Mechanical Interactions - Preventive Biomechanics - page 262

Fig. 6.15 Path locations at the sacrum (a) and at the ischial tuberosity (b). Abbreviations: F: fat
tissue (pink), M: muscle tissue (brown), B: bone (grey), S: support, 1?/2: path initiating at
position 1 and running to position 2

• E-BSS 1: Homogenous block-shaped soft foam HR-material (Fig. 6.14 a)
• E-BSS 2: Homogenous block-shaped soft foam VE-material (Fig. 6.14 b)
• E-BSS 3: Two-layer structured soft foam mattress (D UNLOPILLO -Design, top
layer: VE-material, bottom layer: HR-material, Figs. 6.14 c and 6.2 )
• E-BSS 4: Two-layer structured soft foam mattress with gap (W ULFF -Design, top
layer: VE-material, bottom layer: HR-material, Figs. 6.14 d and 6.2 )

For comparison purposes, all mattresses have equal dimensions
(L 9 W 9 H = 1280 9 560 9 120 mm). Figure 6.14 a-c depict the employed
mattresses in loaded configuration with and without body model.
The contour plots, Fig. 6.14 a, d qualitatively show that interface pressure dis-
tribution varies, depending on the particular support mattress material and design.
Regions of increased compressive stress are depicted in red.
In the following, tissue stress and strain evaluation at the body sites 1 and 2 of
Figs. 6.12 and 6.13 is presented. Static analysis was performed for all four
mattresses under body weight loading. Tissue stress and strain at element inte-
gration points were evaluated and compared at static equilibrium. Tissue stress and
strain evaluation was done along a path leading through the tissue and indicated by-
'' 1 ! 2'', cf. Fig. 6.15 , initiating at skin level (path distance = 0.0 mm) and
running to the bone surface. The previously described paths are depicted in cross
sections views at the sacrum, Fig. 6.15 a and at the ischial tuberosity, Fig. 6.15 b.
Tissue stress and strain quantities are depicted in the following figures,
Figs. 6.16 , 6.17 , 6.18 , where the pink shaded background indicates the thickness of
the skin/fat tissue layer and curve markers indicate the affiliation to the particular
foam material/design, i.e. high resilient HR foam, viscoelastic VE foam,

D UNLOPILLO -design and W ULFF -design.
Comparison of tissue direct stress components S 11 ,S 22 and S 33 at the ischial
tuberosity and the sacrum shows that values nearly coincide, Fig. 6.19 .
The static analysis previously presented provides insight into tissue stress/strain
distribution at static equilibrium, i.e. at time t !1 . From the previous figures
derived from static interaction analysis, it can generally be concluded that