## 2 Materials and Methods
### Measurements of Backface Signature Depth, Diameter and Volumes  
#### 2.4.1 Scanning of Backface Signature at the Back of Plastilina  
The backface signature measurement is one of the parameters which could help to assess the energy absorbed and other ballistic performances of the ballistic materials. It is normally produced on the back of the ballistic material during the ballistic impact. Therefore, the backface signature should be measured with great care and accuracy. Unlike the traditional BFS measurement systems (using caliper or rulers), the current research has introduced a new system for precise and quick measurements of the different BFS values. Such measuring system involves scanning of the shot backing material through hand scanning. Later, the scanned images has been cured using rapid form software and then modeling and measured its values (depth and volume) using 3D modeling software. Before scanning, the panel target along with the backing material box (Figure 6) was detached from the fixed ballistic box holder. Then, the panel target will be carefully removed from the backing material. This would help not only to keep the tested target but also not to distort the BFS measurements created on the backing material surfaces. According to NJJ Standard, the backface signature depth should not be greater than 44 mm; otherwise, it will bring a fatal injury in the vital organ of the wearer. During the impact, the projectile might perforate the panel and pass throughout the thickness or stuck inside the fabrics. In the non-perforation case, the projectile will be stopped inside the panel or rebound back by creating some back face indentation on the backing material. Thus, such back face indentations on the backing clay should be measured after each panel shooting for analyzing the ballistic performances of the panel target. Various reflecting dot marks were placed on the deformed backing material surface for easy detection and modeling of the backface indentation before scanning. Later, the back face indentation on the backing clay was scanned at a time after shooting all the 6 projectiles on the panel target using a handy scanner as shown in Figure 6. Such scanning methods not only give a better scanning process and precise measurement but also it is a time-saving process.  
Using such a handheld scanning device greatly used to better handle the measurement process and scan the molded surface with very clear and precise 3D model representations. Besides, as shown from Figure 7, only the face of the target panel with no perforation during ballistic tests at different shots was displayed. The handy scanner displays a very good resolution with accurate  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Target Panel Designations** & **Plastilina Temperature of at 1 st** & **Test Condition Temp. (\({}^{\circ}\)C)** \\  & **and 6 th Shot (\({}^{\circ}\)C)** & **and RH (\%)** \\ \hline
2D-35 & 32.8/30.8 & 25/34 \\
3D-40-8B:0S & 39/35.8 & 22.9/45.5 \\
3D-40-8B:4S & 39.7/37.8 & 22.9/37.5 \\
3D-40-8B:8S & 39.3/37.8 & 22.2/45.5 \\
3D-40-4B:8S & 38.2/37.2 & 22.7/43.5 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Ballistic-testing parameters and conditions during the test.  
high- and low-resolution scan modes. The resolution measurement is 0.050 mm with an accuracy of 0.040 mm. The volumetric accuracy and laser cross-area are 0.020 mm, 0.100 mm/m and 210 mm \(\times\) 210 mm, respectively. It was employed to capture the whole backing material surface without any physical contact for further computing of the backface signature values.