## 4 Conclusions  
Aiming at the problem of insufficient impact resistance of honeycomb sandwich structures, a composite honeycomb sandwich structure is designed in this paper. The structure ensures the same thickness and lightweight conditions as the original body structure. Considering the problem of weak transient bearing energy consumption of the honeycomb core layer of the existing structure, the honeycomb core is designed with high-strength materials, and the bearing mode of the single core layer of the existing structure is changed. Finally, a new composite honeycomb sandwich body structure with a double-core  
Figure 12: Energy–time curves of six different honeycomb sandwich structures. (**a**) Top 3/Bottom 3. (**b**) Top 3/Bottom 6.4. (**c**) Top 6.4/Bottom 3. (**d**) Top 6.4. (**e**) Al-NOMEX. (**f**) C-NOMEX.  
layer, multi-skin bearing and high-strength honeycomb core are obtained. In this paper, the energy absorption characteristics of the composite honeycomb sandwich structure are verified by the drop hammer collision experiment. The damage response of the composite honeycomb sandwich structure to different impact energy is studied. The displacement, force and energy curves related to energy absorption characteristics and time variables are analyzed. The difference between the composite honeycomb sandwich structure and existing body structure protection performance is compared and studied. The accuracy of numerical simulation is verified, and the optimal structural design parameters are obtained. The study found the following:  
1. The transient energy absorption characteristics of the composite honeycomb sandwich structure are mainly related to the cell size of the honeycomb structure. The larger the cell size, the better the transient energy absorption effect of the structure. However, the ability of the structure to resist damage is the opposite, but with a decrease in the cell size, the damage degree of the structure is weakened, and the structural resistance is enhanced.
2. When the average cell density of the composite honeycomb sandwich structure is the same, the cell size of the front core layer determines the overall anti-impact ability. The smaller the cell size of the front core layer, the stronger the overall impact resistance, and the less serious the damage of the underlying skin of the composite honeycomb sandwich structure.
3. The 7075 aluminum alloy-NOMEX and carbon fiber-NOMEX honeycomb sandwich panels were completely broken down under the impact energy of 100 J, the energy absorption limit was 80 J and 64 J, and the energy absorption per unit volume was only 181.7 \(\times\) 103 J/m\({}^{3}\) and 149.7 \(\times\) 103 J/m\({}^{3}\). At this stage, the maximum energy absorption per unit volume of the structure with the upper and lower core layers of 3 mm was 493.82 \(\times\) 103 J/m\({}^{3}\), which was 171.7% and 229.8% higher than that of NOMEX-AL and NOMEX-C structures. Therefore, whether it is the impact resistance or energy absorption characteristics, the composite honeycomb sandwich structure exceeds the 7075 aluminum alloy-NOMEX and carbon fiber-NOMEX honeycomb sandwich structures.  
Conceptualization, B.C. and G.B.; Methodology, B.C.; Software, G.B.; Validation, B.C.; Investigation, B.C. and Z.W.; Experiment, G.B.; Data curation, G.B.; Writing--original draft preparation, B.C.; Writing--review and editing, G.B. and Z.W.; Supervision, G.B.; Project administration, G.B. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to programming privacy in structural design.  
Author [PERSON] was employed by the company Chongqing Hongyu Precision Industry Group Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.