Page 364 - Control Theory in Biomedical Engineering

330 Control theory in biomedical engineering

5.3.4 Missing rib structure
The missing rib pattern (Fig. 10) can be classified as a hybrid of the chiral and
re-entrant designs. This structure is formed by taking the base hexagonal
honeycomb re-entrant design and removing two opposite ribs out of the
four. This is done because unit cells with four ribs are much stiffer than those
with two ribs, and, as such, can display auxetic behavior at much lower loads.
The missing rib model has broadly two types of auxetic geometries, namely
the Lozenge grid and the square grid. For our testing, we used the Lozenge
grid design as shown in the CAD in Fig. 11. The in-plane Poisson’s ratio for

Compression/
heating process
Uniaxial
Auxetic
loading

Fig. 10 Auxetic behavior of missing rib pattern.

Fig. 11 CAD drawing of the missing rib design.