## 3 Results and Discussions
### Low-Velocity Impact Properties  
Figure 4 shows the low-velocity impact performance of samples with different mixing ratios. In the initial stage of impact, due to the load transferred by the punch to the specimen, the impact surface produces compressive deformation, and the specimen stiffness is redistributed [35]. During this stage, the specimen transitions from the undamaged state to the damaged state, which manifests as a sudden drop of load in the load-time diagram of impact. The brittle carbon fibers in the core layer begin to fracture and small cracks begin to appear simultaneously, as the impact continues to move downwards, resulting in oscillation in the process, as shown in Figure 4a. Taking sample S-3 as an example, once the punch contacts the sample, the impact process initiates Phase I loading as the penetration depth increases. When the impact load reaches the extreme value, the impact enters the second stage, and the curve oscillation intensifies. Plastic failure such as reinforcement fiber fracture, extraction, pits, and delamination occurred in the composite, resulting in load decrease. The impact of the punch continues, and the impact enters Stage III. The load rapidly drops, and the impact process of the sample ends, as shown in Figure 4b.  
It can be seen that the extreme value of the impact load of the sample was positively correlated with the hybrid ratio of the sample in Figure 4c. The loading capacity of the sample to the impact load was improved by inserting carbon fiber into the glass fiber preform. This reduction in strength caused significant oscillations in the load-time curve. The damage progression in the hybrid composite remains gradual owing to the toughening effect of glass fibers. The load-time curve displayed no pronounced oscillations during Stage I, with Stage III exhibiting gradual load decay devoid of significant fluctuations. Therefore, it can be seen that the sandwich hybrid composite has better impact resistance. Compared with S-1 (2.25 J), the impact energy absorption of S-2, S-3, and S-4 increased to 2.53 J (S-2), 2.69 J (S-3), and 2.44 J (S-4), respectively, by 12.44%, 19.56%, and 8.44%. The comparative evaluation of the impact performance of the sample shows that fiber mixing has a significant impact on the impact performance of the sample, and with the increase in the mixing ratio, the impact performance of the sample is significantly improved. Due to the high brittleness of carbon fiber, the impact performance of S-4 is decreased compared with that of S-3. In summary, similar to the bending properties, as the hybrid ratio increases, impact resistance increases initially but declines after a certain hybrid ratio, with a significant deterioration observed when the hybrid ratio exceeds a critical threshold.  
Figure 3: The three-point bending properties of samples with different hybrid ratios: (**a**) load–displacement curve along the L direction; (**b**) comparison of EA along the L direction; (**c**) comparison of SEA along the L direction; (**d**) load–displacement curve along the W direction; (**e**) comparison of EA along the W direction; (**f**) comparison of SEA along the W direction.