As the widespread adoption of autonomous vehicles is anticipated, a greater diversity of occupant postures is expected. However, current vehicle safety systems are not adequately designed to accommodate these varied postures, particularly relaxed seating positions, in which severe injuries have been reported during frontal collisions. Therefore, it is essential to investigate the biomechanical responses and injury tolerances of occupants in relaxed postures. In this study, the head kinematics and injury responses of the Hybrid-III and THOR anthropomorphic test devices, as well as the THUMS human body model, in a relaxed posture are analyzed using frontal impact sled simulations equipped with the sled system model developed in the previous study. The simulation results are evaluated through comparison with post-mortem human surrogate data. The findings of this study are expected to contribute to the fundamental design of new head restraint systems for human heads in autonomous vehicles.

PURPOSES : The purpose of this study is to investigate the correlation between occupant impact velocities and occupant injury indices under the restraint of an airbag and a seat belt, during frontal crash events. METHODS : The frontal crash test data of 93 tests conducted according to the Korea New Car Assessment Program (KNCAP) were investigated. The test data was measured by using a dummy to obtain occupant injury indices for the head, chest, neck, and upper legs. Occupant impact velocities (OIVx and OIVz) were calculated from the head acceleration of the test dummy. Pearson's correlation analysis and regression analysis were used to investigate the correlation between occupant impact velocities and occupant injury indices. In addition, the occupant impact velocities at the center of gravity of a vehicle, obtained by using the accelerations measured at the test vehicle's B-pillars, were investigated. RESULTS: The OIVx threshold obtained from the test dummies, which corresponds to the HIC15 of 700, was 70 km/h for a sedan, and 72 km/h for an SUV, which is significantly higher than the occupant impact velocity of 44 km/h, the limit of the domestic guideline on “Installation and management guide for roadside safety facilities”. This difference can be attributed to the influence of the air bags and seat belts. Additionally, the OIVx threshold obtained from the center of gravity of the vehicle corresponding to the HIC15 of 700 was approximately 72 km/h. CONCLUSIONS: Occupant safety performance criteria for the condition that airbags operate and seat belts are restrained, are required for the frontal impact tests of road safety facilities using a collision velocity of 60 km/h or higher.