Biomedical Engineering Reference
In-Depth Information
Fig. 11
Contour plot of
maximum principal stress in
the deformed uni-axial tensile
test FE model
Ta b l e 2
Constitutive model parameters, experimental stress and normalised stress difference as
measure for the model accuracy for non-degraded scaffold samples (
T
=
0) and after various peri-
ods of degradation (data are provided as mean
±
stdev)
T
(days)
Material
coefficient
c
1
Material
coefficient
m
1
Stress at 20 % strain
σ
20 %
,
exp
(kPa)
Normalised stress
difference
ψ
(%)
0
0
.
167
±
0
.
057
16
.
0
±
2
.
6
136
±
27
3
.
3
±
0
.
6
5
0
.
331
±
0
.
154
12
.
7
±
2
.
2
196
±
59
2
.
5
±
0
.
7
10
0
.
236
±
0
.
105
15
.
2
±
3
.
4
180
±
23
2
.
5
±
0
.
6
14
0
.
146
±
0
.
076
17
.
5
±
5
.
2
137
±
18
2
.
2
±
0
.
6
18
0
.
208
±
0
.
065
14
.
4
±
2
.
0
150
±
14
2
.
5
±
0
.
6
22
0
.
103
±
0
.
023
18
.
4
±
1
.
4
123
±
7
.
0
2
.
4
±
0
.
7
26
0
.
157
±
0
.
113
16
.
0
±
2
.
3
129
±
60
2
.
2
±
0
.
5
30
0
.
040
±
0
.
014
21
.
7
±
3
.
1
72
.
0
±
9
.
0
2
.
2
±
0
.
5
34
0
.
008
±
0
.
003
24
.
8
±
7
.
6
29
.
0
±
18
3
.
2
±
2
.
3
Figure
11
illustrates the distribution of the maximum principle stress predicted
in a sample utilising the optimised constitutive parameters. The optimisation suc-
cessfully identified the constitutive coefficients
c
1
and
m
1
of the Ogden material
model, for each of the degradation time points, to represent the non-linear force-
displacement relationship of the scaffold with stiffening in the cyclic strain range
observed in the experiments. The values for
c
1
varied between 0
.
008
±
0
.
003 and
0
.
331
0
.
154, with a general trend of decreasing value with increasing degradation
time (see Table
2
). The values for
m
1
ranged between 12
.
7
±
7
.
6,
without exhibiting an apparent trend. The normalised difference between experi-
mental and computed stress,
ψ
, used as indicator for the fitness of the model was
found to be between 2
.
2
±
2
.
2 and 24
.
8
±
±
0
.
5 % and 3
.
3
±
0
.
6 % and is summarised in Table
2
.
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