Progressive crushing of fiber-reinforced composite structural components of a Formula One racing car

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Abstract

The present paper describes an experimental and numerical investigation on energy absorbers for Formula One side impact and steering column impact. The crash tests are performed measuring the load-shortening diagram and the energy absorbed by the structure. A finite element model is then developed using the non-linear, explicit dynamic code LS-DYNA. To set up the numerical model, tubes crushing testing are conducted to determine the material failure modes and to characterise them with LS-DYNA. The results presented in this study show that the composite structural components of the investigated Formula One racing car possess high value of specific absorbed energy and crash load efficiency around 1.1. The finite element simulations accurately predict the overall shape, magnitude and pulse duration in all the types of impact as well as the deformation and failure of the structures. Comparing the numerical data of the specific absorbed energy to the experimental results, the differences are around 10%.

Introduction

The Federation Internationale De L'Automobile (FIA) has started in 1963 to ask safety requirements that have brought nowadays to a variety of safety systems used in Formula One [1]. They include arrester beds, safety barriers, reinforced survival cells, collapsible steering columns, safety belts, helmets and headrests and provide an excellent level of pilot protection during the vast majority of accidents so that it is increasingly rare for a pilot to suffer an injury during an accident.

Safety requirements are prescribed for the circuit, the car and the pilot equipment. In particular the cars are subjected to a number of tests, both static and dynamic, to ensure that the required level of safety performance is achieved. Each of these tests is performed in a laboratory under controlled conditions and in the presence of a FIA technical delegate. Four types of impact are requested for the survival cell: frontal, rear, side and steering column. All the four types of impact involve composite structures, that absorb a high amount of energy by means of a complex combination of fracture mechanisms including matrix cracking, delamination and fiber breakage.

Nowadays most of the research on the energy absorption of composite materials has been limited to the axial compression of tubolar structures and most of the research done has been experimental [2], [3], [4], [5], [6]. To date, only a few models have been proposed to predict the energy absorption characteristics of tubolar structures [7], [8]. With no doubt, the validation of analytical and numerical tools for accurate simulation of structural response to crash impacts is an important aspect of crashworthiness research. Indeed, crash modelling and simulation may be used during the design phase to study the response of the structures to dynamic crash loads and to predict occupant response to impact with probability of injury.

Some studies can then be found in literature, concerning composite fuselage sections for light aircraft [9] as well as composite helicopter structures [10], [11], [12], [13] or automotive structures [14], [15] but they are still few and do not cover all the composite structure modelling. It is much more difficult to find data regarding impact tests [16] or simulation of Formula One composite survival cells due to the confidentiality of the data.

The present paper describes the results of an experimental investigation and finite element analysis of some composite structures impacts of a Formula One racing car. In particular, energy absorbers for Formula One side impact and steering column impact are investigated. They are collapsible absorbers of crash energy, i.e. structural members that are able to absorb large amounts of impact energy, while collapsing progressively in a controlled manner. To set up the numerical model of the energy absorbers, tubes crushing testing are at first performed and simulated.

Section snippets

Experimental crash tests of the fiber-reinforced composite tubes

The tubes present a height of 300 mm, an internal radius of 35 mm and a thickness of 1.12 mm. All the specimens have a 45° outside chamfer, so that the crushing initiates in the highly stressed region at the tip of the chamfer and then develops into a stable crush zone. Two series of tubes are investigated with different type of lamina: fabric lamina in carbon fibers and unidirectional lamina in carbon fibers. The first series of tubes is made of four fabric lamina oriented [45°/−45°]S, while

Finite element analysis of the fiber-reinforced composite tubes

All the finite element analyses of the investigation reported in this paper are performed using the commercial code LS-DYNA [18], that has been developed especially for impact and non-linear dynamic simulations. It is an explicit finite element code, which uses a Lagrangian formulation. The equations of motion are integrated in time explicitly using central differences. The method requires very small time steps for a stable solution, thus is particularly suitable for impact and crash

Energy absorber for Formula One side impact

A Formula One racing car is designed with four impact structures: front, rear, side and steering column. Regarding the side impact structures, the FIA test procedure [1] prescribes the side test, that must be performed with an impact mass of 780 kg travelling at a velocity of 10 m/s. The resistance of the test structure must be such that during the impact:

  • the average deceleration of the object, measured in the direction of impact, does not exceed 20 g;

  • the force applied to any one of the four

Formula One steering column

In 1997, the FIA introduced the impact test on the steering column. This test is of fundamental importance as the first element that goes in contact with the pilot head in case of a frontal impact is the steering column. If it is not able to absorb correctly the impact, it can cause serious injuries to the pilot.

The FIA test procedure [1] prescribes the steering column test, that must be performed with an impact mass of 8 kg travelling at a velocity of 7 m/s. The impact mass must be

Conclusion

The present paper describes an experimental and numerical investigation of energy absorbers for Formula One side impact and for Formula One steering column impact.

The crash tests are performed measuring the load-shortening diagram and the energy absorbed by the structure. A finite element model is then developed using the non-linear, explicit dynamic code LS-DYNA. To set up the numerical model, tubes crushing testing are conducted to determine the material failure modes and to characterise them

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