Abstract
Keywords: Finite Element Head model, Injury criteria, Impact Biomechanics
The headand more specifically the brain is among the most vital organs of the human body. From a mechanical point of view, the biological evolution of the head has lead to a number of integrated protection devices. The scalp and the skull but also to a certain extent the pressurized sub arachnoidal space and the dura matter are natural protections for the brain. However, these are not adapted to the dynamical loading conditions involved in modern accidents such as road and sport accidents. The consequences of these extreme loadings are often moderate to severe injuries. Preventing these head injuries is therefore a high priority.
Over the past forty years, a slant has been put by the biomechanical research on the understanding of the head injury mechanisms. One of the main difficulties of this research field is that a functional deficiency is not necessarily directly linked to a damaged tissue. Nevertheless, an injury is always a consequence of an exceeded tissue tolerance to a specific loading. Even if local tissue tolerance has very early been investigated, the global acceleration of the impacted head and the impact duration are usually being used as impact severity descriptors. The Wayne State University Tolerance Curve has therefore been proposed since the early Sixties thanks to several works by Lissner et al. (1960) and Gurdjian et al. (1958, 1961). This curve shows the link between the impact of the head described by the head acceleration and the impact duration and, on the other hand the head injury risk. Hence, after the work of Gadd (1966), the National Highway Traffic Safety Administration (NHTSA) proposed the Head Injury Criterion (HIC) in 1972. This is the tool used nowadays in safety standards for the head protection systems using headforms. Since it is based solely on the global linear resultant acceleration of a one mass head model, some limitations of this empiric criterion are well-known, such as the fact that it is not specific to direction of impact and that it neglects the angular accelerations. This is why Newman proposed the GAMBIT (Newman et al. 1986) and more recently the Head Impact Power (HIP) in the end of the nineties (Newman et al. 2000). A methodology was described to assess brain injuries, based on multiple accident reconstructions of American football players' head collisions during recorded games.