## 4 Conclusions  
Through the experimental and numerical simulation analysis of six kinds of composite honeycomb sandwich structures under the impact conditions of different angles and velocities, it is found that the designed honeycomb sandwich structure has different types of structural responses to oblique impact and positive impact. The failure mode and impact resistance of the honeycomb sandwich structure under oblique impact mode are quite different, but the overall energy absorption effect is still similar. For the oblique impact type of fragments, the established numerical model is still in good agreement with the experimental results. Due to the limitation of experimental conditions, the research conditions are less, and the oblique impact honeycomb sandwich structure in practice will produce more failure modes. Therefore, the impact resistance and energy absorption performance of the honeycomb structure will also produce many different laws, which need to be further studied in the next step. The main conclusions of this paper are the following:  
(1) Due to the non-vertical impact of the fragment during the impact process, the contact area between the skin and the fragment increases, the stress deformation becomes relatively large, and the damage to the underlying skin is more serious. Among them, the NOMEX-AL core material has a large area of damage and accumulates in the hole; the NOMEX-C front skin has neat openings, and the damaged aperture of the rear skin is relatively small. ST-6-6-6 and ST-6-3 are greatly affected by the sabot, and the material is obviously accumulated around the aperture;  
(2) The four groups of structures, ST-3-3, ST-3-6, ST-6-3, and ST-6-6, were 160.6%, 127.3%, 123.65%, and 102.85% and 766.67%, 655.83%, 643.69%, and 574.53% higher than NOMEX-AL and NOMEX-C, respectively. The energy absorption effect of a honeycomb structure composed of NOMEX and unidirectional carbon fiber is very poor. The best energy absorption structure in oblique impact is the ST-3-3 structure, which can be about 16.5% higher than other structures in the same design type and about 25.4% higher than vertical impact;  
(3) There is a certain similarity in the response process of different honeycomb structures to oblique impact. With the increase in inclination angle, the damage aperture of each structure increases and the deformation influence area increases. The impact resistance of the structure mainly comes from the front and rear skins and core materials of the honeycomb sandwich structure. The smaller the cell size is, the stronger the impact resistance of the structure is. The greater the strength of the skin, the more favorable the overall oblique impact resistance of the structure.  
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 was funded by the 2024 Shanxi Graduate Innovation Project, grant number 2024 KY571.  
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.