Addressing Female Whiplash Injury Protection - A Step Towards 50th Percentile Female Rear Impact Occupant Models

Doctoral thesis, 2012

Whiplash Associated Disorder (WAD) – commonly denoted whiplash injury – to vehicle occupants involved in collisions, is of worldwide concern. These injuries occur at relatively low velocity changes, typically between 10–25 km/h, and in all impact directions. Rear impacts are, however, the most common in the accident statistics. Since the mid-1960´s, statistical data has shown that females have up to three times higher risk of sustaining whiplash injuries than males, in similar crash conditions. The overall objective was to improve the understanding of why females are at greater risk of sustaining whiplash injuries in rear impacts, compared to males. Two rear impact studies involving ~50th percentile female and male volunteers were carried out. In both studies, response corridors for ~50th percentile females were generated and compared to previously published response corridors for 50th percentile males. Additionally, the Neck Injury Criterion (NIC) values, head-to-head restraint distances and contact times were compared between female and male volunteers. Thereafter, a 50th percentile female rear impact dummy Finite Element (FE) model, EvaRID V1.0, was developed from an existing BioRID II model. The anthropometry and mass distribution of the 50th percentile female were specified based on published data. Its mechanical response was evaluated with data from one of the volunteer studies. Finally, a scaled-down rear impact dummy prototype – BioRID50F – was developed using modified BioRID II dummy components. The scaled-down dummy was representative of a 50th percentile female in mass and key dimensions and intended to function as a representative seat loading device. The BioRID50F was evaluated against new volunteer test results from low-speed rear impact sled tests including female volunteers close to a 50th percentile female in size. A series of rear impact tests with the BioRID50F were performed in four different seats from four different car models. The results were compared to previously performed BioRID tests in equivalent setup. It was found that the overall biofidelity of the EvaRID V1.0 was acceptable at low velocity changes (7 km/h). A general stiffness reduction in EvaRID V1.0 of 30 percent compared to the BioRID II, proved to be a promising first iteration. However, further improvements are of the EvaRID V1.0 as well as BioRID II models are required with regards to the stiffness of the thoracic spine. The results from the rear impact test series comprising volunteers and the BioRID50F supported the findings from earlier publications, indicating that there may be characteristic differences in the rear impact dynamic seat back interaction between males and females. A mechanical or computational model of a 50th percentile female would be an important complement to the existing 50th percentile male BioRID II occupant models when evaluating seat performance. These models can be used, not only as a tool when designing protective systems, but also in the process of further evaluation and development of injury criteria.