Evaluating performance of occupant retention countermeasures at the side windows through full-scale crash tests are typically expensive and yield inconclusive results. The results are inconclusive due to the non-repeatable nature of this testing. Another approach utilizes guided impact testing that propels an attached headform into a window to evaluate performances of these safety systems. This may provide some procedural value in generating repeatable results with limited objectives.

The capability to limit the guided impact headform displacement relative to a vehicle's exterior window plane is assumed to represent reduced risk of occupant ejection. However, it is not known what ejection risk is represented for a given headform excursion.

This study characterized headform excursions in guided impact testing for a given window airbag design with a range of restraint capabilities. Not surprising, disparities in the headform excursions were observed depending on the impact location of the impact on the airbag. System level evaluation of the airbag design in a rollover environment was conducted to determine which restraint capabilities represented a reduced risk of occupant ejection.

A correlated computer model of NHTSA’s Dynamic Rollover Fixture (DRF) was used to identify the restraint characteristics for the airbags in which occupant ejection occurred as well as those where occupant retention was achieved in order to establish a relationship to headform excursion. However, the relationship for a given headform excursion to ejection risk was not apparent due to disparity in the headform excursion results.

Review of simulations in the DRF showed that as the occupant interacted with the airbag, occupant moved from the region of the airbag where excursions were the lowest, towards the region of the airbag where headform excursion was greatest. The dummy moved forward until it “pocketed” in the uninflated front zone of the airbag or until it escaped out of the zone with the highest allowable excursion.