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.