Effects of seat back force-deflection properties on injuries for both front and rear seat occupants in rear impacts.

The public debate over the most appropriate seat design to best protect occupants at all rear impact speeds is more than an decade old. There have been numerous publications in the technical literature discussing the relative merits of lower versus higher seat back strength. Proponents of lower seat back strength assert that the larger rearward deformation of seat backs allowed by most current seats is less injurious to the seats' occupants than seats with higher seat back strength. However, proponents of higher seat back strength assert that stiffer seat backs provide greater overall safety benefits to occupants of the seats and also protect passengers that may be seated behind them. The current study used a modified version of a validated MADYMO computer model of a 1986-1994 GM Grand Am production seat, originally developed by the University of Virginia (UVA), to determine the effect of seat back strength on occupant injury in rear impacts. Both a single seat and tandem seat arrangement were modelled at a crash change of velocity (delta V) approximately seventeen and thirty kilometers-per-hour. Seat occupants were 5th percentile female, 50th and 95th percentile male Hybrid III dummies. The maximum injury measure for each dummy, normalised by performance limits, were used to assess the results. The single seat results for 30 kph delta V rear impacts indicate that the least severe injury occurs at a seat strength three to five times the baseline seat for all dummy sizes, except the 95th percentile male. For the 95th percentile male a slightly lower injury value was obtained for a non-deforming or rigid seat. The 17 kph delta V rear impacts results varied with occupant size and head restraint position. In the dual seat simulations with a baseline front seat, highly injurious contact occurred between the 95th percentile male front seat dummy and 5th percentile female rear seat dummy. Increasing the front seat strength by three times prevented this contact. For a single out-of-position 50th percentile male dummy, the injury measures for the baseline seat were similar to those for a seat with three times the baseline strength.