Biomedical Engineering Reference
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of a pilot in the condition of ejection occurring. The displacement of the thorax in the direction
vertical to the seat back and the displacement of the hip joint along with the pan of the seat were
evaluated. The hip has a similar rotational response to the thorax, while the thorax region translated
far more than the hip. The possible reason is that the compression of the spring caused slack in the
belt, which produced more space for the trunk of the pilot to move.
With the boundary condition from restraint systems, more accurate mechanical information on
the spine can be acquired. The von Mises stress distribution on the thoracolumbar spine at 0.12 s
(Figure 18.16) indicates that high stresses were mainly concentrated on the anterior parts of T12,
L1, and the region close to the pedicle bases of the lower lumbar spine. A similar stress distribution
was reported by Qiu et al. (2006) and can be used to explain why the thoracolumbar spine, espe-
cially the region of T12 and L1, is the most common site where fractures appear. In this model, the
maximum stress on the cortical bone reached 103 Mpa, which is close to the yield stress of cortical
bone (110 Mpa).
With the present model, a parametric study can be undertaken to analyze how factors such as the
features of the accelerative load, body posture, and configuration of the restraint harness affect the
dynamic response of the thoracolumbar spine to ejection and can be used to inform the design of
protective devices for ejection-induced spinal injury. Figure 18.17 is an example of the effect of the
onset rate of impact loading on the peak values of stress on the thoracolumbar spine. Both the slope
of the stress historical curve and the peak value throughout the duration of impact increased with
the increase of the onset rate of loading.
FIgure 18.16
(See color insert.)
Stress distribution on the thoracolumbar spine during ejection (
t
= 0.12 s).
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