Vehicle Chassis, Body, and Seat Belt Buckle Acceleration Responses in the Vehicle Crash Environment

For over 30 years, field research and laboratory testing has consistently demonstrated that proper utilization of a seat belt dramatically reduces the risk of occupant death or serious injury in motor vehicle crashes. The injury prevention benefits of seat belts require that they remain fastened during collisions. Federal Motor Vehicle Safety Standards and SAE Recommended Practices set forth seat belt requirements to ensure proper buckle performance in accident conditions. Numerous analytical and laboratory studies have investigated buckle inertial release properties. Studies have repeatedly demonstrated that current buckle designs have inertial release thresholds well above those believed to occur in real-world crashes. Nevertheless, inertial release theories persist. Various conceptual amplification theories, coupled with high magnitude accelerations measured on vehicle frame components are used as support for these release theories.

This study investigates vehicle frame, vehicle floor pan and seat belt buckle acceleration responses in various laboratory environments on a mid-size body-on-frame sport utility vehicle. This is accomplished through the analysis of acceleration data from a frontal barrier crash test, a vehicle drop test and direct floor pan impulse response tests. These tests demonstrate that the magnitudes and durations of the accelerations experienced by the buckle are well below those necessary for inertial release. Analysis of buckle acceleration magnitudes in conjunction with the coincident seat belt webbing tensions re-affirms that inertial release of a seat belt buckle in the vehicle crash environment is unlikely. Lastly, data analysis of the performed tests demonstrates that the acceleration pulse transmitted from the vehicle chassis through the floor pan to the buckle was attenuated.