Biomedical Engineering Reference
In-Depth Information
Fig. 4.16 Comparison of experimental HR-foam material data with simulation output of a the
plate creep compression test and b the indenter creep test
degrees of freedom of bottom foam sample nodes were constrained for the HR-
foam model. Modelling of contact interaction between bottom foam sample and
bottom support surface in the VE-foam model was shown to be crucial in matching
experimental data, since the sample outer edges lost ground contact during load-
ing. All indenters were modelled as analytical rigid bodies.
Comparison of creep test data with simulation output for HR-foam material,
Fig.
4.16
, and VE-foam material, Fig.
4.17
, is shown based on optimized long-
term material parameters provided in Tables
4.2
and
4.3
as well as optimized
viscoelastic Prony series parameters, as provided in Table
4.4
. For visualization
purposes, the plotted time range is reduced from 10,800 to 3,600 s.
Optimized viscoelastic Prony-series parameters of HR-foam material and VE-
foam material are as follows.
Verification: To verify the derived long-term moduli a
k
, l
k
and m
k
(cf. Table
4.2
and
4.3
) as well as derived Prony series parameters k
i
, g
i
, s
i
and s
i
(cf. Table
4.4
) under complex loading conditions other than indenter loading, a
test scenario was conducted intended to approximately correspond to physical
buttock-support interaction. A physical buttocks model based on plaster casts of
the human buttocks was built, Fig.
4.18
. The cast negative was covered with thin
fibre glass sheets and covered with resin. After hardening, the surfaces were fin-
ished. The buttocks model was mounted into a test rig and linearly guided to assure
vertical movement only. Additional masses were attached to the model to adjust
