Biomedical Engineering Reference
In-Depth Information
l
R
R
l
l
0
l
0
R
0
R
0
(a) Ideal elongation experiment
(b) Actual elongational experiment
including end effects
Figure 5.4
Schematic representation of an elongation experiment for fluids.
time
Figure 5.5
Example of uniaxial testing experiment with a fluid.
x
v
A
B
Figure 5.6
Point B is moved with a constant velocity
v
.
Fig.
5.5
shows an experiment, where the fluid is a little extended initially, after
which gravitational sag continues the filament stretching process. Ideally, a fila-
ment stretching experiment should be performed at a constant elongational rate.
This is not trivial to achieve. For instance, let one end of the dashpot, say point A
positioned at the origin (i.e.
x
A
=
0), be fixed in space, while the other end, point
B is displaced with a constant velocity
v
, as depicted in Fig.
5.6
. In that case the
position of point B is given by
