Investigation of Potential Injury Patterns and Occupant Kinematicsin Frontal Impact with PMHS in Reclined Postures

The reality of the autonomous vehicle in a near future is growing and is expected to induce significant change inthe occupant posture with respect to a standard driving posture. The delegated driving would allow sleeping and/or resting in a seatwith a reclined posture. However, the data in the literature are rare on the body kinematics, human tolerance, and injury types insuch reclined postures. The current study aims at increasing the knowledge in the domain and providing useful data to assess therelevance of the standard injury assessment tools such as anthropomorphic test devices or finite element human body models. For that purpose, a test series of three male Post-Mortem Human Subjects (PMHS) were performed in frontal impact at a 13.4 m/sdelta V. The backseat inclination was 58 degrees with respect to the vertical axis. The semi-rigid seat developed by Uriot et al.(2015) was used with a stiffer seat ramp. The restraint was composed of a lap belt equipped with two 3.5 kN load limiters, and ofa shoulder belt equipped of a 4 kN load limiter on the upper anchorage placed in the vicinity of the shoulder. The belts, the semi-rigid seat, and the footrest were equipped with force sensors. The rotations of the seat pan and of the seat ramp were also measured. The PMHS were instrumented with multi-axis accelerometers and Y angular velocity sensors attached to the head, thorax (T1 andT12 vertebrae), and sacrum. Strain gauges were glued onto the anterior face of the L1 to L5 lumbar vertebrae and onto the anteriorface of the iliac wings. To estimate the pelvis kinematics, a rigid support equipped with targets was fixed onto the femur shaft. Prior to test, X-ray imagery was performed to exhibit the initial curvature of the lumbar spine. After the tests, an in-depth necropsywas done, with a specific attention to the lumbar spine. In the chosen test conditions, no lap-belt submarining was observed for the three PMHS. One PMHS sustained an AIS2 pelvic ringfracture and another one sustained an AIS4 injury with complete separation of the left and right sacroiliac joints. Lumbar discruptures and vertebral fractures were observed for the three PMHS (AIS 2 and AIS3 coding). The number of separated rib fractureswere very different from one PMHS to another (0, 6 and 33). Response corridors for the external forces and kinematics were builtand are presented in the paper. The results are discussed by comparing with existing data for which the backseat was in standardposture.