Parameter estimation for head impacts and brain injury in crash reconstruction

Abstract

Abstract An alternative to detailed and complex mathematical reconstruction of head impacts is to use a well-justified simple estimation method with known error potentials. The Pedestrian Head Injury Calculation (PHIC II) model was derived from a simple method developed at the NHMRC Road Accident Research Unit of the University of Adelaide. This model utilises basic data from each crash investigation, the autopsy and carefully chosen and tested parameter relationships. The PHIC II model was used to establish peak angular acceleration and maximum angular velocity change parameters for head impacts at differing impact velocities, head-vehicle impact stiffnesses, and impact offsets. The potential brain injury severity of these impacts was evaluated from a brain shear strain model. It was found that for impacts with a head-vehicle stiffness greater than about 130 kN/m the only effective way to reduce brain injury severity is to reduce the head impact velocity while for impacts with a stiffness less than 130 kN/m both stiffness and head impact velocity will have an effect on the severity of the brain injury. At stiffnesses around 130 kN/m there appears to be a change in injury mechanism related to the natural frequency of the brain skull system. Both the PHIC II and the shear strain models correctly predict brain injury in actual pedestrian head impacts. The results of this study suggest that the PHIC II model works well as a simple field analysis method.