Page 366 - Control Theory in Biomedical Engineering

332 Control theory in biomedical engineering

Poisson’s ratio of 0.8. However, they have been measured to exhibit a Pois-
son’s ratio of 0.92 at smaller strains (Kolken and Zadpoor, 2017).

6 Continuum metastructural test
6.1 Mechanical test specifications

As mentioned in the previous section, the five designs were all fabricated
using the three different materials and assembled into a concentric tube
structure with the auxetic material as the inner tube and the normal PPR
tube as the outer tube. For each of the assemblies, we performed a three-
point bending test (Instron universal testing machine) as it is the most typical
representation of the type of movement that our surgical device undergoes
during its course of operation. Each sample assembly was subjected to three
test cases.
The first test case is a simple three-point bending with no horizontal
extensions or loads (Fig. 14). This case represented the control case where
there is no jamming between the layers. The second and the third test case
involve applying a 3mm and 6mm horizontal elongation, respectively, to
the sample and then conducting the three-point bending tests with the
stretched samples. These cases were meant to represent the situations when

Fig. 14 Bending test of the sample using the Instron machine.