World’s first carbon roll cage for production cars

Dr. Ing. h.c. F. Porsche AG (Germany)

Partners(s): Action Composites GmbH, Austria - Kube GmbH Ingenieurbüro, Germany - Lab for Lightweight Design, IKTD, University of Stuttgart, Germany

Extreme lightweight carbon roll cage, to be road legally fitted into a production car, enabled by engineering a unique geometry.

The initial metal design withstands extreme elongations. Thus the use of carbon fibres, presented a major challenge for this application due to the low elongations at break. First FE calculations showed that the shape had to be adapted significantly to bear the loads. The performed structural optimization led to the innovative shape of the cage requiring also an innovative production process. The Engineering innovation of the project is a new 3 step structural optimization process providing a specific design suitable for CFRP under full consideration of an extremely limited design space as well as multiple crash and FIA load cases:

1. topology optimization regarding minimized local deflection & weight
2. FE-analysis on surrogate framework models using explicit solvers to identify an initial layup and local reinforcements
3. geometry optimization to convert the framework model into a bionic design suitable for composite materials under styling aspects

Based on the topology optimization, a weight-optimised plybook was developed and crosschecked by production. This went back into the simulation model by using a tailored transfer process, which runs automatically. This automated data transfer enabled the team to conduct a magnitude of iteration steps (i.e. layup) in an extremely short timeline, requiring very little effort. The effectiveness of this procedure allowed an extensive variation of design parameters which lead to a thorough understanding of the part and by this to cut the weight to an absolute minimum.

A remarkable result of this approach is the predominant use of unidirectional fibres (>90%) The manufacturing process is prepreg pressing in a closed hot mold assisted by a complex lost core technology. This approach yields the highest quality standards in a completely integrated part including node elements. It is manufactured in one single shot. The visible carbon surface is obtained by pre-consolidating the prefabricated surface shell with the structure responsible general design and project management, OEM.

Key benefits

• High weight reduction compared to steel and even titanium
• Topology optimized, unique bionic design
• Innovative calculation approach – automated link between CAD an FE
• Innovative manufacturing process – structural hollow part in serial production
• Fulfills FIA load collective