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Design of a lightweight chassis for a small formula style race car

Author
A.P. de Boer

Date
Delft, March 2002

Summary
Formula Student is an international competition in which students are challenged to design, fabricate and compete with small formula style race cars. In July 2001 Delft University of Technology participated in this competition as a first Dutch entry.
This report describes the design and building process of the chassis of the first Formula Student race car from Delft University of Technology. One of the production techniques for products, made form fibre reinforced plastics, is Vacuum Assisted Resin Transfer moulding (VARTM). In general this technique can be used to fabricate high quality, lightweight products at relative low cost. The main goal of this thesis is to evaluate the VARTM method as a production technique to fabricate the chassis for a small formula style car. This is done by designing and building the car from scratch. First the requirements and boundary conditions are analysed. Next the concept of the car is designed where general design, materials and production techniques are considered at the same time. Then the design is further worked out in the preliminary and detailed design phase. Finally the chassis is fabricated.

The chassis must meet the requirements, which are given by the Formula Student Organisation. The car must also have good performance. Therefore the chassis must have sufficient torsional rigidity (4000Nm/deg) and I must have low weight and low centre of gravity.

The chassis consists of two parts. The front of the chassis is a carbon fibre reinforced epoxy monocoque. The rear of the chassis consists of a space truss combined with an aluminum box. These two parts have a strong interaction. According to the 'three boxes concept', the chassis is an effective rigid structure when the shear panels of the open section of the monocoque are inhibited from warping. Therefore a closed box structure (or equivalent) must be present in front and aft of the open section of the monocoque. The closed part of the monocoque and rear section has sufficient rigidity to inhibit the shear panels of the monocoque from warping. The chassis as a whole is an efficient torsional rigid structure.

The monocoque is made from carbon fibre reinforced epoxy, and fabricated with the VARTM techniques. The monocoque is a stiffened shell structure with additional frames for attachment of the suspension and for safety regulations. The lay-up of the monocoque is initially based on an approximation of the rigidity. It is verified by finite element analysis in a later stage. Also strength considerations, which is influenced by the use of a sandwich structure, are taken into account. The closed section of the monocoque is a single skin structure while the shear panels of the open part of the monocoque are sandwich structures with integrated beams. The bottom of the monocoque is also a sandwich structure.

The space truss is mounted to the monocoque and holds the semi-stressed engine. The truss is built up from tetraeders in order to let it be a true, rigid truss (not a frame). The aluminium box holds the differential and the suspension are mounted to it.

The chassis has a total weight of 32 kg (monocoque 12 kg; frames inside monocoque 3kg; aluminium box 4 kg). The chassis has a torsional rigidity of 4800Nm/deg.

The monocoque is fabricated with VARTM. No significant problems have occurred during the fabrication of the monocoque itself. Though, inserting other components did lead to some problems.

It is concluded that the VARTM method is suitable to fabricate a high quality, lightweight monocoque. More conclusions are given concerning the required torsional rigidity and the design aspects for the chassis to get an efficient rigid chassis.

Finally some recommendations for future formula student projects are given. Recommendations are given concerning an evaluation of the design of the current chassis. Recommendations are given to take close attention to certain aspects of the design, in case the concept of this chassis is used. Finally some recommendations are given concerning the fabrication of future formula student race cars with use of the VARTM method.

 

Naam auteur: bhese
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