Biomedical Engineering Reference
In-Depth Information
6.2.3 FE-Model Verification
Chapters 4
and
5
referred to the mechanical characterization of materials employed
in body support systems (BSS) and the generation of human models (B
OSS
-Models),
including characterization of soft tissue material properties of relevant body regions.
Whether the material characterizations reflect complex three-dimensional behaviour
during mechanical interaction must be verified in separate tests. One such verifica-
tion experiment follows, whereby the interacting components are the human gluteal
region on one side and a defined support material sample on the other. In a second
step, the experiment is FE-modelled and simulated and simulation results are
compared with experimental data. The employed material parameters have been
6.2.3.1 Buttock Loading Experiment
To validate the previously established material parameters for gluteal fat and
muscle tissue under complex loading, an indentation experiment was experi-
mentally performed as well as numerically simulated. Data acquisition was
performed on the same male individual from whom long-term tissue data had been
derived (see
Sect. 5.2.3.2
,
Table
5.3
). The experimental requirement was to ensure
defined reproducibility in the FE-modeling and simulation process. Due to this, the
face-up supine body position was discarded since it involved an error-prone test
set-up in the geometrically restricted MRI-environment. Instead, a foam sample
was pushed onto the buttock tissue in a controlled manner.
The subject was placed face-down in a plastic holder (see Fig.
6.6
a). The hip
was fixed using a plaster mold attached to the base frame of the holder. This
ensured embedment so that the pelvis could not escape the outer loading. Fixed to
the top plate and positioned directly above the skin surface, block-shaped high
resilient open-cell polyether soft foam with the dimensions H 9 W 9 D:
100 9 350 9 220 mm was pushed onto the buttock, vertically displacing the plate
for Du = 64 mm. This displacement value was derived through separate testing
outside the MR-environment where vertical reaction forces of the following
configurations were compared: (a) body in face-up supine position on a foam
support whereby the support for the buttocks was separated from the support for
back and legs and (b) body in face-down position in the holder with the foam
support specimen displacement recorded until the forces coincided with those
encountered in the face-up position. Thus, the force value corresponding to buttock
support was determined.
The foam specimen displacement was mechanically driven, and the top plate
was guided at all four edges, ensuring horizontal positioning (see Fig.
6.6
b).
To gain visible contour information of the foam specimen in the MR-environment,
the outer surface of the specimen was covered with a thin film of soft paraffin. The
