoil would be of 5.3 mm when applying a load of 2,500 N in a 3-point bending test, whilst, utilising computer-aided FEA analysis, it was determined for the maximum deflection to be 6.6 mm.

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With a configuration of a deflection rate of 5mm/minute, 5% accuracy of the LVDT sensor (top and bottom), and accounting that data recording was made in percentages (100% being equivalent to 15 mm of deflection), the 3-point bending test yielded a 9.5 mm at given load, which is 58% more than predicted and accepted. 

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Given variability from the theoretical and practical approach was believed to come from the following reasons:

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Natural fibres are inefficient for load application due to fibre discontinuity and inhomogeneous characteristics.

The direction of the natural fibres of the spar were not the adequate for the application of the load (perpendicular to each other).

Variability and mistakes made during the manufacturing process of the wing that could've allowed for delamination or "voided" segments.

Not enough layers.

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Some suggestions were made to further improve this, both in testing as in the mathematical approach, for further iterations.​

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Please find attached below the relevant documents to this project.