## 2 Materials and Methods
### Structure Design  
In a related study, a hybrid structure combining regular honeycomb and auxetic structure was studied on 3D printed samples. The deformation and failure modes of the different cells and their performance were investigated. Compared with the honeycomb and auxetic structures, the new hybrid structure had better mechanical properties. The compressive strength of the hybrid structure is \(\sim\)300% greater than that of the honeycomb structure and \(\sim\)65% greater than that of the auxetic structure. Compared with other structures, the new design is able to absorb more energy [48]. In another study, a new 3D hybrid lattice structure was developed using auxetic and honeycomb, and simulations were conducted on these structures to investigate and compare their energy absorption characteristics. The results show that there are significant improvements. The smallest value of energy absorption under tensile loading was 86% greater than the largest value under compressive loading. Research has indicated that the stiffness and energy absorption of traditional 3D auxetic structures can be improved by combining auxetic and honeycomb structures [46]. In this study, a novel approach is presented that differs from that in the literature. As shown in Figure 4, a hybrid model was created that combines honeycombs and auxetic. This study is unique in that hybrid modeling was developed. The design variables are defined as the maximum edge length (p1), wall thickness (p2) and plane angle (p3). To understand and verify the development condition of the hybrid model, FEA was performed for all three conditions. A 100 kN force was applied in the compression direction to the fixed panels and displacements were taken into account to compare performance. The panel dimensions were 500 \(\times\) 500 \(\times\) 50 mm, and the material was determined as glass fiber. The FEA results are given in Figure 5. The displacement at 100 kN is 13.8 mm for the honeycomb structure, 6.56 mm for the auxetic structure, and 4.82 mm for hybrid structure. The maximum von Mises stress in the honeycomb structure is 131 MPa, that in the auxetic structure is 75.2 MPa, and that in the hybrid structure is 52.4 MPa. In terms of displacement and stress distribution, the hybrid structure is the best choice compared with the honeycomb and auxetic structures. Crash performance was calculated as the displacement divided by the mass. These units require displacement per weight, which means that the lowest value provides the best performance. On the basis of calculations given in Table 4, the performance value for honeycombs is 0.002233 mm/g, that for auxetics is 0.000911 mm/g, and that for hybrid structures is 0.000485 mm/g. It has been determined that the hybrid structure has a better crash performance. The performance of the new hybrid design is \(\sim\)360% greater than that of the honeycomb structure and \(\sim\)88% greater than that of the auxetic structure. To investigate the impact of the new hybrid structure on the battery box side profile, lattice structures were generated with design variables that are subject to the following lower and upper limits:  
\[60\;\mathrm{mm}\leq\mathrm{p1}\leq 100\;\mathrm{mm}\]  
\[6\;\mathrm{mm}\leq\mathrm{p2}\leq 12\;\mathrm{mm}\]  
\[15^{\circ}\leq\mathrm{p3}\leq 135^{\circ}\] \begin{table}
\begin{tabular}{l l l l} \hline
**Lattice Type** & **Mass (g)** & **Displacement (mm)** & **Performance (mm/g)** \\ \hline Honeycomb & 6181 & 13.8 & 0.002233 \\ Auxetic & 7198 & 6.56 & 0.000911 \\ Hybrid structure & 9936 & 4.82 & 0.000485 \\ \hline \end{tabular}
\end{table} 
Table 4: Performance comparison of honeycomb, auxetic and hybrid structures. Second, as shown in Figure 6, battery box side profile sections were generated by trimming the hybrid lattice structures generated with design variables and the outer contours of the current model from each other. The thickness of the outer contour of the current model was maintained.