## 3 Experimental Results and Discussion
### In-Plane Test
#### 3.2.2 Dynamic Compression
As shown in Figures 24 and 26, some parts were squeezed out of the specimen's main body, while some parts remained. The stress-strain curves of \(8\times 8\times 8\) specimens are shown in Figure 27b. The fracture stress and strain also increased with increasing strain rate. The modulus decreased slightly with increasing strain rate, as shown in Figure 28b. Figure 26: The morphological differences of \(8\times 8\times 8\) specimens under increasing strain rate (s\({}^{-1}\)): (**a**) 1813.5829 \(\pm\) 48.4181; (**b**) 2146.7858 \(\pm\) 12.5833; (**c**) 2309.9629 \(\pm\) 30.2695. Figure 24: The failing process of specimen under in-plane loading: (**a**) t = 0 \(\upmu\)s; (**b**) t = 23.69 \(\upmu\)s; (**c**) t = 52.12 \(\upmu\)s; (**d**) t = 201.38 \(\upmu\)s.  
Figure 25: The energy absorption of \(8\times 8\times 8\) specimens. As shown in Figure 26, a higher strain rate resulted in the remaining parts being more compact due to squeezing. In addition, as the strain rate increased, more pieces were squeezed out of the specimens, and the pieces that were squeezed out were more folded. (d) Effect of Size  
Specimens of different sizes showed similar strain rate effects. Firstly, as shown in Figure 27, with the increase in strain rate, the corresponding stress-strain curves of specimens of the same size were not significantly different. The only difference was that the position of the fracture point kept moving forward. As shown in Figure 30, the same trend can be found, whereby an increase in strain rate led to both fracture stress and strain increasing for all specimens with different sizes. Secondly, by taking the first derivative of the stress-strain curves shown in Figure 28, there was a specific period in which the first derivative oscillated steadily for specimens of all sizes. It could be inferred that this period of the stress-strain curve could be regarded as linear. The slope of  
According to Figures 22 and 28, the linear modulus of the \(8\times 8\times 8\) specimens could be fitted using the points in the stable oscillation linear period of the stress-strain curves, as shown in Figure 29. The modulus of the specimens of different sizes is presented in Table 4. It seems that the influence of thickness was greater than the influence of area on the modulus of specimens. There were also some differences between specimens of different sizes. Firstly, as shown in Figure 27, the stress-strain curves of the \(8\times 8\times 8\) specimens were more stable, and the tendency of the stress-strain curves increasing with the strain rate was more regular than for the curves of \(4\times 8\times 8\) specimens and \(8\times 8\times 5\) specimens. As shown in Figure 28b, the values of the first derivative in this period for the \(8\times 8\times 8\) specimens under different strain rates were more similar and fluctuated less. This is maybe because the area and thickness of the \(8\times 8\times 8\) specimens were bigger and, thus, the properties inside the specimens were more uniform and consistent. Secondly, as shown in Figure 30, the fracture points of the \(4\times 8\times 8\) specimens were closer to the fracture points of the \(8\times 8\times 8\) specimens, while the fracture points of the \(8\times 8\times 5\) specimens were obviously further away. This is because the modulus values of the \(8\times 8\times 8\) and \(4\times 8\times 8\) specimens were more similar than that of the \(8\times 8\times 5\) specimens, as shown in Figure 21:0 Thirdly, it seems that the size of the specimens mainly influenced the modulus but did not obviously influence the fracture stress.