Keywords: helmet, protective function, head injury criterion, drop test, finite element method, LS DYNA.

Injuries to the head are serious with respect to the complicated treatment and often have permanent consequences or result in death. During the impact the bone of the skull can be broken and the brain undergoes strong acceleration which can also cause severe injuries. As a result of these phenomena the protective devices are designed for the protection of the skull as well as for the reduction the brain's acceleration peak. Thus, the most important thing is to prevent serious or fatal injuries using a protective helmet. Nowadays the head injury criterion (HIC) is used as a criterion for assessment of the head injuries during impact events. The area under the acceleration history curve is integrated not in the whole interval of the impact, but in a region that maximizes the value of the integral. The critical value of the HIC is about 1000. Thus, the most important aspect is to prevent serious or fatal injuries using a protective helmet.

In-mould and double-mould technologies are constructive solutions that increase strength and reliability of the bicycle protective helmet. The finite element model of the dummy head with protective bicycle helmet was derived for simulation of a drop test for assessment of the HIC. For creating a specific model of a bicycle protective helmet we used three-dimensional scanning. The effects of the fall of the head with the bicycle protective helmet on a pad were studied by means of the programme ANSYS LS DYNA. The initial conditions were set to correspond to process during actual drop tests.

The results of parametric studies prove the significant influence of hardening of the surface layer of the bicycle protective helmet by means of special techniques "in mould technology and double mould technology" on the course of the acceleration of the mechanical system the "dummy head with helmet". The results of the numerical analysis show the very favourable influence of both of the above mentioned technologies on the decrease in the size of the HIC value. The calculation showed the possibility of a drop test simulation of a dummy head with a protective helmet using ANSYS LS DYNA. The modelling of the drop test serves for computational studies and monitoring of the properties and behaviour of the protective helmets in various situations. The numerical modelling of the behaviour of protective helmets during impact loading will become an important tool for their development and assessment of their protective properties.

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