Mechanical Interactions - Preventive Biomechanics - page 274

Fig. 6.33 Skin interface stress along the stress path 1 and path 2 exemplarily for foam material
S AF as a function of six points in time: a path 1, b path 2
Fig. 6.34 Time effects of a tissue material point of the body model BoMo 0 and a viscoelastic
homogenous support material S AF : a skin interface stress relaxation, b zoomed image of the
initial relaxation process of a and c displacement-time curve of the chosen tissue material point
in the gluteal region (creep)
level, Fig. 6.31 , are evaluated and compared. Path 1 (brown) proceeds along the os
scarum region and path 2 (blue) proceeds at the ischial tuberosity region.
Figure 6.32 exemplarily depicts the interface stress S 33 at skin level at six dif-
ferent points in time: initially (no contact) and 6 h (static equilibrium). A distinct
increase of contact area and a decrease of contact stress can be observed as the time
increases.
Figure 6.33 depicts the stress decrease due to contact with the viscoelastic
support material over a time span of 8 h. In addition, the stress state at both
indicated regions at infinite time is given. The observed asymmetry of the stress
paths is based on the (natural) geometric asymmetry of the pelvic of the BoMo 0
model (the model has not been built based on mirroring a half model, but on the
actual MR-scan and manual reconstruction of both body sides). It can be observed
that for foam material S AF , the skin stress beginning at 5 s decreases to a nearly
constant level after 2 h.
Figure 6.34 points out the simultaneously existing time effects of the elastic
tissue properties of the BoMo 0 and the viscoelastically defined S AF material at a