## 4 Discussion  
The base material (ABS) of the chiral structures showed low specific strength and elongation at break values as previously reported in Table 4. The low specific stiffness and strength, and low ductility values directly affected the pre-crushing and progressive crushing stages and caused crush behavior with inadequate performance. The main limitation caused by the material specification of ABS is the prevention of the wrapping mechanism. The premature failure of ligaments while wrapping around the nodes inhibits the auxetic mechanism. The SEA values for out-of-plane crush of chiral lattices were found to be \(20.23\) J/g and for in-plane, the SEA value was \(2.25\) J/g. During the in-plane crush process, at first, elastic bending of the ligaments takes place, and it is followed by the bending of the nodes and a fracture of the ligaments and nodes, successively. However, in the out-of-plane loading, local buckling and global buckling can be experienced. In fact, global buckling is an efficient energy-absorbing mechanism, yet it is not preferred due to the instant load drop and the state of instability. This also explains the considerable difference between hollow and filled tube's uniaxial and lateral energy absorption abilities. In uniaxial loading of hollow and chiral-filled tubes, global buckling and catastrophic failure have not been observed, and the general deformation behavior had characteristics of a progressive failure for the hollow composite tube, which is a desirable failure mechanism [48]. This is provided by the selection of the geometrical parameters to prevent catastrophic failures [19; 20; 21; 22]. The similarities between the images shown in Figure 10b and [PERSON]'s results [38] for an ideal progressive failure can be easily appreciated. Moreover, the presence of a tearing mode and micro-fragmentation can be seen in Figure 12A-C; these  
Figure 11: Load–displacement curves of the lateral and uniaxial crush of chiral structures, hollow tubes and chiral-filled tubes. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**UNIAXIAL** & **PCF (kN)** & **MCF (kN)** & **CFE** & **AE (J)** & **SEA (J/g)** \\ \hline Chiral & \(29.09\pm 0.19\) & \(15.81\pm 1.61\) & \(0.54\pm 0.05\) & \(1104.90\pm 110\) & \(20.23\pm 2.06\) \\ Hollow & \(72.17\pm 7.01\) & \(39.61\pm 1.15\) & \(0.55\pm 0.06\) & \(3152.97\pm 104.97\) & \(79.90\pm 2.66\) \\ Filled Tube & \(76.37\pm 1.12\) & \(48.85\pm 3.54\) & \(0.64\pm 0.04\) & \(3480.23\pm 98.97\) & \(37.00\pm 1.05\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Average crush properties of the chiral structure, hollow tube and filled tube under uniaxial loading. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**LATERAL** & **PCF (kN)** & **MCF (kN)** & **CFE** & **AE (J)** & **SEA (J/g)** \\ \hline Chiral & \(11.54\pm 0.15\) & \(9.10\pm 0.66\) & \(0.79\pm 0.05\) & \(123.20\pm 0.01\) & \(2.26\pm 0.20\) \\ Hollow & \(0.81\pm 0.05\) & \(0.67\pm 0.03\) & \(0.83\pm 0.02\) & \(16.70\pm 0.59\) & \(0.42\pm 0.02\) \\ Filled Tube & \(13.16\pm 1.39\) & \(7.31\pm 1.03\) & \(0.55\pm 0.04\) & \(143.69\pm 22.35\) & \(1.53\pm 0.24\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Average crush properties of the chiral structure, hollow tube and filled tube under lateral loading. failure mechanisms were also presented in [PERSON]'s work [49]. The existence of similar failure modes could also be observed in the chiral-lattice-filled composite tubes, until a specific compression stroke. Beyond that critical value, the chiral lattices expanded laterally and forced the wall of the composite tubes to move radially, which caused a catastrophic failure. That is the reason why no composite tube surrounding chiral lattices is present, and some undeformed large pieces of the composite parts are left at the end of the tests as presented in Figure 12D-F. Observing the load-displacement curves for uniaxially loaded chiral lattices filled composite tubes the densification starts at about 68 mm of compression, and two different peak loads can be observed.