Production of a Composite Monocoque Frame for a Formula SAE Racecar 2013-01-1173

A carbon-fiber-reinforced plastic (CFRP) monocoque racecar frame was designed and constructed by students for the 2012 Formula SAE (FSAE) collegiate design series competition. FSAE rules require that the monocoque frame have strength equal to or greater than the traditional steel space frames that they replace. The rules also specify minimum values for perimeter shear strength, main roll hoop attachment strength and driver harness attachment (pullout) strength. Overcoming limitations imposed by locally available finite element analysis tools, a variety of tests were devised to determine required laminate thicknesses and layup orientations. These included perimeter shear tests, pin shear tests, three-point bend tests and tensile tests. Based on the results of these tests, a sandwich construction using composite skins fabricated from carbon/epoxy prepreg and aluminum honeycomb core was selected. Starting from the outside, the sandwich consisted of a single layer of bi-directional woven carbon/epoxy, three unidirectional layers of carbon/epoxy, a single layer of bi-directional woven carbon/epoxy, 16-mm-thick aluminum honeycomb core, a layer of bi-directional woven carbon/epoxy, three unidirectional layers of carbon/epoxy and a final layer of bi-directional woven carbon/epoxy (F/0₃/F/core/F/0₃/F). Additional layers of carbon/epoxy weave were used in side impact regions and for various hard point attachments.

Details of the mold design and manufacture as well as the composite lamination are summarized. The monocoque frame resulted in a 53% reduction in component weight and a 43% increase in torsional rigidity as compared to a steel space frame. The composite monocoque frame also provided a qualitative improvement in vehicle handling and aesthetics and more importantly proof that composite techniques suitable for the motorsports environment are achievable on an undergraduate level.