Relationships Between Impact Pulse Duration and Occupant Kinematics in Low Speed Rear Impacts 2002-01-0029

Vehicle change in velocity is recognized as one of the most influential parameters on occupant kinematics and injury potential in motor vehicle collisions. Basic engineering principals and some recent epidemiological research indicate the characteristics of the vehicle velocity change, such as the shape and duration of the acceleration vs. time pulse, may also be important. Automotive bumper designs could be enhanced by recognizing these characteristics to potentially influence occupant kinematics and Whiplash Associated Disorders (WAD) in low speed rear impacts.

Low speed rear impacts were conducted with a Delta V of 11 km/h using the BioRID P3 anthropomorphic test device. Nominal pulse durations of 80, 100, 140 and 180 msec were tested by varying the dimensions of a foam interface between the impacting pendulum and the rear surface of the test vehicle. An additional 100 msec pulse was also tested, with the shape of the pulse altered by delaying the time at which the peak acceleration occurred. Tests were conducted using 2 seats, one with relatively good head-to-head restraint geometry and the other with relatively poor geometry. Three tests were conducted on each impact pulse -seat combination.

The results found that no one impact duration resulted in significantly different occupant kinematics than the others (p<0.05). However, when grouped together, impacts employing the good geometry seat with a duration of 140 or 180 msec resulted in significantly improved occupant kinematics, including head X acceleration relative to T1, head velocity relative to T1, and NIC. Regression analysis found good correlation between pulse duration and several important kinematic variables for the seat with good geometry (p<0.05). Significant differences between the 100 msec pulses with the early and late onset of peak acceleration were mixed, and no clear improvement was realized. It is concluded that extending the pulse duration in a low speed rear impact from 100 msec to 140 msec may yield benefits in occupant kinematics and WAD potential, particularly for seats with good geometry.