This paper used measurements of the impulse frequency response of head imp act points on both the exterior and interior of a car. The aim was to calculate both the modal mass and stiffness for each point. These points were arranged in an hierarchy of increasing stiffness, and were grouped into three classes. The thirty-two head impact cases used include: (a) 13 pedestrians; (b) 4 car occupants; and (c) 15 fall victims. The distribution of injury to the brain in these cases had been recorded in detail. The cases were grouped, according to both the stiffness of the object struck, and to the location of the impact on the head. The distribution of the brain injury lesions in the anterior, middle and posterior brain regions were deter mined: (i) for each class of stiffness (soft, medium or hard); and (ii) for each impact location (occipital or lateral). Three probable mechanisms of brain injury were distinguished. These were: (1) relative motion between the brain and the skull; (2) local bone deformation; and (3) intra-cerebral strains. Each mechanism was related to both a range of stiffness, and to the natural frequency of the structure impacted. These theories of brain injury mechanisms are consistent with both the observed epidemiological data, and with the conclusions drawn from mathematical modelling.
Abstract