Page 24 - VTE JUNE

Feature | MEEA Lumber Spine
Effect of Lumbar Spine Assemblies and Body-Borne Equipment Mass on Anthropomorphic Test Device Responses During Drop Tests - continued
of spinal injury. A DRI over 17 registers a 10% probability of spinal injury, whereas a DRI over 21.0 registers a greater than 50% probability of spinal injury. SAE filtering was applied to all experimental results. The testing completed for each ATD is displayed in Table 1. Additional Experiments
The experimental schedule also enabled
three additional, cases to be assessed. The first case involved attaching a 7.2 kg mass directly above the lumbar load cell underneath the jacket skin on the Hybrid III with the pedestrian spine. The weight was attached with cable ties, preventing any movement as shown in Figure 6. This test was performed
at a pulse of 161 g to validate that the lumbar load cell was working.
An experiment was conducted in an attempt to further understand how the attachment affected loading. In this particular experiment, 7.2 kg of equipment mass was attached
to the jacket skin of the Hybrid III with the curved spine with adhesive tape under an acceleration pulse of 161 g in Figure 7. The mass included the instrumented magazine to assess the acceleration of the weight. Finally, to understand how much protection the pelvis was receiving from the EVA foam, the EVA foam was removed and tested at the lower acceleration pulse of 161 g with the Hybrid III with the pedestrian spine.
Repeatability of Velocity and Temperature
The velocity is derived by integrating the acceleration of the drop tower carriage during the arresting phase. The peak acceleration pulse to the carriage table is reached in 3 ms. The coefficients of variation of the change in velocity for the two loading conditions were 0.003, demonstrating good repeatability of testing conditions. The temperature at the drop tower was maintained between 19°C and 23°C.
RESULTS
Effect of lumbar spine assemblies and their resultant ATD sitting postures
The results for vertical pelvis acceleration are displayed in Figures 8-11 for both acceleration pulses. With and without BBE mass, the Hybrid III with the curved spine generated
the lowest peak vertical pelvis acceleration by up to 22% compared to the FAA Hybrid III. The latter generated the highest peak vertical pelvis acceleration. When BBE mass was added, there was no consistent change to peak vertical pelvis acceleration across all
three lumbar spines and both acceleration pulses, although a trend toward increasing peak vertical pelvis acceleration may be evident for the FAA Hybrid III.
Vertical lumbar load is compared in Figures 12-15. Across both acceleration pulses,
and for all three lumbar spines, there was
no consistent trend with respect to the
peak vertical lumbar load. For the lower acceleration pulse, the peak vertical lumbar load did not vary between the FAA Hybrid III and the Hybrid III with the pedestrian spine under the same BBE mass conditions by more than 3%. For the higher acceleration pulse,
the peak vertical lumbar load varied no more than 10% between the FAA Hybrid III and
the Hybrid III with the pedestrian spine; this was for the experimental condition without body-borne equipment mass. The Hybrid III with the curved spine recorded the highest peak vertical lumbar load, producing a 13% greater peak vertical lumbar load than the FAA Hybrid III when both spines with and without BBE are compared for an acceleration pulse of 161 g. The two straight spine assemblies for an acceleration pulse of 161 g showed
a reduction in peak vertical lumbar load from the condition without BBE mass to the conditions with BBE mass. In contrast, the Hybrid III with the curved spine registered a similar peak vertical lumbar load both with and without BBE
Investigating the influence of equipment taped to the body
With the addition of 7.2 kg BBE mass on the lumbar load cell of the Hybrid III with the pedestrian spine, the peak vertical lumbar load increased by 20% compared to the case with the heavy BBE. This was in spite of the fact that more mass was present with the heavy condition. However, the peak vertical pelvis acceleration was approximately the same
as the cases without BBE and with heavy
BBE mass. For the experiment conducted without the foam pad, the peak vertical pelvis acceleration increased by 20%, yet the lumbar load did not increase, generating similar loads to the cases without BBE and with heavy BBE. The results are displayed in Figure 16 and Figure 17.
Monitoring the magazine pouch accelerometer
The data from the magazine pouch accelerometer demonstrated that the equipment did not begin to accelerate in the vertical direction until 7 ms, approximately the same time as peak pelvis acceleration.
That data also showed that the peak vertical acceleration was not reached
until approximately 15 ms after the peak pelvis acceleration has occurred. Figure
18 compares the vertical acceleration of
the surrogate magazine mass and the pelvis acceleration, for the heavy BBE mass condition. The peak vertical acceleration of the surrogate mass occurs approximately 7 ms after the peak pelvis acceleration. Figure
24 | June 2018