The reality of the autonomous vehicle in a near future is growing and is expected
to induce significant change in the occupant posture with respect to a standard
driving posture. The delegated driving would allow sleeping and/or resting in a
seat with a reclined posture. However, the data in the literature are rare on
the body kinematics, human tolerance, and injury types in such reclined
postures. The current study aims at increasing the knowledge in the domain and
providing useful data to assess the relevance 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/s delta 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 of a 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 and T12 vertebrae), and sacrum. Strain gauges
were glued onto the anterior face of the L1 to L5 lumbar vertebrae and onto the
anterior face 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 necropsy was 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 ring fracture and another one sustained
an AIS4 injury with complete separation of the left and right sacroiliac joints.
Lumbar disc ruptures and vertebral fractures were observed for the three PMHS
(AIS 2 and AIS3 coding). The number of separated rib fractures were very
different from one PMHS to another (0, 6 and 33). Response corridors for the
external forces and kinematics were built and are presented in the paper. The
results are discussed by comparing with existing data for which the backseat was
in standard posture.
