Investigation on occupant ejection in high severity rear impact based on post mortem human subject sled tests

Area of Science:

• Biomechanics
• Crash Safety Engineering
• Forensic Science

Background:

• Occupant protection in rear impacts presents a challenge balancing energy absorption and ejection risk.
• Occupant ejection significantly increases the risk of severe injury and fatality in traffic accidents.
• Previous research lacks full-scale rear impact tests with Post Mortem Human Subjects (PMHS) leading to ejection.

Purpose of the Study:

• To investigate the conditions leading to occupant ejection in rear impact scenarios using Post Mortem Human Subjects (PMHS).
• To systematically evaluate the influence of seat design parameters and occupant characteristics on ejection likelihood.
• To identify critical factors contributing to rearward seat ejection in simulated car crashes.

Main Methods:

• Conducted 10 sled tests on 3 belted PMHS with a simplified seat model.
• Varied parameters including seatback angle, range of motion, occupant size, seatbelt slack, seatback stiffness, and headrest use.
• Maintained a constant rear impact pulse (17 G peak acceleration, 30 ms rise time, 95 ms duration).

Main Results:

• Rearward seat ejection of a Post Mortem Human Subject (PMHS) was observed only for the 95th percentile occupant under specific conditions: 22° initial seatback angle, 44° range of motion, and no headrest.
• Activating the seatbelt pretensioner did not prevent ejection under these conditions.
• The 50th percentile belted occupant did not experience rearward seat ejection in tests with a headrest.

Conclusions:

• Specific geometric configurations (large occupant, reclined seat, high seatback motion, no headrest) increase rearward ejection risk in rear impacts.
• Headrests play a crucial role in preventing occupant ejection in rear-end collisions.
• Findings provide valuable data for improving vehicle seat and restraint system design for enhanced occupant safety.