Mechanical Interactions - Preventive Biomechanics - page 259

Fig. 6.12 Pelvic bone
structure with region
(yellow, hatched) covered
by the pelvic diaphragm
musculature and mesh
refinement at the sacral
bone region

region to the rigid body bone structure. High compliance, however, corresponds to
neglect of the pelvic floor muscles. Tissue then moves introversive, without
restriction. Particularly, stress magnitude at the tail bone is mostly dependent on this
effect. Regarding the difference in stress values due to modelling, it is feasible that if
the compliance in the pelvic floor region is not taken into account, the efforts made to
characterize material parameters of support and tissue material are dispensable.

6.2.5 Interaction FE-Analysis Comprising
Body-Support-Systems (BSS)

Based on the model verification of the previous Sect. 6.2.3.4 it can be assumed that
complex interaction scenarios can also be simulated quite realistically. Thus, in the
following, various Body-Support-Systems (BSS) including elastic and viscoelastic
materials are presented in interaction with different B OSS -Models. Mechanical skin
level as well as internal tissue stress and strain (especially in the gluteal region)
resulting from these interactions are simulated, analyzed and compared.
In the interaction modelling process, the B OSS -Models, especially the FE-model
of the gluteus was based upon anatomically adequate, 3-dimensional surface data
obtained from MR-images as described in Sect. 5.3 . In addition, compliance of the
pelvic diaphragm musculature was taken into account. Simulation of body-support
interaction was performed by loading the mattresses with the B OSS -Models in a
supine position. Hereby, the pelvic bone structure was free to move in the vertical
loading direction and to rotate about the lateral body axis. All other degrees of
freedom were constrained.
In the following outlines, the symbol S ij is used for C AUCHY Stress, equivalent to
r ij as used in Sect. 3.2.4 . Similarly, LE ij and NE ij are used for logarithmic strain
and nominal strain, respectively, where NE ij is equivalent to the definition of the
generalized G REEN -L AGRANGE strain tensor G g : ¼ V a I

ð Þ = a for the special case