Building a Formula 1 race car requires accurate analysis of structural features and constraints.
The monocoque chassis of a Formula 1 race car is a sandwich structure, made of high-performance carbon-epoxy composite face sheets and an aluminum or aramidic honeycomb core. High-modulus and high-strength composites, with aerospace-class toughened epoxy resins, are used in order to obtain the maximum safety performance/weight ratio. All attachment points for the engine, suspensions, rollhoop, etc., are made through inserts embedded in the lamination stack during the production phase. In order to minimize weight and thermal expansion differential, and maximize the adhesion, the inserts are made as thick (about 18-mm) laminated composite plates to be machined to the required dimensions and thickness.
At the first stage of the design, where the global shape of the chassis has to be defined, the main things to take into account are:
- desired wheelbase
- engine interface (width, height, fittings)
- desired fuel capacity (the fuel is between the pilot back and the engine interface wall)
- aerodynamics design, especially for the front nose position
- suspension system layout
- driver measurements
Under all of the above constraints, the general criterion used for determining the shape of the chassis is that it should have the smoothest and flattest shape possible. This has advantages, considering the peculiarities of the prepreg composites technology. The fiber orientation actually obtained in the hand layup process can be very similar to what has been designed, if the mold surface is regular. In addition, the ply overlapping and cuts that have to be made in the production phase are at a minimum, and the fibers must work in tension/compression conditions and are not bent.
The safety regulation requirements are the main driver of the chassis design, both from the global layup and from the local reinforcement standpoints. There are a number of impact tests to pass. The main tests are:
- Side crash. This is the most restrictive. A 780-kg trolley impacts the side of the chassis at a speed of 10 m/s. The impact is first taken by lateral crash appendices (crash cones). Requirements are maximum deceleration of less than 20 g, maximum force on a cone of less than 80 kN, each cone must take from 15% to 35% of the total energy, and no damage can be found on the chassis.
- Crash cone push-off. These are flexural tests on the cones to verify the robustness of their attachments to the chassis.
- Front crash. This test mainly determines the nose design. The chassis is not highly stressed.
- Penetration test. A square, flat plate with the same layup of the chassis in the side area is quasi-statically (2 mm/s) penetrated with an aluminum conical impactor until a penetration of 150 mm is measured. Requirements are absorbed energy greater than 6000 J and reaction load greater than 250 kN.
- Main roll-bar crush. The roll-bar is statically pushed with a force of about 120 kN via an inclined plate, impacting the main roll-bar top. Requirements are deformation of less than 50 mm, and the damaged area must be within 100 mm from the load application plate.
- Front roll-bar crush. The front roll-bar is a reinforcing structure located just behind the steering wheel. A similar test as above is made, with a 75 kN vertical force.
- Lateral local crushes. Several specific locations of the chassis side have to be loaded with forces varying from 12.5 kN to 30 kN. Maximum displacement and no damage requirements are prescribed.