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Rear-End Impacts - Part 2: Sled Pulse Effect on Front-Seat Occupant Responses
Abstract:
This study was conducted to assess the effects of differing rear impact pulse characteristics on restraint performance, front-seat occupant kinematics, biomechanical responses, and seat yielding. Five rear sled tests were conducted at 40.2 km/h using a modern seat. The sled buck was representative of a generic sport utility vehicle. A 50th percentile Hybrid III ATD was used. The peak accelerations, acceleration profiles and durations were varied. Three of the pulses were selected based on published information and two were modeled to assess the effects of peak acceleration occurring early and later within the pulse duration using a front and rear biased trapezoidal characteristic shape.
The seatback angle at maximum rearward deformation varied from 46 to 67 degrees. It was lowest in Pulse 1 which simulates an 80 km/h car-to-car rear impact. The seatback plastic deformation was greater in the pulse with the rear biased trapezoidal acceleration profile, Pulse 4, than in the front biased trapezoidal acceleration profile, Pulse 5 (46 degrees v 41 degrees). Coincidingly, the longitudinal head displacement was slightly greater in the Pulse 4. There was limited relative motion between the ATD torsos and the seatbacks. The relative motion between the ATD torso and the seatback was less than 7 cm in all tests. The head, chest and pelvis peak acceleration and timing varied depending on the pulse. All peak head, chest, pelvis and upper and lower-neck moments occurred prior to maximum seatback dynamic deflection. The biomechanical responses were all well below injury assessment reference values. The seatback structural restitution was the highest in Pulse 1 which had the lowest amount of dynamic and plastic seatback deformation and had the highest lap belt load. All peak belt loads occurred in the rebound phase of the ATD.
The sled coordinate-based data was used to determine the effective restraint stiffness. The results were used to develop a spring-mass model. The model will help understand the effects of pulse characteristics on predicted chest acceleration for future research.
In conclusion, the results from this study show that pulse shape has a measurable effect of seat and ATD kinematics in high-speed rear impacts and should considered for future research and testing.