Drop tower testing was conducted using 50th percentile male PMHS at 15G peak
acceleration in a rigid seat, with a seat pan-to-seatback angle of 90°. Subjects
were instrumented with 6DOF motion blocks at T1, T4, T12, L3, and S1 to capture
detailed vertebral body kinematics. Pressure sensors were also placed throughout
the lumbar spine to estimate force in the intervertebral discs from S1-L2. PMHS
were restrained using a pilot torso harness attached to the seat at the
shoulders and lap belt, both pretensioned to 89 N. Reaction forces were measured
in the seat using six-axis loads under the seat pan. Final positioning of the
occupant was documented using a FARO arm point probe and laser scanner. To
recreate the experimental setup, CAD models of the experimental fixture were
meshed using a commercial FE modeling software (Hypermesh) and imported into
LS-Dyna for incorporation with the THUMS model. The belt routing tool in
LS-PrePost v4.9.12 was used to develop the torso harness and shoulder and lap
belts. Pre-simulation was performed to position the THUMS model in accordance
with recorded FARO data, and the experimentally recorded seat vertical
acceleration was assigned using Boundary_Prescribed_Motion. Finally,
instrumentation locations were duplicated within the THUMS model to match the
PMHS experimental setup. The THUMS model showed similar head kinematics compared
to the experiment, which went first into extension, followed by flexion during
the primary pulse. The torso of the model, however, experienced an increased
flexion/compression response compared to PMHS. The peak reaction force in the
simulated seat load cells measured 12.7 kN, which was within one standard
deviation of the average normalized experimental values (average = 12.8 kN,
standard deviation = 0.4 kN). The average load in the lumbar spine in the model
was found to be 3.3 kN, which was lower than PMHS average by more than two
standard deviations.
