Biomedical Engineering Reference
In-Depth Information
5.5
For a material the following relaxation and creep function was found,
G
(
t
)
=
1
+
e
−
t
1
2
e
−
t
/
2
.
J
(
t
)
=
1
−
When we relate a force to strain the unit for
G
(
t
) is [N] and the unit for
J
(
t
)is[N
−
1
]
(a) Does this material law satisfy Eq. (
5.34
)?
(b) Test 1: Assume that at
t
=
0 a step in the force is applied of 1 [N].
After 1.5 [s] the step is removed. What is the strain after 3 [s]?
(c) Test 2: At
t
0 a step in the strain is applied equal to 0.01. This
strain is removed at
t
=
=
1.5 [s]. What is the value of the force
after 3 [s]?
5.6
A piece of tendon material is subjected to the following strain history. At
t
=
0 [s] a step in the strain is applied of 0.01. After 4 [s] the strain is
increased by an extra step of 0.01. After 8 [s] the strain is reduced by 0.005.
The total strain evolution is given in the figure below.
Applied strain as a function of time
0.03
0.025
0.02
0.015
0.01
0.005
0
0
2
4
6
8
10
time [s]
The only information that is available for the material is the result from
a creep test as given in the figure below. In the creep test a tendon spec-
imen was loaded with a mass of 500 [kg]. The gravitational constant is
10 [m s
−
2
].
