Biomedical Engineering Reference
In-Depth Information
Table 7.11 Comparison of peak stress S
ij
(i, j = 1, 2, 3) of variations sagopt and transopt. The
columns show the percentage increase of the variation sagopt compared to the variation transopt
Stress (Mpa)
Transopt -variation
Sagopt -variation
Percentage increase of variation
sagopt
Tension
Compression
Tension
Compression
Tension (%)
Compression (%)
S
11
0.0354
-0.0751
0.0406
-0.0927
+14.79
+23.36
S
22
0.0825
-0.0659
0.1000
-0.0894
+21.12
+35.80
S
33
0.0330
-0.0625
0.0347
-0.0830
+5.09
+32.81
S
12
0.0151
-0.0366
0.0202
-0.0452
+33.69
+23.74
S
13
0.0527
-0.0326
0.0534
-0.0413
+1.25
+26.77
S
23
0.0982
-0.0107
0.1215
-0.0090
+23.73
-16.55
Von mises 0.2223 0.2754 +23.89
Note in Table
7.11
, the captions ''tension'' and ''compression'' apply to direct stress, not to shear
stress!
Fig. 7.65 Graph of the stress
values from Table
7.11
Fig.
7.68
). This agrees with the previously introduced optimization goal of tissue
stress reduction at the ischial tuberosity (only).
Figure
7.68
depicts the distribution of vertical direct stress S
22
at the bone
surface from different perspectives prior to and after cushion optimization. Distinct
stress reduction occurred at the ischial tuberosity.
Stress profiles along two node paths: Figs.
7.69
and
7.70
provide information
about the progression of tissue stress evaluated along two arbitrarily chosen paths in
the buttocks region, initiating at skin level and ending at the tip of the tailbone and the
ischial tuberosity. The stress curves resulting from the interaction simulation with the
non-optimzed seat cushion are displayed as continous lines and the dashed curves
belong to the interaction simulations including the optimized seat cushion.
The results along the tail bone-path show significant stress reduction of stress
components S
ij
(i, j = 1, 2, 3) (cf. Fig.
7.69
) in the mechanical interaction sim-
ulation involving the optimized seat cushion. Note that very low tissue stress is
apparent for the first 20 mm of tissue, from the skin level towards the bone surface.
Closer towards the bone, stress increases significantly.
