Neck Biomechanical Responses with Active Head Restraints: Rear Barrier Tests with BioRID and Sled Tests with Hybrid III

Active head restraints are being used to reduce the risk of whiplash in rear crashes. However, their evaluation in laboratory tests can vary depending on the injury criteria and test dummy. The objective of this study was to conduct barrier tests with BioRID and sled tests with Hybrid III to determine the most meaningful responses related to whiplash risks in real-world crashes. This study involved: (1) twenty-four rear barrier tests of the Saab 9000, 900, 9-3 and 9-5 with two fully instrumented BioRID dummies placed in the front or rear seats and exposed to 24 and 48.3 km/h barrier impacts, and (2) twenty rear sled tests at 5-38 km/h delta V in three series with conventional, modified and SAHR seats using the Hybrid III dummy. A new target superposition method was used to track head displacement and rotation with respect to T1. Insurance data on whiplash claims was compared to the dummy responses.

NIC is not a sufficient criterion to assess whiplash because it does not consistently correlate with seat performance in field crashes and its peak can occur at head restraint contact before the primary neck loads and displacements. Clear response differences were seen with head rotation and x-displacement with respect to T1 among the various seats and rear delta Vs. These responses describe neck kinematics in extension and flexion, and address many of the possible whiplash injury mechanisms. A Neck Displacement Criterion (NDC) is proposed to supplement other criteria until there is a clearer understanding of whiplash injury criteria. It is based on the displacement and rotation of OC-T1 and comparison to the natural range of motion. Responses are viewed in cross-plots of rotation vs x-displacement and z- vs x-displacement of OC with respect to T1.