A high fatality rate of the elderly in traffic crashes is an important issue to consider when facing an aging society in the future. Left side impacts have been found to be the most frequent when considering severe crashes involving elderly people that resulted in Abbreviated Injury Scale (AIS) 4+ injuries in the United States. Additionally, the frequency of rib fractures in female occupants is significantly higher than males in those over sixty years in a side impact. Therefore, there is a need to reduce rib fractures in elderly females in side impacts, which should significantly decrease the number of fatalities in these types of crashes. Currently there are no evaluation tools for elderly female occupants with increased fragility. The objective of this study was to develop a Human Body Model (HBM) of an elderly female with increased fragility to use in simulations which focus on side impacts.
The material properties of rib cortical bone were determined using average data from published literatures. A rib bending simulation was conducted to compare force-deflection response with published experimental data. The rib cortex model included thirty-two sections of a rib, in which the thickness of each section was determined by comparing to published precise cross-sectional data. The evaluated rib model was then applied to the full-body HBM of an elderly male which was developed in a past study. Using the full body model geometrically scaled to elderly female, published side impact sled tests at 28 km/h of delta-V with post mortem human subjects were simulated to compare kinematics, rib fracture locations, and thoracic deflection obtained from chest band data. Comparison of the force-deflection response of the rib in bending showed that the simulation result fell within the overall experimental range. In the side impact sled simulations, the predicted trajectories of T1, T12, and the pelvis were found to be similar to those from the experiment. The number of rib fractures, fracture timing, fracture locations and overall thoracic deflection in the simulation exhibited a similar trend to the experimental data.
The HBM developed by applying rib material properties and geometrical scaling for an elderly female well represented upper body kinematics, rib fractures and thoracic deflection in a side impact when compared to published PMHS experiments.