Biomedical Engineering Reference
In-Depth Information
Fig. 6.25 Tissue direct stress S
33
at skin level, fat-muscle interface and bone surface as a
function of time adjacent to the ischial tuberosity using E-BSS 1 and E-BSS 2 body supports
Fig. 6.26 Tissue direct stress
S
33
at skin level and bone
surface as a function of time
adjacent to the sacrum using
E-BSS 1 and E-BSS 2 body
supports
Static Transient Analysis: Tissue direct stress, logarithmic direct strain and
logarithmic shear strain were evaluated at element integration points. This was
carried out over a simulated time span of 3 h in transient static analysis using the
homogenous mattress design, E-BSS 1 and E-BSS 2 (homogenous HR- and
VE-foam material, respectively), Figs.
6.25
,
6.26
,
6.27
,
6.28
,
6.29
,
6.30
.
The static transient analysis previously presented provides insight of tissue
stress/strain distribution as a function of time including viscoelastic tissue material
behaviour. From the previous figures, Figs.
6.25
,
6.26
and
6.27
derived from static
transient interaction analysis, several observations can be made:
• Direct stress S
33
is significantly higher at the sacrum using the E-BSS 2 system
compared to E-BSS 1 system (in this context, it is important to mention that the
reason for higher stress and strain at the sacrum with VE-foam as opposed to HR-
material, is likely due to the employed mattress thickness of 120 mm and that
VE-material tends to highly compress (block) at the sacrum region. Blocking
effects of VE-material may thus inappropriately influence tissue stress/strain
results and may show a greater influence on the tissue than the material itself).
