Head impact mechanics and injury

In order to assess helmet design requirements, the armour designer must have a thorough and comprehensive understanding of head impact biomechanics. In the past, few were concerned about the biomechanics of helmeted head impact (Shuaeib et al, 2002). Therefore, the various biomechanical aspects of head injury will be reviewed in this section, with an emphasis on the head impact situations encountered, from typical motorcycle accidents to high-velocity impacts where helmets are generally used. 

Head combat injury may be broadly defined as temporary or permanent damage to one or more of the head componerrts from a blow to the head such as might be encoimtered in a battlefield. In general terms, head injrrries can be grouped into 

1 Mid-sagittal cross-sectional view of human head and neck (Voo eta ., 1994). 

Voo et al. (1994) classify head injuries as follows (i) skull fracture, (ii) focal brain injuries, and (iii) diffuse brain injuries. Scalp damage does not have the same importance as brain injury or skull fracture. The seriousness of neck injuiy is also low compared with brain injury or skull fracture (Hume et al., 1995). Compared with skull fracture, brain injury is far more serious, and needs to be given particular importance when considering the protective effect of the helmet under direct impact (Moss et al., 2009). It should be noted that this classification is intended pmely to specify the type of damage and not its occurrence, as in the majority of accidents these injuries overlap to some extent. In this chapter, skull fractures are briefly mentioned before brain injury is reviewed in more detail. 

Skull fracture is not a major criterion for helmeted-head impact due to the fact that brain damage by acceleration will occur well before the impact load causes a depressed skull fracture. However, during a projectile impact (on a battlefield, for example) a skull fracture may occur due to penetration of the skull by a sharp object, such as shrapnel, fragments or bullets. Depending on the extent of helmet coverage and the shell thickness, the outer shell of the helmet should prevent such penetration. Furthermore, some minor fiuctures to the skull do not cause fatal injury (Bullock and Graham, 1997). However, it seems that there is a need to 

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