We replaced the high-strength steel tube frame with a carbon fiber monocoque. The same technology is used to construct F1 carriages. Students from CTU CarTech are the first in the Czech Republic to produce a composite monocoque for use on a racing car. Our first frame on FS.01 weighed 57.8 kg, today we value 26 kg (monokok + tube frame).
The basis of high strength and low weight structure is the so-called sandwich construction. Sandwich because there is a lightweight core between two rigid covers to transmit shear loads. The thickness of the core and its material is selected according to the desired properties of a particular part of the monocoque. In the side impact zone, the aluminum honeycomb is used, in less stressed areas, the core is very light foam.
Monocoque production alone required hundreds hours of work. To achieve high strength, the monocoque was literally to be baked in the autoclave (pressurized furnace). The LA Composite, a producer of composite parts for transport aircraft, helicopters and Prague metro wagons, has a sufficiently large autoclave. To ensure consistent thermal expansion and stability at high temperature and high pressure, the molds themselves had to be made of carbon fiber. At the very beginning of the production of carbon molds, the molds were once again made of a special epoxy. Precision machining of these epoxy molds has been provided by MBtech Bohemia, who has extensive experience in producing such molds.
Following a several-month marathon laying of individual layers of carbon fiber, inserts, and cores, this was always interlaced with many hourly autoclave curing. Precise laying of individual layers is key to the mechanical properties of the resulting product, so laser projector is used when applying layers.
The monocoque must meet the strict strength criteria given by the Formula Student / SAE rules. At the same time, it serves as the basic carrier of the vehicle, to which the front axle suspension, the steering, the front wing and the rear of the car with the drivetrain and the rear axle are attached. Fulfillment of the safety criteria is demonstrated by the results of stress tests of prescribed samples long before racing.