Seat Performance in Rear Impacts: Seatback Deflection and Energy Dissipation 2021-01-0916

Occupant protection in rear crashes is complex. While seatbelts and head restraints are effective in rear impacts, seatbacks offer the primary restraint component to front-seat occupants in rear impacts. Seatback deflection due to occupant loading can occur in a previous rear crash and/or in multiple-rear event crashes. Seatback deflection will in-turn affect the plastic seatback deformation and energy absorption capabilities of the seat.

This study was conducted to provide information on seatback deflection and seat energy consumption in low and high-speed rear impacts. The results can be used to examine seatback deflection and energy consumed in a previous rear impact, or in collisions with multiple rear impacts. Prior seatback deflection and energy absorption can affect the total remaining energy absorption and seat performance for a subsequent rear impact.

Rear sled tests included eight 16 km/h tests conducted with the BioRID and eight matched 40 km/h tests with the 50th percentile male Hybrid III ATD. Measurements included the energy transfer to the seat, plastic, elastic and maximum dynamic deformation. The average seatback plastic deformation was approximately 4 degrees for the 16 km/h and approximately 17 degrees for the 40 km/h tests.

Thirteen quasi-static seat-pull tests were conducted to characterize seatback defection; 8 tests were run to maximum yield and five, in a hysteresis manner. Seat stiffness and yield strength were determined. In the hysteresis tests, the energy absorption from various plastic deformations was analyzed with respect to available energy capacity of the seat. Each pull of the hysteresis testing had permanent deformation and energy consumed that could be compared the sled testing plastic deformation. For example, the seatback deflection was about 4 degrees in the 16 km/h rear sled tests with occupants weighing about 78 kg. A 4-degree deformation coincided with about 17 percent of the total seatback energy capacity in the seat pull hysteresis tests.

The results obtained in this study highlighted that a seat involved in a low-to-moderate rear impact can result in plastic deformation, affecting the total remaining energy capacity of the seat. The results can also be used to better understand the effect seat energy absorption capabilities in multiple rear impact accidents or in a prior rear impact.