## 4 Results and Discussion
### Dynamic Mechanical Tests  
The dynamic Hopkinson compression bar is used to test the dynamical performances of metal-ceramic hybrid honeycomb structures, and samples with the conventional hex hybrid structure and the re-entrant hex hybrid structure are of the same weight. Figure 4a shows the impact displacement-load curve of the re-entrant hex hybrid and conventional hex hybrid structures at different impact speeds. The re-entrant hex can provide a more significant load with a minor strain than the conventional hexagonal honeycomb at the same strain rate. With the increase in strain rate, this phenomenon becomes more and more prominent at the strain rate of 2.54 \(\times\) 10\({}^{3}\)/s. The maximum load of these two structures is 47.5 kN and 60.4 kN, respectively. The re-entrant hexagonal hybrid honeycomb structure can bear a 27.3% higher load than the conventional hex hybrid structure at a strain rate of 2.54 \(\times\) 10\({}^{3}\)/s. Compared with the conventional hexagonal honeycomb the re-entrant hex has a minor ultimate strain under the same dynamic impact loading conditions. In the maximum impact involved in the experiment, the strains of conventional and re-entrant hexagonal honeycomb structures are 7.29% and 5.81%, respectively. Figure 5c,d shows the strain-load curves and synergistic effect analysis of hybrid honeycombs under the dynamic Hopkinson compression bar experiments at the strain rate of 2.54 \(\times\) 10\({}^{3}\)/s. The compression experiment of the single ceramic and single metal phase was also conducted with the ZDSHPB-40-100 dynamic compression rod system. Similar to the results of quasi-static experiments, the re-entrant hexagonal auxetic structure shows mechanical advantages over the conventional hexagonal structure, in terms of the single ceramic phase, the single metal phase, and hybrid structures, respectively. The peak load produced by the single re-entrant hexagonal ceramic phase under dynamic impact is even higher than that produced by the metal-ceramic composite structure. In the experiment, although the single re-entrant hexagonal ceramic provides a higher peak load, the single re-entrant hexagonal ceramic is more completely crushed than the conventional hex structure after the dynamic impact loading experiment. After the dynamic impact load, conventional hexagonal ceramic was crashed into fragments composed of blocks, and the re-entrant hexagonal ceramic was smashed into powder or particle. After the introducing of metal frame, only cracks appeared in the conventional hexagonal structure, and there are no visible cracks that appeared in the concave honeycomb after impact loading. Figure 6a illustrates the protective effect of the metal frame on the built-in ceramics under impact load. With the increase in strain rate, the ultimate load of the conventional hex hybrid structure does not change much. While the strain rate changes from 1.86 \(\times\) 10\({}^{3}\)/s to 2.54 \(\times\) 10\({}^{3}\)/s, the maximum load only increased by 6.2%. For the re-entrant hex hybrid structures, the ultimate load changes obviously with the strain rate, and the maximum load increased by 16.0% under the exact strain rate change within the strain rate variation range of the experimental study. The metal frame will contract when the hybrid structure is under dynamic loading, and the infilled ceramic is compressed along both the impact direction and the direction perpendicular to the impact direction. With the increase in impact velocity, the phenomenon of simultaneous pressure along two orthogonal directions becomes more obvious, thus the re-entrant hybrid structure can generate elevated ultimate strength at higher speed. architected sample after impact, and it can be seen that a crack is triggered within the internal ceramic matrix. The external metal cells are also impacted and deformed, which is similar to the compression deformation of the conventional hex structure. Figure 6d,e show the test sample of the re-entrant hybrid structure sample consisting of a one unit cell before and after impact.