Influence of seat foam and geometrical properties on BioRID P3 kinematic response to rear impacts

As the primary interface with the human body during rear impact, the automotive seat holds great promise for mitigation of Whiplash Associated Disorders (WAD). Recent research has chronicled the potential influence of both seat geometrical and constitutive properties on occupant dynamics and injury potential. Geometrical elements such as reduced head to head restraint, rearward offset, and increased head restraint height have shown strong correlation with reductions in occupant kinematics. The stiffness and energy absorption of both the seating foam and the seat infrastructure are also influential on occupant motion; however, the trends in injury mitigation are not as clear as for the geometrical properties. It is of interest to determine whether, for a given seat frame and infrastructure, the properties of the seating foam alone can be tailored to mitigate WAD potential. Rear impact testing was conducted using three model year 2000 automotive seats (Chevrolet Camaro, Chevrolet S-10 pickup, and Pontiac Grand Prix), using the BioRID P3 anthropometric rear impact dummy. Each seat was distinct in construction and geometry. Each seat back was tested with various foams (i.e., standard, viscoelastic, low or high density). Seat geometries and infrastructures were constant so that the influence of the seating foams on occupant dynamics could be isolated. Three tests were conducted on each foam combination for a given seat (total of 102 tests), with a nominal impact severity of Delta V = 11 km/h (nominal duration of 100 msec). The seats were compared across a host of occupant kinematic variables most likely to be associated with WAD causation. No significant differences (p < 0.05) were found between seat back foams for tests within any given seat. However, seat comparisons yielded several significant differences (p < 0.05). The Camaro seat was found to result in several significantly different occupant kinematic variables when compared to the other seats. No significant differences were found between the Grand Prix and S-10 seats. Seat geometrical characteristics obtained from the Head Restraint Measuring Device (HRMD) showed good correlation with several occupant variables. It appears that for these seats and foams the head-to-head restraint horizontal and vertical distances are overwhelmingly more influential on occupant kinematics and WAD potential than the local foam properties within a given seat.