## 3 Results and Discussion  
### Bulletproof Performance of the Different Composite Plates  
To test the bulletproof performance of the fabricated composite plates, bullets were fired from a distance of 10 m. After the bullets penetrated the composite plates, the witness clay pieces, which were bonded on the backside of the plates, were perforated (Figure 1). Therefore, the perforated area of the witness clay piece, \(\alpha\), and initial bullet projection area, \(\beta\), were determined. The perforated area was calculated from the perforated hole diameter (witness clay diameter), D, using the following popular formula:  
\[\alpha=\pi D^{2}/4. \tag{1}\]  
Moreover, the initial bullet projection area was the same as the bullet cross-section area, which could be easily obtained from the 9-mm diameter of bullet. Using these area values (\(\alpha\) and \(\beta\)), the normalized perforated area, U, was calculated as follows:  
\[\text{U}=\ \alpha/\beta. \tag{2}\]  
The normalized perforated area (U) is an important parameter for evaluating bulletproof performance. For example, if the normalized perforated area is small, the overall bulletproof performance of the composite is considered satisfactory. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Thickness of Cornstarch Suspensions (mm)** & **Number of Hanji Sheets** \\ \hline A & 0 & 60 \\ B & 0 & 120 \\ C & 0 & 180 \\ D & 10 & 60 \\ E & 20 & 60 \\ F & 30 & 60 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Types of composite plates fabricated. The normalized perforated area of the composites was analyzed for evaluating the bulletproof performance of the composites (Figure 2a,b). To evaluate the bulletproof performance of only Hanji layers without the cornstarch layers, the bulletproof experiment was conducted for composites composed of Hanji layers of different thicknesses without the cornstarch layers. Results showed that the normalized perforated area of the composites with different numbers of Hanji layers (60, 120, and 180 layers) gradually increased to 11.1, 47.3, and 75.5, respectively (Figure 2a). Furthermore, to analyze the influence of STF layers on the bulletproof performance of these composites, the bulletproof experiment was conducted for composites comprising Hanji layers and cornstarch suspension layers (Figure 2b). The normalized perforated area for the composites with a constant number of Hanji layers (60 layers) and different thicknesses of the cornstarch suspension layers (10, 20, and 30 mm) continuously reduced from 35.3 to 8.5 and then 3.9, respectively. Furthermore, (Figure 2a) the relationship between normalized perforated area, Y, and number of Hanji sheets, X, was expressed as:  
\[\text{Y}=0.54\text{ X}-19.87. \tag{3}\]  
Moreover, the relationship between normalized perforated area and STF thickness, Z, was expressed as:  
\[\text{Y}=-1.57\text{ Z}+47.30. \tag{4}\]  
Throughout the relationships between the normalized penetrated area and the thickness of materials, the STF had a negative gradient on this relationship. Theoretically, the STF had the transition on its own state from liquid to solid under a high shear rate. This phenomenon contributed to the hydroclustered effect from the jamming of colloidal particles in STF. Thus, the resistance to the momentum of bullet was reinforced with this effect, and the normalized perforated area was decreased with increase of STF thickness. Figure S3 shows the actual perforated witness clay images obtained during the bulletproof experiments for the composite without cornstarch layers and having 120 Hanji layers along with that for the composite with a 20-mm-thick cornstarch suspension layer and 60 Hanji layers (Figure S3). In addition, the witness clay diameters for all composites were measured to calculate the normalized perforated area (Figure S4). Figure 1: Schematic representation of the bullet penetrating the composite plate composed of Hanji and shear thickening fluids (STF) layers and clay perforation (clay diameter).