INFLUENCE OF SEAT PROPERTIES ON HUMAN CERVICAL VERTEBRAL MOTION AND HEAD/NECK/TORSO KINEMATICS DURING REAR-END IMPACTS

The properties of seat with head restraint are important parameters for the optimum design of the seat system performance during rear-end impacts. The aim of this study is to verify the influence of different seat properties on human cervical vertebral motion using X-ray cineradiography and head-neck-torso kinematics under low-speed rear-end impacts. The six volunteers sat on a seat mounted on a sled that simulated actual car impact acceleration. Impact speeds (4, 6, and 8 km/h), and seat stiffness (hard or soft) without headrest were selected as the influence parameters for the cervical vertebrae at impact. It is also analyzed to quantify the cervical motion and the head-neck-torso motion under different impact conditions with the combination of influence parameters. The difference in seat characteristics affects the timing of the spine straightening, which in turn markedly affects the load to be applied to each cervical vertebral segment. In case of higher seat stiffness, the motion of upper torso in the initial phase of impact becomes sharp, and the axial compression force on the cervical spine tends to become greater. Even if the stiffness is low, however, the rebound of the upper torso is greater in the latter half of impact. Therefore, it is necessary to verify more clearly the spine straightening and cervical vertebral motion regarding the difference in seat characteristics in order to design a seat system that can reduce minor cervical injury. For the covering abstract of the conference see ITRD E203725.