Keywords: helmet, cranium, FE model, head injury, skull, brain, acceleration at the impact, contact forces, drop test.

Many thousands people die every year because of traffic accidents. One of the most frequent causes of death is the injury of the human head. During the impact the bone of the human skull can be broken and the brain undergoes strong acceleration, which can cause severe injuries too. Due to these phenomena the protective devices are designed for the protection of the skull as well as for the reduction the brain's acceleration peak. Every helmet entering a market has to be proved using a drop test. The standardized model of the human head [1] for experiments with the helmet is dropped from the prescribed height by the free-fall on the drop board and the impact is measured by means of the acceleration in the gravity centre of the model.

This paper is concerned with the modelling of the drop of the head with the bike protective helmet using the programme ANSYS LS-DYNA [2]. The goal of the numerical modelling is to obtain acceleration data of the centre of gravity of the head during fall on the drop board and to obtain information concerning the magnitudes of contact forces. The whole preparation of the model geometry was made using the NURBs modelling software. The geometry was set to be similar to the cycling helmet, which was used in the drop experiments. The ASSC model (automatic single surface contact) was used for modelling contact.

The following research concerned the analysis of the behaviour of the human skull with the cycling helmet during drop. The reconstruction of the finite element (FE) model of human skull [3] was based on data obtained from computer tomography (CT). The FE model of the human skull including brain was investigated together with the FE model of the helmet.

Numeric analyses were made for (i) the fall of the human skull on the drop board, (ii) the fall of the skull with the protective cycling helmet on the drop board. Numerical analysis was also carried out for the acceleration of the centre of gravity of the head, stress state of the skull without and with the helmet and the influence of the protective helmet on contact forces [4]. The results showed significant deformation of the brain of the skull without the helmet during impact. The acceleration in the centre of gravity of the head was compared for fall of the skull without the helmet and for the FE model with the cycling helmet. After the numerical results had been gathered, the selected numerical data were compared with the experimental results from the drop tests [5].

1

Standard CSN EN Change A1 83 2140, "Full-scale model of head for measuring safety helmets".

2

LS-DYNA, Livermore Software Technology Inc., URL

3

O. Jiroušek, J. Jírová, J. Jíra and J. Máca, "Finite Element Models of Human Musculosceletal System Constructed from CT Data", in "Proceedings of 7th Internternational Conference on Computational Structures Technology", Lisbon - Portugal, Civil-Comp-Press UK, 2004. doi:10.4203/ccp.79.102

4

V. Krumphanzl, M. Micka, "Numerical modelling of interaction between maquette of skull and protective helmet", in "Proceedings of Conference Engineering Mechanics 2005", Svratka, Czech Republic, 2005.

5

J. Kunecký, O. Jiroušek, J. Jírová, "Drop tests used for validation of FE models of human head for HIC assessment", in "Proceedinges of Conference Engineering Mechanics 2006", Svratka, Czech Republic, 2006.

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