Exploiting the fracture properties of carbon fibre composites to design lightweight energy absorbing structures

The survivability of a Formula driver in an accident is achieved by a combination of the crash resistance of the car and its ability to absorb energy. This has been achieved by providing a survival cell (the chassis), which is extremely resistant to damage, around which energy absorbing devices are placed at strategic points on the vehicle. Since the late 1980s the controlling body of Formula 1, FIA, has introduced a series of regulations to ensure that the cars conform to stringent safety requirements and build quality. Each vehicle must satisfy a list of requirements, in the form of officially witnessed tests, before it is allowed to race. There are two groups of tests that must be passed. The first is a series of static loads applied to the chassis, which guarantees the strength and integrity of the survival cell. The second series defines the position, and effectiveness of the energy absorbing structures. In order to keep the weight of the car to a minimum, some of the energy absorbing devices are also required to perform a structural function in addition to their ability to absorb energy by controlled disintegration. The Rear Impact Structure (RIMP), for example, sits on the differential cover at the rear of the gearbox. The function of this device is to react the downforce generated by the rear wing assembly as well as to provide protection in the event of a crash. Engineering structures are generally designed such that they do not fail. Producing a component, which is specifically intended to fail in a catastrophic, but controlled manner, presents a unique set of problems to the designer. When the same piece is also required to perform as a load-bearing member, the engineering problems are far more acute. The design process from materials selection to a finished component is discussed for an F1 RIMP. Particular reference is made to the design and analysis process and how it deals with the conflicting aspects of controlled fracture and load bearing durability. The analysis and testing process required to prove the piece fit for purpose and homologated for competition are also covered.