## 2 Implosive Loading Experiments  
### Introduction of Experimental Conditions  
Figure 1 shows the schematic diagram for the cylindrical shell's experimental structure, composed of the cylindrical shell, connection rod, end cover, and explosive. The 20# steel-made test shell featuring a high-quality carbon structure included chemical compositions of 0.24%C, 0.27%Si, 0.52%Mn, \(\leq\)0.035%S, \(\leq\)0.035%P, \(\leq\)0.25%Cr, \(\leq\)0.25%Ni, and \(\leq\)0.25%Cu. The yield strength and tensile strength were 245 MPa and 410 MPa, respectively. The experimental parameters of the cylindrical shell are shown in Table 1, while thicknesses of 8, 14, and 20 mm-, and minimum scaled distances (see Formula 1) of 0.091, 0.075, and 0.065 m/kg\({}^{1/3}\) were applied. The above size is based on the design size of an explosion-proof container with a scale ratio of 1:3 to 1:5, and the specific distance was also selected according to the actual designed explosive yield.  
\[R^{\prime}_{\text{min}}=R_{\text{min}}/\sqrt[3]{Q} \tag{1}\]  
where \(R^{\prime}_{\text{min}}\) is the minimum scaled distance, m/kg\({}^{1/3}\); \(R_{\text{min}}\) is the minimum distance from the inside of the cylindrical shell to the explosive, m; and \(Q\) is the explosion yield, kgTNT.  
Figure 1: The cylindrical shell experiment structure.  
Two kinds of explosives were used in the experiment. One is a spherical explosive detonated at the center, which had a less than 30 g TNT equivalent and is pressed with micron Penta erythrite Tetrantrate (PETN) powder, as shown in Figure 2a. It is used for initiation by a soft lead skin blasting cable with a diameter of 1 mm and a linear charge density of 0.5 gRXD/m. The white crystal PETN is a simple explosive, with a melting point of 141.3 \({}^{\circ}\)C, crystal density of 1.77 g/cm\({}^{3}\), explosive velocity of 8300 m/s, and explosive heat of 5895 kJ/kg. In addition, it is not hygroscopic, and is insoluble in water but dissolves easily in acetone. The explosive of more than 30 g TNT equivalent is composed of two main hemispheric explosives and a small explosive ball for detonating in the center, as shown in Figure 2b. The white ball with a diameter of 10 mm is a detonating ball (PETN) with 1 gTNT equivalent, and the main explosive composition of Hexogen/Trinitrotoluene (RDX/TNT:60/40) has an equivalent ratio of 1.25 and a density of 1.65 g/cm\({}^{3}\).  
A strain gauge was pasted on the outer wall of the cylindrical shell to measure the dynamic strain and to understand the stress and deformation of the container. Parameters of stain gauge are shown in Table 2. From the center of the explosion, four strain measuring points were laid at 0 mm, R, and 2R, respectively, each being divided into two channels of a toroidal and axial signals, forming a total of eight channels of signals and eight test cables. The signal produced and then amplified by the strain gauge was transmitted to the oscilloscope for recording.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number**} & **Thickness** & **Internal** & **External** & **Explosive** & **Minimum** \\  & **(h, cm)** & **Diameter** & **Diameter** & **(Q, gTNT)** & **Scaled Distance** \\  & **(d\({}_{1}\), cm)** & **(d\({}_{2}\), cm)** & **(R\({}_{min}^{\prime}\), m/kg\({}^{1/3}\))** \\ \hline No.1 & & & & 16 & 0.091 \\ No.2 & 0.8 & 4.6 & 6.2 & 29 & 0.075 \\ No.3 & & & & 41.6 & 0.066 \\ \hline No.4 & & & & 85 & 0.091 \\ No.5 & 1.4 & 8 & 10.8 & 152 & 0.075 \\ No.6 & & & & 233 & 0.065 \\ \hline No.7 & & & & 233 & 0.091 \\ No.8 & 2 & 10.6 & 14.6 & 416 & 0.075 \\ No.9 & & & & 640 & 0.065 \\ \hline \end{tabular}
\end{table}
Table 1: The arrangement of each experiment.  
Figure 2: Two kinds of explosives. (**a**) PETN; (**b**) RDX/TNT.