CHASSIS
Throughout the years, body shells are replacing space frames in every racing car category.
424 Chassis Bonded Assembly
424 car chassis is made of several components listed below:
Main chassis
Bonded seat bulkhead (acting as firewall to fuel cell or battery aera)
Bonded side impact panel (made of zylon high strength laminate)
Bonded roll hoop beam
Bonded floor (to allow access during manufacturing of main chassis)
Bolted refill / recharge hatch
Bolted front impact structure (nose)
424 chassis parts
424 sub assemblies
424 Sub Assemblies
On a Le Mans car, floor, wings and body panels are also manufactured in composite materials, in addition to the chassis. Here are some of the sub assemblies you can observe on the image:
Floor
Detachable front wing
Detachable rear wing
Side body panels
Engine cover
Body Shells are made of high performance Composite Materials
Composite materials have very interesting strength-to-weight ratios and have replaced other materials such as aluminium for race cars chassis construction. There is a wide variety of resin and fibres combination which enables to find the right material for each application. Here are some general characteristics that must be kept in mind when considering composite materials:
Design as thin shells (either as a surface in CAD or better, as a solid shell with wall thickness).
Laminate is the combination of resin and fibres cured at temperature above 100°C for a few hours inside an autoclave oven (in order to apply pressure on the surface of the mould).
Typical laminate thickness:
For bodywork panels (non-structural) 0.5 to 1.5mm (2 to 6 layers of prepreg)
For structural parts (chassis, crash box) generally 2.5mm can go up to 6mm in places around mountings, suspension inserts.
Too thick can lead to thermal instability during cure (bubbles)
To increase panel thickness, we embed a core between 2 laminate layers. Core can be honeycomb (for large constant thickness panels), Rohacell®(can be machined to shape, for beams or complex shape), wood (for cheap constructions)
Where there will be other parts mounted, we are embedding inserts. Inserts can be made of aluminium, or solid carbon. After the component is cured, it is post machined to add holes, threads, mating faces in the inserts.
Body Shells Manufacturing
Body shells are lighter and stronger but more expensive to manufacture. Body shells require surface tooling (pattern and moulds) whereas space frames only require welding jigs. Tooling is required to build a smooth, accurate surface:
Machine a pattern using resin block (male shape of the component)
Cure multi part mould using thick composite (female shape of the component)
Cure the final component using the mould into the autoclave oven. (The component and the mould are inside a sealed bag with vacuum pressure inside so atmospheric pressure is applied on the surface).
One pattern and one mould is required to build multiple components.
A core embedded in 2 laminate layers
Glickenhaus SCG007 bodywork in composite materials
Internal bonded beams strength test
The Chassis: a key element for dynamic behaviour
The structure of a racing car is made of components assembled in series for strength and low weight:
Front suspension
Chassis
Engine / electrical battery
Gearbox / rear frame
Rear suspension
If one of the element is not stiff enough, the complete car dynamic behaviour will suffer.
The Chassis is a key element for Safety
Structural components are subject to very strict safety tests by the FIA. There is a lot of work required to optimise those structures, keep the weight down, while ensuring those tests are passed at the first attempt for homologation.
Dynamic crash tests are also mandatory to homologate the car. These are still difficult to simulate. We use a simple model to evaluate the behaviour of the structure and we then have 3-4 variations of the structure (different laminate thickness) that we test during the FIA homologation.
Rollover structure test