Fig. 4 (a) Measured strut thickness (b) Normal distribution of measured
strut thickness for different strut orientation
Relating the strut thickness to porosity, the random struts had the
highest thickness and hence trabecular structures had the lowest
porosity. Cross based structures with oblique struts had the highest
porosity, followed by star based structures which had one extra vertical
strut when compared to cross based structures. But, the thickness
difference in the horizontal and irregular struts can be clearly seen
when comparing the porosity of cubic regular and cubic irregular
structures. The lower thickness of horizontal struts increases the
porosity of cubic regular structures by 5% when compared to cubic
irregular.
Quasi-static compression
test
The typical stress-strain curve for cellular structures consists of
three regions, linear elastic deformation followed by plastic
deformation forming a plateau region and finally densification of strain
takes place when the failed struts come in contact with each other. The
plastic deformation and the shape of the plateau region are highly
dependent on the topology and density of the material30. In this study, the testing was stopped before all
the struts failed and before the densification stage. This was done in
order to better identify a posteriori; the location of the weak
areas that first yielded or failed. The stress-strain curves of all the
specimens are shown in Fig.5. The stress-strain curves were quite
different for different topologies under monotonic testing as shown in
Fig. 5a. The curve of the regular cubic structure indicates that the
stress drops down to 20 MPa at very small strain, showing a catastrophic
failure of struts. The failure is mainly due to buckling of vertical
struts under axial loading and due to the absence of struts in other
directions which introduce bending moment29.