## 3 Experimental Results
### Fragment Size Distribution  
A series of standard sieves with 17 sizes from 0.08 mm to 100 mm were used to screen the post-blast fragments. The fragments with sizes larger than 100 mm were weighted individually. The weights of fragments are listed in Table A1 Appendix A. The summarized sieving results are shown by scatterplots in Figure 16.  
The extended Swebrec function \(P(x)\) was used to fit the sieving data. Its expression is [45]:  
\[P(x)=\frac{1}{1+a\cdot\left[\ln(x_{\max}/x)/\ln(x_{\max}/x_{50})\right]^{b}+(1- a)\cdot\left[\left(\frac{x_{\max}}{x}-1\right)/\left(\frac{x_{\max}}{x_{50}}-1 \right)\right]^{c}} \tag{1}\]  
The extended Swebrec function with five parameters can fit most fragment size distributions with extreme accuracy [44], where \(x_{\max}\) is the maximum size, \(x_{50}\) is the mean size, and \(a\) (\(0\leq a\leq 1\)) is the partition coefficient. \(b\) and \(c\) are the undulation exponents. The least-squares method was used to fit the curve. The function (\(1/P^{2}\)) was used as the weighting function [49]. The fitted parameters of each specimen are listed in Table 2.  
The fitted curves and sieving data are shown in Figure 17. The accumulated mass passing is usually classified as very fine (\(<\)2%), fine (2-20%), central (20-80%), and coarse (\(>\)80%) [50]. At the same accumulated mass passing, smaller particle sizes mean finer fragments. Four percentages were selected as the given accumulated mass passing, i.e., 0.1%, 1%, 50%, and 100%. The fragment sizes of all experiments at the four percentages of mass passing are listed in Table 3. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Specimen No.**} & **Delay Time** & \(x_{\max}\) & \(x_{50}\) & \multirow{2}{*}{\(a\)} & \multirow{2}{*}{\(b\)} & \multirow{2}{*}{\(c\)} & \multirow{2}{*}{\(R^{2}\)} \\  & **(\(\mu\)s)** & **(mm)** & **(mm)** & & & & \\ \hline DT1 & 13.69 & 152.3 & 122.1 & 0.2227 & 1.438 & 0.907 & 0.9784 \\ DT2 & 27.36 & 161.5 & 127.6 & 0.9568 & 1.249 & 1.528 & 0.9629 \\ DT3 & 54.72 & 189.4 & 140.1 & 0.9996 & 1.599 & 2.425 & 0.9514 \\ DT4 & 60 & 142.3 & 123.3 & 0.3709 & 1.357 & 0.9428 & 0.9631 \\ DT5 & 90 & 237.7 & 179.9 & 0.9998 & 1.889 & 1.968 & 0.9637 \\ DT6 & 120 & 133.6 & 100.1 & 0.9995 & 1.365 & 2.443 & 0.9654 \\ DT7 & 180 & 126.2 & 95.7 & 0.9989 & 1.266 & 2.145 & 0.9728 \\ DT8 & 339.6 & 111.0 & 57.1 & 0.9987 & 1.929 & 2.601 & 0.9441 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of fitted curves using the extended Swebrec function. Figure 16: Accumulated mass passing vs. particle size. In Figure 17a, the fitted curves of DT1-DT3 experiments moved down with the delay time increasing in the 10-100% mass passing. The movement indicates that the fragment size increased with the delay time (in the range of 13.69-54.72 \(\upmu\)s) at the same accumulated mass passing. When the delay time was increased to 60 \(\upmu\)s in the DT4 experiment, the fitted curve did not continue to move down. Table 3 shows that the particle size of DT4 was smaller than that of DT3 in the 50-100% mass passing. It suggests that the further delay time increase did not make the fragments coarser. Taking 100% mass passing as an example, the particle size of DT3 was 189.4 mm, but that of DT4 was 142.3 mm. The 100% passing size of DT3 was 1.3 times greater than that of DT4. Meanwhile, the \(x_{100}\) of DT4 was also smaller than those of DT1 and DT2. Figure 17b shows the fitted curves of DT5-DT8 experiments. The fitted curve and particle size of DT5 showed that fragments presented extremely at both ends of the accumulated mass passing. In the 100% mass passing, the fragment size of DT5 reached 237.7 mm. However, in the 0.1% mass passing, the fragment size of DT5 was only 0.37 mm, which was significantly smaller than those of other experiments except DT1. DT5 produced more coarse fragments and more fine materials. Obviously, DT5 obtained the worst fragment size distribution. The fitted curves of DT6-DT8 presented a gradual upward trend in the logarithmic space at the range of 10-100% mass passing.