The Influence of Reclined Seatback Angles on Occupant Injury Risks in Frontal Impacts

The reclined seatbacks will be increasingly used with the advanced technologies of the intelligent automobile. The occupant collision protection must rise to the challenge facing to the new impact scenarios. It is necessary to understand the injury mechanisms of the reclined occupants in order to design the resistant system and testing protection regulations. In this study, the Frontal Full Width Impact (FRB) and Mobile Progressive Deformable Barrier Frontal Impact (MPDB) tests were conducted as specified in China New Car Assessment Programme (C-NCAP, 2021 version). The simulation used the biomechanical model of the 5th female occupant exhibiting the detailed anatomical structures and a seat model with large-angle seatback. The occupant injury risks and mechanisms with 25°, 45° and 60° seating postures were investigated by analyzing the kinematic and biomechanical parameters, and the influence of the seatback angle on occupant injury was discussed. The results indicate that reclined seatback significantly affects the kinematic responses of the head and neck, with head and neck injuries acting as primary contributors to C-NCAP score reductions. Seatback angle and collision type are key factors influencing the risk of visceral and lumbar spine injuries. In FRB impact condition, the risk of visceral injury reduces by 18% and 17% with the increasing seatback angle, respectively, while the risk of lumbar spine injury decreases by 1% and increases by 38%. In MPDB impact condition, the risk of visceral injury reduces by 28% and 32% with increasing seatback angle, and increases the risk of lumbar spine injury by 51% and 32%, respectively. In conclusion, the head, neck, and visceral organs are common injury sites for occupants in reclined seatbacks, and the collision types influence the injury mechanisms. Mitigating the range of head and neck motion and the compressive forces on visceral organs is critical for protecting reclined posture occupants. These findings from this study could contribute significantly to the development of regulations and restraint systems for reclined occupant protection.