This paper describes in detail the importance of seat back properties in its influence on head injuries in a car crash. The dynamic pressure distribution on the seat back generated by a 50th percentile H III dummy is analyzed during rear end impacts. Common injury criteria like the neck injury criterion (NIC), 3ms max, accelerations and neck forces/moments of the dummy are investigated as well. The seats have been tested on an active sled facility with a fully reproducible acceleration pulse. The acceleration of the sled was used to simulate the real acceleration of a rear end crash. The comparison of the dynamic pressure distribution shows that with a soft seat back cushion the pressure starts building up in the lower back and then during acceleration moves up to the upper back. With a stiffer seat back cushion the pressure is distributed more evenly over the whole back of the dummy. The body of the dummy dives into the seat back almost without any rotation and therefore the distance between head and head restraint is bigger than with soft cushions. To enlarge the effect of the torso rotation it is helpful to use a hard cushion on the lower part of the seat back and soft foams on the upper part. The results of this study show that it is also important to have a look on the cushion of the seat back and not only on the stiffness of the construction and the development of active head restraint systems. There is still a big potential in decreasing the risk of neck injuries by selecting the appropriate material for the seat back cushion in connection with the seat back construction itself. (A)
Abstract